Showing papers in "Experimental Brain Research in 1987"

Signals in tactile afferents from the fingers eliciting adaptive motor responses during precision grip.

Abstract: While human subjects lift small objects using the precision grip between the tips of the fingers and thumb the ratio between the grip force and the load force (i.e. the vertical lifting force) is adapted to the friction between the object and the skin. The present report provides direct evidence that signals in tactile afferent units are utilized in this adaptation. Tactile afferent units were readily excited by small but distinct slips between the object and the skin revealed as vibrations in the object. Following such afferent slip responses the force ratio was upgraded to a higher, stable value which provided a safety margin to prevent further slips. The latency between the onset of the a slip and the appearance of the ratio change (74 ±9 ms) was about half the minimum latency for intended grip force changes triggered by cutaneous stimulation of the fingers. This indicated that the motor responses were automatically initiated. If the subjects were asked to very slowly separate their thumb and the opposing finger while the object was held in air, grip force reflexes originating from afferent slip responses appeared to counteract the voluntary command, but the maintained upgrading of the force ratio was suppressed. In experiments with weak electrical cutaneous stimulation delivered through the surfaces of the object it was established that tactile input alone could trigger the upgrading of the force ratio. Although, varying in responsiveness, each of the three types of tactile units which exhibit a pronounced dynamic sensitivity (FA I, FA II and SA I units) could reliably signal these slips. Similar but generally weaker afferent responses, sometimes followed by small force ratio changes, also occurred in the FA I and the SA I units in the absence of detectable vibrations events. In contrast to the responses associated with clear vibratory events, the weaker afferent responses were probably caused by localized frictional slips, i.e. slips limited to small fractions of the skin area in contact with the object. Indications were found that the early adjustment to a new frictional condition, which may appear soon (ca. 0.1–0.2 s) after the object is initially gripped, might depend on the vigorous responses in the FA I units during the initial phase of the lifts (see Westling and Johansson 1987). The role of the tactile input in the adaptation of the force coordination to the frictional condition is discussed.

Single unit activity in the rat hippocampus during a spatial memory task

Abstract: Single unit activity was recorded from complex spike cells in the hippocampus of the rat while the animal was performing a spatial memory task. The task required the animal to choose the correct arm of a 4 arm plus-shaped maze in order to obtain reward. The location of the goal arm was varied from trial to trial and was identified by 6 controlled spatial cues which were distributed around the enclosure and which were rotated in step with the goal. On some trials these spatial cues were present throughout the trial (spatial reference memory trials) while on other trials they were present during the first part of the trial but were removed before the rat was allowed to choose the goal (spatial working memory trials). On these latter trials the animal had to remember the location of the cues and/or goal during the delay in order to choose correctly. 55 units were recorded during sufficient reference memory trials for the relationship between their firing pattern and different spatial aspects of the environment to be determined. 33 units had fields with significant relations to the controlled cues while 16 had significant relations to the static background cues, those cues in the environment which did not change position from trial to trial. Of 43 units which could be tested for their relation to the shape of the maze arms themselves, 15 showed such a relationship. Therefore the place units can be influenced by different aspects of the spatial environment but those related to the task requirement appear to be more potent. Interaction effects between the different spatial factors also influenced the firing pattern of some units. Of particular interest was the interaction between the controlled cues and the static background cues found in some cells since this might shed some light on how the hippocampus enables the rat to solve the memory task. 30 units with place fields related to the controlled cues were recorded during successful performance on spatial working memory trials as well as during spatial reference memory trials. The place fields of 90% of these units were maintained during the retention phase of the memory trials. During the recording of some units, other types of trial were given as well. On control trials, the cues were removed before the rat was placed on the maze. These trials provided controls for the potential influence of information left behind by the controlled cues and for the influence of the animal's behaviour on the unit activity. They also provided information about the unit firing in the absence of the controlled spatial cues and about the animal's choice of goal under these circumstances. During control trials, the units typically maintained their place fields but these fields had no relation to the experimenter-defined goal. The rat's choice of goal arm at the end of the trial, however, continued to show the usual spatial relationship to the fields. The data from these control trials, taken together with the interaction between the controlled cues and the static background cues seen in some of the cells and the characteristic mistakes made by each rat, suggest that the animal enters the task on each trial with an expected or preferred orientation of the controlled spatial cues relative to the background cues and that it must reorient its cognitive map of the environment or search for a different map when the actual orientation of the controlled cues departs from this default condition. Detour trials differed from working memory trials in that the animal was not immediately allowed to choose the goal at the end of the retention period but was forced to enter a non-goal arm instead. These trials ruled out the possibility that the animal was remembering the specific turn required to reach the goal and demonstrated that the place fields for the entire maze are set up as a result of exposure to the controlled spatial cues in any one of the start arms. Overall, the results provide strong support for the cognitive map theory of hippocampal function. In particular, they demonstrate that the representations of places within an environment are connected together to form a map, that the orientation of this map relative to an environment can be changed from trial to trial, and that this orientation is “remembered” following the removal of the controlled spatial cues.

Proprioceptive input resets central locomotor rhythm in the spinal cat.

Abstract: The reflex regulation of stepping is an important factor in adapting the step cycle to changes in the environment. The present experiments have examined the influence of muscle proprioceptors on centrally generated rhythmic locomotor activity in decerebrate unanesthetized cats with a spinal transection at Th12. Fictive locomotion, recorded as alternating activity in hindlimb flexor and extensor nerves, was induced by administration of nialamide (a monoamine oxidase inhibitor) and L-DOPA. Brief electrical stimulation of group I afferents from knee and ankle extensors were effective in resetting fictive locomotion in a coordinated fashion. An extensor group I volley delivered during a flexor burst would abruptly terminate the flexor activity and initiate an extensor burst. The same stimulus given during an extensor burst prolonged the extensor activity while delaying the appearance of the following flexor burst. Intracellular recordings from motoneurones revealed that these actions were mediated at premotoneuronal levels resulting from a distribution of inhibition to centres generating flexor bursts and excitation of centres generating extensor bursts. These results indicate that extensor group I afferents have access to central rhythm generators and suggest that this may be of importance in the reflex regulation of stepping. Experiments utilizing natural stimulation of muscle receptors demonstrate that the group I input to the rhythm generators arises mainly from Golgi tendon organ Ib afferents. Thus an increased load of limb extensors during the stance phase would enhance and prolong extensor activity while simultaneously delaying the transition to the swing phase of the step cycle.

Responses in glabrous skin mechanoreceptors during precision grip in humans.

Abstract: Impulses in single tactile units innervating the human glabrous skin were recorded percutaneously from the median nerve using tungsten electrodes. The units were classified as belonging to one of the four categories: fast adapting with small receptive fields (FA I), fast adapting with large receptive fields (FA II), slowly adapting with small fields (SA I), and slowly adapting with large fields (SA II). A small test object was lifted, positioned in space and replaced using the precision grip between fingers and thumb. The grip force, the load force (vertical lifting force), the vertical movements of the object and vibrations (accelerations) in the object were recorded. After being virtually silent between lifts, the FA I units whose fields contacted the object became highly active during the initial period of grip force increase (initial response). This was also true for most SA I units. Accordingly, most of the skin deformation changes took place at low grip forces (below ca. 1 N). Later, while the load and grip forces increased in parallel during isometric conditions, the FA I and SA I units continued firing but generally at declining impulse rates. As long as the object was held in the air, the SA I units generally maintained firing with a tendency to adaptation. A minority of the FA I unit also discharged, especially during periods of pronounced physiological muscle tremor. The SA I units usually became silent when the grip and load forces in parallel declined to zero during isometric conditions after the object had contacted the table. However, during the very release of the grip the FA I units and some SA I units showed brief burst discharges (release response). The FA II units responded distinctly to the mechanical transients associated with the start of the vertical movement and especially with the sudden cessation of movement at the terminal table contact. FA II units whose end organs were remotely located in relation to the skin areas in contact with the object also responded. Most FA II units also discharged at the initial touch and at the release of the object, albeit less reliably than the type I units. In addition to weak dynamic responses during the phase of isometric force increase, the SA II units showed comparatively strong tonic responses while the object was held during static conditions. High firing rates also were maintained during long-lasting lifts. Moreover, it was established that the signals in SA II afferents were related to the three dimensional force profile in the grip.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholinergic neurons containing GABA-like and/or glutamic acid decarboxylase-like immunoreactivities in various brain regions of the rat.

Abstract: The coexistence of immunoreactivities for choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) and/or gamma-aminobutyric acid (GABA) was revealed in some brain regions of the rat, using the peroxidase-antiperoxidase method. Consecutive 40 μm thick vibratome sections were incubated in different antisera and those cells which were bisected by the plane of sectioning so as to be included at the paired surfaces of two adjacent sections were identified. The coexistence of the immunoreactivities for ChAT and GAD or GABA in the same cell could thus be determined by observing the immunoreactivity of the two halves of the cell incubated in two different antisera. In the retina, cerebral cortex, basal forebrain and spinal cord, colocalization of ChAT-like and GAD-like or GABA-like immunoreactivities was observed in some cell types, whereas no such colocalization was observed in cells in the striatum or brainstem. In the retina, the majority of ChAT-like immunoreactive (ChAT-LI) amacrine cells contained GABA-like or GAD-like immunoreactivity. About half of the ChAT-LI neurons in the cerebral cortex showed GABA-like immunoreactivity. In the basal forebrain only a small proportion of ChAT-LI neurons (0.6%) contained GAD-like immunoreactivity. In the spinal cord, about one-third of ChAT-LI central canal cluster cells and about half of ChAT-LI dorsal horn cells showed GAD-like and/or GABA-like immunoreactivities. These observations indicate the possible coexistence of two classical transmitters, GABA and acetylcholine, in various brain regions and spinal cord of the rat.

Responses of neurons in the inferior temporal cortex in short term and serial recognition memory tasks.

Abstract: Gaffan and Weiskrantz (1980) and Mishkin (1982) have shown that lesions to the inferior temporal visual cortex can impair the performance of serial visual recognition memory tasks. In order to provide evidence on whether the inferior temporal visual cortex contains a mechanism which enables memory to span the intervening items in a serial recognition task, or whether the inferior temporal cortex is merely afferent to such recent memory mechanisms, we analysed the activity of single neurons in the inferior temporal visual cortex and the adjacent cortex in the superior temporal sulcus in both delayed match to sample and serial recognition memory tasks. In the serial recognition task, various numbers of stimuli intervened between the first and second presentations of a stimulus. A considerable proportion (64/264 or 26%) of visually responsive inferotemporal neurons showed a different response to the “novel” and “familiar” presentations of a stimulus in the serial recognition memory task, and often a corresponding difference in response between the sample and match presentations of a stimulus in the delayed match to sample task. For the majority of neurons this difference was not sustained across even one intervening stimulus in the serial recognition task, and no neurons bridged more than 2 intervening stimuli. These results show that neurons in the inferior temporal cortex have responses which would be useful for a short term visual memory for stimuli, but would not be useful in recency memory tasks in which more than one stimulus intervenes between the first and second presentations of a stimulus. In this investigation, neurons were recorded both in the cortex on the inferior temporal gyrus (commonly called inferior temporal visual cortex, and consisting of areas TE3,TE2 and TE1 of Seltzer and Pandya 1978), and in the cortex in the adjacent anterior part of the superior temporal sulcus, in which a number of different temporal cortical visual areas have now been described (see Baylis et al. 1986).

Neurons of area 7 activated by both visual stimuli and oculomotor behavior.

Abstract: Behavioral and clinical studies have long implicated the posterior parietal cortex of primates in spatial perception and spatially oriented behavior. However, recordings from single neurons in behaving monkeys by different laboratories have resulted in divergent views with some ascribing a largely motor and others a largely sensory role for this region. We have designed paradigms to separate the sensory and motor components of the neural activity and have found that the cells in this area respond to both sensory stimulation and motor behavior. Thus, it is likely that this area is not solely sensory or motor, but rather is involved in higher order aspects of sensory-motor integration.

Forward and backward axial synergies in man

Abstract: 1. Upper trunk and head forward and backward movements were analyzed in human subjects standing on a force platform. EMG of several flexor and extensor muscles was recorded together with the kinematics of the movement (EL.I.TE. system). 2. It was found that upper trunk movements are accompanied by movements of hip and knees in the opposite direction, resulting in a slight displacement of the center of gravity projection on the ground. 3. In fast movements, all the body segments were displaced at the same time, which suggests a feedforward control, whereas in slow movements, onset of displacement of the body segments was found to take place sequentially in a cranio-caudal direction. 4. EMG analysis during fast movements revealed two different types of control, utilized in forward and backward movements. With forward bending movements the action of two sets of muscles could be recognized: the prime mover (R. Abd.), the activation of which was not correlated with that of the other muscles and preceded the onset of movement with a fairly constant lead, and a group of postural muscles, the activation (VM, TA) and inhibition (Sol) of which were closely correlated. By contrast, with backward movements, the prime mover (Er.S.) and the postural leg muscles (Hamstrings, Sol) were activated simultaneously. In both cases, a feedforward type of control is evident. 5. Performance of the fast forward movements was accompanied by an initial forward displacement of the knee. The function of this phenomenon is discussed in term of a destabilizing action favouring the forward bending of the body or a prestretching of the knee extensor muscles increasing the strength of their subsequent contraction.

Effects of arm acceleration and behavioral conditions on the organization of postural adjustments during arm flexion

Abstract: Nine standing subjects performed unilateral arm flexion movements over an eight-fold range of speeds, under two behavioral conditions. In the visually-guided condition, a visual target informed subjects about the correct movement speed. Seven subjects also made movements of different speeds during a self-paced condition, without a visual target. Angular displacement and acceleration of the arm, and EMG activity from the hamstrings (HM), erector spinae (ES) and the anterior deltoid (AD) muscles were measured. The following results were observed. (1) Mean rectified amplitudes of EMG activity in HM and ES were typically correlated with the average arm acceleration and presumably the disturbance to posture and/or balance. HM and ES amplitudes were correlated for only six subjects. Functions relating the ratios of HM/ES EMG amplitudes to acceleration varied between subjects. (2) HM onset latencies were highly variable for slow movements and usually lagged movement. For movements above a threshold-like point in acceleration, HM latencies were correlated with arm acceleration and recruited before movement. ES latencies were constant for fast movements, and negatively correlated with acceleration for slower movements. (3) The recruitment order of HM and AD was influenced by the behavioral condition but not by arm acceleration for fast movements. HM and AD were recruited coincidentally for visually-guided movements, while for self-paced movements, HM was recruited before AD. We conclude that for the arm flexion task: (1) HM and ES are not tightly coupled; (2) both behavioral and mechanical conditions affect the recruitment of postural muscles; and (3) postural and focal components of the movement are probably organized by parallel processes.

Reflex pathways from group II muscle afferents. 1. Distribution and linkage of reflex actions to alpha-motoneurones.

Abstract: The convergence of group II muscle afferents on interneurones in reflex pathways has been elucidated by investigating interaction in transmission to motoneurones. Recording was also made from interneurones activated from group II afferents. Maximal group II EPSPs evoked in motoneurones from different muscles (extensors or flexors and extensors) did not summate linearly but with a deficit of 35–40%. The corresponding deficit in summation with Ia EPSPs was 7%. It is suggested that the difference in deficit is caused largely by occlusion due to shared interneuronal discharge zones and that it gives an approximate minimal measure of the convergence of group II afferents from different muscles on the interneurones. Tests with weak group II volleys from different muscles gave no or little evidence for spatial facilitation in the disynaptic excitatory pathway to flexor motoneurones, and there was no or little temporal facilitation of transmission in this pathway. It is suggested that group II excitation of the interneurones in this pathway depends on few afferents giving large unitary EPSPs. Convergence of cutaneous afferents and joint afferents on the interneurones was evidenced by spatial facilitation from these afferents of group II transmission to motoneurones. Convergence on interneurones in the trisynaptic inhibitory pathway from group II afferents to extensor motoneurones was also investigated with the spatial facilitation technique. There was convergence on common interneurones of group II afferents from different muscles (extensors or flexors and extensors) and from cutaneous afferents as well as joint afferents. Trisynaptic group II IPSPs, including those depending on spatial facilitation from different muscles were resistant to recurrent depression from motor axon collaterals and are therefore not mediated by the reciprocal Ia inhibitory pathway. Interneurones with monosynaptic group II EPSPs were recorded from in the dorsal horn and intermediate region. Graded stimulation revealed large unitary EPSPs from few group II afferents. The EPSP evoked by a single group II afferent may produce firing (extracellular recording). Convergence of monosynaptic group II EPSPs from different muscles was rather limited but could be from flexors and extensors. Extensive multisensory convergence onto some of these interneurones was indicated by di-or polysynaptic EPSPs from group II and III muscle afferents, from joint afferents and from cutaneous afferents. The discussion of the functional role of the group II reflex pathways is based on previous findings suggesting the existence of alternative pathways to both flexors and extensors and demonstrating that the reciprocity of the spinal state is not obligatorily under control from the brain (Holmqvist and Lundberg 1961). It is postulated that the excitatory group II pathways mediate commands from the brain for movements engaging flexors and/or extensors and that group II inhibition may contribute spatial selectivity by lateral inhibition.

Excitability of the soleus H-reflex arc during walking and stepping in man

Abstract: In eight normal subjects, the excitability of the soleus (Sol) H-reflex was tested in parallel with Sol length changes, EMGs of leg and thigh muscles and ground contact phases, during three different pacing movements: bipedal treadmill walking, single limb treadmill walking, and single-limb stepping on one spot. A computerized procedure was used which compensated for changes in stimulus effectiveness that occurred during free motion. In the three paradigms examined, significant excitability modulations were observed with respect to a control level determined in standing weight-bearing position. During bipedal treadmill walking, excitability was decreased in the early stance, maximally enhanced in the second half of the stance, and again decreased during the end-stance and the whole swing phase, with a minimum value around the toe off period. The main modulation pattern was retained during single-limb treadmill walking. During single-limb stepping on one spot, the stance-phase increase in excitability and the swing phase depression were still present. However, in the second half of the swing phase, reflex responsiveness returned to reference level, which was maintained during the subsequent contact period. Moreover, a decrease in reflex excitability was detected around the mid-stance. The time course of the described modulations was only partly correlated with the EMG and length changes of the Sol muscle. Furthermore, in the three movements tested, during the early stance phase, the excitability of the H-reflex arc did not correspond to the one expected on the basis of the available H-reflex studies performed under static conditions. It is suggested that, at least in certain stride phases (e.g. around the early contact period), an active regulation affects the transmission in the Sol myotatic arc during the pacing movements investigated.

Local precision of visuotopic organization in the middle temporal area (MT) of the macaque.

Abstract: The representation of the visual field in the middle temporal area (MT) was examined by recording from single neurons in anesthetized, immobilized macaques. Measurements of receptive field size, variability of receptive field position (scatter) and magnification factor were obtained within the representation of the central 25°. Over at least short distances (less than 3 mm), the visual field representation in MT is surprisingly orderly. Receptive field size increases as a linear function of eccentricity and is about ten times larger than in V1 at all eccentricities. Scatter in receptive field position at any point in the visual field representation is equal to about one-third of the receptive field size at that location, the same relationship that has been found in V1. Magnification factor in MT is only about onefifth that reported in V1 within the central 5° but appears to decline somewhat less steeply than in V1 with increasing eccentricity. Because the smaller magnification factor in MT relative to V1 is complemented by larger receptive field size and scatter, the point-image size (the diameter of the region of cortex activated by a single point in the visual field) is roughly comparable in the two areas. On the basis of these results, as well as on our previous finding that 180° of axis of stimulus motion in MT are represented in about the same amount of tissue as 180° of stimulus orientation in V1, we suggest that a stimulus at one point in the visual field activates at least as many functional “modules” in MT as in V1.

Reflex pathways from group II muscle afferents. 3. Secondary spindle afferents and the FRA: a new hypothesis.

Abstract: A hypothesis is forwarded regarding the role of secondary spindle afferents and the FRA (flexor reflex afferents) in motor control. The hypothesis is based on evidence (cf. Lundberg et al. 1987a, b) summarized in 9 introductory paragraphs. Group II excitation. It is postulated that subsets of excitatory group II interneurones (transmitting disynaptic group II excitation to motoneurones) may be used by the brain to mediate motor commands. It is assumed that the brain selects subsets of interneurones with convergence of secondary afferents from muscles whose activity is required for the movement. During movements depending on coactivation of static gamma-motoneurones impulses in secondary afferents may servo-control transmission to alpha-motoneurones at an interneuronal level. The large group II unitary EPSPs in interneurones are taken to indicate that, given an adequate interneuronal excitability, impulses in single secondary afferents may fire the interneurone and produce EPSPs in motoneurones; interneuronal transmission would then be equivalent to that in a monosynaptic pathway but with impulses from different muscles combining into one line. It is postulated that impulses in the FRA are evoked by the active movements and that the role of the multisensory convergence from the FRA onto the group II interneurones is to provide the high background excitability which allows the secondary spindle afferents to operate as outlined above. The working hypothesis is put forward that a movement governed by the excitatory group II interneurones is initiated by descending activation of these interneurones, but is maintained in a later phase by the combined effect of FRA activity evoked by the movement and by spindle secondaries activated by descending activation of static gamma-motoneurones. As in the original "follow up length servo" hypothesis (Rossi 1927; Merton 1953), we assume that a movement at least in a certain phase can be governed from the brain solely or mainly via static gamma-motoneurones. However, our hypothesis implies that the excitatory group II reflex connexions have a strength which does not allow transmission to motoneurones at rest and that the increase in the gain of transmission during an active movement is supplied by the movement itself. Group II inhibition. It is suggested that the inhibitory reflex pathways like the excitatory ones have subsets of interneurones with limited group II convergence. When higher centres utilize a subset of excitatory group II interneurones to evoke a given movement, there may mobilize inhibitory subsets to inhibit muscles not required in the movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Trajectory control in targeted force impulses. II. Pulse height control

Abstract: The present report examines the control strategy adopted by subjects to modulate the amplitude of transient force responses aimed to a target. Previous studies (Freund and Budingen 1978; Ghez and Vicario 1978) suggest that subjects modulate the rate of rise of force while maintaining force rise time at a near-constant value, independent of peak force. Such studies, however, have examined only the most rapid responses where force rise time could have been at a physiological limit. We now examine whether this control policy is dependent on an instruction to produce the fastest possible trajectories, or whether it is freely selected by subjects to maximize accuracy when rise time is unconstrained. We compared responses made by six subjects, under two task conditions: 1. Fast, "make the force impulse as brief as possible"; and 2. Accurate, "be as accurate as possible without regard to rise time". Subjects were trained to produce monotonic flexion force impulses at the elbow to match the amplitudes of visually presented target shifts. Targets of three different were presented in randomized order. Responses made under the Accurate condition were less variable at each target amplitude than those under the Fast condition. Under both conditions, the initial peaks of the first and second time derivatives of force, early measures of trajectory dynamics, were strongly predictive of the peak force achieved and were correlated with the required force (target amplitude). Therefore, response trajectories must have been largely preprogrammed, and, further, the degree to which the initial peak d2F/dt2 predicts the peak force achieved represents a measure of the contribution of a preplanned motor program to trajectory formation. Subjects showed two systematic differences in trajectories between conditions. First, in all subjects force rise time was greater in the Accurate condition than in the Fast condition. Second, while in the Fast condition there was a modest dependence of force rise time on peak force, in the Accurate condition this dependence disappeared. Thus, when subjects were attempting to be as accurate as possible, they more consistently regulated force rise time around a constant value. This pulse height control policy allows responses of different amplitudes to be produced by proportional scaling of a stereotyped waveform. We conclude that a pulse height control policy with regulation of force rise time is a strategy adopted by subjects to simplify accurate control of response amplitude.

Spatial learning and memory following fimbria-fornix transection and grafting of fetal septal neurons to the hippocampus.

Abstract: The ability of intrahippocampal grafts of fetal septal-diagonal band tissue, rich in developing cholinergic neurons, to ameliorate cognitive impairments induced by bilateral fimbria-fornix transections in rats was examined in three experiments using the Morris water-maze to test different aspects of spatial memory. Experiment 1. Rats with fimbria-fornix lesions received either septal cell suspension grafts or solid septal grafts; normal rats and rats with lesions alone were used as controls. Sixteen weeks after surgery, the rats' spatial learning and memory were tested in the water-maze using a place test, designed to investigate place navigation performance, in which rats learned to escape from the water by swimming to a platform hidden beneath the water's surface. After 5 days of training, the rats were given a spatial probe test in which the platform was removed from the tank to test spatial reference memory. Experiment 2. The same rats used in Exp. 1 were tested in a delayed-match-to-sample, working memory version of the water-maze task. The platform was located in one of two possible locations during each trial, which was composed of 2 swims. If the rat remembered the location of the platform on the 2nd swim of a trial, it should find the platform more quickly on that swim, and thereby demonstrate working memory. Experiment 3. Prior to receiving fimbria-fornix lesions, normal rats were trained in a modification of the water-maze task using alternating cue navigation and place navigation trials (i.e., with visible or non-visible escape platforms). The retention and reacquisition of the place task and the spatial probe test were examined in repeated tests up to 6 months after the lesion and intrahippocampal grafting of septal cell suspensions. The effects of central muscarinic cholinergic receptor blockade with atropine were also tested. Normal rats performed well in both the place and spatial probe tests. In contrast, rats with fimbria-fornix lesions only were unable to acquire or retain spatial information in any test. Instead, these rats adopted a random, nonspatial search strategy, whereby their latencies to find the platform decreased in the place navigation tasks. Sixty to 80% of the rats with septal suspension or solid grafts had recovered place navigation, i.e., the ability to locate the platform site in the tank, in Exp. 1 and 3, and they showed a significantly improved performance in the working memory test in Exp. 2. Atropine abolished the recovered place navigation in the grafted rats, whereas normal rats were impaired to a lesser extent. In contrast, atropine had no effect on the non-spatial strategy adopted by rats with fimbria-fornix lesions only. The results show that: (1) fimbria-fornix lesions disrupt spatial learning and memory in both naive and pretrained rats; (2) with extended training the fimbria-fornix lesioned rats develop an efficient non-spatial strategy, which enables them to reduce their escape latency to levels close to those of intact controls; (3) intrahippocampal septal grafts can restore the ability of the lesioned rats to use spatial cues in the localization of the platform site; and (4) the behavioural recovery produced by grafts is dependent upon an atropine sensitive mechanism.

Postural coactivation and adaptation in the sway stabilizing responses of normals and patients with bilateral vestibular deficit.

Abstract: The experiments were designed to test two hypotheses and their corollaries: 1 That adaptation of EMG responses to support surface rotations is due to a decrease in the gain of proprioceptively triggered long-loop stretch reflexes (Nashner 1976), and that the adaptation is dependent on a normally functioning vestibular system (Nashner et al 1982); 2 That EMG responses to rotations are generated primarily by vestibulo-spinal reflexes triggered by head accelerations (Allum and Pfaltz 1985) and comprise a coactivation of opposing leg muscles (Allum and Budingen 1979) Adaptation with successive dorsi-flexive rotations of the support surface was investigated in the EMG responses of the ankle muscles, soleus (SOL) and tibialis anterior (TA), as well as the neck muscles, trapezius (TRAP) and splenius capitis (SPLEN CAP), both for normal subjects and for patients with bilateral peripheral vestibular deficit Both normals and patients who first received the stimulus with their eyes open demonstrated decreasing activation at medium latency (ML), that is, with an onset at about 125 ms, and long latency (LL) responses with an onset ca 200 ms This was the case for both ankle and neck muscles when the EMG response areas for the first 3 and second 7 of 10 trials were compared Ankle muscle responses in the patients were diminished in area with respect to normals both with the eyes open and with the eyes closed Ankle torque recordings from the patients were also smaller in amplitude, and these attenuated differently from normal torque responses Functional coupling of the opposing ML and LL SOL and TA muscle responses was confirmed by the nearly coincident onset times and significantly correlated EMG response areas At ML, ankle torque was highly correlated with TA activity when the influence of SOL was controlled At LL, SOL activity was highly correlated with torque when the influence of TA was controlled The delay of torque adaptation beyond the period of ML activity in normals, but not in the patients was attributed to the proportionally balanced coactivated muscle patterns producing a consistent force output and level of stability in normals The results indicate that the adaptation in EMG response amplitudes during a sway stabilisation task is not dependent on a normally functioning vestibular system nor on visual inputs but rather appears to be due to a generalized habituation in the postural control system Evidence against a change in the gain of proprioceptively triggered long loop reflexes being responsible for adaptation is based on the fact that the adaptation is not restricted to the stretched SOL muscle but includes its agonist, TA, and that the adaptation is not local but also occurs in neck muscles The results supported the hypothesis that postural reflexes to support surface rotations may well be triggered by stretch reflexes in the lower leg or neck muscles, however, their amplitude modulation is overwhelmingly under the control of vestibulo-spinal signals

Anatomical and electrophysiological evidence for a direct projection from ammon's horn to the medial prefrontal cortex in the rat

Abstract: Following microinjection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the medial prefrontal cortex (defined as the neocortical area innervated by the thalamic mediodorsal nucleus) labelled cells were observed in the pyramidal layer of the CA1 field of Ammon's horn. Observations made using antidromic stimulation confirmed these results, and revealed the slow conduction velocity of the fibres of the hippocampal cells innervating the prefrontal cortex. Taken together, these data provide evidence for a direct projection of CA1 cells to the medial prefrontal cortex.

Postembedding light- and electron microscopic immunocytochemistry of amino acids: description of a new model system allowing identical conditions for specificity testing and tissue processing.

Abstract: Specificity testing should be performed under conditions identical to or closely similar to those of the immunocytochemical procedure. This paper describes a new model system that meets this requirement for postembedding immunocytochemistry of amino acids at the light- and electron microscopic levels. Test conjugates, obtained by reacting different amino acids with brain macromolecules in the presence of glutaraldehyde, were freeze-dried and embedded in an epoxy resin (Durcupan) exactly as for brain tissue. One section from each of the embedded amino acid conjugates and from a brain protein-glutaraldehyde conjugate (without amino acid) were piled on top of each other and embedded anew. Transverse semithin (0.5 μm) and ultrathin sections were cut through the stack. These test sections, in which all the different conjugates were represented, were then processed in the same drops of sera as the tissue sections to permit identical conditions for testing and immunocytochemistry. After immunogold labelling for electron microscopy, a quantitative expression of crossreactivity was obtained by computer-assisted calculation of gold particle densities over the different conjugates. The antisera used in the present study (glutamate anti-serum 13, taurine antiserum 20, and GABA antiserum 26) showed highly selective labelling of the respective amino acid conjugates and produced distinct labelling patterns in simultaneously processed cerebellar sections.

Relationship between EMG patterns and kinematic properties for flexion movements at the human wrist

Abstract: EMG patterns associated with voluntary wrist flexion movements were studied in normal human subjects. Initially, subjects were trained to produce movements within five specified velocity ranges while the amplitude of the movement and the opposing load remained constant. In a second set of experiments, subjects were required to produce movements at four different amplitudes, moving as rapidly as possible against a constant load. Finally, with movement velocity and amplitude kept constant, the external load was varied so that different forces were required to generate the movements. The slowest movements were associated with a prolonged burst of EMG activity from the agonist muscle with little or no antagonist activity. With increasing movement velocity, there was a gradual evolution to the characteristic "triphasic" pattern associated with rapid voluntary movements. As velocity of movement increased further, the amplitude and area of the EMG bursts increased while burst duration and interburst intervals decreased. Increases in movement amplitude were accomplished mainly by changing the timing of the EMG bursts; with larger amplitude movements the antagonist burst occurred later. With movements against larger loads there was an increase in the size of the agonist burst and a decrease in the antagonist burst, but no change in the relative timing of the EMG bursts. These systematic changes in EMG patterns associated with different types of movement provide an indirect method of obtaining information concerning the motor programs which generate the movements.

Sensory perception during movement in man.

Abstract: The ability of subjects to perceive innocuous stimuli in the presence and absence of movement was evaluated using electrical stimulation of the skin. The subjective intensity of suprathreshold stimuli was unchanged during movement. Discrimination of small differences in the intensity of suprathreshold stimuli (difference thresholds) was also not altered by movement while, in the same subjects, detection thresholds were increased during movement of the stimulated arm. These results suggest that the elevation of detection thresholds during movement can be explained by masking. Both active and passive movement of the stimulated limb increased detection thresholds, with active movement having a slightly greater and more consistent effect than passive movement. Thus, both central and peripheral feedback factors appear to play a role in diminishing one's ability to detect weak stimuli during movement. Attention was also shown to influence performance of the detection task.

Trajectory control in targeted force impulses. III. Compensatory adjustments for initial errors

Abstract: In the preceding study (Gordon and Ghez 1987), we showed that accurately targeted isometric force impulses produced by human subjects are governed by a pulse height control policy. Different peak forces were achieved by modulating the rate of rise of force while force rise time was maintained close to a constant value and independent of peak force. An early measure of the rate of rise of force, peak d2F/dt2, was scaled to the required force (target amplitude) and highly predictive of the peak force achieved. In six subjects examined, peak d2F/dt2 accounted for between 70% and 96% of the total variance in peak force. In the present study, we further examined these targeted responses to determine whether the residual variability not predicted by peak d2F/dt2 could be accounted for by adjustments to the force trajectories which compensated for initial errors in the scaling of the d2F/dt2. A statistical model of the determinants of peak force was tested. This model included two paths by which the target amplitude could independently influence the peak force achieved. The first path was preprogrammed pulse height control. In this path, target amplitude determined the initial rate of rise of force (peak d2F/dt2) which in turn determined the final peak force achieved. The second path was an independent influence of errors in the initial scaling of peak d2F/dt2 on peak force. Multiple regression analysis was performed on trajectory variables within the sets of responses by each subject in each condition to determine whether the second path contributed significantly to explaining the variance in peak force. In each subject and condition, there was a significant independent influence of error in d2F/dt2 on peak force, and the direction of this effect was to decrease the magnitudes of peak force errors. These compensatory adjustments accounted for between 1% and 14% of the total variance in peak force. Further multiple regression analyses revealed that inappropriate scaling of the initial phase of the trajectories was compensated for by shortening or prolonging the force rise time. These trajectory adjustments were in turn implemented by modulation of the timing and magnitude of the contractions in the agonist and antagonist muscles that produced the force trajectories. Because these compensatory adjustments were evident in the EMG pattern at latencies too short to be accounted for by peripheral feedback, we assume that they depend on internal monitoring of the unfolding neural commands. These internal feedback processes act in parallel with the programmed commands, both determining the force trajectory. Language: en

Trajectory control in targeted force impulses. I. Role of opposing muscles.

Abstract: The functional role of opposing muscles in the production of isometric force trajectories was studied in six adult subjects producing impulses and steps of elbow flexor force, with different rise times and amplitudes. Rapidly rising forces were invariably associated with an alternating pattern of EMG activity in agonist and antagonist muscles: an agonist burst (AG1) initiated the development of force in the desired direction while a reciprocal burst in the antagonist (ANT-R) led to the deceleration of the force trajectory prior to the peak force. The temporal pattern of agonist and antagonist activation was dependent on force rise time. Force trajectories with long rise times (greater than 200 ms) were entirely controlled by the agonist, and EMG activity closely followed the contours of the rising force trajectory. For rise times of about 120 to 200 ms, agonist activation formed a discrete EMG burst, and force continued to rise during the subsequent silent period. For brief force rise times (less than 120 ms), reciprocal activation of the antagonist muscle occurred at about the time of the peak dF/dt. The integrated magnitude of AG1 was dependent on peak force but was independent of force rise time. AG1 duration varied directly with both peak force and force rise time. The integrated value of ANT-R varied as an inverse function of force rise time and was minimally influenced by peak force. ANT-R was present with the same magnitude and timing in both force impulses and steps when rise times were equal; therefore it did not serve to return force to baseline. Rather it served to truncate the rising force when very brief rise times were required, thus compensating for the low-pass filter properties of the agonist muscle. Subjects were able to voluntarily suppress ANT-R in rapidly accelerated force trajectories, indicating that the linkage between the commands controlling agonist and antagonist is not obligatory; however AG1 was then prolonged. Our findings emphasize that neuronal commands to opposing muscles acting at a joint must be adapted to constraints imposed by the properties of the neuromuscular plant.

Frontal eye field lesions in monkeys disrupt visual pursuit

Abstract: Discussions of the cortical control of eye movement have generally attributed the generation of saccadic movements to the frontal eye fields (FEF) and the control of pursuit movements to posterior parietal or prestriate cortex. Monkeys were trained to perform a series of oculomotor tasks, including both saccade and pursuit paradigms. Surgical ablation of the frontal eye fields produced only minor disruption of saccade performance, but caused a dramatic deficit in the ability of monkeys to visually track a slowly moving target. This disorder has not previously been associated with FEF lesions. These results necessitate a major re-evaluation of the way in which the cerebral cortex participates in oculomotor control.

The origin of corticospinal projection neurons in rat

Abstract: The distribution of corticospinal projection neurons in adult rats was determined using a retrograde tracing technique. Horseradish peroxidase (HRP) and an emulsifier (Nonidet) were injected into the 5th and 6th segments of the cervical spinal cord. The greatest concentrations of HRP-positive neurons were distributed in area 4 and rostral area 6/8 (motor cortices) and medial area 3 and caudal area 2 (somatosensory cortices). The largest labeled neurons were in areas 4 and 3. HRP-positive neurons were absent or few in regions of motor and somatosensory fields which contained the face representation. Less dense concentrations of retrogradely labeled neurons were also in posterior parietal and association areas 14, 39 and 40, rostral occipital visual areas 18a and 18b, and anterior cingulate and prefrontal areas 24a, 24b, and 32. The topography of the corticospinal pathway was determined by injecting HRP without Nonidet into the cervical, upper thoracic, lower thoracic, or lumbar spinal cord. Although the distribution of labeled neurons decreased with distance down the spinal cord, the size of the corticospinal neurons in each cytoarchitectonic area was not significantly different regardless of where the injection was placed. For example, upper thoracic cord injections retrogradely labeled neurons in each of the regions containing neurons filled by cervical cord injections, however, lumbar injections retrogradely labeled neurons only in caudal areas 4 and 3 and in area 18b. The distribution of corticospinal neurons in rats is similar to the organization of the corticospinal system in higher animals. The origin of corticospinal neurons in occipital and cingulate cortices may be related to visuomotor and visceromotor control.

Cognitive spatial-motor processes. 1. The making of movements at various angles from a stimulus direction.

Abstract: Naive human subjects (N = 18) were asked to move a manipulandum on a phase in directions other than going straight towards a visual stimulus. They were instructed verbally to generate a movement at an angle from a stimulus direction which varied in 2-dimensional (2-D) space from trial to trial in a pseudorandom fashion. Each subject performed eight sets of twenty consecutive trials: one for moving in the stimulus direction and seven for moving in directions at an angle from it. The angles were 5, 10, 15, 35, 70, 105 and 140 degrees. Nine subjects were instructed to move in the clockwise (CW) departure and 9 to move in either (EI) the clockwise or the counterclockwise (CCW) departure, as they wished. The direction of the movement in 2-D space and the reaction time (RT) were measured. The mean angle achieved in a given set overshot the instruction angle, especially in the lower range (5-35 degrees). The reaction time, RT phi, of movements made at an angle from the stimulus direction showed two kinds of change; first, a step increase from the reaction time, RT0, of movements in the stimulus direction, and second, superimposed upon it, a linear increase with the amplitude of the angle. The slope of the line was similar for the CW (2.37 ms/degree) and the EI case (2.28 ms/degree), but the step increase (y-intercept) for the EI case (84 ms) was substantially less than that of the CW case (155 ms). The linear increase of the RT with angle is compatible with the idea that performance in the task may involve a mental rotation of the imagined movement vector about its origin. The rotation would begin from the stimulus direction and end when the required angle is judged to have been reached; in addition, corrections of this angle at the end of the rotation could be made. The slope of 2.37 ms/degree observed in the CW case would correspond to a rotation rate of 422 degrees/s. The finding of a similar rate for the EI case indicates a similarity in strategy with regard to achieving a desired angle. In contrast, the lower intercept observed for the EI case suggests significant savings in processing information which is unconstrained with regard to angular departure. Assuming this model of internal motion, we analyzed the amplitude-accuracy relations using Fitts' (1954) approach to real movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronal sources of theta rhythm in the entorhinal cortex of the rat. II. Phase relations between unit discharges and theta field potentials.

Abstract: The discharge patterns and layer distribution of entorhinal cortex (EC) units were investigated in paralysed and locally anesthetized rats injected with physostigmine in order to induce theta (θ) rhythm. Entorhinal unit activity and field potentials were recorded simultaneously with the same micropipette. Hippocampal CA1 θ rhythm was used as reference. Statistical analysis included auto- and cross-correlations and interval histograms. Results showed: a. the existence of rhythmic and non-rhythmic cells, both tending to fire in a constant phase relationship with θ rhythm; b. in all EC subdivisions, most rhythmic cells were located in superficial cell layers (II–III); c. on the average, rhythmic cells from the medial EC fired synchronously; d. non-rhythmic cells tended also to fire synchronously but with an opposite phase relationship with respect to rhythmic neurons. Although a complex organization in the rhythmicity of EC units is revealed, it is concluded that the neuronal sources of θ activity in the EC are located in superficial cell layers, and it is strongly suggested that the EC output through the perforant path may rhythmically modulate the discharge pattern of hippocampal pyramidal and dentate granule cells.

Neuronal activities in the primate motor fields of the agranular frontal cortex preceding visually triggered and self-paced movement.

Abstract: Single cell activity was examined in the three motor fields of the monkey frontal cortex with the aim of comparing the neuronal activity preceding movements triggered by a visual signal to that preceding nontriggered (self-paced) movements. The following findings emerged from this study. 1. Neuronal activity changes were observed at two different phases in relation to the movement onset; the shortlead type observed within 480 ms prior to the movement onset and the long-lead type, beginning earlier (typically 1 to 2 s). 2. Neurons in both the supplementary motor area (SMA) and premotor area (PM) exhibited the short-lead activity changes prior to the triggered and self-paced movement. Their magnitudes were similar in 63% of SMA and in 36% of PM neurons, whether the movement was triggered or self-paced. 3. SMA neurons, as a whole, were not less active before the triggered than self-paced movement. 4. On the other hand, as many as 92 PM neurons (61%) were related exclusively or peferentially to the triggered movement. 5. The majority of precentral motor cortex (MC) neurons exhibited similar activity changes before the two modes of movement initiation. 6. The long lead type of activity changes were observed mainly prior to the self-paced and much less frequently before the triggered movement. They were particularly abundant among SMA neurons. These results do not support the simple dichotomy hypothesis that SMA primarily takes part in self-paced movement and PM is only involved in visually triggered movement. However, PM neurons show relatively more prominent responses to the visual trigger signal and SMA neurons are intimately related to a long-lasting process leading to initiation of the self-paced movement.

Organization of the projections from barrel cortex to thalamus in mice studied with Phaseolus vulgaris-leucoagglutinin and HRP.

Abstract: In order to elucidate the geometric organization of projections from the barrel cortex to the thalamus, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were made. The injections were confined to one barrel column (i.e. barrel in layer IV + cortical tissue above and below it). Axonal terminations could be demonstrated in three thalamic nuclei: reticularis (RT), ventrobasalis (VB) and posterior (PO). Anterograde terminal labelling was obtained in RT + VB; in PO only; or in RT + VB + PO. The terminals labelled in PO were much larger than those in RT and VB. The termination areas in RT, VB and PO were shaped like rods which have a rostro-caudal orientation. These cortico-thalamic projections are discretely and topographically organized. The clearest such arrangement was found in VB. Here, projections from the A row of barrels in BF terminate dorsally, whereas those from the C row end ventrally. Barrel A1 projects to the lateral part of VB, whereas A4, to more medial parts; other rows are arranged similarly. These results were compared with the distribution of thalamo-cortical projection neurons that were labelled after iontophoretic HRP injections in individual barrels. We concluded that the corticothalamic projections originating from one barrel column contact an arc of barreloids in VB.

Enhancement of the responses of ascending tract cells in the cat spinal cord by acute inflammation of the knee joint.

Abstract: 1. Recordings were made from 16 ascending tract cells in the spinal cords of anaesthetized, spinalized cats before and after an acute arthritis was produced by injection of kaolin and carrageenan into the knee joint. 2. The responses tested routinely were to passive flexion of the knee, an innocuous movement. In some cases, responses to other movements were also tested, and changes in background discharge rates were monitored. 3. Control recordings for a period of 1 h or in 3 cases of 3 h indicated that the responses to flexion were reasonably stationary. 4. Four tract cells that initially showed little or no response to flexion of the knee joint developed large responses within 1 to 2 h after inflammation of the joint. 5. Another 9 cells were tested that had responses to flexion of the knee joint prior to inflammation. In 6 cases, inflammation produced enhanced static or transient responses. In 2 cases, the effect of flexion was initially inhibitory or variable, but after inflammation these cells showed large excitatory responses. In the other case, inflammation had no effect. Background discharges were increased by inflammation in 6 of these 9 cells. 6. The effect of inflammation of the knee joint was tested on 3 tract cells that had no clearly defined receptive field in the knee. In 1 case, a response developed to knee flexion after acute inflammation was produced. In the other 2 cases, there were initially responses to knee flexion, but these were unchanged by inflammation. 7. Two of the cells tested had bilateral receptive fields in or around the knee joints. Inflammation of one knee joint enhanced the responses to flexion of the same but not of the contralateral knee in one case but greatly increased the responses to flexion of both knees in the other case. 8. Injections of prostaglandin (PGE2) caused an enhancement of the responses to knee flexion beyond that caused by inflammation in 5 of 7 cases. One cell whose responses to flexion of the knee were unaffected by inflammation showed inhibitory responses to prostaglandin injections into the inflamed knee joint. 9. The effects of inflammation on the responses of ascending tract cells of the spinal cord appear to serve as a useful neural model of the events responsible for the development of arthritic pain.

Human cerebral potentials evoked by CO2 laser stimuli causing pain.

Abstract: Brief radiant heat pulses, generated by a CO2 laser, were used to activate slowly conducting afferents in the hairy skin in man. In order to isolate C-fibre responses a preferential A-fibre block was applied by pressure to the radial nerve at the wrist. Stimulus estimation and evoked cerebral potentials (EP), as well as reaction times, motor and sudomotor activity were recorded in response to each stimulus. With intact nerve, the single supra-threshold stimulus induced a double pain sensation: A first sharp and stinging component (mean reaction time 480 ms) was followed by a second burning component lasting for seconds (mean reaction time 1350 ms). Under A-fibre block only one sensation remained with characteristics and latencies of second pain. The heat pulse evoked potential consisted of a late vertex negativity at 240 ms (N240) followed by a prominent late positive peak at 370 ms (P370). Later activity was not reliably present. Under A-fibre block this late EP was replaced by an ultralate EP beyond 1000 ms, which in the conventional average looked like a slow halfwave of 800 ms duration. This potential was distinct from eye movements, skin potentials or muscle artefacts. With cross-correlation methods waveforms similar to the N240/P370 were detected in the latency range from 900 to 1500 ms during A-fibre block, indicating a much greater latency jitter of the ultralate EP. Latency corrected averaging with a modified Woody filter yielded a grand mean ultralate EP (N1050/P1250), the shape of which was surprisingly similar to the late EP (N240/P370). The similarity of these components indicates that both EPs may be secondary responses to afferent input into neural centers, onto which myelinated and unmyelinated fibres converge. Such convergence may also explain through the known mechanisms of short term habituation and selective attention, why ultralate EPs are not reliably present without peripheral nerve block.