Showing papers in "Experimental Brain Research in 1989"

Alteration of proprioceptive messages induced by tendon vibration in man: a microneurographic study.

Abstract: The activities of single proprioceptive fibres were recorded from the lateral peroneal nerve using transcutaneously implanted tungsten microelectrodes. Unitary discharges originating from muscle spindle primary and secondary endings and Golgi tendon organs were identified by means of various physiological tests. The sensitivity of proprioceptors to mechanical vibrations with a constant low amplitude (0.2–0.5 mm) applied at various frequencies to the tendon of the receptor-bearing muscle was studied. Muscle spindle primary endings (Ia fibres) were found to be the most sensitive to this mechanical stimulus. In some cases their discharge could be driven in a one-to-one manner up to 180 Hz. Most of them also fired harmonically with the vibration up to 80 Hz and then discharged in a subharmonic manner (1/2–1/3) with increasing vibration frequencies. Muscle spindle secondary endings (II fibres) and Golgi tendon organs (Ib fibres) were found to be either insensitive or only slightly sensitive to tendon vibration in relaxed muscles. The effects of tendon vibration on muscle spindle sensory endings response to muscle lengthening and shortening induced by imposed constant velocity or sinusoidal movements of the ankle joint were studied. Modulation of the proprioceptive discharge frequency coding the various joint movement parameters was either completely or partly masked by the receptor response to vibration, depending on the vibration frequency. Moreover, vibrations combined with sinusoidal joint movements elicited quantitatively erroneous proprioceptive messages concerning the movement parameters (amplitude, velocity). The sensitivity of the Golgi tendon organs to vibration increased greatly when the receptor-bearing muscle was tonically contracted. These data confirm that vibration is able to preferentially activate the Ia afferent channel, even when the vibration amplitude is low. They define the frequency sensitivity of the muscle spindle primary and secondary endings and the Golgi tendon organs. They also show that the physiological messages triggered by ongoing motor activities undergo a series of changes during the exposure of muscles to vibration.

Comparison of human infants and rhesus monkeys on Piaget's AB task: evidence for dependence on dorsolateral prefrontal cortex.

Abstract: This paper reports evidence linking dorsolateral prefrontal cortex with one of the cognitive abilities that emerge between 7.5-12 months in the human infant. The task used was Piaget's Stage IV Object Permanence Test, known as AB (pronounced "A not B"). The AB task was administered (a) to human infants who were followed longitudinally and (b) to intact and operated adult rhesus monkeys with bilateral prefrontal and parietal lesions. Human infants displayed a clear developmental progression in AB performance, i.e., the length of delay required to elicit the AB error pattern increased from 2-5 s at 7.5-9 months to over 10 s at 12 months of age. Monkeys with bilateral ablations of dorsolateral prefrontal cortex performed on the AB task as did human infants of 7.5-9 months; i.e., they showed the AB error pattern at delays of 2-5 s and chance performance at 10 s. Unoperated and parietally operated monkeys succeeded at delays of 2, 5, and 10 s; as did 12 month old human infants. AB bears a striking resemblance to Delayed Response, the classic test for dorsolateral prefrontal function in the rhesus monkey, and indeed performance on AB and Delayed Response in the same animals in the present study was fully comparable. These findings provide direct evidence that AB performance depends upon dorsolateral prefrontal cortex in rhesus monkeys and indicates that maturation of dorsolateral prefrontal cortex may underlie the developmental improvement in AB performance of human infants from 7.5-12 months of age. This improvement marks the development of the ability to hold a goal in mind in the absence of external cues, and to use that remembered goal to guide behavior despite the pull of previous reinforcement to act otherwise. This confers flexibility and freedom to choose and control what one does.

Two classes of cortical gaba neurons defined by differential calcium binding protein immunoreactivities

Abstract: Calcium ions play a key role in many aspects of neuronal behavior and certain calcium binding proteins that may influence this behavior are differentially distributed in the central nervous system. In this study it is shown that immunoreactivity for calbindin-28 and for parvalbumin is localized in separate populations of inhibitory GABA interneurons in all areas of the neocortex of Old World monkeys. Virtually all GABA neurosn show immunoreactivity for one or other calcium binding protein but, except for a few cells in layer IV, GABA cells do not show immunoreactivity for both proteins. Among the two cell populations, parvalbumin immunoreactivity characterizes basket neurons while calbindin immunoreactivity characterizes double bouquet neurons. These findings suggest that the two GABA cell types differ in their regulation of calcium homeostasis and may yield clues to their different roles in intracortical circuitry.

Hippocampal granule cells are necessary for normal spatial learning but not for spatially-selective pyramidal cell discharge

Abstract: The effects of massive destruction of granule cells of the fascia dentata on the spatial and temporal firing characteristics of pyramidal cells in the CA1 and CA3 subfields of the hippocampus were examined in freely moving rats Microinjections of the neurotoxin colchicine were made at a number of levels along the septo-temporal axis of the dentate gyri of both hemispheres, resulting in destruction of over 75% of the granule cells By contrast there was relatively little damage to the pyramidal cell fields As assessed by three different behavioral tests, the colchicine treatment resulted in severe spatial learning deficits Single units were recorded from the CA1 and CA3 subfields using the stereotrode recording method while the animals performed a forced choice behavioral task on the radial 8-arm maze Considering the extent of damage to the dentate gyrus, which has hitherto been considered to be the main source of afferent information to the CA fields, there was remarkably little effect on the spatial selectivity of “place cell” discharge on the maze, as compared to recordings from control animals There was, however, a change in the temporal firing characteristics of these cells, which was manifested primarily as an increase in the likelihood of burst discharge The main conclusion derived from these findings is that most of the spatial information exhibited by hippocampal pyramidal cells is likely to be transmitted from the cortex by routes other than the traditional “trisynaptic circuit” These routes may include the direct projections from entorhinal layers II and III to CA3 and CA1, respectively

Neuronal activity in the human lateral temporal lobe. I. Responses to speech.

Abstract: Single and multiple unit neuronal activity was recorded from the cortex of the lateral temporal lobe in conscious humans during open brain surgery for the treatment of epilepsy. Recordings were obtained from the right and left superior, middle and inferior temporal gyrus of 34 patients (41 recording sites). Recordings were restricted to regions to be resected during subsequent surgery. This excluded recordings from language areas proper. Neuronal responses to words and sentences presented over a loudspeaker and during free conversation were recorded. No significant differences between the right and left hemisphere were obvious. All neurons in the superior temporal gyrus responded to various aspects of spoken language with temporally well defined activation/inhibition patterns, but not or only little to non-linguistic noises or tones. Excitatory responses were typically short or prolonged (up to several hundred ms) bursts of discharges at rates above 20/sec, reaching peak rates of 50-100/s. Such responses could be specifically related to certain combinations of consonants suggesting a function in categorization, they could depend on word length, could differentiate between polysyllabic and compound words of the same length or could be unspecifically related to language as such. No formant specific responses were found, but the prolonged excitations across syllables suggest that consonant/vowel combinations may play a role for some activation patterns. Responses of some neurons (or neuronal populations) depended on the attention paid to the words and sentences, or the task connected with them (repeat words, speech addressed to the patient demanding something). Neurons in the middle and inferior temporal gyrus were only little affected by listening to single words or sentences, but some were unspecifically activated by words or while listening to sentences. Excitatory responses varied within a limited range of discharge rates usually below 5-10/s. Phonetic distortion of spoken language could reduce responses in superior temporal gyrus neurons, but also the slight changes in discharge rate of middle temporal neurons could be absent during distorted and uncomprehensible speech sounds. We conclude that superior temporal gyrus neuron responses reflect some general phonetic but not semantic aspects of spoken language. Middle and inferior temporal gyrus neurons do not signal phonetic aspects of language, but may be involved in understanding language under certain conditions.

Cognitive spatial-motor processes. 3. Motor cortical prediction of movement direction during an instructed delay period.

Abstract: We studied the activity of 123 cells in the arm area of the motor cortex of three rhesus monkeys while the animals performed a 2-dimensional (2-D) step-tracking task with or without a delay interposed between a directional cue and a movement triggering signal. Movements of equal amplitude were made in eight directions on a planar working surface, from a central point to targets located equidistantly on a circle. The appearance of the target served as the cue, and its dimming, after a variable period of time (0.5–3.2 s), as the “go” stimulus to trigger the movement to the target; in a separate task, the target light appeared dim and the monkey moved its hand towards it without waiting. Population histograms were constructed for each direction after the spike trains of single trials were aligned to the onset of the cue. A significant increase (3–4×) in the population activity was observed 80–120 ms following the cue onset; since the minimum delay was 500 ms and the average reaction time approximately 300 ms, this increase in population activity occurred at least 680–720 ms before the onset of movement. A directional analysis (Georgopoulos et al. 1983, 1984) of the changes in population activity revealed that the population vector during the delay period pointed in the direction of movement that was to be made later.

Unitary characteristics of presumptive cholinergic tegmental neurons during the sleep-waking cycle in freely moving cats.

Abstract: A total of 260 neurons were recorded in the rostral pontine tegmentum of freely moving cats during the sleep-waking cycle. Of these, 207 neurons (80%) were located in the dorsal pontine tegmentum containing monoaminergic and choline acetyltransferase (ChAT)-immunoreactive, or cholinergic neurons. In addition to presumably monoaminergic PS-off cells (n = 51) showing a cessation of discharge during paradoxical sleep (PS) and presumably cholinergic PGO-on cells (n = 40) exhibiting a burst of discharge just prior to and during ponto-geniculo-occipital (PGO) waves, we observed tonic (n = 108) and phasic (n = 61) neurons exhibiting, respectively, tonic and phasic patterns of discharge during wakefulness and/or paradoxical sleep. Of 87 tonic cells histologically localized in the dorsal pontine tegmentum rich in cholinergic neurons, 46 cells (53%) were identified as giving rise to ascending projections either to the intralaminar thalamic complex (n = 26) or to the ventrolateral posterior hypothalamus (n = 13) or to both (n = 9). Two types of tonic neurons were distinguished: 1) tonic type I neurons (n = 28), showing a tonic pattern and high rates of discharge during both waking and paradoxical sleep as compared with slow wave sleep; and 2) tonic type II neurons (n = 20), exhibiting a tonic pattern of discharge highly specific to the periods of paradoxical sleep. Tonic type I neurons were further divided into two subclasses on the basis of discharge rates during waking: a) rapid (Type I-R; n = 17); and b) slow (Type I-S; n = 11) units with a discharge frequency of more than 12 spikes/s or less than 5 spikes/s, respectively. Like monoaminergic PS-off and cholinergic PGO-on cells, both tonic type II and type I-S cells were characterized by a long spike duration (median: 3.3 and 3.5 ms), as well as by a slow conduction velocity (median = 1.8 and 1.7 m/s). In the light of these data, we discuss the possible cholinergic nature and functional significance of these ascending tonic neurons in the generation of neocortical electroencephalographic desynchronization occurring during waking and paradoxical sleep.

Projections from inferior temporal cortex to prefrontal cortex via the uncinate fascicle in rhesus monkeys.

Abstract: In five rhesus monkeys (Macaca, mulatta) we used anterograde and retrograde tracing techniques to investigate the projection from the inferior temporal cortex (area TE) to the prefrontal cortex as well as the course of the projecting fibers. The results showed that TE projects to both the inferior convexity and orbital surface of prefrontal cortex and that these projections course almost exclusively via the uncinate fascicle. Transection of the uncinate fascicle deprives the prefrontal cortex of virtually all input from TE, but leaves intact inputs from prestriate and parietal visual areas as well as the amygdala. Such transection also leaves intact many projections from TE to targets other than the prefrontal cortex, including the amygdala, ventral putamen, tail of the caudate nucleus, and pulvinar.

Methodological implications of the post activation depression of the soleus H-reflex in man.

Abstract: A long lasting inhibition (> 8 s) of the soleus Hoffmann reflex (H-reflex) was evoked by a preceding soleus H-reflex, by a brief voluntary ankle flexor or extensor muscle contraction or by a tap applied to the Achilles tendon. The time course of this long lasting inhibition was similar in all these cases, suggesting that the same spinal mechanism is involved. Furthermore, it was shown that the post-activation depression may interfere with the determination of inhibitory or facilitatory effects on the H-reflex. It is stressed that when the onset of inhibitory or facilitatory effects on the soleus H-reflex is to be determined in relation to start of an ankle movement, either very long stimulus intervals (> 8 s) must be used, or the onset must be determined in relation to a reference value of the soleus H-reflex, which may be influenced by the long lasting inhibitory effect, but not yet by the succeeding muscle contraction.

Single-unit analysis of pattern-motion selective properties in the middle temporal visual area (MT).

Abstract: The middle temporal visual area (MT) in macaque extrastriate cortex is characterized by a high proportion of neurons selective for the direction of stimulus motion, and is thus thought to play an important role in motion perception Previous studies identified a population of cells in MT that appeared capable of coding the motion of whole visual patterns independent of the motions of contours within them (Gizzi et al 1983; Movshon et al 1985) These “pattern-motion selective” neurons are unlike motion sensitive cells that have been observed at earlier stages of the visual system Using very different criteria, we have also previously indentified an apparently functionally distinct group of MT neurons (Albright 1984) We predicted that these “Type II” neurons correspond to the pattern-motion neurons In the present study, we have applied both sets of criteria to individual neurons in MT and found that these two differently defined sets of cells actually form the same population These results support the idea that MT contributes to a specialized type of motion processing which reflects the integrity of normal perception

A face-responsive potential recorded from the human scalp.

Abstract: Evoked potentials were recorded to the separate tachistoscopic presentation of a variety of faces and other simple and complex visual stimuli. A positive potential of 150–200 ms peak latency which responds preferentially, but not exclusively, to faces was identified in 8 out of 9 subjects. This potential, best recorded from midline central and parietal electrodes, was evoked by all face stimuli, including photographs, outline drawings, and fragmentary figures. Changes in stimulus size and other parameters which do not affect the clarity of the face, generally had little effect on the peak amplitude. Stimulus changes such as face inversion, reversing the contrast polarity of photographic images, and selectively removing particular facial features, produced a marked increase in latency but often only slight attenuation of this peak. These response properties correspond well with those reported for face-related single cells in the temporal cortex of the rhesus monkey. The scalp distribution of this face-responsive peak also appears consistent with bilateral sources in the temporal cortex.

Prefrontal cortex and spatial sequencing in macaque monkey.

Abstract: 1. Single neuron activity was recorded from the prefrontal cortex of two macaque monkeys during the performance of a task involving spatial sequencing. The monkeys faced a panel displaying a central fixation point and three fixed targets (two lateral and one above the point of fixation). In the first phase of each trial, the three targets were turned on in random order: in the second phase, the animal had to press each target, still lighted, in the order of their illumination. Thus, successful performance of the task depended strongly on temporal memory. The animals were fitted with DC-EOG electrodes. 2. Three hundred and two task-related neurons were recorded in the superior arcuate area and caudal part of sulcus principalis. Among the cells whose pattern of activity appeared to be related to the sequencing task, five classes were distinguished: Visual tonic (VT), fixation, context, saccade related and visual phasic cells. In addition, a small number of cells appeared to be related to other aspects of the behavior, but not to the sequencing task. Our present analysis concentrates on two groups of sequencing task-related cells (VT and context cells). 3. The VT cells (35/302-11.5%) were recorded exclusively from the superior arcuate area. All VT cells increased their firing rate (sustained activation) during fixation of the central fixation point (FP) following onset of one of the three targets used, specific for a given cell (directional or spatial selectivity). In one group of VT cells, a shift in the eye position towards the specific peripheral target resulted in the return of the cells' firing rate to the pre-trial level. In the other group of VT cells, reset of the firing rate to pre-trial level was not related to the onset of fixation of the peripheral target. Sustained activation of the VT cells depended also on the sequential order of illumination of the specific target (temporal selectivity). In twenty-four cells (68.5% of VT cells) sustained activation was observed when the target came first in the sequence. Onset of the target in the second or third rank elicited either no response or only a short lasting phasic activation. In the remaining eleven cells (31.5% of VT cells), sustained activation was only observed when the target came second in a given sequence. The firing of the VT cells was correlated with the animals' performance of the task. On trials where the animals selected successive targets in an incorrect order, the temporal pattern of activation of VT cells was different from that in the correctly performed trials. Thus, the correct temporal encoding of a target appeared to be a prerequisite for the correct performance of a sequence. 4. The context cells (36.5%-16/302) were activated when the animal fixated a particular target during execution of the sequence and, like VT cells, were encountered exclusively in the penetrations through the superior arcuate area. Activation also depended on the state (illuminated vs extinguished or hit vs non-hit) of the non-fixated targets and/or on their time-relationships with respect to the fixated target hence context cells. 5. Properties of VT and context cells revealed in the present experiment are consistent with the idea that the superior arcuate area is involved in temporally and spatially extended structures of behavior. If so, the arcuate area would constitute a specialized part of prefrontal cortex implicated in construction of oculomotor plans.

Neuronal activity in the human lateral temporal lobe. II. Responses to the subjects own voice.

Abstract: We have recorded neuronal responses in the lateral temporal lobe of man to overt speech during open brain surgery for epilepsy. Tests included overt naming of objects and reading words or short sentences shown on a projector screen, repetition of tape recorded words or sentences presented over a loudspeaker, and free conversation. Neuronal activity in the dominant and non-dominant temporal lobe were about equally affected by overt speech. As during listening to language (see Creutzfeldt et al. 1989), responses differed between recordings from sites in the superior and the middle or inferior temporal gyrus. In the superior temporal gyrus all neurons responded clearly and each in a characteristic manner. Activation could be related to phonemic aspects, to segmentation or to the length of spoken words or sentences. However, neurons were mostly differently affected by listening to words and language as compared to overt speaking. In neuronal populations recorded simultaneously with one or two microelectrodes, some neurons responded predominantly to one or the other type of speech. Excitatory responses during overt speaking were always auditory. In the middle temporal gyrus more neurons (about 2/3) responded to overt speaking than to listening alone. Activations elicited during overt speech were seen in about 1/3 of our sample, but they were more sluggish than those recorded in the superior gyrus. A prominent feature was suppression of on-going activity, which we found in about 1/3 of middle and in some superior temporal gyrus neurons. This suppression could precede vocalization by up to a few hundred ms, and could outlast it by up to 1 s. Evoked ECoG-potentials to words heard or spoken were different, and those to overt speech were more widespread.

The response variability of striate cortical neurons in the behaving monkey.

Abstract: In order to relate single cell performance to behavioral discrimination one needs measurements of the response variance of the units. We recorded from 183 single units of area V1 of monkeys performing an orientation discrimination task. The response variance was found to increase with increasing response strength. This relationship between response variance and response strength was well described by a power function with a power close to one. The response variance was on average 1.9 times the response strength. Despite important differences in preparation, the behaving monkey data are in good agreement with those previously obtained in paralysed and anesthetised animals.

Object-centered encoding by face-selective neurons in the cortex in the superior temporal sulcus of the monkey

Abstract: Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and in the inferior temporal cortex respond to faces. To determine if some face responsive neurons encode stimuli in an object-centered coordinate system rather than a viewer-centered coordinate system, a large number of neurons were tested for sensitivity to head movement in 3 macaque monkeys. Ten neurons responded only when a head undergoing rotatory movements was shown. All of these responded to a particular movement independently of the orientation of the moving head in relation to the viewer, maintaining specificity even when the moving head was inverted or shown from the back, thereby reversing viewer-centered movement vectors. This was taken as evidence that the movement was encoded in object-centered coordinates. In tests of whether there are neurons in this area which respond differently to the faces of different individuals relatively independently of viewing angle, it was found that a further 18 neurons responded more to one static face than another across different views. However, for 16 of these 18 cells there was still some modulation of the neuronal response with viewing angle. These 16 neurons thus did not respond perfectly in relation to the object shown independently of viewing angle, and may represent an intermediate stage between a viewercentered and an object-centered representation. In the same area as these neurons, other cells were found which responded on the basis of viewercentered coordinates. These neurophysiological findings provide evidence that some neurons in the inferior temporal visual cortex respond to faces (or heads) on the basis of object-centered coordinates, and that others have responses which are intermediate between object-centered and viewer-centered representations. The results are consistent with the hypothesis that object-centered representations are built in the inferior temporal visual cortex.

Asymmetric velocity and acceleration profiles of human arm movements.

Abstract: Displacement, velocity, acceleration and jerk (change of acceleration with time) were analyzed for arm flexion movement over a wide range of movement amplitudes and speeds Relative time to peak velocity or relative duration of acceleration, k, was approximately 05 for the movements with intermediate speed (about 05 s in movement time), ie, symmetric velocity and acceleration profiles For the slow and ballistic movements, k shifted towards values below and above 05, respectively creating asymmetric profiles Consistent k-dependence of movement time, peak velocity, maximum acceleration and maximum deceleration were observed “Jerk cost”, the square of the magnitude of jerk integrated over the entire movement, was calculated for each movement A dynamic optimization technique to minimize jerk cost under the constraint on jerk input was applied to interpret the results, assuming that a major goal of skilled movements was to produce optimally smooth movements The constrained minimum-jerk model explained speed dependent asymmetry of the velocity and acceleration profiles Jerk cost consumed by the movements with intermediate speed approximately satisfied minimum-cost criterion predicted by the model but was higher than the criterion for slow and ballistic movements The results suggested that optimality criteria other than jerk cost also should be considered to predict movement profiles over the entire range of speeds

Sensory components facilitating jaw-closing muscle activities in the rabbit

Abstract: The role of oral and facial sensory receptors in the control of masticatory muscle activities was assessed from the effect of acute deafferentiation on cortically induced rhythmic jaw movements (CRJMs) in anesthetized rabbits. When a thin polyurethane-foam strip (1.5, 2.5 or 3.5 mm thick) was placed between opposing molars during CRJMs, masseteric activities were facilitated in association with an increase in the medial excursion of the mandible during the power phase. The effects varied with the pattern of CRJMs, and the rate of facilitation was greater for small circular movements than for the crescent-shaped movements. Furthermore, the response of the masseter muscle was greater in the anterior half of the muscle, where muscle spindles are most dense, than in its posterior half. It was also demonstrated that the response increased with an increase in the thickness of the test strip. In contrast, the activities of the jaw-opening muscle were not affected significantly. The duration of masseteric bursts increased during application of the test strip and the chewing rhythm tended to slow down. However, the latter effect was not significant. After locally anesthetizing the maxillary and inferior alveolar nerves, the facultative responses of the masseter muscle to the test strip was greatly reduced but not completely abolished. Lesioning of the mesencephalic trigeminal nucleus (Mes V) where the primary ganglion cells of muscle spindle afferents from jaw-closing muscles and some periodontal afferents are located, also reduced the facilitative effects. Similar results were obtained in the animals with the kainic acid injections into the Mes V 1 week before electrical lesioning of this nucleus. In these animals the effects of electrical lesioning of the Mes V could be attributed to the loss of muscle receptor afferents since the neurons in the vicinity of the Mes V were destroyed and replaced by glial cells, whereas the Mes V neurons are resistant to kainic acid. When electrical lesioning of the Mes V and sectioning of the maxillary and inferior alveolar nerves were combined in animals with a kainic acid injection into the Mes V, the response of the masseter muscle to application of the strip was almost completely abolished. From these findings, we conclude that both periodontal receptors and muscle spindles are primarily responsible for the facilitation of jaw-closing muscle activities. Furthermore, it is suggested that the transcortical loop may not be the only path producing this facilitation since similar effects were induced in animals with ablation of the cortical masticatory area (CMA), when the test strip was placed between the molars during rhythmic jaw movements induced by pyramidal tract stimulation.

Distribution of corticospinal neurons with collaterals to the lower brain stem reticular formation in monkey (Macaca fascicularis).

Abstract: An earlier retrograde double-labeling study in cat showed that up to 30% of the corticospinal neurons in the medial and anterior parts of the precruciate motor area represent branching neurons which project to both the spinal cord and the reticular formation of the lower brain stem. These neurons were found to be concentrated in the rostral portion of the motor cortex, from where axial and proximal limb movements can be elicited. In the present study the findings in the macaque monkey are reported. The fluorescent retrograde tracer DY was injected unilaterally in the spinal cord at C2 and the fluorescent tracer FB was injected ipsilaterally in the medial tegmentum of the medulla oblongata. In the contralateral hemisphere large numbers of single DY-labeled corticospinal neurons and single FBlabeled corticobulbar neurons were present. A substantial number of DY-FB double-labeled corticospinal neurons were also found, which must represent branching neurons projecting to both the spinal cord and the bulbar reticular formation. These neurons were present in: 1. The anterior portion of the “cingulate corticospinal area” in the lower bank of the cingulate sulcus; 2. The supplementary motor area (SMA); 3. The rostral part of precentral corticospinal area; 4. The upper portion of the precentral face representation area; 5. The caudal bank of the inferior limb of the arcuate sulcus; 6. The posterior part of the insula. In these areas 10% to 30% of the labeled neurons were double-labeled. The functional implications of the presence of branching corticospinal neurons in these areas is discussed.

Environmentally-specified patterns of movement coordination in normal and split-brain subjects.

Abstract: Rhythmic movement patterns between the hands in response to environmental signals are studied in normal (musicians and nonmusicians) and split-brain subjects. Only two phase-locked states — in-phase and anti-phase — are shown to be stable for all subjects. Split-brain subjects show an even greater attraction to these patterns, thus providing no support for the notion that reduced cortical interaction between the hemispheres allows for independent visuomotor control of the hands in such tasks. Moreover, differences in trajectories produced by normal individuals and those without an intact corpus callosum are remarkable. The resultant patterns of coordination afford 1) a generalization of previous results on intrisincally generated rhythmic behavior to environmentally-specified movement patterns; and 2) a discussion of neural mechanisms underlying stable phase relations.

Place memory and scene memory: effects of fornix transection in the monkey.

Abstract: Five experiments examined the effects of fornix transection upon some spatial and visual learning tasks in monkeys (Macaca fascicularis). For each trial of each task, the monkey was brought to a test tray and allowed to choose between 2 objects on the tray. In different tasks, different cues were provided by the experimenter to guide the monkey's choices. In total 5 different tasks were run (Experiments 1 to 5) and the results showed that the effects of fornix transection varied markedly between tasks: the animals with fornix transection were severely impaired in experiments 1, 3 and 5 but learned normally in experiments 2 and 4. It is concluded that the results cannot be explained by the simple hypothesis of a deficit in place learning, since some forms of place learning are unimpaired by fornix transection. A better general hypothesis is that the memory disrupted by fornix transection is like a snapshot memory, which stores the spatial arrangement of items in a witnessed scene.

The effect of learning on the face selective responses of neurons in the cortex in the superior temporal sulcus of the monkey.

Abstract: Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and the inferior temporal gyrus of macaque monkeys respond to faces. These neurons provided a consistently identifiable substrate with which studies of the storage of visual information were performed. To determine whether face responsive neurons change how much they respond to different novel faces as they become familiar, neurons were tested with two experimental designs. In the first experiment, 22 neurons were tested on their responsiveness to the different members of a large set of novel faces as the set was presented repeatedly until the faces became familiar. 6 neurons altered the relative degree to which they responded to the different members of the set between the first two presentations and subsequent presentations. In a control condition, only 1 out of 17 neurons showed a significant response difference between the first two presentations and subsequent presentations when the experiment started with faces which were already familiar to the monkey. In the second experiment, 26 neurons were tested on their responsiveness to the different members of a set of familiar faces before and after the addition of a novel face to the set. 5 neurons altered the relative degree in which they responded to the different members of the set of familiar faces after addition of a novel face. It is suggested that these changes in neuronal responsiveness to different stimuli reflect the setting up of an ensemble encoded representation of face stimuli. This alteration of neuronal responsiveness as novel faces become familiar suggests that face responsive neurons may store information useful in visual recognition. In addition to this relatively long-term alteration of relative neuronal responsiveness to different stimuli, it was found that a large number of cells showed a higher mean response to the first presentation of a set of novel faces than to subsequent presentations of the faces. However, the response to the first presentation of a set of familiar faces was also higher than to subsequent presentations in that sequence. This pattern indicates a short term recency effect in the response of these neurons to visual stimuli which is similar to that previously reported (Baylis and Rolls 1987).

Effects of fornix transection and cingulate cortical ablation on spatial memory in rhesus monkeys.

Abstract: This study, together with a parallel study in rats (Markowska et al. 1988), attempted to relate the effects of hippocampal-system damage on similar tasks in both rats and monkeys. Not only were monkeys given a task (Experiment 1) which was of the sort usually used with rats, but in the companion study rats were given tasks (Experiment 2) like those usually used with monkeys. Experiment 1 examined the performance of rhesus monkeys with hippocampal-system damage on a spatial working memory task. Monkeys were trained preoperatively on delayed nonmatching-to-sample in a T-maze, placed into groups matched for their preoperative learning scores, and then received one of three treatments: 1) transection of the fornix; 2) ablation of the cingulate cortex; or 3) a sham operation. Monkeys with fornix transection were severely and significantly impaired, but monkeys with cingulate cortical ablations were not significantly impaired, relative to the controls. The results demonstrate that monkeys with fornix transection are severely impaired on a spatial working memory task requiring locomotion and, taken together with earlier work, suggest that the effect of fornix transection in both rodents and nonhuman primates is at least qualitatively similar (see Markowska et al. 1988). Experiment 2 assessed the role of the fornix and cingulate cortex in three conditional tasks in which the monkeys were provided with various spatial cues to indicate which one of two objects was rewarded. Both experimental groups were unimpaired, relative to the control group, on all three tasks, indicating that fornix transection does not produce a general impairment in place learning.

Release of oxytocin within the supraoptic nucleus during the milk ejection reflex in rats.

Abstract: To investigate the hypothesis that oxytocin may be released within the magnocellular nuclei in vivo, push-pull cannula perfusions were performed in anaesthetized lactating rats in one supraoptic nucleus of the hypothalamus while recording the intramammary pressure and/or the electrical activity of oxytocin cells in the contralateral supraoptic nucleus. Oxytocin content was measured in samples collected over 15 min, under various conditions: 1) with no stimulation; 2) during suckling and suckling-induced reflex milk ejections; 3) during electrical stimulation of the neurohypophysis by trains of pulses that mimicked oxytocin cell bursts; 4) under osmotic stimulation by i.p. injection of 2 ml of 1.5 M NaCl to evoke a tonic and sustained oxytocin release from the neurohypophysis. Oxytocin release within the supraoptic nucleus increased significantly during the milk ejection reflex and, to a lesser extent, during burst-like electrical stimulation of the neurohypophysis. In suckled rats, the increase started before the first reflex milk ejection occurred. There was no apparent correlation between the amount of oxytocin in the perfusates and the number of milk ejections and oxytocin cell bursts occurring during each perfusion period. The amount of oxytocin in the perfusates further increased during facilitation of the milk ejection reflex by intraventricular injections of oxytocin or its analogue, isotocin. When suckling failed to evoke the milk ejection reflex, there was no change in intra-supraoptic oxytocin release. There was also no change after osmotic stimulation. When the push-pull cannula was positioned outside the supraoptic nucleus, there was no increase in the amount of oxytocin during the three types of stimulation tested. These results provide evidence for an endogenous release of oxytocin within the magnocellular nuclei in lactating rats. It is suggested that the increase in such a release induced by suckling is likely to be a pre-requisite for the onset and the maintenance of the characteristic intermittent bursting electrical activity of oxytocin cells leading to milk ejections.

Unit activity in monkey parietal cortex related to haptic perception and temporary memory.

Abstract: The neural responses of 456 single units were recorded in parietal cortex of behaving monkeys during a haptic delayed matching-to-sample task. (1) In areas 2 and 5 together, 22% of the neurons were activated by the auditory cue that signalled the beginning of a trial. Virtually all of these cells were also activated during the arm movements required by the task. These neurons, showing both auditory-related and movement-related responses, may function in sensorimotor integration. (2) Responses related to arm projection frequently began before movement onset, sometimes as much as 320 ms before. Such “premovement” responses were approximately equally common, and showed the same latency distribution, in areas 2, 5a, and 5b. (3) There was a topographic rostral-to-caudal gradient of decreasing neural responsiveness to the animal's manipulation of the cue (sample) objects. Eleven percent of manipulation-activated cells responded preferentially to one of the sample objects. (4) Many cells showed sustained (> 3 s) activation during the delay period (the time between handling of the sample object and palpation of the choice objects), even though at that time the monkey was sitting quietly and without stimulation. (5) Cells with sustained activation throughout most or all of the 18-s delay period were rare in all areas tested except area 5a. These cells, especially those that were preferentially activated depending on which sample object was palpated, may function in the temporary retention of haptic attributes. (6) The population of cells activated during sample manipulation was largely distinct from the population of cells showing sustained activation during the delay period. These two cell populations may represent different but complementary aspects of haptic perception. (7) The most common response during the delay period was sustained inhibition. This may be an expression of a nonspecific mechanism for decreasing background noise and enhancing neural responses to an anticipated perceptual event. (8) Relatively little evidence was found to support a functional distinction between the neural response properties of areas 2 and 5 a. This suggests that area 2 may be at a higher level in the somatosensory heirarchy of the posterior parietal cortex than usually considered.

Differences in the activation of m. biceps brachii in the control of slow isotonic movements and isometric contractions

Abstract: We have compared muscle activation in the control of slow isotonic movements and isometric contractions. Specific attention has been given to the contribution of the two force-grading mechanisms, the recruitment of motor units and the modulation of firing frequency in motor units that have already been recruited. The recruitment order of the m. biceps motor units under study was the same during isometric contractions and slow isotonic movements. However, the recruitment thresholds of the m. biceps units were considerably lower for both isotonic flexion and extension movements, even at velocities as low as 2 deg/s, than for isometric contractions. Furthermore, firing frequency at recruitment was found to depend on the motor task: at recruitment the motoneurone starts firing with a higher firing frequency during isotonic flexion movements and a lower firing frequency during isotonic extension movements than during isometric contractions. Two main conclusions can be drawn from these results. First of all, the concept of one single activation parameter (total synaptic drive?) cannot account for the motor-unit behaviour observed during our experiments: the relative contribution of the two forcegrading mechanisms is different for different tasks. Secondly, the distribution of activity among flexor motoneurone pools is different for isometric contractions and isotonic movements.

Sensory and affective aspects of pain perception: is medial thalamus restricted to emotional issues?

Abstract: Lateral and medial thalamus are traditionally thought to have separate roles in pain processing, with lateral lemniscal regions transmitting discriminative information about location and intensity, while medial nonspecific regions are involved in emotional responses. Contrary to this view, the present study shows that some single neurons in medial thalamus of alert monkey discriminate changes in the intensity of noxious stimuli that are equal to or below the monkey's own discrimination threshold. Since these neurons are also modulated by anesthesia and attentional factors, we suggest that parts of medial thalamus may participate in both discriminative and affective dimensions of pain.

Force production characteristics in Parkinson's disease.

Abstract: This experiment examined the preparation and the production of isometric force in Parkinson's disease (PD). PD patients, elderly, and young subjects generated force levels that were a percentage of their maximum (15, 30, 45, and 60%). Subjects were cued on the upcoming target force level and they were asked to produce the required response as fast as possible. PD patients showed a similar progression of force variability and dispersion of peak forces to that of control subjects, implying they have an accurate “internal model” of the required forces. Force production impairments were seen, however, at the within-trial level. PD patients had more irregular force-time curves that were characterized by changes in the rate of force production. The results suggest a more “noisy” output from the motor system and an inability to produce smooth forces. PD patients were also substantially slower in initiating a force production and the delay was localized in the pre-motor reaction time.

Neurotransmitters, neuropeptides and binding sites in the rat mediobasal hypothalamus: effects of monosodium glutamate (MSG) lesions.

Abstract: Indirect immunofluorescence histochemistry and receptor autoradiography were used to study the localization of transmitter-/peptide-containing neurons and peptide binding sites in the mediobasal hypothalamus in normal rats and in rats treated neonatally with repeated doses of the neurotoxin monosodium-glutamate (MSG) In the arcuate nucleus, the results showed a virtually complete loss of cell bodies containing immunoreactivity for growth hormone-releasing factor (GRF), galanin (GAL), dynorphin (DYN), enkephalin (ENK), corticotropin-like intermediate peptide (CLIP), neuropeptide Y (NPY), and neuropeptide K (NPK) Tyrosine hydroxylase(TH)-glutamic acid decarboxylase(GAD)-, neurotensin(NT)- and somatostatin(SOM)-immunoreactive (IR) cells were, however, always detected in the ventrally dislocated, dorsomedial division of the arcuate nucleus In the median eminence, marked decreases in numbers of GAD-, NT-, GAL-, GRF-, DYN-, and ENK-IR fibers were observed The numbers of TH-, SOM- and NPY-IR fibers were in contrast not or only affected to a very small extent, as revealed with the immunofluorescence technique Biochemical analysis showed a tendency for MSG to reduce dopamine levels in the median eminence of female rats, whereas no effect was observed in male rats Autoradiographic studies showed high to moderate NT binding sites, including strong binding over presumably dorsomedial dopamine cells In MSG-treated rats, there was a marked reduction in GAL binding in the ventromedial nucleus The findings implicate that most neurons in the ventrolateral and ventromedial arcuate nucleus are sensitive to the toxic effects of MSG, whereas a subpopulation of cells in the dorsomedial division of the arcuate nucleus, including dopamine neurons, are not susceptible to MSG-neurotoxicity The results indicate, moreover that the very dense TH-IR fiber network in the median eminence predominantly arises from the dorsomedial TH-IR arcuate cells, whereas the GAD-, NT-, GAL-, GRF- and DYN-IR fibers in the median eminence to a large extent arise from the ventrolateral arcuate nucleus Some ENK- and NPK-positive cells in the arcuate nucleus seem to project to the lateral palisade zone of the median eminence, but most of the ENK-IR fibers in the median eminence, located in the medial palisade zone, seem to primarily originate from an area(s) located outside the arcuate nucleus, presumably the paraventricular nucleus(ABSTRACT TRUNCATED AT 400 WORDS)

A comparative analysis of the role of fornix and cingulate cortex in memory: rats.

Abstract: In order to compare the role of the fornix (FX) and cingulate cortex (CC) in memory, rats were trained in a series of discriminations using procedures that were the same as those used for monkeys (Murray et al. 1986, 1988). A spatial delayed nonmatching-to-sample (DNMS) discrimination tested recent memory for spatial location in a T maze using interrun intervals (IRI) that varied from 5 s to 15 min. FX and CC lesions produced a substantial impairment in the performance of this task during postoperative testing. Three conditional discriminations (CD) followed. In each one, the rat was presented with two objects, only one of which was correct. The nature of the conditional stimuli changed in each discrimination: the place of the maze in the room; the direction that the rat moved to approach the objects; the side (left or right) to which the rat turned. Control rats learned all three types of conditional discriminations. FX and CC lesions did not impair choice accuracy. In a subsequent repetition of the spatial DNMS procedure, FX and CC lesions again produced a substantial impairment, indicating that the lack of an impairment in the three CDs was not due to recovery of function. These data indicate that the hippocampal system and its connections through the fornix are importantly involved in spatial working memory in both rats and monkeys, and that the CDs do not require this type of memory. The results are discussed in the context of different theories of the brain mechanisms involved in memory.

NMDA receptor antagonists can enhance or impair learning performance in animals.

Abstract: The effects of NMDA receptor antagonism on learning and memory were investigated using competitive (DL-2-amino-7-phosphonoheptanoate, AP7) and non-competitive (MK 801) blockers in three different learning tasks. Administration (i.p.) of drugs prior to training resulted in impaired learning performance in the place-navigation and dark-avoidance paradigms, and improved performance in the step-down passive avoidance task; however, using this treatment protocol, the possibility of druginduced non-mnemonic effects modifying learning performance could not be excluded. Drug administration immediately post-trial had no effect in the place-navigation paradigm, and improved retention performance in the dark-avoidance and step-down avoidance tasks. The similar results obtained with both types of antagonist indicate that the observed effects are indeed due to NMDA receptor blockade, and hence that such blockade modifies learning in a task-dependent manner. Exclusion of non-mnemonic effects by using the post-trial treatment regime demonstrates that NMDA antagonists facilitate learning of passive avoidance tasks.