Showing papers in "Journal of Neurophysiology in 1990"

Functional reorganization of primary somatosensory cortex in adult owl monkeys after behaviorally controlled tactile stimulation

Abstract: 1. Multiple microelectrode maps of the hand representation within and across the borders of cortical area 3b were obtained before, immediately after, or several weeks after a period of behaviorally controlled hand use. Owl monkeys were conditioned in a task that produced cutaneous stimulation of a limited sector of skin on the distal phalanges of one or more fingers. 2. Analysis of microelectrode mapping experiment data revealed that 1) stimulated skin surfaces were represented over expanded cortical areas. 2) Most of the cutaneous receptive fields recorded within these expanded cortical representational zones were unusually small. 3) The internal topography of representation of the stimulated and immediately surrounding skin surfaces differed greatly from that recorded in control experiments. Representational discontinuities emerged in this map region, and "hypercolumn" distances in this map sector were grossly abnormal. 4) Borders between the representations of individual digits and digit segments commonly shifted. 5) The functionally defined rostral border of area 3b shifted farther rostralward, manifesting either an expansion of the cutaneous area 3b fingertip representation into cortical field 3a or an emergence of a cutaneous input zone in the caudal aspect of this normally predominantly deep-receptor representational field. 6) Significant lateralward translocations of the borders between the representations of the hand and face were recorded in all cases. 7) The absolute locations--and in some cases the areas or magnifications--of representations of many skin surfaces not directly involved in the trained behavior also changed significantly. However, the most striking areal, positional, and topographic changes were related to the representations of the behaviorally stimulated skin in every studied monkey. 3. These experiments demonstrate that functional cortical remodeling of the S1 koniocortical field, area 3b, results from behavioral manipulations in normal adult owl monkeys. We hypothesize that these studies manifest operation of the basic adaptive cortical process(es) underlying cortical contributions to perception and learning.

Interaural time sensitivity in medial superior olive of cat

Abstract: 1. We studied the sensitivity of cells in the medial superior olive (MSO) of the anesthetized cat to variations in interaural phase differences (IPDs) of low-frequency tones and in interaural time differences (ITDs) of tones and broad-band noise signals. Our sample consisted of 39 cells histologically localized to the MSO. 2. All but one of the cells had characteristic frequencies less than 3 kHz, and 79% were sensitive to ITDs and IPDs. More than one-half (56%) of the cells responded to monaural stimulation of either ear, and both the binaural and monaural responses were highly phase locked. All of the cells that were sensitive to IPDs and monaurally driven by either ear responded in accord with that predicted by the coincidence model of Jeffress, as judged by comparisons of the phases at which the monaural and binaural responses occurred. The optimal IPDs were tightly clustered between 0.0 and 0.2 cycles. Most cells exhibited facilitation of the response at favorable ITDs and inhibition at unfavorable ITDs compared with the monaural responses. 3. Cells in the MSO exhibited characteristic delay, as judged by a linear relationship between the mean interaural phase and stimulating frequency. Characteristic phases were clustered near 0 indicating the most cells responded maximally when the two input tones were in phase. With the use of the binaural beat stimulus we found no differential selectivity for either the direction or speed of interaural phase changes. 4. The cells were also sensitive to ITDs of broad-band noise signals. The ITD curve in response to broad-band noise was similar to that predicted by the composite curve, which was calculated by linearly summating the tonal responses over the frequencies in the response area of the cell. Most (93%) of the peaks of the composite curves were between 0 and +400 microseconds, corresponding to locations in the contralateral sound field. Moreover, computer cross correlations of the monaural spike trains were similar to the ITD curve generated binaurally for both correlated and uncorrelated noise signals to the two ears. Thus our data suggest that the cells in the MSO behave much like cross-correlators. 5. By combining data from different animals and lcoating each cell on a standard MSO, we found evidence for a spatial map of ITDs across the anterior-posterior (A-P) axis of the MSO.(ABSTRACT TRUNCATED AT 400 WORDS)

Preparation for movement : neural representations of intended direction in three motor areas of the monkey

Abstract: 1. The purpose of this study was to compare the functional properties of neurons in three interrelated motor areas that have been implicated in the planning and execution of visually guided limb mo...

Primate frontal eye fields. III. Maintenance of a spatially accurate saccade signal

Abstract: 1. We studied the activity of single neurons in the monkey frontal eye fields during oculomotor tasks designed to assess the activity of these neurons when there was a dissonance between the spatial location of a target and its position on the retina. 2. Neurons with presaccadic activity were first studied to determine their receptive or movement fields and to classify them as visual, visuomovement, or movement cells with the use of the criteria described previously (Bruce and Goldberg 1985). The neurons were then studied by the use of double-step tasks that dissociated the retinal coordinates of visual targets from the dimensions of saccadic eye movements necessary to acquire those targets. These tasks required that the monkeys make two successive saccades to follow two sequentially flashed targets. Because the second target disappeared before the first saccade occurred, the dimensions of the second saccade could not be based solely on the retinal coordinates of the target but also depended on the dimensions of the first saccade. We used two versions of the double-step task. In one version neither target appeared in the cell's receptive or movement field, but the second eye movement was the optimum amplitude and direction for the cell (right-EM/wrong-RF task). In the other the second stimulus appeared in the cell's receptive field, but neither eye movement was appropriate for the cell (wrong-EM/right-RF task). 3. Most frontal-eye-field cells discharged in the right-EM/wrong-RF version of the double-step task. Their discharge began after the first saccade and continued until the second saccade was made. They usually discharged even on occasional trials in which the monkey failed to make the second saccade. They discharged much less, or not at all, in the wrong-EM/right-RF version of the double-step paradigm. Thus most presaccadic cells in the frontal eye fields were tuned to the dimensions of saccadic eye movements rather than to the coordinates of retinal stimulation. 4. Eleven movement cells (including 1 which also had independent postsaccadic activity for saccades opposite its presaccadic movement field) were studied, and all had significant activity in the right-EM/wrong-RF task. 5. Almost all (28/32) visuomovement cells, including 12 with independent postsaccadic activity, discharged in the right-EM/wrong-RF task. None of the four that failed had independent postsaccadic activity. 6. The majority (26/40) of visual cells were responsive in the right-EM/wrong-RF task.(ABSTRACT TRUNCATED AT 400 WORDS)

Visuospatial coding in primate prefrontal neurons revealed by oculomotor paradigms.

Abstract: 1. Visual responses and their relationship to delay-period activity were studied by recording single neuron activity from the prefrontal cortex of rhesus monkeys while they performed an oculomotor ...

The spino(trigemino)pontoamygdaloid pathway: electrophysiological evidence for an involvement in pain processes.

Abstract: 1. Neurons were recorded in the parabrachial (PB) area, located in the dorsolateral region of the pons (with the use of extracellular micropipette), in the anesthetized rat. Parabrachioamygdaloid (PA) neurons (n = 67) were antidromically identified after stimulation in the centralis nucleus of the amygdala (Ce). The axons of these neurons exhibit a very slow conduction velocity, between 0.26 and 1.1 m/s, i.e., in the unmyelinated range. 2. These PA neurons were located in a restricted region of the PB area: the subnuclei external lateral (PBel) and external medial (PBem). A relative somatotopic organization was found in this region. 3. These units were separated into two groups: 1) a group of nociceptive-specific (NS) neurons (69%), which responded exclusively to noxious stimuli, and 2) a group of nonresponsive (NR) neurons (31%). 4. The NS neurons exhibited low or lacked spontaneous activity. They responded exclusively to mechanical (pinch or squeeze) and/or thermal (waterbath or waterjet greater than 44 degrees C) noxious stimuli with a marked and sustained activation with a rapid onset and generally without afterdischarge. Noxious thermal stimuli generally induced a stronger response than the noxious mechanical stimuli. These neurons exhibited a clear capacity to encode thermal stimuli in the noxious range: 1) the stimulus-response function was always positive and monotonic; 2) the slope of the curve progressively increased up to a maximum where it was very steep, then the steepness of the slope decreased close to the maximum response; and 3) the mean threshold was 44.1 +/- 2 degrees C, and the point of steepest slope of the mean curve was around 47 degrees C. 5. The excitatory receptive fields of the NS neurons were large in the majority (70%) of the cases and included several areas of the body. A more marked activation was often obtained from stimuli applied to one part of the body, denoted as the preferential receptive field (PRF). In the other cases (30%), the excitatory receptive field was relatively small (SRF) and restricted to one part of the body (the tail, a paw, a hemiface, or the tongue). Both the PRF and SRF were more often located on the contralateral side. In addition, noxious stimuli applied outside the excitatory receptive field were found to strongly inhibit the responses of NS neurons. 6. All the NS neurons responded to intense transcutaneous electrical stimulation applied to the PRF or SRF with two peaks of activation.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopamine neurons of the monkey midbrain: contingencies of responses to active touch during self-initiated arm movements.

Abstract: 1. Previous studies have shown that midbrain dopamine (DA) neurons in monkeys respond to external stimuli that are used to initiate behavioral reactions. In the present study, we investigated to what extent changes in neuronal activity would occur when behavioral acts are generated internally or whether they would depend solely on external stimuli. 2. Monkeys performed self-initiated arm movements from a resting key into a covered, food-containing box at a self-chosen moment and without external preparatory or triggering signals. In a second task, the arm movement was triggered by rapid opening of the door of the food box. This stimulus was either audible and visible or only audible to the animal. Impulses of DA neurons were recorded with movable microelectrodes from the pars compacta of substantia nigra (area A9) and areas A8 and A10 and were discriminated from those of other neurons by their long duration (1.5-5.0 ms) and low spontaneous frequency (0.5-8.5 imp/s). 3. The activity of 12% of 104 DA neurons increased slowly and moderately up to 1,500 ms before the onset of individual self-initiated arm movements. Median increases amounted to 91% over background discharge rate. A further 16% of DA neurons were activated together with the onset of muscle activity and during the movement. 4. During self-initiated movements, a nonhabituating, phasic burst of impulses occurred when the monkey's hand touched a morsel of food inside the box. This response was seen in 84% of 154 neurons on the contralateral side, with median onset latency of 65 ms and duration of 160 ms. A comparable percentage of neurons responded to ipsilateral touch with similar latency and duration. 5. The touch response during self-initiated movements was absent, both on the contra- and ipsilateral sides, when the animal's hand touched the bare wire normally holding the food, when touching nonfood objects, or during tactile exploration of the empty interior of the food box. Thus responses appeared to be related to the appetitive properties of the object being touched rather than the object itself. 6. In the task employing stimulus-triggered movements, 77% of 86 DA neurons discharged a burst of impulses in response to door opening but entirely failed to respond to the touch of food in the box. The response to door opening in this task was similar to the touch response during self-initiated movements in the same neurons in terms of latency, duration, and magnitude.(ABSTRACT TRUNCATED AT 400 WORDS)

Neural representations of the target (goal) of visually guided arm movements in three motor areas of the monkey

Abstract: 1. This study was designed to determine whether the supplementary motor area (SMA), the primary motor cortex (MC), and the putamen, all of which are components of the basal ganglia-thalamocortical ...

Phase-dependent reflex reversal in human leg muscles during walking.

Abstract: 1. Reflex responses during walking were elicited in humans by stimulation of the tibial nerve at the ankle. The stimulus intensity was controlled by monitoring the M-wave from an intrinsic foot mus...

Visual responses of Purkinje cells in the cerebellar flocculus during smooth-pursuit eye movements in monkeys. I. Simple spikes

Abstract: 1. We have identified a visually driven output from the flocculus of the monkey by studying the simple-spike responses of Purkinje cells (P-cells) during the initiation of smooth-pursuit eye movements. We report on two groups of P-cells that appear to be the horizontal and vertical gaze-velocity P-cells (GVP-cells) studied previously during periodic target and head motion. 2. During pursuit of periodic target motion, one group of P-cells prefers downward motion (down GVP-cells), and the other prefers motion toward the side of recording (ipsi GVP-cells). The two groups have mean directional preferences that are nearly orthogonal, but their responses during pursuit of sinusoidal target motion and sinusoidal vestibular stimulation are in other respects quantitatively similar. 3. During the initiation of pursuit to step-ramp target motion, GVP-cells show a large transient change in simple-spike firing rate followed by a sustained change in firing that persists during steady-state pursuit. 4. The transient response is directionally selective, so that GVP-cells show a pulse of simple spikes for pursuit in the ON-direction and a dip in simple-spike firing for pursuit in the OFF-direction. The amplitude of the transient response is too large to be explained by the sensitivity of GVP-cells to eye velocity measured during pursuit of sinusoidal target motion. 5. To test whether the transient change in simple-spike firing was related to a visual input or to an eye-acceleration input to the flocculus, we recorded the firing of ipsi GVP-cells during a rapid eye acceleration caused by a transient vestibular stimulus in darkness. Most GVP-cells showed little or no transient response under these conditions, even though eye acceleration was greater than during the initiation of pursuit. We conclude that the transient response at the initiation of pursuit is probably caused by visual mossy-fiber inputs to the flocculus. 6. The sustained change in simple-spike firing is also directionally selective, with large increases in simple-spike firing for pursuit in the ON-direction and smaller decreases for pursuit in the OFF-direction. For pursuit in the ON-direction, the amplitude of the sustained response is well predicted by the sensitivity of GVP-cells to eye velocity measured during pursuit of sinusoidal target motion. 7. To determine whether the sustained response was driven by visual inputs, we recorded simple-spike firing when image motion was prevented by electronically stabilizing the target image on the fovea during steady-state pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopamine neurons of the monkey midbrain: contingencies of responses to stimuli eliciting immediate behavioral reactions.

Abstract: 1. This study investigates the behavioral conditions in which dopamine (DA) neurons of substantia nigra and adjoining areas A8 and A10 respond with impulses to visual and auditory trigger stimuli eliciting immediate arm- and eye-movement reactions. 2. In a formal task, the rapid opening of the door of a small, food-containing box located at eye level ahead of the animal served as visible and audible trigger stimulus. Most DA neurons on the contralateral side responded to this stimulus with a short burst of impulses with median onset latency of 50 ms and duration of 90 ms (75% of 164 neurons). Similar responses were seen in a comparable fraction of DA neurons during ipsilateral task performance, suggesting that responses were not specific for the limb being used. 3. When the sensory components of the door opening stimulus were separated, DA neurons typically responded in a similar manner to the moving visual stimulus of the opening door, the low-intensity sliding noise of the opening door, and the 1-kHz sound of 90-92 dB intensity emitted from a distant source at the onset of door opening. Responses to each component alone were lower in magnitude than to all three together. 4. In a variation of the task, a neighboring, identical food box opened in random alternation with the other box but without permitting animals to reach out (asymmetric, direct-reaction go/no-go task). With each sensory component, DA neurons typically responded both to opening of go and no-go boxes. Responses were enhanced when stimuli elicited limb movements in go trials. 5. Monkeys reacted to door opening with target-directed saccadic eye movements in the majority of both go and no-go trials. Neuronal responses were equally present during the occasional absence of eye movements. Thus responses were not specific for the initiation of individual arm or eye movements. 6. Neuronal responses were absent when the same stimuli occurred outside of the behavioral task with target-direct arm and eye movements lacking. This shows that responses were not of purely sensory nature but were related to the capacity of the stimulus for eliciting behavioral reactions. 7. In a variation of the go/no-go task, an instruction light illuminated 2-3 s before door opening prepared the animal to perform the reaching movement on door opening or to refrain from moving (asymmetric, instruction-dependent go/no-go task).(ABSTRACT TRUNCATED AT 400 WORDS)

Movement-Related Neuronal Activity Selectively Coding Either Direction or Muscle Pattern in Three Motor Areas of the Monkey

Abstract: 1. Movement-related neuronal activity in the supplementary motor area (SMA), primary motor cortex (MC), and putamen was studied in monkeys performing a visuomotor tracking task designed to determine 1) the extent to which neuronal activity in each of these areas represented the direction of visually guided arm movements versus the pattern of muscle activity required to achieve those movements and 2) the relative timing of different types of movement-related activity in these three motor areas. 2. A total of 455 movement-related neurons in the three motor areas were tested with a behavioral paradigm, which dissociated the direction of visually guided elbow movements from the accompanying pattern of muscular activity by the application of opposing and assisting torque loads. The movement-related activity described in this report was collected in the same animals performing the same behavioral paradigm used to study preparatory activity described in the preceding paper. Of the total sample, 87 neurons were located within the arm region of the SMA, 150 within the arm region of the MC, and 218 within the arm region of the putamen. 3. Movement-related cells were classified as "directional" if they showed an increase in discharge rate predominantly or exclusively during movements in one direction and did not have significant static or dynamic load effects. A cell was classified as "muscle-like" if its directional movement-related activity was associated with static and/or dynamic load effects whose pattern was similar to that of flexors or extensors of the forearm. Both directional and muscle-like cells were found in all three motor areas. The largest proportion of directional cells was located in the putamen (52%), with significantly smaller proportions in the SMA (38%) and MC (41%). Conversely, a smaller proportion of muscle-like cells was seen in the putamen (24%) than in the SMA (41%) or MC (36%). 4. The time of onset of movement-related discharge relative to the onset of movement ("lead time") was computed for each cell. On average, SMA neurons discharged significantly earlier (SMA lead times 47 +/- 8 ms, mean +/- SE) than those in MC (23 +/- 6 ms), which in turn were earlier than those in putamen (-33 +/- 6 ms). However, the degree of overlap of the distributions of lead times for the three areas was extensive.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemosensitivity of fine afferents from rat skin in vitro

Abstract: 1. Properties of sensory receptors with slowly conducting nerve fibers (less than 10 m/s) were studied using a rat skin-saphenous nerve in vitro preparation where receptive fields of identified sin...

Neural mechanisms generating respiratory pattern in mammalian brain stem-spinal cord in vitro. I. Spatiotemporal patterns of motor and medullary neuron activity.

Abstract: 1. An analysis of the spatial and temporal patterns of activity of neurons of the respiratory motor-pattern generation system in an in vitro neonatal rat brain stem-spinal cord preparation is presented. Impulse discharge patterns of spinal and cranial moto-neurons as well as respiratory neurons in the medulla were analyzed. Patterns of motoneuronal discharge were characterized at the population level from recordings of motor-nerve discharge and at the single-cell level from intracellular recordings. These patterns were compared to patterns generated in the neonatal rat and adult mammal in vivo to establish the correspondence between in vitro and in vivo states. 2. The in vitro system generated a complex spatiotemporal pattern of spinal and cranial motoneuron activity during inspiratory (I) and expiratory (E) phases of the respiratory cycle. The respiratory cycle consisted of three distinct phases of neuronal activity (I, early E, and late E phase) similar to the temporal organization of the cycle in the intact mammal. The spike discharge pattern of motoneurons during the I phase consisted of a rapidly peaking-slowly decrementing discharge envelope with a high degree of synchronization on a time scale of 25-50 ms (approximately 20-40 Hz). A similar pattern was generated in the neonate in vivo under conditions comparable with the in vitro state (i.e., nervous system isolated from mechanosensory afferent inputs). However, the I-phase-motoneuron discharge pattern and cycle-phase durations differed from those characteristic of the intact neonatal or adult systems in vivo. This difference could be accounted for primarily by removal of vagal mechanosensory afferent inputs. 3. The synaptic drive potentials of spinal motoneurons during the I phase in vitro consisted of a rapidly peaking-slowly decrementing potential envelope similar in shape to the spike-frequency histogram of single motoneurons and the envelope of the motoneuron-population discharge. The drive potentials had prominent high-frequency amplitude fluctuations superimposed on the slower drive-potential envelope that were temporally correlated with the generation of motoneuron action potentials. The dominant frequency components of these fast-membrane-potential oscillations (20-35 Hz) were similar to the frequency components of the amplitude fluctuations in the motoneuron-population discharge. One class of medullary neurons with I-phase discharge also exhibited a rapidly peaking-slowly decrementing pattern of impulse discharge and synaptic drive potential with similar high-frequency components.(ABSTRACT TRUNCATED AT 400 WORDS)

Gustatory responses of single neurons in the caudolateral orbitofrontal cortex of the macaque monkey.

Abstract: 1. In recordings made from 3,120 single neurons, a secondary cortical taste area was found in the caudolateral part of the orbitofrontal cortex of the cynomolgus macaque monkey, Macaca fascicularis...

Gaze control in the cat: studies and modeling of the coupling between orienting eye and head movements in different behavioral tasks.

Abstract: 1. Orienting movements, consisting of coordinated eye and head displacements, direct the visual axis to the source of a sensory stimulus. A recent hypothesis suggests that the CNS may control gaze position (gaze = eye-relative-to-space = eye-relative-to-head + head-relative-to-space) by the use of a feedback circuit wherein an internally derived representation of gaze motor error drives both eye and head premotor circuits. In this paper we examine the effect of behavioral task on the individual and summed trajectories of horizontal eye- and head-orienting movements to gain more insight into how the eyes and head are coupled and controlled in different behavioral situations. 2. Cats whose heads were either restrained (head-fixed) or unrestrained (head-free) were trained to make orienting movements of any desired amplitude in a simple cat-and-mouse game we call the barrier paradigm. A rectangular opaque barrier was placed in front of the hungry animal who either oriented to a food target that was visible to one side of the barrier or oriented to a location on an edge of the barrier where it predicted the target would reappear from behind the barrier. 3. The dynamics (e.g., maximum velocity) and duration of eye- and head-orienting movements were affected by the task. Saccadic eye movements (head-fixed) elicited by the visible target attained greater velocity and had shorter durations than comparable amplitude saccades directed toward the predicted target. A similar observation has been made in human and monkey. In addition, when the head was unrestrained both the eye and head movements (and therefore gaze movements) were faster and shorter in the visible- compared with the predicted-target conditions. Nevertheless, the relative contributions of the eye and head to the overall gaze displacement remained task independent: i.e., the distance traveled by the eye and head movements was determined by the size of the gaze shift only. This relationship was maintained because the velocities of the eye and head movements covaried in the different behavioral situations. Gaze-velocity profiles also had characteristic shapes that were dependent on task. In the predicted-target condition these profiles tended to have flattened peaks, whereas when the target was visible the peaks were sharper. 4. Presentation of a visual cue (e.g., reappearance of food target) immediately before (less than 50 ms) the onset of a gaze shift to a predicted target triggered a midflight increase in first the eye- and, after approximately 20 ms, the head-movement velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

Cross-excitation in dorsal root ganglia of nerve-injured and intact rats.

Abstract: 1. Experiments based on teased fiber recording from rat sciatic nerve have shown that a small proportion of primary afferent neurons in intact dorsal root ganglia (DRGs) fire spontaneously. The prevalence of this discharge is substantially increased if the sciatic nerve has been chronically injured. 2. We now show that in most cases this ongoing DRG activity can be augmented by tetanic stimulation of the axons of neighboring neurons, where the active neuron itself has not been stimulated. In addition, some previously silent DRG neurons can be cross-excited by neighbors. This novel form of neuron-to-neuron communication is termed "DRG crossed afterdischarge." Cross-excitation never occurred at fixed latency in response to single stimulus pulses and is therefore not a case of ephaptic cross talk. 3. Crossed afterdischarge occurred only if the spontaneously active neuron and the stimulated neighbors shared the same DRG. It occurred in 83.5% of the spontaneously active neurons sampled that had myelinated (A) axons, but in only 4.4% of spontaneously active neurons with unmyelinated (C) axons. Among initially silent neurons, stimulation of neighbors evoked firing in 3.1% of A-fibers but in no C-fibers. 4. Crossed afterdischarge responses began within 500 ms of stimulation onset (with the use of 50-Hz tetani) and increased in magnitude for about the first 30 s of stimulation, declining thereafter. Intense excitations were often followed by a short period of depression until the original rate of ongoing discharge was restored. 5. The magnitude of crossed afterdischarge responses increased with increasing stimulation frequency until saturation. Minimal responses occurred with the use of tetani of as little as 1 Hz. Maximal responses occurred with the use of 100-200 Hz tetani. 6. The inclusion of C-fibers in the afferent volley produced little if any augmentation of responses. 7. Cross-excitation was demonstrated in DRGs in which many or all peripheral afferent axons were intact and continued to innervate hind limb skin. In these preparations natural cutaneous stimulation was shown to be capable of evoking crossed afterdischarge responses. The most effective stimuli were gentle or firm rubbing of the foot. Noxious pinch, heat, cold, and chemical stimulation was ineffective. 8. DRG crossed afterdischarge is a mechanism whereby sensation in response to peripheral stimulation may be distorted in time, space, and modality. Because its prevalence is much increased after axotomy, it might contribute to neuropathic sensory abnormalities, including pain, in patients with nerve injury.

Tactile detection of slip: surface microgeometry and peripheral neural codes.

Abstract: 1. The role of the microgeometry of planar surfaces in the detection of sliding of the surfaces on human and monkey fingerpads was investigated. By the use of a servo-controlled tactile stimulator to press and stroke glass plates on passive fingerpads of human subjects, the ability of humans to discriminate the direction of skin stretch caused by friction and to detect the sliding motion (slip) of the plates with or without micrometer-sized surface features was determined. To identify the associated peripheral neural codes, evoked responses to the same stimuli were recorded from single, low-threshold mechanoreceptive afferent fibers innervating the fingerpads of anesthetized macaque monkeys. 2. Humans could not detect the slip of a smooth glass plate on the fingerpad. However, the direction of skin stretch was perceived based on the information conveyed by the slowly adapting afferents that respond differentially to the stretch directions. Whereas the direction of skin stretch signaled the direction of impending slip, the perception of relative motion between the plate and the finger required the existence of detectable surface features. 3. Barely detectable micrometer-sized protrusions on smooth surfaces led to the detection of slip of these surfaces, because of the exclusive activation of rapidly adapting fibers of either the Meissner (RA) or the Pacinian (PC) type to specific geometries of the microfeatures. The motion of a smooth plate with a very small single raised dot (4 microns high, 550 microns diam) caused the sequential activation of neighboring RAs along the dot path, thus providing a reliable spatiotemporal code. The stroking of the plate with a fine homogeneous texture composed of a matrix of dots (1 microns high, 50 microns diam, and spaced at 100 microns center-to-center) induced vibrations in the fingerpad that activated only the PCs and resulted in an intensive code. 4. The results show that surprisingly small features on smooth surfaces are detected by humans and lead to the detection of slip of these surfaces, with the geometry of the microfeatures governing the associated neural codes. When the surface features are of sizes greater than the response thresholds of all the receptors, redundant spatiotemporal and intensive information is available for the detection of slip.

Behaviorally contingent property of movement-related activity of the primate putamen.

Abstract: 1. In this study, the movement-related activity of putamen neurons was investigated in behaving monkeys. The objective of the study was to examine whether the activity occurring in phase with body movements is directly related to the movement per se by encoding movement parameters or whether it is dependent on the circumstances in which the movement is performed. 2. Sensorially triggered arm movements were used as a behavioral task. A sequence of three visually triggered repetitive flexion-extensions of the elbow joint across the target were followed by the delivery of a juice reward. 3. There are two classes of putamen cells: type I, with tonic spontaneous discharges (2-7 Hz) and broad extracellularly recorded action potentials, and type II, with very low spontaneous discharge rate (less than 1 Hz). The movement-related phasic discharges occur exclusively in type II cells. 4. The movement-related activity of type II cells is classified into two contrasting types of cells: type IIa that exhibit burst discharges preceding the first movement of a sequence of repetitive arm or orofacial movements but that are almost inactive during succeeding movements, and type IIb that show movement-locked burst discharges with one-to-one correspondence. The somatotopic location of the cells was identified by microstimulation and/or sensory responses to passive somatosensory manipulation of the periphery. 5. The activities of type IIa cells occur with a short and fairly constant latency after the visual trigger stimulus and cease as soon as the sequence of the learned movements is initiated. In the condition in which the monkey attended to the visual trigger stimulus without initiating learned movements and waited for the delivery of juice reward at a fixed time after the stimulus, type IIa cells exhibited slight but consistent phasic discharges after the visual stimulus with short latency. This indicates that the type IIa cells have a visuomovement property. The type IIb cells, on the other hand, have a longer latency of activity after the visual trigger than type IIa cells and do not have the visuomovement property. 6. The type IIa cells change their activity pattern depending on whether the direction of initial movement is predictable before the trigger stimulus or not. 7. The activities of type IIa cells in the arm area of the putamen precede the electromyogram (EMG) of prime mover muscles by greater than 100 ms on average, whereas most type IIb cells are activated after the EMG during a learned arm-movement task.(ABSTRACT TRUNCATED AT 400 WORDS)

Inferotemporal units in selective visual attention and short-term memory.

Abstract: 1. This research was designed to further clarify how, in the primate, the neurons of the inferotemporal (IT) cortex support the cognitive functions of visually guided behavior. Specifically, the aim was to determine the role of those neurons in 1) selective attention to behaviorally relevant features of the visual environment and 2) retention of those features in temporary memory. Monkeys were trained in a memory task in which they had to discriminate and retain individual features of compound stimuli, each stimulus consisting of a colored disk with a gray symbol in the middle. A trial began with brief presentation of one such stimulus, the sample for the trial. Depending on the symbol in it, the monkey had to memorize the symbol itself or the background color; after 10-20 s of delay (retention period), two compound stimuli appeared, and the animal had to choose the one with the symbol or with the color of the sample. Thus the test required attention to the symbol, in some trials also to the color, and short-term retention of the distinctive feature for each trial, either a symbol or a color. Single-unit activity was recorded from cortex of the IT convexity, lower and upper banks of the superior temporal sulcus (STS), and from striate cortex (V1). Firing frequency was analyzed during intertrial periods and during the entirety of every trial, except for the (match) choice period. 2. In IT cortex, as in V1, many units responded to the sample stimulus. Some responded indiscriminately to all samples, whereas others responded selectively to one of their features, i.e., to one symbol or to one color. Fifteen percent of the IT units were symbol selective and 21% color selective. These neurons appeared capable of extracting individual features from complex stimuli. Some color cells (color-attentive units) responded significantly more to their preferred color when it was relevant (i.e., had to be retained) than when it was not. 3. The latency of IT-unit response to the sample stimulus was, on the average, relatively short in unselective units (mean 159 ms), longer in symbol units (mean 203 ms), and longest in color-attentive units (mean 270 ms). This order of latencies corresponds to the presumed order of participation of those three types of units in the selective attention to the component features of the sample as required by the task. It suggests intervening steps of serial processing before color information reached color-attentive cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Spatial and temporal response properties of lagged and nonlagged cells in cat lateral geniculate nucleus.

Abstract: 1. It has recently been shown that the X- and Y-cell classes in the A-layers of the cat lateral geniculate nucleus (LGN) are divisible into lagged and nonlagged types. We have characterized the vis...

Gustatory responses of single neurons in the insula of the macaque monkey.

Abstract: 1. In recordings made from 2,925 single neurons, a region of primary taste cortex was localized to the rostral and dorsal part of the insula of the cynomolgus macaque monkey, Macaca fascicularis. The area is part of the dysgranular field of the insula and is bordered laterally by the frontal opercular taste cortex. 2. The responses of 65 single neurons with gustatory responses were analyzed in awake macaques with the use of the taste stimuli glucose, NaCl, HCl, quinine HCl (QHCl), water, and black currant juice. 3. Intensity-response functions showed that the lowest concentration in the dynamic part of the range conformed well to human thresholds for the basic taste stimuli. 4. A breadth-of-tuning coefficient was calculated for each neuron. This is a metric that can range from 0.0 for a neuron that responds specifically to only one of the four basic taste stimuli to 1.0 for one that responds equally to all four stimuli. The mean coefficient for 65 cells in the taste insula was 0.56. This tuning is sharper than that of neurons in the nucleus of the solitary tract of the monkey, and similar to that of neurons in the primary frontal opercular taste cortex. 5. A cluster analysis showed that at least six different groups of neurons were present. For each of the taste stimuli, glucose, NaCl, HCl, QHCl, water, and black currant juice, there was one group of neurons that responded much more to that tastant than to the other tastants. Other subgroups of these neurons responded to two or more of these tastants, such as glucose and black currant juice, or NaCl and QHCl. 6. On the basis of this and other evidence, it is concluded that the primary insular taste cortex, in common with the primary frontal opercular taste cortex, represents a stage of information processing in the taste system of the primate at which the tuning of neurons has become sharper than that of neurons in the nucleus of the solitary tract, and is moving toward the fineness achieved in the secondary taste cortex in the caudolateral orbitofrontal taste cortex, where motivation-dependence first becomes manifest in the taste system.

Dynamic response of human muscle spindle afferents to stretch

Abstract: 1. One hundred and twenty-four muscle afferents from the finger extensor muscles were recorded from the radial nerve in human subjects. 2. The afferents were provisionally classified as muscle spindle primary (78/124) and secondary afferents (25/124), and Golgi tendon organ afferents (21/124), on the basis of their response to 1) maximal twitch contractions, 2) 20- and 50-Hz sinusoids superimposed on ramp-and-hold stretches, 3) stretch sensitization, and 4) isometric contractions and sudden relaxations. 3. Ramp-and-hold stretches at two velocities, 10 and 50 degrees/s, were applied to the appropriate metacarpophalangeal (MCP) joint while the parent muscle remained relaxed. For each unit three discrete parameters were assessed: the presence or absence of 1) an initial burst at the commencement of the ramp stretch, 2) a deceleration response at the beginning of the hold phase, and 3) a prompt silencing at muscle shortening. In addition, two kinds of dynamic indexes were calculated for 79 of the muscle spindle afferents. 4. Most spindle afferents responded readily to stretch, whereas the Golgi tendon organ afferents produced very poor stretch responses. All of them lacked a static response, whereas the dynamic response, when present at all, consisted of only a few impulses. 5. The dynamic index was higher for spindle primaries than for secondaries, and this difference was statistically significant although the distribution was unimodal for spindle afferents as a group. Hence, this parameter was a poor discriminator. 6. Initial bursts, deceleration responses, and silences during imposed shortening were more common in spindle primaries than in secondaries. The differences were significant in all these respects. 7. The three discrete parameters were statistically pairwise independent for the spindle afferents, justifying the combination of the three into a useful battery for discrimination between primary and secondary spindle afferents and the use of this battery as a partial data base for a probability approach towards a solid classification of human muscle afferents.

Temporal encoding of two-dimensional patterns by single units in primate primary visual cortex. I. Stimulus-response relations.

Abstract: 1. Previously we developed a new approach for investigating visual system neuronal activity in which single neurons are considered to be communication channels transmitting stimulus-dependent codes in their responses. Application of this approach to the stimulus-response relations of inferior temporal (IT) neurons showed that these carry stimulus-dependent information in the temporal modulation as well as in the strength of their responses. IT cortex is a late station in the visual processing stream. Presumably the neuronal properties arise from the properties of the inputs. However, the discovery that IT neuronal spike trains transmit information in stimulus-dependent temporally modulated codes could not be assumed to be true for those earlier stations, so the techniques used in the earlier study were applied to single-striate cortical neurons in the studies reported here. 2. Single-striate cortical neurons were recorded from three awake, fixating rhesus monkeys. The neurons were stimulated by two sets of patterns. The first set was made up of 128 black-and-white patterns based on a complete, orthogonal set of two-dimensional Walsh-Hadamard functions. These stimuli appear as combinations of black-and-white rectangles and squares, and they fully span the range of all possible black-and-white pictures that can be constructed in an 8 x 8 grid. Except for the stimulus that appeared as an all-white or all-black square, each stimulus had equal areas of white and black. The second stimulus set was made up of single bars constructed in the same 8 x 8 grid as the Walsh stimuli. These were presented both as black against a gray background and white against a gray background. The stimuli were centered on the receptive field, and each member of the stimulus set was presented once before any stimulus appeared again. 3. The responses of 21 striate cortical neurons were recorded and analyzed. Two were identified as simple cells and the other 19 as complex cells according to the criteria originally used by Hubel and Wiesel. The stimulus set elicited a wide variety of response strengths and patterns from each neuron. The responses from both the bars and the Walsh set could be used to differentiate and classify simple and complex cells. 4. The responses of both simple and complex cells showed striking stimulus-related strength and temporal modulation. For all of the complex cells there were instances where the responses to a stimulus and its contrast-reversed mate were substantially different in response strength or pattern, or both.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional topography of cat primary auditory cortex: distribution of integrated excitation.

Abstract: 1. Neuronal responses to tones and transient stimuli were mapped with microelectrodes in the primary auditory cortex (AI) of barbiturate anesthetized cats. Most of the dorsoventral extent of AI was mapped with multiple-unit recordings in the high-frequency domain (between 5.8 and 26.3 kHz) of all six studied cases. The spatial distributions of 1) sharpness of tuning measured with pure tones and 2) response magnitudes to a broadband transient were determined in each of three intensively studied cases. 2. The sharpness of tuning of integrated cluster responses was defined 10 dB above threshold (Q10 dB, integrated excitatory bandwidth). The spatial reconstructions revealed a frequency-independent maximum located near the center of the dorsoventral extent of AI. The sharpness of tuning gradually decreased toward the dorsal and ventral border of AI in all three cases. 3. The sharpness of tuning 40 dB above response threshold was also analyzed (Q40 dB). The Q40 dB values were less than one-half of the corresponding Q10 dB value. The spatial distribution showed a maximum in the center of AI, similar to the Q10 dB distribution. In two out of three cases, restricted additional maxima were recorded dorsal to the main maximum. Overall, Q10 dB and Q40 dB were only moderately correlated, indicating that the integrated excitatory bandwidth at higher stimulus levels can be influenced by additional mechanisms that are not active at lower levels. 4. The magnitude of excitatory responses to a broadband transient (frequency-step response) was determined. The normalized response magnitude varied between less than 1% and up to 100% relative to a characteristic frequency (CF) tone response. The step-response magnitude showed a systematic spatial distribution. An area dorsal to the Q10 dB maximum consistently showed the largest response magnitude surrounded by areas of lower responsivity. A second spatially more restricted maximum was recorded in the ventral-third of each map. Areas with high-transient responsiveness coincided with areas of broad integrated excitatory bandwidth at comparable stimulus levels. 5. The distribution of excitation produced by narrowband and broadband signals suggest that there exists a clear functional organization in the isofrequency domain of AI that is orthogonal to the main cochleotopic organization of the AI. Systematic spatial variations of the integrated excitatory bandwidth reflect underlying cortical processing capacities that may contribute to a parallel analysis of spectral complexity, e.g., spectral shape and contrast, at any given frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrophysiological studies of acetylcholine and the role of the basal forebrain in the somatosensory cortex of the cat. ii, cortical neurons excited by somatic stimuli

Abstract: 1. Of the sample of 322 neurons located in somatosensory cortex and tested for their responsiveness to somatic stimulation, 91 (28%) responded to stimuli applied to the skin. The majority were located in the middle cortical layers. Each of the cells subjected to tests with glutamate and acetylcholine (ACh) was rapidly adapting to cutaneous stimuli, giving a response at the onset of skin indentation and sometimes after the stimulus withdrawal. 2. Of the 30 cells tested by pairing basal forebrain (BF) stimulation with cutaneous stimulation. 18 (60%) displayed enhanced responses to the same cutaneous stimulus after the pairing. These effects lasted for greater than 5 min in 17 cases, persisting for as long as the cell was studied, sometimes greater than 1 h. 3. The enhanced responsiveness to cutaneous stimuli could not be reversed by atropine, but in each of the 11 cells where atropine was administered while the BF stimulus was paired with the skin stimulus, the pairing produced no enhancement. 4. We conclude that pairing a BF stimulus with a cutaneous stimulus leads to long-term facilitation of the responsiveness of the cortical neuron subjected to this treatment and that this effect is mediated by the release of acetylcholine from BF cholinergic neurons that act on muscarinic receptors found on neurons in the somatosensory cortex.

Voltage- and transmitter-gated currents in isolated rod bipolar cells of rat retina.

Abstract: 1. Bipolar cells were isolated from adult rat retinas after enzymatic and mechanical treatment. The cells could be unequivocally identified from their morphology because of high retention of their axon and dendritic processes after isolation. 2. Protein kinase C (PKC) immunoreactivity performed on sections of the rat retina labeled rod bipolar cells and a few amacrine cells. Virtually all bipolar cells in the dissociates expressed PKC immunoreactivity and were, therefore, rod bipolar cells. 3. Rod bipolar cells were examined with the tight-seal whole-cell and excised-patch recording techniques. Resting potentials of the isolated cells recorded under current-clamp conditions showed a broad unimodal distribution around -37 mV. 4. Membrane depolarization from a holding potential of -90 mV resulted in an outward current. A fast sodium inward current was not observed. Membrane hyperpolarization from a holding potential of -40 mV activated an inwardly rectifying current. 5. gamma-Aminobutyric acid (GABA) and glycine, the putative retinal neurotransmitters that mediate the bipolar cells' receptive field surround in vivo, activated chloride conductances in almost all isolated bipolar cells. GABA- and glycine-evoked currents were both desensitizing and could be antagonized by the classical blockers bicuculline, picrotoxin, and strychnine, respectively. 6. Pressure application of the drugs from fine microcapillaries to various parts of the isolated cells suggests a high GABA sensitivity at the axonal endings compared with either the somatic or dendritic region. A similar distribution was not found for glycine. On the contrary, glycine-induced single-channel events with main conductances of 52 and 34 pS were recorded from membrane patches excised from the cells' somata. 7. Conductances induced by glutamate and several excitatory amino acid agonists were observed in a number of the cells. Application of the glutamate agonist 2-amino-4-phosphonobutyric acid (APB) induced an inward current at negative holding potentials associated with the opening of ion channels. In only 5 of 93 cells, APB closed ion channels, leading to a decrease in membrane conductance.

Evidence for a central component in the sensitization of spinal neurons with joint input during development of acute arthritis in cat's knee.

Abstract: 1. In the spinalized cat, nociceptive spinal neurons with knee input show enhanced responses to mechanical stimulation of that joint once an inflammation has developed in the knee. Enhanced responses may result from increased afferent inflow as well as from modifications of the nociceptive processing within the spinal cord. To examine the significance of these components, we tested in 30 chloralose-anesthetized, spinalized cats whether, during development of arthritis, changes of responsiveness in spinal neurons are restricted to stimulation of the inflamed joint or whether responsiveness in these neurons is altered in general. While continuously recording from a neuron, we injected kaolin and carrageenan into one knee and tested the responses to mechanical stimuli applied to the joint and to regions adjacent to and remote from the knee during the developing arthritis. In addition, in six cats we monitored the neurons' responses to electrical stimulation of the sural nerves and the rostral lumbar spinal cord. 2. Of 32 neurons in laminae VI, VII, and VIII of the lumbar spinal cord, 15 ascending and eight nonascending cells were driven by mechanical stimulation of one or both knee joint(s). Nine of these were nociceptive specific (NS), responding exclusively or predominantly to noxious compression of the knee and other deep tissue, and 12 were wide-dynamic-range (WDR) cells with graded responses to gentle and noxious stimuli applied to the knee joint(s), deep tissue, and skin. Two neurons with high ongoing discharges had some excitatory joint input but showed marked inhibition by most stimuli used (INH neurons). The majority of the neurons had receptive fields on both legs. Nine of the 32 neurons had no input from the knee(s). 3. All 23 neurons with joint input became sensitive or more responsive to movements and gentle compression of the inflamed knee once the inflammation had developed. In general, these neurons also showed enhanced responses to compression of the adjacent muscles in thigh and lower leg. In 20 neurons, response properties were even altered for stimuli applied to regions remote from the inflamed joint, including the contralateral leg in 18 cases. We found expansion of initially restricted receptive fields (mainly in NS cells), enhancement of preexisting responses, and/or lowering of threshold to mechanical stimuli applied to these regions; few neurons developed inhibitory reactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Muscle afferent responses to isometric contractions and relaxations in humans

Abstract: 1. One hundred and two single afferents from the finger extensor muscles of humans were studied with the microneurography technique. 2. The afferents were provisionally classified as primary muscle spindle afferents (62/102), secondary spindle afferents (22), and Golgi tendon organ afferents (18) on the basis of their responses to four tests: 1) ramp-and-hold stretch, 2) 20- and 50-Hz small-amplitude sinusoidal stretch superimposed on ramp-and-hold stretch, 3) maximal isometric twitch contraction, and 4) stretch sensitization. 3. The response profiles of the three unit types were analyzed during slowly rising isometric contraction terminating with an abrupt relaxation. About 75% (61/84) of all muscle spindle afferents increased their discharge during isometric contraction, whereas the discharge was reduced for the remaining afferents. All Golgi tendon organs increased their discharge during the contraction. 4. The level of extrafusal contraction at which a spindle afferent increased its discharge rate often varied from trial to trial, speaking against a fixed fusimotor recruitment level of the individual spindle ending. 5. In 70% of the spindle afferents, a distinct burst of impulses appeared when the subject rapidly relaxed after the isometric contraction. The burst was more common and usually much more prominent with primary than secondary afferents, often reaching instantaneous discharge rates well above 100 Hz. 6. Whereas all Golgi tendon organ afferents displayed an increased discharge during the contraction phase, only one of them exhibited a rate acceleration close to the relaxation phase. However, this response could clearly be identified as being of different nature than the spindle bursts.(ABSTRACT TRUNCATED AT 250 WORDS)

Triggering of preprogrammed movements as reactions to masked stimuli

Abstract: 1. Visual stimuli were presented to normal human subjects to test simple and more complex voluntary motor responses. Large and small visual stimuli were presented. In some trials, the small stimulus was followed 50 ms later by the large stimulus, so that the small stimulus was not perceived; this is the phenomenon of "backward masking." 2. Although subjects were not able to detect the masked, visual stimulus on forced-choice testing, they performed motor, reaction-time (RT) tasks in response to it. The RTs for responses to the masked stimulus were the same as those for responses to the easily perceived, nonmasked stimulus. 3. This result confirms and extends the findings of Fehrer and Biederman and was demonstrated with both simple and more complex motor responses. 4. Discussion of the findings focuses on their implications for motor control, particularly with respect to the preprogramming of voluntary movement.