Purkinje cell simple spike activity during grasping and lifting objects of different textures and weights

1. Three monkeys (2.5-3.5 kg) were trained to pinch an object between the thumb and forefinger and to lift it a vertical distance of 1.0-2.0 cm. Either the object weight (15, 65, or 115 g) or the surface texture (sand paper or polished metal) contacting the fingers could be varied. The object was equipped with a vertical position transducer, an accelerometer, and strain gauges that measured the grip force and the vertical load force. 2. In accordance with similar previously published studies on human subjects, it was found that monkeys appropriately scaled the grip forces according to the weight and coefficient of friction of the object. The grip force preceded the load force by 25 ms, and they both covaried with the changes in surface friction. 3. An analysis of electromyograms (EMGs) recorded intramuscularly from the muscles of the wrist and fingers including both flexors and extensors indicated that 26 muscles were active during pinching and lifting. Of these, 17 produced the maximum activity for the slippery surface and the greatest weight and the least activity with the roughest surface and lightest weight. 4. A total of 59 Purkinje cells and 123 unidentified units recorded from the paravermal and lateral cerebellar cortex were found to change their firing frequency during lifting the experimental object. 5. Increased discharge during the grasping and lifting was found for 56% (33/59) of the Purkinje cells and 80% (98/123) of the unidentified neurons, whereas 44% (26/59) of the Purkinje cells and 20% of the unidentified neurons decreased activity during the same period. 6. Significant modulations of the firing frequency with surface texture or object weight occurred for 59% (35/59) of the Purkinje cells and 67% (82/123) of the unidentified neurons. 7. One hundred and three Purkinje and unidentified neurons recorded in the paravermal and lateral region of the cerebellar cortex were examined for peripheral receptive fields, and of these, 43/103 (42%) responded exclusively to imposed displacements and tapping of muscles suggesting afferents originating from proprioceptors. A further 28/103 (27%) had exclusively cutaneous receptive fields on the hand that could be stimulated by brushing the skin lightly with a sable hair brush. Only six neurons demonstrated convergent cutaneous and proprioceptive receptive fields and no response to peripheral stimulation could be found for 26 neurons. No difference was found between the receptive fields of Purkinje cells and those of the unidentified neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Activity in rostral motor cortex in response to predictable force-pulse perturbations in a precision grip task

The purpose of this investigation was to characterize the discharge of neurons in the rostral area 4 motor cortex (MI) during performance of a precision grip task. Three monkeys were trained to grasp an object between the thumb and index finger and to lift and hold it stationary for 2-2.5 s within a narrow position window. The grip and load forces and the vertical displacement of the object were recorded on each trial. On some trials a downward force-pulse perturbation generating a shear force and slip on the skin was applied to the object after 1.5 s of static holding. In total, 72 neurons were recorded near the rostral limit of the hand area of the motor cortex, located close to the premotor areas. Of these, 30 neurons were examined for receptive fields, and all 30 were found to receive proprioceptive inputs from finger muscles. Intracortical microstimulation applied to 38 recording sites evoked brief hand movements, most frequently involving the thumb and index finger with an average threshold of 12 microA. Slightly more than one-half of the neurons (38/72) demonstrated significant increases in firing rate that on average began 284 +/- 186 ms before grip onset. Of 54 neurons tested with predictable force-pulse perturbations, 29 (53.7%) responded with a reflexlike reaction at a mean latency of 54.2 +/- 16.8 ms. This latency was 16 ms longer than the mean latency of reflexlike activity evoked in neurons with proprioceptive receptive fields in the more caudal motor cortex. No neurons exhibited anticipatory activity that preceded the perturbation even when the perturbations were delivered randomly and signaled by a warning stimulus. The results indicate the presence of a strong proprioceptive input to the rostral motor cortex, but raise the possibility that the afferent pathway or intracortical processing may be different because of the slightly longer latency.     

Encoding of movement dynamics by Purkinje cell simple spike activity during fast arm movements under resistive and assistive force fields

It is controversial whether simple-spike activity of cerebellar Purkinje cells during arm movements encodes movement kinematics like velocity or dynamics like muscle activities. To examine this issue, we trained monkeys to flex or extend the elbow by 45 degrees in 400 ms under resistive and assistive force fields but without altering kinematics. During the task movements after training, simple-spike discharges were recorded in the intermediate part of the cerebellum in lobules V-VI, and electromyographic activity was recorded from arm muscles. Velocity profiles (kinematics) in the two force fields were almost identical to each other, whereas not only the electromyographic activities (dynamics) but also simple-spike activities in many Purkinje cells differed distinctly depending on the type of force field. Simple-spike activities encoded much larger mutual information with the type of force field than that with the residual small difference in the height of peak velocity. The difference in simple-spike activities averaged over the recorded Purkinje-cells increased approximately 40 ms before the appearance of the difference in electromyographic activities between the two force fields, suggesting that the difference of simple-spike activities could be the origin of the difference of muscle activities. Simple-spike activity of many Purkinje cells correlated with electromyographic activity with a lead of approximately 80 ms, and these neurons had little overlap with another group of neurons the simple-spike activity of which correlated with velocity profiles. These results show that simple-spike activity of at least a group of Purkinje cells in the intermediate part of cerebellar lobules V-VI encodes movement dynamics.     

Primary motor cortical responses to perturbations of prehension in the monkey.

1. Two monkeys were trained to grasp, lift, and hold an object within a vertical position window. A downward force-pulse perturbation was delivered during stationary object holding to simulate slip of the object due to gravity. The responses evoked by the perturbation were studied in 189 neurons of the hand area of the primary motor cortex. In addition, the slip-evoked responses were compared with the modulation of neural discharge with textures and weights described in the previous paper. 2. The perturbation evoked responses with sharp onsets in the majority of motor cortical neurons (115/189, 61%) active during the task. The majority of the responses were of sufficiently short latency (43.17 +/- 17.24 ms, mean +/- SD) to have participated in the reflex grip force increase that followed at latencies from 50 to 100 ms. 3. Although a similar proportion of neurons with cutaneous (43/70) or proprioceptive (35/59) receptive fields (RFs) were responsive to the perturbation, the cutaneous afferents provided a stronger excitation of motor cortical cells than the feedback originating from proprioceptive receptors. 4. The covariation of the neural discharge related to the surface texture of the grasped object and the responsiveness to object slip was studied in 89 cells tested with the perturbation and with more than one surface texture on unperturbed trials. Within this population, motor cortical cells with cutaneous RFs were more sensitive to the perturbation (25/31) than neurons receiving proprioceptive input (8/16). Furthermore, all (17/17) neurons with cutaneous RFs that were more active with the smooth than with the rough surface textures showed a vigorous response to the perturbation. 5. A detectable downward displacement of the object was not always necessary to excite neurons with cutaneous RFs and whose activity increased with the smooth textures. Their sensitivity to the perturbation was consistent with the hypothesis that the cutaneous afferent activity generated by object slips or shear forces on the skin contributed to the increased discharge when lifting objects of slippery surface textures. The activity of these slip- or shear-sensitive cells may have contributed to the reflex grip force increases and to the greater sustained muscular activity needed to lift smooth objects. 6. Ten cells that were excited by stroking of the glabrous skin of the hand decreased their discharge frequency during the task even though their RFs were in direct contact with the object. Most of these neurons (7/10) did not respond to the object slip, and three cells had very weak responses to the perturbation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Purkinje cells signal hand shape and grasp force during reach-to-grasp in the monkey

The cerebellar cortex and nuclei play important roles in the learning, planning, and execution of reach-to-grasp and prehensile movements. However, few studies have investigated the signals carried by cerebellar neurons during reach-to-grasp, particularly signals relating to target object properties, hand shape, and grasp force. In this study, the simple spike discharge of 77 Purkinje cells was recorded as two rhesus monkeys reached and grasped 16 objects. The objects varied systematically in volume, shape, and orientation and each was grasped at five different force levels. Linear multiple regression analyses showed the simple spike discharge was significantly modulated in relation to objects and force levels. Object related modulation occurred preferentially during reach or early in the grasp and was linearly related to grasp aperture. The simple spike discharge was positively correlated with grasp force during both the reach and the grasp. There was no significant interaction between object and grasp force modulation, supporting previous kinematic findings that grasp kinematics and force are signaled independently. Singular value decomposition (SVD) was used to quantify the temporal patterns in the simple spike discharge. Most cells had a predominant discharge pattern that remained relatively constant across object grasp dimensions and force levels. A single predominant simple spike discharge pattern that spans reach and grasp and accounts for most of the variation (>60%) is consistent with the concept that the cerebellum is involved with synergies underlying prehension. Therefore Purkinje cells are involved with the signaling of prehension, providing independent signals for hand shaping and grasp force.     

Responses of cerebellar Purkinje cells to mechanical perturbations during locomotion of decerebrate cats

During the locomotion of cats which had been decerebrated at the precollicular and premammillary level, mechanical perturbations (taps of 50-550 g wt.) were applied to the paw dorsum of the left forelimb. Purkinje cells were recorded from the vermis of the cerebellar anterior lobe, and those connected to Deiters' neurons controlling the right forelimb were identified by antidromic and orthodromic stimuli. Taps on the left forelimb induced in these Purkinje cells two types of responses; I-type is a depression of simple spike discharge, often preceded by a brief phase of facilitation, and E-type is entirely a facilitation of simple spike discharge. Complex spikes, representing activation through climbing fiber afferents, were frequently evoked by the taps in both I- and E-types. The I-type depression in Purkinje cells closely corresponds to the previously reported facilitation in Deiters' neurons and forelimb extensor muscles, suggesting that the interlimb coordination during cat's locomotion is effected by linked activity of vermal Purkinje cells and Deiters' neurons.     

Force field effects on cerebellar Purkinje cell discharge with implications for internal models

The cerebellum has been hypothesized to provide internal models for limb movement control. If the cerebellum is the site of an inverse dynamics model, then cerebellar neural activity should signal limb dynamics and be coupled to arm muscle activity. To address this, we recorded from 166 task-related Purkinje cells in two monkeys performing circular manual tracking under varying viscous and elastic loads. Hand forces and arm muscle activity increased with the load, and their spatial tuning differed markedly between the viscous and elastic fields. In contrast, the simple spike firing of 91.0% of the Purkinje cells was not significantly modulated by the force nor was their spatial tuning affected. For the 15 cells with a significant force effect, changes were small and isolated. These results do not support the hypothesis that Purkinje cells represent the output of an inverse dynamics model of the arm. Instead these neurons provide a kinematic representation of arm movements.     

Interaction of norepinephrine with Purkinje cell responses to cerebellar afferent inputs in aged rats

Age-related differences in the modulatory actions of NE on the evoked activity of cerebellar Purkinje cells were examined in young (3 month) and old (18-20 month) Fischer 344 rats. We have previously shown that NE is more potent in young than in old rats, in terms of its ability to inhibit spontaneous activity. In this investigation complex spike excitation, simple spike excitation, and inhibition of Purkinje cell discharge were elicited by stimulation of climbing fibers, mossy fibers, and cerebellar parallel fibers, and quantified by computing post-stimulus time histograms of the neuronal response, recorded extracellularly. Histograms were compared before, during and after local ejection of NE from multibarreled micropipettes. In young rats NE preferentially inhibits spontaneous discharge more than evoked excitations. The inhibitory response of the Purkinje cell to activation of basket and stellate cell afferents is potentiated by NE with respect to the inhibition of spontaneous discharge. In old rats the NE-induced potentiation of both excitatory and inhibitory responses was significantly diminished. The loss of noradrenergic enhancement of the relative responsiveness of Purkinje neurons to afferent inputs in senescent animals may relate to behavioral deficits seen in aging.     

Primary motor cortical activity related to the weight and texture of grasped objects in the monkey.

1. Two monkeys were trained to grasp an object between the thumb and index finger and lift it to a vertical distance of 12-25 mm. Up to 12 different conditions defined by different combinations of object weights (15, 65, and 115 g) and four surface textures (oiled metal, smooth metal, fine and coarse sandpaper) were used. The apparatus was equipped to measure grip (prehensile) force, vertical (load) force, and object displacement. 2. The monkeys appropriately scaled the grip force for the weight and the coefficient of friction of the object. However, during the dynamic phase of the task (grasping and lifting), the monkeys increased the prehensile force in multiple steps, suggesting that they relied on sensory feedback from the fingers to attain an adequate grip force to lift the object rather than programming the lift in advance. 3. Single-unit activity of 248 neurons was recorded in the hand area of the primary motor cortex while the monkeys performed the task. Of 208 neurons tested for cutaneous and proprioceptive receptive fields (RFs), 96 were sensitive to cutaneous stimulation of the glabrous skin of the hand, whereas 82 received proprioceptive input from wrist and finger muscles. The concentration of neurons with cutaneous input was significantly greater in the rostral bank of the central sulcus compared with cells with proprioceptive RFs, which were more concentrated in the convexity of the precentral gyrus. 4. From the global sample, 199 cells were tested with the three object weights, and 128 of these with at least two surface textures were used in combination with the object weights. The discharge of 58/199 (29%) cells was modulated with the object weight. Cells with cutaneous (20/84, 24%) and proprioceptive (23/71, 32%) RFs were about equally responsive to the object weight. 5. A greater number of motor cortical neurons were influenced by surface texture than by object weight. Of 128 cells tested with at least two surface textures, 67 (52%) showed a modulation of their activity as a function of texture. A significantly greater proportion of neurons with cutaneous RFs (40/63, 63%) showed differential activity as a function of object texture than cells receiving proprioceptive input (21/47, 45%). 6. Weight- and texture-related neurons were not distributed equally in the rostrocaudal dimension of the motor cortex. Only 8% of texture-related cells were located in the convexity of the precentral gyrus, whereas 30% of weight-related neurons were recorded from this rostral zone.(ABSTRACT TRUNCATED AT 400 WORDS)     

Alterations in simple spike activity and locomotor behavior associated with climbing fiber input to Purkinje cells in a decerebrate walking cat

Recently we reported significant modulation of climbing fiber discharge in cerebellar Purkinje cells during normal and perturbed locomotion in the decerebrate cat walking on a treadmill. In this study covariation of simple spike activity and step cycle behavior with complex spike discharge were studied in decerebrate cats. Purkinje cell simple and complex spike discharge was recorded extracellularly in the intermediate region of lobules IV and V. Forelimb triceps and biceps electromyographic activity and displacement were monitored during the step cycle. A series of analyses were carried out to determine the temporal relationship between the complex spike discharge and forelimb step cycle, electromyographic activity and simple spike discharge. In this paper only the complex spike discharge associated with the onset of locomotion was evaluated. Using a sorting technique the amplitude of the forelimb step cycle and the associated triceps and biceps electromyographic activity covaried with complex spike discharge. For the majority of cells the alterations in the step cycle followed or occurred with the increase in complex spike discharge. However, in some cells the step cycle modifications preceded the increase in climbing fiber afferent activity. Another series of analyses employing an alignment technique demonstrated that a short term increase in simple spike discharge followed and was tightly coupled to the complex spike discharge. Additionally in most Purkinje cells an "oscillation" of simple spike activity which followed the complex spike discharge was uncovered. These observations support an important role for the climbing fiber afferent system in ongoing motor behavior. The results are consistent with the speculation that increased climbing fiber afferent input alters cerebellar cortical output which in turn can alter the ongoing motor behavior.     

Single trial coupling of Purkinje cell activity to speed and error signals during circular manual tracking

The simple spike firing of cerebellar Purkinje cells encodes information on the kinematics of limb movements. However, these conclusions have been primarily based on averaging the discharge of Purkinje cells across trials and time and there is little information on whether Purkinje cell simple spike firing encodes specific motor errors during limb movements. Therefore, this study investigated single-trial correlations between the instantaneous simple spike firing of Purkinje cells with various kinematics and error signals. Purkinje cells (n = 126) were recorded in the intermediate and lateral zones centered on the primary fissure while three monkeys intercepted and tracked a target moving in a circle. Cross-correlation analysis was performed between the instantaneous simple spike firing rate and speed, the directional component of the velocity vector, and error signals during single movement trials. Significant correlations at physiologically relevant lags of ±250 ms were observed with tracking speed for 37% of Purkinje cells, with the velocity component in 39%, with direction error in 6% and speed error in 25%. Simple spike firing of the majority of Purkinje cells with significant correlation showed a negative lag with respect to speed and a positive lag with respect to error signals. We hypothesize that the cerebellum is involved in movement planning and control by continuously monitoring movement errors and making intermittent corrections that are represented as fluctuations in the speed profile.     

Changes in the responses of Purkinje cells in the floccular complex of monkeys after motor learning in smooth pursuit eye movements

We followed simple- and complex-spike firing of Purkinje cells (PCs) in the floccular complex of the cerebellum through learned modifications of the pursuit eye movements of two monkeys. Learning was induced by double steps of target speed in which initially stationary targets move at a "learning" speed for 100 ms and then change to either a higher or lower speed in the same direction. In randomly interleaved control trials, targets moved at the learning speed in the opposite direction. When the learning direction was the ON direction for simple-spike responses, learning was associated with statistically significant changes in simple-spike firing for 10 of 32 PCs. Of the 10 PCs that showed significant expressions of learning, 8 showed changes in simple-spike output in the expected direction: increased or decreased firing when eye acceleration increased or decreased through learning. There were no statistically significant changes in simple-spike responses or eye acceleration during pursuit in the control direction. When the learning direction was in the OFF direction for simple-spike responses, none of 15 PCs showed significant correlates of learning. Although changes in simple-spike firing were recorded in only a subset of PCs, analysis of the population response showed that the same relationship between population firing and eye acceleration obtained before and after learning. Thus learning is associated with changes that render the modified population response appropriate to drive the changed behavior. To analyze complex-spike firing during learning we correlated complex-spike firing in the second, third, and fourth 100 ms after the onset of target motion with the retinal image motion in the previous 100 ms. Data were largely consistent with previous evidence that image motion drives complex spikes with a direction selectivity opposite that for simple spikes. Comparison of complex-spike responses at different times after the onset of control and learning target motions in the learning direction implied that complex spikes could guide learning during decreases but not increases in eye acceleration. Learning caused increases or decreases in the sensitivity of complex spikes to image motion in parallel with changes in eye acceleration. Complex-spike responses were similar in all PCs, including many in which learning did not modify simple-spike responses. Our data do not disprove current theories of cerebellar learning but suggest that these theories would have to be modified to account for simple- and complex-spike firing of floccular Purkinje cells reported here.     

Inferior olivary neurons in the awake cat: detection of contact and passive body displacement

We have recorded from 306 neurons in the inferior olive of six alert cats. Most of the cats were trained to perform a simple task with the forelimb. We observed the neural responses to a wide variety of cutaneous and proprioceptive stimuli, as well as responses during spontaneous and learned active movements. Neurons responsive to somatosensory stimulation were found in all parts of the inferior olive, and they were roughly evenly divided between those responsive to cutaneous stimulation and those responsive to proprioceptive stimulation. In the dorsal accessory olive all neurons were responsive to somatosensory stimulation. In the medial accessory nucleus 88% and in the principal olive 74% of cells were responsive to somatosensory stimulation. Cells responsive to cutaneous stimulation usually had small receptive fields, commonly on the paw. These cells had low-threshold responses to one or more forms of cutaneous stimulation and typically fired one spike at the onset of the stimulus on 80% or more of stimulus applications. Cells responsive to proprioceptive stimulation most commonly responded to passive displacements of a limb. These cells were often very sensitive, responding to linear displacements of less than 1 cm in one specific direction. No cells in our sample responded reliably during active movement by the animal. Only 21% of cells responding to passive proprioceptive stimulation showed any modulation during active movement, and the modulation was weak. Likewise, cells responsive to cutaneous stimulation generally failed to respond when a similar stimulus was produced by an active movement by the animal. Exceptions to this were stimuli produced during exploratory movements or when the receptive field unexpectedly made contact with an object during active movement. Electrical stimulation applied in the inferior olive failed to evoke movements or to modify ongoing movement. Our results are consistent with the hypothesis that inferior olivary neurons function as somatic event detectors responding particularly reliably to unexpected stimuli.     

Cerebellar feedback signals of a passive hand movement in the awake monkey

From three intact and awake monkeys, 149 Purkinje cells and 44 presumed mossy fibres were recorded in the intermediate part of the cerebellar anterior lobe, and this activity was analyzed with regard to different parameters of a passive hand movement. The tonic discharge rate of the simple spikes (SS) varied according to different joint positions only in a single Purkinje cell, whereas such a position relation was found in nine out of 44 presumed mossy fibres. A phasic increase of the complex spike (CS) discharge rate of Purkinje cells in response to passive wrist movements usually occurred within 100 ms after movement onset. However, in some units a phase of increased CS rate was observed which lasted for the whole movement duration. The amount of this phasic increase in the CS rate depended on the acceleration of movement, but the SS response to movements of different velocity remained unchanged.     

Cerebellar neuronal activity related to whole-arm reaching movements in the monkey

1. Three monkeys were trained to make whole-arm reaching movements from a common central starting position toward eight radially arranged targets disposed at 45 degrees intervals. A sample of 312 cerebellar neurons with proximal-arm receptive fields or discharge related to shoulder or elbow movements was studied in the task. The sample included 69 Purkinje cells, 115 unidentified cortical cells, 65 interpositus neurons, and 63 dentate units. 2. The reaching task was divided into three movement-related epochs: a reaction time, a movement time, and holding over the target. All neurons demonstrated significant changes in discharge during one or more of these three epochs. Almost all of the cells (95%) showed a significant change in activity during the movement, whereas 68-69% of the cells showed significant changes from premovement activity during the reaction time and holding periods. 3. During the combined reaction time-movement period, 231/312 cells were strongly active in the task. Of these, 151 cells (65.4%) demonstrated unimodal directional responses. Sixty-three had a reciprocal relation to movement direction, whereas 88 showed only graded increases or decreases in activity. A further 37 cells (16.0%) were nondirectional, with statistically uniform changes in discharge in all eight directions. The remaining 43 cells (18.6%) showed significant differences in activity for different directions of movement, but their response patterns were not readily classifiable. 4. The proportion of directional versus nondirectional cells was consistent across the four cell populations. However, graded response patterns were more common and reciprocal responses less common among Purkinje and dentate neurons than among unidentified cortical cells and interpositus neurons. 5. The distribution of preferred directions of the population of cerebellar neurons covered all possible movement directions away from the common central starting position in the horizontal plane. When the preferred direction of each cell in the sample population was aligned, the mean direction-related activity of the cerebellar population formed a bell-shaped tuning curve for the activity recorded during both the reaction time and the movement, as well as during the time the arm maintained a fixed posture over the targets. A vector representation also showed that the overall activity of the cerebellar population during normal reaching arm movements generated a signal that varied with movement direction. 6. These results demonstrate that the cerebellum generates a signal that varies with the direction of movement of the proximal arm during normal aimed reaching movements and is consistent with a role in the control of the activity of muscles or muscle groups generating these movements.     

Properties of proprioceptive neurons in the cuneate nucleus of the cat

Fifty-two slowly adapting proprioceptive neurons in the cuneate nucleus of chloralose-anesthetized cats were studied. Recordings were made from 3 mm rostral to the obex to 5 mm caudal. The highest densities of proprioceptive neurons were found above and more than 3 mm caudal to the obex. Analysis of the spike trains produced with the forelimb held fixed revealed three basic periodic patterns. Neurons exhibiting these patterns were partitioned into three groups, referred to as the A, B, and C classes. Class A neurons (42%; 22/52) produced regular spike trains that were qualitatively similar to muscle spindle fibers. Interval distributions for this class were typically unimodal and slightly positively skewed. Adjacent intervals were frequently positively correlated. Spectral analysis suggested that 91% of class A spike trains had one to two periodic components. Class B neurons (21%; 11/52) had additional spikes interposed in their periodic discharge; these "interrupting" spikes did not significantly alter the timing of the dominant periodic discharge. Interval distributions were typically bimodal and adjacent intervals were negatively correlated. Spectral analysis suggested that two or more periodic components were present in their spike trains. Class C neurons (36%; 26/52) had spike trains with a basic rhymicity, but when this specific discharge was interrupted, the subsequent interval was near modal length; thus, they were "reset." Interval distributions were usually multimodal and adjacent intervals were frequently negatively correlated. Spectral analysis suggested that C spike trains usually had four or more periodic components. Estimates of information-carrying capacity of each class using a mean rate code and those of primary muscle spindle fibers suggested that a sizable information loss may occur in synaptic transmission. This potential loss was smaller for A-neurons (40%) than for B- (69%) or C-neurons (64%). Electrical stimulation of cutaneous structures influenced 55% (22/52) of the sample. All were members of the B and C classes. Responses were typically biphasic. The cutaneous receptive fields nearly always included a portion of the forepaw. No relationship was found between movement sensitivity and receptive field topography. Contralateral input was found in half (10/20) the neurons tested.     

Inferior olive lesion induces long-term modifications of cerebellar inhibition on Deiters nuclei

The frequency of discharge of cerebellar Purkinje cells and lateral vestibular nuclear cells were recorded at different intervals of time after injection of 3-acetylpyridine (3AP), which destroys the inferior olivary nucleus. During the first few days, Purkinje cells showed an increase of simple spike firing, while Deiters cells showed a strong depression of their discharge. Recordings up to 3 months demonstrated, for both groups of cells, a recovery, whose time course is faster for Deiters cells than for Purkinje cells. A reduced inhibitory efficacy of Purkinje cells, as a consequence of climbing fibre deprivation, is suggested.     

Receptive fields of cerebellar cells receiving exteroceptive input in a Gymnotid fish.

Single neurons in the caudal lobe of the cerebellum of the weakly electric fish Apteronotus albifrons respond to distortions in the normal electric field produced by the animal. Moving plastic or metal objects as well as a simpler stimulus, a moving electrical dipole, produce adequate distortions of the fish's field to cause the cerebellar cells to respond. The moving dipole stimulated small enough areas of the fish's skin, as determined by the responses of single electroreceptors, to allow maps of the receptive fields of single cerebellar cells to be produced. The receptive fields seen varied widely in complexity from relatively small excitatory or inhibitory areas to larger fields containing multiple excitatory and inhibitory areas usually bordering one another. Most cells studied displayed directional responses. Usually qualitatively different responses resulted from opposite directions of movement, and less frequently units were seen in which no response resulted from movement opposite the direction which caused responses; Varying the rate of stimulus movement caused only small changes in the responses of cerebellar cells; however, motionless stimuli applied over areas of skin known to respond to moving stimuli produced weaker responses of the appropriate sign for that area. Movement seems to be an important component of the stimulus for these cells. Cells were also seen which responded to visual as well as to electroreceptive input. Responses to each of these two modalities presented above were quite different. The cells recorded from frequently displayed burst discharges similar to those produced by Purkinje cells in other lower vertebrates, and most of the cells studied are believed to be Purkinje cells. A somatotopic relationship was found between the position of the center of a receptive field on the fish's body and the position of the cell in the brain. All of the results obtained are compatible with the hypothesis that the caudal lobe of the cerebellum is processing electroreceptive information related to object detection.     

Linear head displacement measured by the otoliths can be reproduced through the saccadic system

Fifty-nine Purkinje cells that responded to electrical stimulation of the glossopharyngeal (IXth) nerve with complex and/or simple spikes were isolated in the frog cerebellum. For these 59 Purkinje cells, changes in the complex and simple spike activity during taste stimulation of the tongue (42 cells for NaCl and 17 for quinine) were investigated. Of 42 Purkinje cells, 23 (54.8%) showed excitatory changes in simple and/or complex spike discharge rate during NaCl stimulation, and the remaining 19 (45.2%) showed no response. On the contrary, only a few Purkinje cells (2 of 17 cells, 11.8%) showed an excitatory change in simple or complex spike discharge rate during quinine stimulation. These results demonstrate that gustatory information influences cerebellar Purkinje cell activity.     

Induction of heat shock proteins and motor function deficits after focal cerebellar injury

A weight drop model of focal cerebellar injury was used to identify heat shock protein induction and motor function deficits in the anesthetized, adult male, Sprague-Dawley rat. All animals were trained on a beam walking test prior to surgery. Groups of animals received severe, mild or sham weight drop injury to the lateral/paravermal region of the cerebellum. The mild and sham-injured animals showed no motor deficits in the beam walking test, whereas animals with severe cerebellar injury showed significant motor deficits in the beam walking test that approached recovery of motor function 20 days after injury. Following severe injury, induction of heat shock protein of 27kDa was observed in Purkinje cells and in neurons of the deep cerebellar nuclei, as well as Bergmann glial cells, glial cells located in the granule cell layer and the underlying white matter. Following mild injury, heat shock protein of 27kDa induction was observed in Purkinje cells and glial cells, but not in neurons of the deep cerebellar nuclei. The labeled Purkinje cells were widely distributed in the ipsilateral cerebellar cortex. Many of the glial cells that were immunostained with heat shock protein of 27kDa co-localized with cells immunoreactive for glial fibrillary acidic protein. After severe injury, heat shock protein of 72kDa was localized mainly in granule cells at the site of the trauma and in the ipsilateral deep cerebellar nuclei whereas, after mild injury, light labeling was observed only in the granule cell layer. The results demonstrate that focal cerebellar injury has profound effects on motor behavior and induces different families of heat shock proteins in specific groups of neurons and glial cells in the cerebellum.