Movement-related Neurons Research Articles

Neuronal activity in the claustrum of the monkey during performance of multiple movements.

1. We studied neuronal activity in the claustrum of monkeys during performance of three different arm movements. We verified recording sites of claustral neurons by histological confirmation of microlesions. For the sake of comparison, we also recorded from the arm area of the precentral motor cortex (MI). Selection of the movements was either visually guided or determined by memorized information. 2. A striking property of claustral neurons is their nonselective relation to the three movements (push, pull, and turn a manipulandum). A vast majority (70%) of movement-related neurons exhibited increase of discharge in relation to all three movements, whereas only 16% were active in relation to one of the three movements. By contrast, about one-half of neurons in the MI were active in relation to a single movement. In both areas, the movement-related activity was similar regardless of whether the movements were selected by visual signals or by memory. 3. The study is the first to reveal involvement of claustral neurons in motor execution, and their activity property suggests that the way they are involved is different from that of MI neurons.

Localization of motor- and nonmotor-related neurons within the matrix-striosome organization of rat striatum

Striatal neurons can be classified as movement- and nonmovement-related depending on their ability to change firing rate in close temporal association with spontaneous movement in an open-field arena. The present study assessed the location of these cell types within the compartmental organization of the striatum by combining single-unit recording techniques in freely moving rats with calbindin immunohistochemistry. Movement-related neurons were found predominately either in the matrix or along the matrix-striosome border. Most of these neurons were nonselective in that they increased activity whenever the animals changed from a quiet resting posture to any form of behavioral activation (e.g., grooming, locomotion, rearing). The remaining neurons in this group responded exclusively to movements of the head. Nonselective units discharged at a significantly slower rate than head-movement units during both quiet rest and periods of actual movement. Nonmovement-related neurons, which failed to show a reliable change in activity to overt behavior, comprised a relatively small portion of the neuronal sample but were also located in either the matrix or along the matrix-striosome border. Collectively, these results suggest that even though striatal neurons can be distinguished on the basis of their responsiveness to ongoing behavior in an open-field paradigm, such distinctions are not clearly linked to sites within the matrix or its striosomal borders.

Activity of area 5 neurons in monkeys during arm movements: effects of dentate nucleus lesion and motor cortex ablation

Area 5 movement-related neurons were recorded in two trained monkeys respectively before and after (i) bilateral lesion of the dentate nucleus (DN), (ii) ablation of the motor cortex (area 4). DN lesion does not modify the proportion of early (command) and late (somaesthetic) neuronal changes. It does, however, increase both cellular and behavioural reaction times. The ablation of area 4 induces a clear-cut increase in the number of early neuronal changes during the period of recovery from arm palsy. These results show that: (i) the neocerebellum enhances the excitability of area 5 movement-related neurons; (ii) area 5 may compensate for the deficiency in area 4 by unmasking silent neurons and thereby subserves rehabilitation mechanisms.

Differential locations in the midbrain of distinct groups of vertical eye movement‐related neurones in cat: their projections and direct connections with oculomotor neurones

The present study was undertaken to investigate the firing patterns, location and projections of vertical eye movement-related neurones in the Forel's field H (FFH), the interstitial nucleus of Cajal (INC), and reticular formation of the mesodiencephalic junction (MDJ) in chronically prepared alert cats. A total of 456 neurones in the medial MDJ with firing closely related to vertical eye movements was examined using antidromic microstimulation and spike-triggered averaging technique. On the basis of their firing patterns, these neurones were classified into five groups, i.e. burst neurones (BNs), burst-tonic neurones (BTNs), tonic neurones (TNs), augmenting neurones (ANs) and pause neurones (PNs). BNs were located mainly in the dorsomedial part of the FFH. Most of TNs were found more caudally than BNs. BTNs and PNs were located further caudally, within the INC and nearby reticular formation. ANs were located mainly in the dorsolateral part of the FFH. Both medium-lead BNs (MLBNs) and BTNs projected to the inferior rectus (IR) subdivision of the oculomotor nucleus on both sides. MLBNs projected to the trochlear nucleus as well through collateral branches of the axon projecting to the oculomotor nucleus. Downward and upward MLBNs made direct excitatory and inhibitory connections, respectively, with IR motorneurones. These results suggest that many kinds of neurones in the paramedian regions of MDJ play a significant role in the genesis of vertical eye movements.

Local dynamic interactions in the collicular motor map: a neural network model

In this paper we explore the possibility that some of the dynamic properties of the neural activity in the gaze-related motor map (located in the intermediate layers of the superior colliculus) might be mediated by local interactions between movement-related neurons and fixation neurons. More specifically, the goal of this research is to demonstrate, from a computational standpoint, which classes of dynamic behaviour of the collicular neurons can be obtained without the intervention of feedback signals, and hence to begin to explore the extent to which the gaze system needs feedback in order to operate. We modelled: (i) the collicular motor map as dynamical system realized with a recurrent neural network: (ii) the dynamics of the neural activity in the map as the trnnsients of that system towards an equilibrium configuration which the network learnt with a recurrent learning algorithm (recurrent backpropagation). The results of our simulations demonstrate the following. (i) The transients of the trained network are hill-flattening patterns as observed by some experimenters in the burst-neuron layer of the superior colliculus of rhesus monkeys. This result was obtained despite the fact that the learning algorithm did not specify what the network's transients should be. (ii) The connections in the trained network are excitatory within the fixation zone of the motor map and inhibitory elsewhere. (iii) The results of the learning are robust in the face of changes in the connectivity pattern and the initialization of the weights, but a local connectivity pattern favours the network's stability. (iv) Nonlinearity is required in order to obtain meaningful dynamic behaviours. (v) The trained network is robust to abnormal stimulation patterns, such as noisy and multiple stimuli, and when multiple stimuli are utilized the response of the network remains a stereotyped flattening one.The results of the learning point to the possibility that the dynamics of the burst-neuron layer of the superior colliculus might be locally regulated rather than feedback-driven, and that the action of the feedback is confined to the layer of the buildup neurons. The results of the multiple-stimulation experiment support the hypothesis asserted by one of the authors in an earlier work (Massone 1994), that the averaging of the direction of movement following double stimulation of the motor map (Robinson 1972) does not occur at the level of the motor map. This paper also constitutes a study of the properties and responses of recurrent backpropagation subject to various choices for the parameters of the network and the algorithm.

Local dynamic interactions in the collicular motor map: a neural network model

In this paper we explore the possibility that some of the dynamic properties of the neural activity in the gaze-related motor map (located in the intermediate layers of the superior colliculus) might be mediated by local interactions between movement-related neurons and fixation neurons. More specifically, the goal of this research is to demonstrate, from a computational standpoint, which classes of dynamic behaviour of the collicular neurons can be obtained without the intervention of feedback signals, and hence to begin to explore the extent to which the gaze system needs feedback in order to operate. We modelled: (i) the collicular motor map as dynamical system realized with a recurrent neural network: (ii) the dynamics of the neural activity in the map as the trnnsients of that system towards an equilibrium configuration which the network learnt with a recurrent learning algorithm (recurrent backpropagation). The results of our simulations demonstrate the following. (i) The transients of the trained n...

Some physiological characteristics of motor cortex neurons of aged rabbits

Neurophysiological alterations occurring in the motor cortex of aged rabbits have been examined. Experiments were performed on rabbits of three age groups: one year old (young), four to five years old (middle-aged) and six to seven years old (aged). Extracellular unit activity was recorded in the motor projection of a forelimb. Several sessions of rhythmic (2 Hz) electrocutaneous stimulation were delivered to contralateral forelimb. The neuronal activity was recorded before and after rhythmic stimulation. We also measured the firing rate during spontaneous electromyogram activity of the extensor carpi radialis. Neurons having slow spontaneous firing activity were predominant in aged rabbits as compared with young animals. In young animals the highest values of spontaneous firing rate (15–20 impulses/s) were observed in neurons related to movement. In aged rabbits spontaneous firing rate of movement-related neurons did not exceed 16 impulses/s. During spontaneous movements of extensor carpi radialis, the level of neuronal activity in young rabbits was twice as high as that in aged ones. In young rabbits after rhythmic electrocutaneous stimulation of a forelimb, 20% of recorded neurons exhibited periodic fluctuations in firing rate with the period of preceding stimulation. The repeated stimulation sessions increased the number of rhythmic firing neurons to 40–50%. In aged rabbits, patterns of firing activity of motor cortex neurons did not change significantly after several sessions of rhythmic electrocutaneous stimulation. Decreased neuronal excitability may be the cause of functional alterations in motor cortex neurons of aged rabbits.

Projections of vertical eye movement-related and head rotation-related neurons in the medial mesodiencephalic junction to pontine reticular formation in cat

Spikes of single neurons related to vertical eye movements and vertical head rotation were recorded extracellularly in the medial mesodiencephalic junction (MDJ) of chronically prepared alert cats, and their antidromic responses to stimulation of the pontine reticular formation (PRF) were studied. Among the vertical eye movement-related neurons, augmenting neurons (ANs) and tonic neurons (TNs) were activated antidromically from the lateral PRF. Stimulation of the midline PRF activated antidromically mainly ANs, long-lead burst neurons (LLBNs) and upward medium-lead burst neurons (MLBNs). The head rotation-related neurons were antidromically activated from the lateral PRF but not from the midline PRF. These results suggest that some MDJ neurons related to vertical eye movements or head rotation directly project to the paramedian PRF.

Differential effects of muscimol microinjection into dorsal and ventral aspects of the premotor cortex of monkeys.

1. A gamma aminobutyric acid (GABAA) receptor agonist, muscimol (Sigma, 5 micrograms/microliters solution), and a GABAB receptor agonist and antagonist, baclofen and phaclofen, respectively, were injected (1.0 microliter) into the dorsal and ventral aspects of the premotor cortex (PM) of two Japanese monkeys (Macaca fuscata), while they were performing a motor task that required wrist flexion or extension to a target. The correct movement was instructed by either 1) a conditional color cue [green or red light emitting diodes (LED)] equidistant from the targets or 2) a directional cue toward extension or flexion (right or left LED). When the green or right LED was illuminated, extension was to be performed. When the red or left LED was illuminated, flexion was required. The movement was triggered by a visual stimulus either simultaneously with the instruction stimulus or after a variable delay. 2. Before drug injection, single-unit recordings were made to select injection sites 1) in the dorsal aspect of the PM (PMd) around the superior precentral sulcus where typical set-related activity was frequently recorded and 2) in the ventral aspect of the PM (PMv) immediately caudal to the genu of the arcuate sulcus where movement-related neurons were densely located. 3. Behavioral deficits were observed primarily at the time muscimol, but not baclofen or phaclofen, was injected. Furthermore, muscimol effects were short-lasting: deficits were most frequently observed during the 10-min injection period but seldom after completion of injection. 4. When muscimol was injected into the PMd, there was an increase in the number of direction errors primarily when the conditional cues were presented. The initiated movements were similar in amplitude and velocity to the preinjection behavior. In contrast, when muscimol was injected into the PMv, many of the initiated movements showed smaller amplitudes and slower velocities, but few direction errors were made. 5. These results suggest that the PMd and PMv play differential roles in motor control: the PMd is more important than PMv in conditional motor behavior and plays a role in the preparation for forthcoming movements. In contrast, the PMv is more specialized for a role in the execution of visually guided movements.

Corticocortical and thalamocortical responses of neurons in the monkey primary motor cortex and their relation to a trained motor task

1. We studied the responsiveness of neurons in the primary motor cortex (MI) of monkeys (Macacafuscata) to electrical stimulation of the supplementary motor area (SMA), primary sensory cortex (SI), and the ventral subnucleus of the thalamus (VPLo) with chronically implanted electrodes. 2. All neurons examined in this study were characterized by their relation to a motor task performed by the animals. They responded to stimulation of the cortical or thalamic area with excitation from one area alone (n = 128) or from multiple areas (n = 84) of all combinations. In a majority of neurons, response latencies to both cortical and thalamic stimulation were within 5 ms. 3. A vast majority of neurons (80%) that were active during a preparatory period for forthcoming reaching movements were activated by SMA stimulation. They were activated only infrequently by SI or thalamic stimulation. 4. Movement-related neurons (active immediately before and during reaching movements) were activated by thalamic, SI, or SMA stimulation or by any combination of those stimuli. More than half of the movement-related neurons activated exclusively by either thalamic or SMA stimulation exhibited activity onset times earlier than those observed in the earliest muscles. By contrast, most movement-related neurons that responded only to SI stimulation were late in their activity onset. 5. These findings suggest that the SMA input to MI is important in developing a preparatory type of activity in MI, whereas the thalamus (VPLo) provides substantial inputs in movement execution. The roles played by inputs from SI and SMA in relation to motor execution are debatable and are discussed here with reference to previous reports.

Physiological Identification of Jaw-Movement-Related Neurons in the Trigeminal Nucleus of Cats

Although neurons responsive to jaw movements have been identified in most parts of the trigeminal brainstem nuclei, little is known about how this information is relayed to the thalamus and ultimately to the cortex for kinesthetic functions and sensorimotor integration. The present extracellular recording experiments showed that a substantial amount of movement-related information is relayed to the thalamus through the caudal part of subnucleus interpolaris (Vi) in adult cats. Vertical jaw displacements, natural mechanical stimuli, and electrical stimulation of the masseter nerve were used to determine the receptive fields and response properties of movement-related neurons. Movement-related responses were observed in 161 units. The receptive fields of these units were located in the masseter muscle, other deep structures, hairy skin, oral mucosa, or some combination of these structures (i.e., convergent). The latency of units responding to masseter nerve stimulation ranged from 1.0 msec to 20 msec, which suggested that some movement-related information was provided by smaller-diameter muscle afferents. Movement responses were either tonic or phasic. Tonic units showed continuous firing at some jaw position; some of these showed a "dynamic" response to jaw displacement. Phasic units were only active, or showed increased activity, when the jaw moved through a specific position. Seventy-one movement-related units were activated by stimulation from the contralateral ventroposteromedial nucleus (VPM) of the thalamus. Most of the brainstem recording sites were located in the dorsal part of Vi between the caudal pole of the facial motor nucleus and the obex. Neurons in caudal Vi may be important for facial kinesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Firing behavior of brain stem neurons during voluntary cancellation of the horizontal vestibuloocular reflex. II. Eye movement related neurons

1. The single-unit activity of neurons in the vestibular nucleus, the prepositus nucleus, and the abducens nucleus, whose activity was primarily related to horizontal eye movements, was recorded in alert squirrel monkeys that were trained to track a small visual target by generating smooth pursuit eye movements and to cancel their horizontal vestibuloocular reflex (VOR) by fixating a head stationary target. 2. The spiking behavior of each cell was recorded during 1) spontaneous eye movements, 2) horizontal smooth pursuit of a target that was moved sinusoidally +/- 20 degrees/s at 0.5 Hz, 3) horizontal VOR evoked by 0.5-Hz sinusoidal turntable rotations +/- 40 degrees/s (VORs), and 4) voluntary cancellation of the VOR by fixation of a head-stationary target during 0.5-Hz sinusoidal turntable rotation at +/- 40 degrees/s (VORCs). The responses of most (28/42) of the units were recorded during unpredictable 100-ms steps in head acceleration (400 degrees/s2) that were generated while the monkey was fixating a target light. The acceleration steps were generated either when the monkey was stationary or when the turntable was already rotating (VORt trials), and the monkey was canceling its VOR (VORCt trials). 3. The firing behavior of all 12 of the abducens neurons recorded was closely related to horizontal eye position and eye velocity during all of the behavioral paradigms used, although there was a small but significant increase in the eye position sensitivity of many of these units when the eye was moving (smooth pursuit) versus when the eye was stationary (fixation). 4. Many neurons in the prepositus nucleus and the medial vestibular nucleus (n = 15) were similar to abducens neurons, in that their firing rate was related primarily to horizontal eye position and eye velocity, regardless of the behavioral paradigm used. These cells were, on average, more sensitive to eye position and smooth pursuit eye velocity than were abducens neurons. 5. The firing rate of 15 other neurons in the prepositus and medial vestibular nucleus was related primarily to horizontal smooth pursuit eye movements. The tonic firing rate of all of these smooth pursuit (SP) cells was related to horizontal eye position, and the majority generated bursts of spikes during saccades in all directions but their off direction. Six of the SP neurons fired in phase with ipsilateral eye movements, whereas the remaining nine were sensitive to eye movements in the opposite direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Premotor cortex of monkeys: set- and movement-related activity reflecting amplitude and direction of wrist movements

1. Neuronal activity was recorded from the premotor cortex (PM) of Japanese monkeys while they performed hand movements with different amplitudes and directions. On each behavioral trial, two instructions were given sequentially: 1) an amplitude instruction (large or small) and 2) a direction instruction (flexion or extension). The onset of movement was triggered by a visual signal after a delay period. 2. Among various kinds of task-related neuronal activity recorded in the PM, two types were selected for study: 1) set-related activity, sustained activity change during the delay period that followed presentation of instruction signals (IS); and 2) movement-related activity, activity change immediately before and during movement, which followed the trigger signal (TS) presentation. 3. Thirty-two of 101 set-related neurons showed activity change after presentation of the first IS (Delay 1 set-related activity), when they were instructed in either amplitude or direction, but not both. All of the set-related neurons showed activity modulation after presentation of the second IS (Delay 2 set-related activity). When neurons showed both Delay 1 and Delay 2 set-related activity, they were usually more active during Delay 2, i.e., when the monkeys had received both amplitude and directional ISs. A majority of neurons with Delay 2 set-related activity (64%) showed relation to both movement amplitude and direction. Twenty-eight percent of the neurons showed relation to either amplitude or direction, but not both. These findings seem consistent with a view that serial, rather than parallel, processes of motor programming operate in preparation of intended movements. 4. A majority of PM neurons with movement-related activity (51%) showed activity change related to both the direction and amplitude of movement. Forty-two percent showed selective relation to either direction or amplitude. These findings support a view that PM contributes to the control of limb movements. 5. Histological reconstruction showed that a vast majority of PM set-related neurons were located in the dorsal aspect of the PM (PMd), medial to the arcuate spur and lateral to the superior precentral sulcus. In contrast, movement-related neurons were distributed in two distinct foci: one in the ventral aspect of the PM (PMv), immediately caudal to the genu of the arcuate sulcus and lateral to the spur of the sulcus; and the other in the PMd, overlap;ing the location of set-related neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Output organization of intermediate cerebellum of the monkey.

1. The goal of this study was to investigate the motor organization of monkey nucleus interpositus (NI) and neighboring regions of the lateral nucleus (NL) by correlating discharge of single neurons with active movements. Neurons were surveyed during free-form movements as well as during operation of six devices that required movement about specific forelimb joints. The paradigm allowed us to test the hypothesis that discharge of individual cells relates to movements about individual joints. 2. One hundred sixty-two isolated nuclear neurons from two monkeys were studied. Eighty-three percent showed large increases in discharge (an average of 3 times resting rate for forelimb neurons) during movement of one body part, either forelimb, hindlimb, mouth/face, or eyes. 3. Anterior interpositus contains neurons related to hindlimb movement in anterior regions and neurons related to forelimb movement in posterior regions. A mouth/face-related area exists in the dorsal-posterior regions and is continuous with a mouth/face area in the dorsal regions of NL. Posterior interpositus (NIP) showed no clear separation between forelimb and hindlimb neurons: forelimb neurons were encountered throughout the nucleus, and hindlimb neurons were encountered in the medial-anterior two thirds. A distinct eye movement area exists in lateral, posterior, and ventral regions of NIP. This area borders regions of NL that also contain eye movement-related neurons. 4. Forelimb interpositus neurons discharged strongly during reach and grasp; discharge rates were recorded for 41 neurons during a stereotyped reach and the average depth of modulation was 149 imp/s. Nineteen neurons that modulated during device tracking were also tested during reaching, and the depth of modulation was much greater during reaching. 5. Fifty-nine forelimb neurons were tested with device tracking. Twenty-seven (46%) produced no audible modulation, regardless of the joint being exercised. The remaining 32 neurons modulated during movement on at least one device (mean depth of modulation = 84 imp/s). Comparison of discharge during use of different devices revealed no strong evidence for device-specific discharge. 6. Discharge modulations during device tracking were phasic, preceded movement, and, for a small number of cells, showed consistent parametric relations to duration, amplitude, and velocity of movement. 7. Despite a clear somatotopy within NI and NL, there is no finer mapping based on active movements about individual joints within forelimb regions. Discharge modulation depends on movements involving the whole limb. Progress in understanding the function of intermediate cerebellum depends on determining the variables required to elicit consistent and high modulation of neural discharge.(ABSTRACT TRUNCATED AT 400 WORDS)

1511 Commissural and vestibular projection of vertical eye movement-related neurons in and around the interstitial nucleus of cajal

1511 Commissural and vestibular projection of vertical eye movement-related neurons in and around the interstitial nucleus of cajal

Projections of vertical eye movement-related neurons in the interstitial nucleus of Cajal to the vestibular nucleus in the cat

In two alert cats, single-unit activity of neurons related to vertical eye movement was recorded in and around the interstitial nucleus of Cajal (INC), and their projections to the ipsilateral vestibular nucleus and response to stimulation of the contralateral vestibular nerve were examined. Of 62 neurons that discharged in relation to vertical eye movement, 41 increased their firing rate for downward positions and 21 for upward positions. About one third of downward-on neurons was antidromically activated by stimulation of the ipsilateral vestibular nucleus with thresholds of 36–220 μA. None of the upward-on neurons were antidromically activated. About 60% of INC neurons (22/36) responded orthodromically to stimulation of the contralateral vestibular nerve. In particular, all the downward-on neurons that projected to the ipsilateral vestibular nucleus exhibited orthodromic responses at disynaptic latencies. The results, together with our previous finding that excitatory secondary vestibular neurons carrying vertical position signals project contralaterally to the INC, suggest that downward-on INC neurons receive direct connection from these secondary vestibular neurons and send the signals back to the ipsilateral vestibular nucleus. Interstitio-vestibular interactions through these pathways may be important in the generation of vertical eye position signals.

GABAergic inhibition of neuronal activity in the primate motor and premotor cortex during voluntary movement.

1. The functional role of GABAergic inhibition in neuronal activity in the forearm-hand area of the motor cortex and the postarcuate premotor cortex was studied while monkeys pressed and released a lever in response to a visual cue. gamma-Aminobutyric acid (GABA), its agonist muscimol (MUS), and its antagonist bicuculline methiodide (BMI), as well as acetylcholine, noradrenaline, and sodium glutamate, were applied iontophoretically to isolated single neurons whose activity was recorded via glass micropipettes that contained carbon fibers. 2. The activity from single neurons recorded in the motor and premotor cortex showed changes during the press or release of the lever by movement of the contralateral wrist. Discharge of most of the movement-related neurons (greater than 90%) was decreased or completely suppressed by iontophoretically applied GABA or MUS. 3. The activity of the movement-related neurons increased after application of BMI. In 70% of neurons tested, the activity during application of BMI was specifically enhanced at or near the phase of their peaks of activity, with or without a noticeable elevation in background activity. 4. About 10% of the neurons that had been unidirectional (i.e., neurons that showed a change in activity at either the lever-press or lever-release phase) became bidirectional (i.e., they showed changes in activity at both phases) when GABA transmission was blocked by the application of BMI. Bidirectional neurons also showed a reduction in the value of the directionality index. 5. One-half of the silent neurons, which had not shown any activity during either the lever-release or the lever-press phase, became active during the movement phases that followed application of BMI. 6. Most of the cortical neurons in layers II-VI in the motor area were found to be subject to GABAergic inhibition during voluntary movement. 7. We conclude that GABAergic inhibition plays a role in regulating the population of task-related neurons, and the levels of the task-related activity. GABAergic inhibition also improves directionality index in the motor cortex neurons to control the activity of target muscles.

Latencies of response of eye movement-related neurons in the region of the interstitial nucleus of Cajal to electrical stimulation of the vestibular nerve in alert cats

Recent studies have shown that the interstitial nucleus of Cajal (INC) in the midbrain reticular formation is involved in the conversion of vertical semicircular canal signals into eye position during vertical vestibulo-ocular reflexes. Secondary vestibulo-ocular relay neurons related to the vertical canals, which constitute the majority of output neurons sending signals from the vestibular nuclei directly to the oculomotor nuclei, have been shown to project axon collaterals to the region within and near the INC. To understand how the INC is involved in the signal conversion, latencies of response of neurons in the INC region to electrical stimulation of the vestibular nerve were examined in alert cats. The responses of 96 cells whose activity was clearly modulated by sinusoidal pitch rotation (at 0.31 Hz) were analyzed. These included 41 cells whose activity was closely correlated with vertical eye movement (38 burst-tonic and 3 tonic neurons), and 55 other cells (called pitch cells as previously). Twenty nine of the 96 cells (30%) were activated at disynaptic latencies following single shock stimulation of the contralateral vestibular nerve. Disynaptically activated cells were significantly more frequent for pitch cells than for eye movement-related cells (25/55 = 45% vs 4/41 = 10%; p less than 0.001, Chi-square test). Conversely, cells that did not receive short-latency activation (less than 6 ms) were more frequent among eye movement-related cells than pitch cells (26/41 = 63% vs 13/55 = 24%; p less than 0.001, Chi-square test).(ABSTRACT TRUNCATED AT 250 WORDS)

Activity of eye movement-related neurons in and near the interstitial nucleus of Cajal during sinusoidal vertical linear acceleration and optokinetic stimuli

1. A total of 43 neurons that showed a close correlation with vertical eye movement with a burst-tonic or tonic type response during spontaneous saccades, were recorded within, and in the close vicinity of, the interstitial nucleus of Cajal (INC) in alert cats. Neuronal responses to sinusoidal vertical linear acceleration (0.2-0.85 Hz, amplitude 10.5 cm) and optokinetic stimuli (0.1-1.0 Hz, amplitude 10.5 cm), were examined. 2. All 43 eye movement-related neurons responded to sinusoidal vertical linear acceleration in the presence of a stationary visual pattern in correlation to robust eye movement responses with compensatory phase. Phase and gain values (re stimulus position) of response of individual cells were independent of the stimulus frequencies tested. Of these, 33 cells were examined during linear acceleration without visual input. Most cells (27/33) did not respond even when a weak linear vestibulo-ocular reflex was present (6/27). The remaining 6 cells (6/33) responded to linear acceleration. Their mean phase values advanced by 80 degrees and gain dropped by 55% compared to the responses with visual inputs. 3. Twenty eight of the 43 cells were examined during vertical optokinetic stimuli. The activity of all 28 cells was modulated in correlation to eye movement responses. Response phase showed more lag, and gain decreased as stimulus frequencies increased, similar to optokinetic eye movement responses. 4. The close correlation between the activity of eye movement-related neurons in the INC region and robust eye movements during linear acceleration with visual inputs and optokinetic stimuli suggest that these neurons are involved in some aspect of vertical eye position generation during such stimuli.

Hypothalamic sites affecting masticatory neurons in rats

The effects of hypothalamic electrical stimulation and dl-sulpiride injections on the unit activity of masticatory trigeminal neurons were assessed in rats. Unilateral electrodes or bilateral cannulas were implanted in the perifomical hypothalamus. The animals which exhibited eating to electrical stimulation or to sulpiride injections were selected. Then, under urethane anesthesia, electrical stimuli or sulpiride injections were applied at sites which elicited eating while a passive jaw movement-related neuron was recorded. Electrical stimulation or sulpiride injections affected the basal firing rate of 15 out of 32 (53%), and 13 out of 17 (76%) jaw movement-related neurons, respectively. The basal firing rate of 3 out of 18 (16.6%) was affected by electrical stimulation of noneliciting feeding nearby places. Facilitation was observed in 7 out of those 13 jaw movement-related trigeminal neurons after intrahypothalamic sulpiride injections. When dopamine was injected in the hypothalamus 3 minutes before sulpiride, this drug could only affect the basal firing rate of 1 out of 12 (8%) jaw movement-related neurons. The electrical stimulation and sulpiride injections into the hypothalamus had the same inhibitory or excitatory effect on a given trigeminal neuron as the passive jaw movement did. A similar phenomenon was observed with the sulphide-induced facilitation. These results suggest that hypothalamic D 2 satiety receptors modulate brain stem feeding reflexes.