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Cerebellar activation was measured using functional magnetic resonance imaging, while seven normal subjects tapped their fingers paced by tone sequences with or without tone omission. The cerebellar anterior lobe (Larsell's H IV-V) ipsilateral to the movement was activated to a similar degree irrespective of the presence or absence of the tone omission. In contrast, the lateral part of the bilateral posterior lobe (H VIIa) was significantly highly activated for the tone sequence with random omission, compared with either that without omission or that with regular omission. The result suggests that the H IV-V is involved in motor execution, while the lateral part of H VIIa is involved in on-line motor adjustment to unpredictable sensory stimuli.

To examine whether the cerebellum is involved in learning and memory of visuomotor sequences, we trained two monkeys on a sequential button press task and inactivated different portions of the cerebellar nuclei by injecting a small amount of muscimol (gamma-aminobutyric acid agonist). Before the injection experiments started, the monkeys had learned a set of sequences (n = 21 and 12) extensively. After each injection, we had the monkeys perform the learned sequences and, in addition, learn new sequences. We found deficits in learning/memory by the injections into the dorsal and central part of the dentate nucleus. The number of errors increased significantly for the learned sequences but not for the new sequences. This effect was present only when the hand ipsilateral to the muscimol injection was used. Consistent with this result, anticipatory saccades, the occurrence of which is correlated closely with motor skill, also became less frequent particularly when the ipsilateral hand was used. No effect on learning/memory was observed after injections into the ventral or lateral parts of the dentate nucleus, interpositus nucleus, or fastigial nucleus. In contrast, hand movements became slower after ipsilateral injections at all of the injection sites. These results suggest that, among the cerebellar nuclei, the dentate nucleus, especially its dorsal and central regions, is related to the storage and/or retrieval of long-term memory for motor skill.

We studied the neural correlates of visuomotor sequence learning using functional magnetic resonance imaging (fMRI). In the test condition, subjects learned, by trial and error, the correct order of pressing two buttons consecutively for 10 pairs of buttons (2 x 10 task); in the control condition, they pressed buttons in any order. Comparison between the test condition and the control condition revealed four brain areas specifically related to learning: the dorsolateral prefrontal cortex (DLPFC), the presupplementary motor area (pre-SMA), the precuneus, and the intraparietal sulcus (IPS). We found that the time course of activation during learning was different between these areas. To normalize the individual differences in the speed of learning, we classified the performance of each subject into three learning stages: early, intermediate, and advanced stages. Both the relative increase of signal intensity and the number of activated pixels within the four areas showed significant changes across the learning stages, with different time courses. The two frontal areas, DLPFC and pre-SMA, were activated in the earlier stages of learning, whereas the two parietal areas, precuneus and IPS, were activated in the later stages. Specifically, DLPFC, pre-SMA, precuneus, and IPS were most highly activated in the early stage, in both the early and intermediate stages, in the intermediate stage, and in both the intermediate and advanced stages, respectively. The results suggest that the acquisition of visuomotor sequences requires frontal activation, whereas the retrieval of visuomotor sequences requires parietal activation, which might reflect the transition from the declarative stage to the procedural stage.

When a visual stimulus (the "cue") is presented and followed by a line, the line is perceived to grow rapidly from the cued side even when it is presented physically simultaneously (the "line-motion effect"). We now report that the same line motion can be observed when the cue is presented in a non-visual modality, such as auditory or somatosensory. A beep sound was presented either from the left or the right speaker as an auditory cue, or an electric pulse was applied to a finger put on the left or the right side of a CRT display as a somatosensory cue. A line probe was then presented between the two possible cue positions. Both the auditory and the somatosensory cues led to line motion, thus the line motion could not be interpreted as a variation of within-modality effects, such as visual apparent motion. When the cue lead time was manipulated, the obtained time courses of the effects were similar across the three cue modalities (Experiment 1). The minor differences could be explained simply in terms of latency of detection, according to results of another experiment (Experiment 2). Finally, the line-motion task was compared with a task of temporal order judgment, where two targets were presented simultaneously at the cued and the uncued sides, and the subject was asked to judge which of the targets had appeared first. As a result, similar dependencies on cue lead time were obtained between the two tasks within subjects (Experiment 3). Thus, the non-visual cue seems to facilitate "prior entry" of a visual stimulus nearby in the spatial representation, much the same way as a visual cue does. These effects should be attributed to modality non-specific spatial attention, i.e., a "gradient" of information processing efficiency across various locations.

We examined age-dependent changes in voluntary eye movements in normal subjects (age : 5-76) using a visually guided saccade (V-saccade) task and a memory guided saccade (M-saccade) task. Changes were more evident in M-saccades. The latencies were long in children (< 12 y.o.) and elderly people (> 50 y.o.). Both young children and elderly people tended to break fixation by making a saccade to the cue stimulus that indicated the future target position. On the other hand, both young children and elderly people tended to be slow in making M-saccade promptly after the central fixation point went off. Thus, they had difficulties both in suppressing unnecessary saccades and in initiating saccades based on memory. Interestingly, similar difficulties were observed, in exaggerated forms, in patients in basal ganglia disorders, such as Parkinson's disease, juvenile parkinsonism, dopa-responsive dystonia, and hereditary progressive dystonia with marked diurnal fluctuation. These findings were consistent with the known functions of the basal ganglia which have been revealed by physiological studies using trained monkeys. The substantia nigra pars reticulata exerts tonic inhibitory influences over the superior colliculus, thereby preventing excitatory inputs from triggering unnecessary saccades. The tonic inhibition, however, is removed by a phasic inhibition largely originating in the caudate nucleus. Thus, inhibition and disinhibition are key mechanisms of the basal ganglia. In fact, experimental manipulations of these serial inhibitory pathway in the basal ganglia led either to the difficulty in initiation of saccades, especially M-saccades, or to the difficulty in suppressing unnecessary saccades. These comparisons suggest that the functions of the basal ganglia are immature in young children while they become deteriorated in elderly people.

Attention is a mechanism to select sensory information. It is a modulatory process which normally cannot be observed as overt responses. We have studied spatial attention using a new visual illusion of motion--line-motion effect: a line, which was presented physically at once, was perceived to be drawn from one side when attention was captured to that side of the line by a preceding visual cue stimulus. This effect was due to acceleration of visual information processing at the locus of attention. The motion illusion was produced by both stimulus-induced (bottom-up) and voluntary (top-down) attention, which suggested that the two kinds of attention act on relatively early stages of visual processing. The objective of this study was to examine how various modes of spatial attention might be represented and reorganized in the brain. Using the induction of illusory line motion as a measure we found that: (1) once attention is captured by a moving object, it follows the object as it moves; and (2) attention moves with a saccade in the retinal coordinates such that its focus remains fixed in space. We then asked whether attention acts across different sensory modalities. We found that both auditory and somatosensory cues induced focal visual attention in space where the cue was presented. Based on these findings we propose a model which would allow (1) matching of visual spatial information obtained across saccades, and (2) matching of spatial information obtained in different sensory modalities.

The synaptic organization of the saccade-related neuronal circuit between the superior colliculus (SC) and the brainstem saccade generator was examined in an awake monkey using a saccadic, midflight electrical-stimulation method. When microstimulation (50-100 microA, single pulse) was applied to the SC during a saccade, a small, conjugate contraversive eye movement was evoked with latencies much shorter than those obtained by conventional stimulation. Our results may be explained by the tonic inhibition of premotor burst neurons (BNs) by omnipause neurons that ceases during saccades to allow BNs to burst. Thus, during saccades, signals originating from the SC can be transmitted to motoneurons and seen in the saccade trajectory. Based on this hypothesis, we estimated the number of synapses intervening between the SC and motoneurons by applying midflight stimulation to the SC, the BN area, and the abducens nucleus. Eye position signals were electronically differentiated to produce eye velocity to aid in detecting small changes. The mean latencies of the stimulus-evoked eye movements were: 7.9 +/- 1.0 ms (SD; ipsilateral eye) and 7.8 +/- 0.9 ms (SD; contralateral eye) for SC stimulation; 4.8 +/- 0.5 ms (SD; ipsilateral eye) and 5.1 +/- 0.7 ms (SD; contralateral eye) for BN stimulation; and 3.6 +/- 0.4 ms (SD; ipsilateral eye) and 5.2 +/- 0.8 ms (SD; contralateral eye) for abducens nucleus stimulation. The time difference between SC- and BN-evoked eye movements (about 3 ms) was consistent with a disynaptic connection from the SC to the premotor BNs.

Unilateral dopamine deficiency of the basal ganglia produced a profound impairment of visual search. Dopaminergic innervation of the monkey striatum was deprived unilaterally by infusing 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into the caudate nucleus. The monkeys were shown a mirror in which they saw their own image and surroundings. Compared with the concentric and symmetrical distribution of visual search before MPTP infusion, the gaze after MPTP infusion was confined and sometimes frozen in peripheral regions in the hemispace ipsilateral to the infusion; the contralateral side was largely neglected. An experiment using a choice saccade task indicated that the contralateral visual signal, which alone was processed normally, was suppressed by the ipsilateral signal.

Spatial attention was studied using a new visual illusion of motion: a line, which was presented physically at once, was perceived to be drawn from one side when attention had been captured to that side of the line by a preceding visual cue stimulus. By comparing with a temporal order task, we showed that the line-motion illusion was produced by acceleration of visual information processing at the locus of attention. The results suggest that the facilitatory effect of attention is exerted at relatively early stages of visual information processing where visual signals are to be fed into the motion detecting mechanism.

The present study provides evidence that the saccadic signals in the caudate nucleus (caudate) are transmitted to the substantia nigra pars reticulata (SNr). We inserted two microelectrodes into the caudate and SNr of monkeys trained to perform saccade tasks. After identifying the functional characteristics of a SNr neuron recorded, we stimulated the caudate (single pulse, < 100 microA) to see whether its discharge rate changed. Among 138 SNr cells tested, 60 showed responses to stimulation of the caudate: inhibition only (n = 21), inhibition-excitation (n = 17), excitation only (n = 9), and excitation-inhibition (n = 13). The latencies were 9.0-32.5 ms (mean 16.7 ms) for the initial inhibitory responses and 6.5-35.0 ms (mean 16.7 ms) for the initial excitatory responses. Pars compacta cells (n = 10) were unresponsive. The effect of caudate stimulation was selective in terms of (1) functional type of SNr cells, (2) location of SNr cells, and (3) stimulation site within the caudate. Functional type of SNr cells: saccadic, visual, expectation-related cells were more responsive than auditory, mouth/hand/arm movement-related, and reward-related cells. Many of the cells whose functional characteristics were unidentified responded to the caudate stimulation. The preferential effects were seen among the functional subtypes: cells related to memory-guided saccades, not visually guided saccades; cells with conditioned visual responses, not simple visual responses. Location of SNr cells: the stimulus effects were seen preferentially in cells in the central part of the SNr, not in the dorsal part. Stimulus site: stronger effects, whether inhibition or excitation, were obtained when the stimulation was applied to the head-body transitional zone where visuooculomotor cells were clustered. Behaviorally contingent correlation of spike activity was found between the caudate-nigral pair of cells. For example when a SNr cell with memory-contingent saccadic activity was inhibited by the caudate stimulation, a caudate cell at or close to the stimulation site may show memory-contingent saccadic activity with a similar movement field.

In the primate postcentral gyrus, the cytoarchitectonic characteristics gradually shift from those of koniocortex to more homotypical parakoniocortex along its rostrocaudal axis. To find the physiological correlates of these changes we examined a large body of data accumulated during a series of our experiments with alert monkeys. Along the rostrocaudal axis of the postcentral gyrus, we found a gradual and continuous increase in the number of neurons with converging receptive fields and those in which receptive field positions or submodalities were not determined. Deep or skin submodality neurons were dominant in area 3a or 3b respectively. The proportion of skin submodality neurons decreased gradually from area 3b to the more caudal part of the gyrus. The proportion of deep submodality neurons was almost constant from area 3b to area 2 inclusive; they were not the majority in area 2. The data are consistent with the hierarchical scheme, i.e., within the postcentral gyrus sensory information is processed from the primary sensory receiving stage to the more associative, integrative stages.

Attention may be drawn passively to a visually salient object. We may also actively direct attention to an object of interest. Do the two kinds of attention, passive and active, interact and jointly influence visual information processing at some neural level? What happens if the passive and active attentions come into conflict? These questions were addressed with the aid of a novel psychophysical technique which reveals an attentional gradient as a sensation of motion in a line which is presented instantaneously. The subjects were asked to direct attention with voluntary effort: to the side opposite to a stimulus change, to an object with a predetermined colour, and to an object moving smoothly. In every case the same motion sensation was induced in the line from the attended side to the unattended side. This voluntary attention, however, can easily and quickly be distracted by a change in the periphery, though it can be regained within a period of 200 to 500 ms. The results suggest that the line motion can be induced in voluntary (top-down) as well as stimulus-driven (bottom-up) situations, thus indicating the truly attentional nature of the effect, rather than it being some kind of retinotopic sensory artifact or response bias. The results also suggest that these two kinds of attention have facilitatory effects acting together on a relatively early stage of visual information processing.

The basal ganglia play an important role in the control of saccadic eye movements. Parkinsonian patients have deficits in saccade initiation; the deficits are more prominent in memory-guided saccade than in visually guided saccade (Hikosaka et al, 1987). These results show that deficiency of nigrostriatal dopaminergic system affects the neural mechanism of saccadic eye movements in the basal ganglia. In order to investigate this hypothesis, we studied saccadic eye movements in MPTP-induced hemiparkinsonian monkeys. We made two models of parkinsonism using two monkeys: 1) unilateral intra-carotid injection of MPTP, and 2) intracaudate injection of MPTP using osmotic minipump. We recorded saccadic eye movements using the magnetic search coil method. After experiments, monkeys were sacrificed and investigated by histological procedures. Following the intracarotid injection, we observed hypokinesia and rigidity in the arm and leg contralateral to the injection. Eye position was shifted to the ipsilateral side and the frequency of saccades towards the contralateral side was reduced. Following the intracaudate injection, we observed hypokinesia and rigidity in the contralateral arm and leg and circling behavior towards the contralateral side. In both monkeys, the saccade amplitude and peak velocity towards contralateral side were reduced. We considered three mechanisms that might account for these results. First, dopaminergic denervation due to MPTP in the caudate nucleus may suppress the activity of neurons projecting to the pars reticulata of the substantia nigra. Second, nigra cell activity may be tonically elevated through an indirect pathway via the external pallidum and the subthalamic nucleus. Third, MPTP may enhance nigra cell activity through dendro-dendritic connections from the pars compacta to the pars reticulata in the substantia nigra.

Discharges of single neurons were recorded in the caudate nucleus of an awake monkey. The monkey was trained to perform a series of behavioral tasks which required him to fixate on a spot of light on a screen and if the spot jumped to another location to make a saccade to refixate it. A significant portion of the neurons in the head and body of the caudate nucleus showed increases in their activities in relation to the behavioral tasks. While some neurons responded to the visual stimulus (light spot), others showed activities preceding a saccade. Another group of neurons showed activities not directly related to such sensory or motor events but presumably related to monkey's cognitive states. Even the visual or saccade-related activities were highly dependent on the behavioral context in which a given visual stimulus was presented or a given saccade was elicited. This report presents typical examples of caudate neural activities related to selective attention, short-term memory and anticipation of future events, and explains how such complex signals in the caudate are converted to oculomotor outputs through a major efferent pathway of the basal ganglia, namely caudate--substantia nigra pars reticulate--superior colliculus.

Three cases of duodenal myogenic tumor are described in detail. All the three were surgically treated and the final diagnoses were histologically established. The three consisted of two leiomyomas and one leiomyosarcoma. To make clinical diagnosis, roentgenologic, endoscopic, and angiographic examinations were empolyed. The selective angiography was more reliable than endoscopic biopsy to make a differential diagnosis whether a tumor was benign or malignant. Surgical procedures were required not only for malignant myomatous lesions but also for benign lesions because the latter also produce a high incidence of hemorrhage from ulceration of the tumor. Out of the three cases, one was successfully treated by enucleation but the other two were undergone more extensive surgery such as a Whipple's procedure or wide resection of the duodenal wall with side-to-side duodenojejunostomy. Operative techniques are discussed in detail basing on the biological characteristics, location, and size of the tumor.

The basal ganglia, substantia nigra pars reticulata (SNr) and caudate nucleus, contribute to the suppression and initiation of saccadic eye movements by imposing a tonic inhibition on the superior colliculus (SC) and by removing it. The tonic inhibition originates from the SNr where neurons show continuous, high frequency discharges. With its inhibitory connection to the SNr, the caudate nucleus transiently suppresses the SNr activity thereby removing the tonic inhibition on the SC. Signals carried by neurons in the SNr and the caudate nucleus are both heavily dependent on or selective for different aspects of learned paradigms. Such task-specific, learned information originating from the basal ganglia may open or close the gate for a variety of excitatory inputs to the SC.

Our previous observations led to the hypothesis that cells in the substantia nigra pars reticulata (SNr) tonically inhibit saccade-related cells in the intermediate layers of the superior colliculus (SC). Before saccades to visual or remembered targets, cells in SNr briefly reduce that inhibition, allowing a burst of spikes of SC cells that, in turn, leads to the initiation of a saccadic eye movement. Since this inhibition is likely to be mediated by gamma-aminobutyric acid (GABA), we tested this hypothesis by injecting a GABA agonist (muscimol) or a GABA antagonist (bicuculline) into the superior colliculus and measured the effects on saccadic eye movements made to visual or remembered targets. An injection of muscimol selectively suppressed saccades to the movement field of the cells near the injection site. The affected area expanded over time, thus suggesting the diffusion of muscimol in the SC; the area never included the other hemifield, suggesting that the diffusion was limited to one SC. One of the monkeys became unable to make any saccades to the affected area. Saccades to visual targets following injection of muscimol had longer latency and slightly shorter amplitudes that were corrected by subsequent saccades. The most striking change was a decrease in the peak velocity of the saccade, frequently to less than half the preinjection value. Saccades to remembered targets following injection of muscimol also showed an increase in latency and decrease in velocity, but in addition, showed a striking decrease in the accuracy of the saccades. The trajectories of saccades became distorted as if they were deflected away from the affected area. After muscimol injection, the area over which spontaneous eye movements were made shifted toward the side ipsilateral to the injection. Saccades toward the contralateral side were less frequent and slower. In nystagmus, which developed later, the slow phase was toward the contralateral side. In contrast to muscimol, injection of bicuculline facilitated the initiation of saccades. Injection was followed almost immediately by stereotyped and apparently irrepressible saccades made toward the center of the movement field of the SC cells at the injection site. The monkeys became unable to fixate during the tasks; the fixation was interrupted by saccadic jerks made to the affected area of the visual field and then back to the fixation point.(ABSTRACT TRUNCATED AT 400 WORDS)

1. We recorded single cell activities in the caudate nucleus of the monkeys trained to perform a series of visuomotor tasks. In the first part of this paper, we summarize the types and locations of neurons in the monkey caudate nucleus. In the second part, we report the characteristics of neurons related to saccadic eye movements. 2. Neurons were classified into two types in terms of spontaneous discharge pattern. A majority of the neurons (2,287/2,559, 89%) had very low-frequency discharges (mostly less than 1 Hz). The rest (n = 272) showed irregular-tonic discharges (3-8 Hz) with broad spikes. 3. Of 2,559 neurons tested, 867 showed spike activity related to some aspects of the tasks; 502 neurons showed discharges in response to environmental changes outside, not in relation to, the tasks. None of the neurons responsive in or outside the tasks belonged to the irregular-tonic type. 4. The task-related activities were classified as: Saccade-related, Visual, Auditory, Cognitive, Fixation-related, and Reward-related. The activities detected outside the tasks were classified into: Visual, Auditory, Movement-related, Reward-related, and Other. Few neurons had both task-related and task-unrelated activities. 5. The locations of recorded neurons were determined using a coordinate system based on the anterior and posterior commissures. Task-related neurons were clustered longitudinally in the central part of the caudate. Neurons responsive outside the tasks were more widely distributed; specifically, auditory neurons were in the medial part, whereas movement-related neurons were in the lateral part. The irregular-tonic neurons were dispersed all over the caudate. 6. The monkey was trained to fixate on a spot of light on the screen and, when the spot moved, to follow it by making a saccade. A visually guided saccade occurred when the spot moved to another location without a time gap (saccade task). A memory-guided saccade occurred when the spot first disappeared and after a time gap reappeared at a fixed location (saccade with gap task). By delivering a cue stimulus while the monkey was fixating, a memory-guided saccade was elicited to a randomly chosen location (delayed saccade task).(ABSTRACT TRUNCATED AT 400 WORDS)

Injection of muscimol (GABA agonist) in the substantia nigra pars reticulata (SNr) of the alert rat induced a continual repetition of fast eye movements to the contralateral side, each of which was followed by a slow returning movement. The fast eye movements were similar to spontaneous saccades. Larger saccades were accompanied by contralateral neck muscle activity. We suggest that the SNr plays an important role in control of eye movements in the rat.

Spatio-temporal patterns of pre- and postsynaptic inhibition were studied in the trigeminal spinal nucleus oralis of cats by means of systematic electrical stimulation of the facial skin. Stimulation of the facial skin induced an EPSP-IPSP sequence in trigemino-thalamic relay cells (TRC). The IPSP was depressed by picrotoxin but was resistant to strychnine. The largest IPSP was evoked from the center of the excitatory area, where stimulation induced the largest EPSP and spike potentials at the lowest intensity in the same TRC. The amplitude of the IPSP decreased with increasing distance from the center in parallel with that of the EPSP. In the great majority of trigeminal primary afferent fibers, the largest primary afferent depolarization (PAD) was not evoked from the center of the excitatory area, where the threshold for spike generation was lowest, but from the adjacent points on the face. Spike activities in a trigeminal primary afferent fiber did not evoke any detectable PAD in itself. The duration of the PAD was definitely longer than the IPSP in TRC. However, the temporal distribution of the peak of PADs was very similar to that of the EPSP in TRC. Inhibition was evoked in glutamate-induced spike discharges of TRC by stimulation of the points on the face, which were located close to the center of the excitatory area of the TRC. However, the afferent inhibition of both spontaneous and peripherally induced spike discharges of TRC outlasted the postsynaptic inhibition. Thus, the late phase of the afferent inhibition is most probably due to presynaptic inhibition. Presynaptic inhibition, together with postsynaptic inhibition, would be involved also in the early phase of afferent inhibition through its mutual inhibitory organization.

Injection of muscimol (GABA agonist) in the finger region of area 2 of the alert monkey led to the striking yet reversible loss of finger coordination, thus disabling the monkey from picking up a small piece of food from a small hole or a funnel. Symptoms varied depending on sites of injection within the finger region. Neither weakness of hand or finger movements nor deficit in hand reach was observed.

1. Visual responses of caudate neurons were studied in monkeys trained to fixate on a small spot of light. A visual stimulus (another spot of light) was presented in various contexts of behavior using different behavioral paradigms. Visual receptive fields were usually large and centered on the contralateral hemifield. Among 217 neurons with visual responses, 184 were further classified into subtypes. 2. Visual responses in 64 neurons were not modulated by changing the paradigms (unconditional visual responses). In the other neurons, visual responses were dependent on the behavioral contexts in which the stimulus was presented. Three types of behavioral modulation were found. 3. A saccade-enhanced visual response (n = 37) was the one that was enhanced if the monkey made a saccade to the stimulus on its appearance. The enhancement was spatially selective: the response was depressed if the saccade was directed away from the stimulus. 4. Memory-contingent visual responses (n = 36) were present preferentially when the monkey remembered the location of the stimulus and a few seconds later made a saccade to the remembered location. Responses were greater when the location of the stimulus was randomized between trials. 5. Expectation-contingent visual responses (n = 46) were present preferentially when the stimulus came on while the monkey was not fixating another spot, and the stimulus was related directly to a reward. Unlike the other types, its receptive field included both contralateral and ipsilateral hemifields without a particular preference. 6. A small number of neurons (n = 16) showed a visual response that easily habituated. 7. Latencies of visual responses were usually between 100 and 200 ms. The latencies of the memory-contingent, expectation-contingent, and habituated visual responses tended to be longer than the others and tended to be more variable between trials. 8. Among auditory responsive neurons only a small proportion were related to the tasks. The response was greater to a contralateral sound. It was enhanced if the monkey used the sound as the cue for the future target location. 9. The results suggest that sensory responses of caudate neurons could be used to guide a subsequent sequence of learned behaviors by confirming predicted environmental states, renewing memory, or establishing a motor set.

Injection of muscimol, a GABA agonist, into the superior colliculus of awake monkeys produces saccades to visual targets in the movement field of colliculus cells near the injection site that have longer latency and shortened amplitude. Bicuculline, a GABA antagonist, leads to irrepressible saccades towards the movement field. These results are consistent with a tonic inhibition by the substantia nigra on the superior colliculus mediated by GABA which is reduced at the time of saccade initiation.

The preceding study (21) showed that a gamma-aminobutyric acid (GABA) agonist or antagonist injected into the superior colliculus (SC) disrupted saccadic eye movements. The purpose of the present experiments was to determine whether this result was due to altering the inhibitory input to the SC from the substantia nigra pars reticulata (SNr). SNr cells are themselves inhibited by GABA. Injection of muscimol, a GABA agonist, into the SNr should increase the inhibition acting on SNr cells and should reduce the inhibition acting on the SC. If the effects of GABA inhibition in the SC results from terminals originating in the SNr, muscimol in the SNr should act like bicuculline in the SC. Muscimol in the SNr has the same general effect as bicuculline in the SC. The monkey made irrepressible saccades toward the contralateral visual field where cells in the SNr at the injection site had their visual or movement field. During visual fixation saccadic jerks occurred, interspersed with spontaneous saccades, instead of saccades to visual targets or to remembered targets. Saccades to remembered targets were more vulnerable to these saccadic intrusions than were saccades to visual targets. Since muscimol in the SNr acts like bicuculline in the SC, we conclude that a substantial fraction of GABA-mediated inhibitory inputs in the SC originates from the SNr. These experiments, in conjunction with previous experiments, show that the SNr exerts a tonic inhibition on saccade-related cells in SC and that this inhibition is mediated by GABA. The role of the SNr in initiation of saccades to remembered targets is particularly important since these saccades are more severely disrupted by muscimol in the SNr as well as in the SC. We suggest that both of these conclusions about eye movement might apply to skeletal movements as well. First, the basal ganglia contribute to the initiation of movement by a release of the target structure from tonic inhibition. Second, this mechanism is particularly critical of the movements based on stored or remembered signals that are not currently available as incoming sensory inputs.

Finger representation on the first somatosensory cortex was mapped in conscious monkeys by single-unit recording. While representation was somatotopic in area 3, this was not the case in area 2, where the representation of different fingers overlapped. Our results indicate that area 2 is not a pure replica of the receptor sheet of the body surface.

Saccadic eye movement is controlled by a midbrain structure, superior colliculus (SC). Cells in its intermediate layer show a burst of spikes before saccades to the contralateral disc. A major input to the SC comes from the substantia nigra pars reticulata (SNr). SNr cells are characterized by their high frequency tonic discharge. Many of them stop discharging before a contralateral saccade only when the saccade is made intentionally. The mirror image-like relationship between the SNr and the SC suggests that the nigro-collicular connection is inhibitory. To determine whether the nigro-collicular inhibition is necessary for normal eye movements, we injected a small amount of GABA-related substances into the SC or the SNr. Following injection of muscimol (GABA agonist) into the SC, contralateral saccades became delayed, hypometric and slower; the monkey finally became unable to make saccades. This result indicated that the SC is crucial for normal saccades and that SC cells have ample GABA receptors. Following injection of bicuculline (GABA antagonist), irrepressible saccades occurred repeatedly to the contralateral side, suggesting that SC cells are under tonic inhibition which is mediated by GABA. Similar involuntary saccades were induced by injection of muscimol into the SNr. This suggested that the SNr is the origin of the GABAergic tonic inhibition. These results suggested that the basal ganglia control the initiation of saccadic eye movement by changing the level of the nigro-collicular inhibition.

Ablation of the superior colliculus (SC) has generally produced limited deficits in the initiation of saccadic eye movements, usually an increase in the latency of saccades. However, recent studies using muscimol, a GABA agonist, to block afferents to the SC showed deficits in not only latency but in amplitude and velocity of saccades as well. These greater deficits might be dependent upon the testing of saccades shortly after the damage of SC before any compensation for the deficits could develop. The present experiments tested this hypothesis by injecting a local anesthetic into SC. The anesthetic inactivated the cells entirely rather than just deafferenting them, but still allowed testing immediately after the injection. Clear deficits were observed following injection of lidocaine into the SC. The amplitudes of saccades to visual targets were shortened, and the peak velocities of the saccades were reduced even if the reduced amplitude of the saccades was taken into account. Latency of saccades usually increased. The deficits were limited to the area of the visual field that overlapped the movement fields of the cells near the injection site. If the movement fields were in the periphery, saccades to the periphery were shortened following the injection of lidocaine. If the movement fields were near the center of gaze, saccades into the area were shortened, but the monkey was able to make saccades over the visual field related to the affected area to more peripheral targets.(ABSTRACT TRUNCATED AT 250 WORDS)

Single cell activity was recorded in the monkey caudate nucleus. The monkey fixated a visual target, and, if the target jumped, followed it by making a saccade. A group of cells showed spike discharges before a contralateral saccade to the target. This activity was related to the saccade rather than the onset of the target, but was conditional in that it was unrelated to spontaneous saccades which were made without a particular target. Some caudate cells showed activity only when the saccade was made to a remembered position of a target. It is suggested that caudate cells contribute to the initiation of saccades in a selective manner by removing nigro-collicular tonic inhibition.

Using the magnetic search coil technique it was shown that the rat made saccadic eye movements spontaneously. Most saccades were horizontal. Although their amplitude was usually less than 10 degrees (deg.), the peak velocity could reach 400 deg/s. The peak velocity increased as a linear function of the amplitude at a rate comparable to that in the monkey and higher than in other species. Only a weak correlation between saccade and neck electromyogram (EMG) activity was observed.