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O Hikosaka

Publications and source records attributed to O Hikosaka.

At least 73 records · Page 4Linked to original sources
PubMed1989

Role of basal ganglia in saccades.

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.

Animals↗
PubMed1987

Dynamic characteristics of saccadic eye movements in the albino rat.

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.

Animals↗
PubMed1986

Cell activity in monkey caudate nucleus preceding saccadic eye movements.

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.

Animals↗
PubMed1986

Saccadic eye movements following injection of lidocaine into the superior colliculus.

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)

Animals↗
PubMed1986

Neural activities in the monkey basal ganglia related to attention, memory and anticipation.

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.

Animals↗
PubMed1985

Deficits in manipulative behaviors induced by local injections of muscimol in the first somatosensory cortex of the conscious monkey.

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.

Animals↗
PubMed1985

Diversity in receptive field properties of vertical neuronal arrays in the crown of the postcentral gyrus of the conscious monkey.

Single neuronal activity was recorded in the crown of the postcentral gyrus (areas 1 and 2) in 5 conscious monkeys. A total of 93 penetrations were made in the hand and finger region of 9 hemispheres and 827 neurons were isolated. The receptive field characteristics of neurons recorded along each of 88 penetrations which entered perpendicularly to the cortical surface were compared. The majority of neurons in this region were responsive to skin stimulation. In 54 penetrations, neurons related to different sensory submodalities were mixed. In 30, skin neurons predominated, and in 8, 'deep' neurons, while in the remaining 16 penetrations neurons related to different submodalities were equally mixed. In 16 penetrations, neurons responded exclusively to stimulation of skin, hair or nails. In 9 penetrations, neurons were exclusively related to joint manipulation or other types of 'deep' submodality. In 9 penetrations, unidentified neurons were in the majority. In each penetration, the receptive field positions varied considerably on the same finger or encompassed more than one finger. Although neurons of the same submodality, either skin or 'deep' tended to be set in an array, the most adequate stimulus could vary among neurons of a given array. The variability in the receptive field positions or the most adequate stimuli remained constant irrespective of the angle of the electrode penetration in the cortex. The results are compatible with the idea that vertically arranged neuronal array receive inputs of multiple sources, both thalamacortical and corticocortical, so that interactions between different inputs can readilly occur.

Afferent Pathways↗
PubMed1985

Vertical neuronal arrays in the postcentral gyrus signaling active touch: a receptive field study in the conscious monkey.

Single neuronal activity was recorded in the crown of the postcentral gyrus (areas 1 and 2) in 5 conscious monkeys. A total of 88 penetrations entered perpendicularly to the cortical surface. Among them, 6 examples are chosen and the receptive field characteristics of constituent neurons were described in some detail. Receptive fields of neurons recorded along a particular penetration were variable in their positions, but the largest receptive field usually covered the others. Neurons with the largest receptive fields were found most frequently in the infragranular layers. Often they included inhibitory receptive fields. The inhibitory receptive fields were arranged side-by-side to the excitatory ones, rather than in a center-surround fashion. The key stimulus common to neurons in a vertical penetration was the contact of an object to the receptive field achieved during animal's active behavior to manipulate the object. We thus designated the largest receptive field as a functional surface. Our results demonstrate that a vertical array of neurons in this cortical region can be regarded as a functional assemblage which deals with a set of information concerning one of various aspects of active touch.

Animals↗
PubMed1985

Modification of saccadic eye movements by GABA-related substances. I. Effect of muscimol and bicuculline in monkey superior colliculus.

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)

Animals↗
PubMed1985

Modification of saccadic eye movements by GABA-related substances. II. Effects of muscimol in monkey substantia nigra pars reticulata.

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.

Animals↗
PubMed1983

Effects on eye movements of a GABA agonist and antagonist injected into monkey superior colliculus.

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.

Animals↗