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Biomedical subjects

A Mikami

Publications and source records attributed to A Mikami.

At least 91 records · Page 5Linked to original sources
PubMed1986

Motion selectivity in macaque visual cortex. II. Spatiotemporal range of directional interactions in MT and V1.

We measured the spatial and temporal limits of directional interactions for 105 directionally selective middle temporal (MT) neurons and 26 directionally selective striate (V1) neurons. Directional interactions were measured using sequentially flashed stimuli in which the spatial and temporal intervals between stimuli were systematically varied over a broad range. A direction index was employed to determine the strength of directional interactions for each combination of spatial and temporal intervals tested. The maximum spatial interval for which directional interactions occurred in a particular neuron was positively correlated with receptive-field size and with retinal eccentricity in both MT and V1. The maximum spatial interval was, on average, three times as large in MT as in V1. The maximum temporal interval for which we obtained directional interactions was similar in MT and V1 and did not vary with receptive-field size or eccentricity. The maximum spatial interval for directional interactions as measured with flashed stimuli was positively correlated with the maximum speed of smooth motion that yielded directional responses. MT neurons were directionally selective for higher speeds than were V1 neurons. These observations indicate that the large receptive fields found in MT permit directional interactions over longer distances than do the more limited receptive fields of V1 neurons. A functional advantage is thereby conferred on MT neurons because they detect directional differences for higher speeds than do V1 neurons. Recent psychophysical studies have measured the spatial and temporal limits for the perception of apparent motion in sequentially flashed visual displays. A comparison of the psychophysical results with our physiological data indicates that the spatiotemporal limits for perception are similar to the limits for direction selectivity in MT neurons but differ markedly from those for V1 neurons. These observations suggest a correspondence between neuronal responses in MT and the short-range process of apparent motion.

Animals↗
PubMed1986

Motion selectivity in macaque visual cortex. III. Psychophysics and physiology of apparent motion.

We have conducted physiological and psychophysical experiments to identify possible neural substrates of the perception of apparent motion. We used identical sequences of flashed stimuli in both sets of experiments to better compare the responses of cortical neurons and psychophysical observers. Physiological data were obtained from two cortical visual areas, striate cortex (V1) and the middle temporal area (MT). In the previous paper we presented evidence that neuronal thresholds for direction selectivity in extrastriate area MT were similar to psychophysical thresholds for motion perception at the largest effective interflash interval, and thus speed, for a given eccentricity. We now examine physiological and psychophysical thresholds for a broad range of speeds to determine whether such a correspondence exists for speeds below the upper threshold considered in the previous paper. Stimuli were presented in stroboscopic motion of constant apparent speed while the spatial and temporal interflash intervals were systematically varied. For each neuron we measured the largest spatial interval that elicited directionally selective responses at each of several apparent speeds. We calculated the composite performance of neurons in both MT and V1 by averaging the spatial interval necessary for direction selectivity at each apparent speed. We employed the same apparent-motion stimuli for psychophysical experiments with human subjects in which we measured the spatial interval necessary for the perception of motion over a similar range of apparent speeds. We obtained a composite profile of psychophysical performance by averaging thresholds across subjects at each apparent speed. For high apparent speeds, physiological data from MT, but not V1, corresponded closely to the psychophysical data as suggested in the preceding paper. For low apparent speeds, however, physiological data from MT and V1 were similar to each other and to the psychophysical data. It would appear, therefore, that neurons in either V1 or MT could mediate the perceptual effect at low speeds, whereas MT is a stronger candidate for this role at high speeds. We suggest that the neuronal substrate for apparent motion may be distributed over multiple cortical areas, depending upon the speed and spatial interval of the stimulus.

Animals↗
PubMed1986

Discharges of neurons in the dorsal paraflocculus of monkeys during eye movements and visual stimulation.

Extracellular recordings were obtained from 319 input units and 304 Purkinje cells (P-cells) in the dorsal paraflocculus of alert monkeys trained to fixate a visual target. They changed discharge rates with either eye movement, eye position, or visual stimulus movement. Of the 319 input units, recorded in the granular layer or white matter, most were mossy fibers (MFs), but 90 (28%) showed characteristic cellular spikes. The latter units were probably granular cells (p-GC). Of the 319 input units, 163 (51%) showed bursts with saccades (burst units) and 62 (19%) showed a prelude on the average 124 ms prior to the onset of saccade (long-lead burst units). Sixty-five (20%) had tonic activity related to eye position and also showed bursts with saccades (burst-tonic units), and the remaining 29 (9%) showed only tonic activity (tonic units). MFs and p-GCs showed no significant differences in the proportion of each type of unit or in their response properties. The majority of burst units (63%) were pan directional, whereas all long-lead burst units had directional selectivity. The preferred directions of long-lead burst, burst tonic, and directionally selective burst units were found in all four quadrants. Position-related activity was found in 48% of the burst-tonic and tonic units to be linearly related to eye position and to show position threshold. The other units also had position thresholds but their activity was not monotonically related to fixation position. Six climbing fibers (CFs), 32 input units (including 13 p-GC), and 8 P-cells showed cyclic responses during sinusoidal movements of a visual pattern. One class of MF units (57%) responded only to the direction, whereas the others responded to both the direction and retinal-slip velocity. Both CF and P-cell units responded to sinusoidal retinal-slip velocity. Of 67 input units, 23 showed cyclic modulation in firing during sinusoidal eye movements in the horizontal plane. Nineteen were burst-tonic and four were tonic units. They also showed position sensitivity. The phase of the cyclic responses tended to lag behind the eye velocity during low-frequency trackings. Of 237 P-cells, 163 (68.8%) discharged with saccades (burst P-cells), 42 (17.7%) paused with saccades (pause P-cells), and 32 (13.5%) discharged with saccades in one direction and paused in the other (burst-pause P-cells). Position sensitivity was found in 38 P-cells; 12 were burst, 5 were pause, and 10 were burst-pause P-cells. Eleven did not respond with saccades.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1985

Comparison of sulfide oxygenation mechanism for liver microsomal FAD-containing monooxygenase with that for cytochrome P-450.

Mechanistic mode for the oxygenation of sulfides with the pig liver microsomal FAD-containing monooxygenase(EC 1.14.13.8) has been conveniently distinguished from that with the phenobarbital induced liver microsomal cytochrome P-450 by analyzing products of the oxygenation of phenacyl phenyl sulfide. Upon oxygenation of phenacyl phenyl sulfide, the FAD-containing monooxygenase gave solely phenacyl phenyl sulfoxide in contrast to the cytochrome P-450 promoted oxygenation which is known to give substantial amounts of C-S bond fission products. The observation suggests that the oxygenation of sulfide with FAD-containing monooxygenase involves the nucleophilic attack of the divalent sulfur on the reactive oxygen atom involved at the enzyme active site, namely electrophilic oxygenation of sulfide, though the oxygenation with the cytochrome P-450 is initiated by a single electron transfer from the sulfide to the enzyme active species.

Acetophenones↗
PubMed1985

Punctate chemical lesions of striate cortex in the macaque monkey: effect on visually guided saccades.

Chemical agents which reversibly or irreversibly disrupt neural processing offer several advantages over traditional techniques for behavioral studies of the central nervous system. In order to evaluate the utility of chemical agents for a behavioral analysis of visual cortical function in primates, we have tested the effects of muscimol and ibotenic acid on the function of striate cortex in awake, behaving monkeys. We studied the monkey's ability to generate saccadic eye movements to visual targets at various locations in the visual field following an injection of one or the other chemical solution into a topographically identified location in striate cortex. Our results show that deficits in the generation of visually guided saccades following such injections are similar to those that result from surgical ablation of striate cortex, although recovery is more rapid following the injections. The experiments indicate that, with certain restrictions, chemical inactivation is a useful technique for behavioral analysis of visual cortical function.

Animals↗
PubMed1985

Deficits in visual motion processing following ibotenic acid lesions of the middle temporal visual area of the macaque monkey.

Physiological experiments have produced evidence that the middle temporal visual area (MT) of the monkey is selectively involved in the analysis of visual motion. We tested this hypothesis by studying the effects of small chemical lesions of MT on eye movements made in response to moving as opposed to stationary visual targets. We observed two deficits for eye movements made to moving targets: a monkey's ability to match the speed of his smooth pursuit eye movements to the speed of the moving target was impaired, and a monkey's ability to adjust the amplitude of a saccadic eye movement to compensate for target motion was impaired. In contrast, saccades to stationary targets were unaffected by the MT lesions, suggesting that monkeys with MT lesions had more difficulty responding to moving than to stationary stimuli. These results provide the first behavioral evidence that neural processing in MT contributes to the cortical analysis of visual motion.

Animals↗
PubMed1982

Posterior inferotemporal neuron activities during a visual fixation task and a visual tracking task.

Single neuron activities were recorded from the posterior inferotemporal cortex (PIT) while a monkey was fixating or tracking a target spot. Of 168 recorded neurons, 86 were activated by the extrafoveal slit stimuli; 48 were activated during eye fixation. Twenty were activated only during tracking, and not by fixation or a extrafoveal slit stimuli. It was suggested the PIT participates not only in the perception mechanisms but also in the foveation mechanisms such as fixation or tracking.

Animals↗
PubMed1980

Neuronal activity in the monkey dorsolateral prefrontal cortex during a discrimination task with delay.

Ninety-nine single neuron activities of the dorsolateral prefrontal cortex of 3 monkeys were recorded during performance of a Konorski task. Green or red lights were presented successively with a separation of fixed delay interval. The monkey responded as soon as the second stimulus was presented. If the two stimuli were color-matched, the 'YES' lever press was rewarded; if the two stimuli were not, the 'NO' lever press was rewarded. In the second task, after paired color stimuli, a tone pip was presented as the 'GO' signal for lever presses. During sample and matching periods 50 neurons increased their discharge rates and 10 decreased. In 86% of increasing type neurons rate increase occurred during both periods. During auditory GO periods, 27 neurons increased their rates and 11 decreased. Discharge peak was before or at the moment of hold key release. In 60% of these neurons were also observed the rate changes to sample and matching stimuli. Differential activations between left and right levers were found in 20%. It was suggested that the prefrontal cortex is related to a sensorial attention mechanism to the visual stimulus which enables correct choice of the behavior to be rewarded.

Animals↗
PubMed1980

[Inferotemporal neuron activities of monkey during Konorski's task (author's transl)].

In order to search inferotemporal (IT) neuron activities related to processes of visual discrimination and visual short-term memory, the monkeys were trained to do so called Konorski's task. In the task, the monkey was seated in a primate chair and a pair of color stimuli (red or green) was presented from the same two colored light-emitting-diode (LED) before and after a fixed delay interval of 1-5 sec. The monkey was rewarded for pressing one of two levers when two stimuli were the same in color, and the other side when two stimuli were different. A total of 101 neurons were recorded from the anterior IT (between A3-A15). About 80% of recorded neurons activated by LED and about 60% of them showed different discharge rates to different colors (color selectivity). About 80% of color selective neurons showed stronger responses to the second visual stimuli than the first stimuli. These color selective neurons were recorded from the posterior part of the anterior IT (between A3-A10). No color dependent activities were observed during delay period. The data suggested that the IT neurons were related to a process of visual discrimination so that a physically identical stimulus which had a different meaning in the behavioral context would be differentiated.

Action Potentials↗