Masao Azuma

Prefrontal neuronal activity during gazing at a light spot in the monkey

We trained monkeys to make rapid key-release when a tiny light spot dimmed, so that they gazed at the spot until it dimmed. While the animal was performing the gaze task, we recorded unit activity in the prefrontal cortex and found that many neurons increased in discharge rate during the gaze trial (G neuron) with a variety of discharge patterns: many units were activated continuously during the gaze period; others were activated phasically only in an earlier portion of the gaze period. The activation of the G neurons was little influenced by stimulus parameters, such as the size, intensity and position of the light spot. However, it was dependent on behavioral state of the animal: error trials with delayed key-release showed a weak activation while extinction procedure induced enhanced activation in the initial several trials. The dependence of the activation on the behavioral state may suggest that the activation is at least involved in attentional process during gazing at a behavioral cue.

A glass-insulated “elgiloy” microelectrode for recording unit activity in chronic monkey experiments

A glass-coated microelectrode made of a stiff cobalt--nickel alloy is described. The thickness of the glass coating and the length of the uninsulated tip can be varied as desired. The electrode is stiff enough to insert through the relatively tough dura of the monkey in chronic experiments. Further, the recording site can be marked by electrolytic deposition of iron and the Prussian blue reaction.

Properties and distribution of auditory neurons in the dorsolateral prefrontal cortex of the alert monkey.

In alert monkeys, some prefrontal neurons located in the superior dorsolateral area were activated to acoustic stimuli delivered in a restricted range of directions with respect to the animals head. The effective direction was usually contralateral to the animal. The function of the auditory neurons in connection to that of the visual ones, which are commonly found in the prefrontal cortex, is discussed.

Effects of eye position on saccades evoked by stimulation of the monkey superior colliculus

Effects of different initial eye positions on saccades evoked by electrical stimulation of the superior colliculus (SC) were investigated in alert monkeys with the head restrained. The dependence of saccade vector on initial eye position was studied quantitatively by multiple regression analysis. Following stimulation at 240 of 367 sites in the SC, saccade vector was influenced by initial eye position. The magnitude of eye position effects on horizontal saccade component was similar to that for vertical component. These effects were mostly found with stimulation in the caudal SC. Results suggest that eye position signals may control excitability of neurones in the SC.

Relation between visual input and motor outflow for eye movements in monkey frontal eye field.

We recorded visual neurons with the Elgiloy microelectrode in the frontal eye field of the alert monkey. After determining their visual receptive field, saccadic eye movements were induced by applying electric pulses at the recording site through the same electrode. The saccades were generally induced so as to bring the gaze angle to a part within the receptive field.

Excitability changes of the visual cortex during discrimination behavior in the cat

Abstract Cats were conditioned to press a bar for food reward with repetitive stimulation of the lateral geniculate nucleus. The stimulation served both as a discriminative stimulus to generate the bar-press and to elicit a series of evoked responses in the visual cortex. With well-trained cats, we recorded evoked responses at the initiation of the bar-press. Each of the responses consisted of positive-negative diphasic waves of about 10 msec duration. The positive wave had small positive deflections on its rising phase. On repetitive stimulation, those waves were small at the beginning, then augmented and reached maximal amplitude. Bar-press occurred several tenths of a second after the maximum enhancement. Large augmentation of the response occurred when the first response was small and vice versa. We also found that single shock stimulation to the geniculate could serve as a discriminative stimulus for initiation of bar-pressing.