Edward V. Evarts

Motor Cortex Reflexes Associated with Learned Movement

In primates, sensory input can generate reflex motor cortex output in association with learned movement when the sensory input has a strong and direct connection to the motor cortex—for example, when a stimulus calling for repositioning of the hand consists of a perturbation of hand position. This finding supports the proposal that neurons of primate motor cortex may function in a transcortical servo-loop.

Gating of motor cortex reflexes by prior instruction

A previous study showed that sensory input can generate reflex motor cortex output in association with learned movement when the sensory input has a strong connection to the motor cortex, e.g., when a stimulus calling for repositioning of the hand consists of a perturbation of hand position. The present study has shown that motor cortex reflexes can be ‘gated’ on or off by the voluntary ‘set’ of the monkey. A monkey was trained to grasp a handle and maintain it in a certain position for 2–4 sec; he was then given an ‘instruction’ as to how he should respond to a forthcoming perturbation of the handle. The ‘instruction’ was a red or green light which appeared between 0.6 and 1.2 sec prior to the handle perturbation. The red light signaled that the monkey should pull toward himself when the perturbation occurred, and the green light meant that he should push away when the perturbation occurred. Two different sorts of perturbation were used, one being a movement of the handle toward the monkey and the other away from the monkey. A given instruction called for a movement synergistic with segmental stretch reflexes for one of the perturbations and antagonistic to these reflexes for the other. Following training, activity of motor cortex neurons was recorded during task performance. Neurons in precentral motor cortex showed changes of activity according to the ‘instruction’ as early as 200 msec following the onset of red or green light. In addition, the short (20 msec) latency motor cortex response evoked by the subsequent perturbing stimuli differed markedly depending upon the prior instruction. The finding that the set and expectancy of the monkey could profoundly modify this ‘reflex’ response indicates that the transcortical serov-loop proposed by Phillips is subject to powerful modulation as a function of learning and volition.

A technique for recording activity of subcortical neurons in moving animals

Abstract The technique which has been described allows stereotaxic orientation of micro-electrodes for single unit recording in the intact monkey. The method provides for vertical penetrations and for minimum loss of time between completion of one penetration and reorientation of the electrode for the subsequent penetration.

Pyramidal tract neurons in somatosensory cortex: central and peripheral inputs during voluntary movement

Recordings with pyramidal tract neurons (PTNs) in the primary somatosensory cortex of the monkey show that these neurons have 3 properties in common with PTNs of primary motor cortex: (1) they exhibit discharge prior to the onset of voluntary movement, (2) their discharge frequency varies as a function of strength of muscular contraction, and (3) they show reflex responses to afferent stimuli that occur during movement. These findings support the view that in addition to its widely recognized role in somesthetic perception, somatosensory cortex has a direct role in the control of movement.

Contrasts between activity of precentral and postcentral neurons of cerebral cortex during movement in the monkey

Abstract Activity of neurons of precentral and postcentral gyrus was recorded in monkeys during performance of learned flexion and extension movements of the wrist. The movements were triggered by a light stimulus, reward being given for short reaction-time responses. Changes of activity in precentral neurons began 60–80 msec prior to changes of activity in postcentral neurons.

Spontaneous Discharge of Single Neurons during Sleep and Waking

Populations of single neurons in visual cortex, middle suprasylvian association cortex, and brain stem of cat show greater variance of spontaneous discharge rates during waking than during sleep; this change in variance occurs in the absence of significant changes in mean discharge rates. Neurons which discharge rapidly during sleep tend to discharge even more rapidly during waking, whereas neurons with relatively low rates of discharge during sleep tend to have reduced spontaneous activity during waking.

Sherrington's concept of proprioception

Proprioceptors respond naturally to active movement, but experimentally these movements must be produced by external means. Edward Evarts explains how this methodological limitation has affected our interpretation of proprioceptor function.

Effect of Interruption of the Visual Pathway on the Response to Geniculate Stimulation

Optic nerve section or destruction of the lateral geniculate nucleus increased the amplitude and elevated the recovery cycle of the cortical response to lateral geniculate radiation stimulation in cats. The lesions may have acted by eliminating tonic inhibitory or occlusive volleys originating in the retina, or both.

The role of the cerebral cortex in movement

The importance of the mammalian cerebral cortex in the control of movement has been accepted for a century. Recent studies indicate that the number of cortical fields involved in motor control is much greater than previously believed. This article summarizes neuroanatomical and neurophysiological investigations which suggest that each of these cortical fields has a specialized role in the control of movement.

Relative Lack of Pharmacologic Action of 3-Methoxy Analogue of Norepinephrine.

Conclusions Normetanephrine is inert as regards those aspects of central nervous system activity which have been studied in cats, and is a relatively weak pressor agent in the dog. An intravenous dose of 5 mg was inactive with regard to circulatory and psychological effects in man. Although a more detailed study of this compound should be done, the findings presented strongly suggest that O-methylation at the 3 position is an effective means of inactivating norepinephrine. It will be of interest to investigate the enzymatic mechanisms involved in this unusual methylation process and to attempt to alter it in vitro and in vivo.