Impaired central error-correcting behavior in schizophrenia.

Previous work has suggested that normal subjects are able to recognize and correct their own errors of movement without using exteroceptive signals. This ability may be impaired in schizophrenia. Twelve normal subjects, 12 alcoholics, and 14 schizophrenics performed a step-function tracking task designed to prevent the use of exteroceptive signals in correcting errors of movement. The mean probability of correcting an error without external cues was approximately .38 in schizophrenics, .70 in normal subjects, and .75 in hospitalized alcoholic patients. There was no difference between groups in the ability to initiate correct responses. The results suggest that schizophrenics are deficient in the ability to monitor ongoing motor behavior on the basis of internal, self-generated cues.

Central error-correcting behavior in schizophrenia and depression.

A previous study suggested that schizophrenic subjects exhibit an impaired ability to correct their own errors of movement without using exteroceptive signals. However, the performance of schizophrenic subjects was compared to that of only one other psychiatric group (alcoholic subjects), and a relatively small number of subjects was studied. To investigate the specificity of the postulated impairment, 9 schizophrenic, 11 depressed, and 8 normal subjects performed a tracking task designed to prevent the use of exteroceptive cues in correcting errors of movement. The depressed and normal groups did not differ significantly on any performance measure, but the schizophrenic subjects again demonstrated a gross impairment in correcting errors, yet no impairment in initiating correct responses. These findings suggest that the impaired ability to monitor ongoing motor behavior on the basis of internal, self-generated cues may be specific to schizophrenia among major psychiatric disorders.

The rebound phenomenon of Gordon Holmes.

Contrary to a prevalent belief, the rebound phenomenon of Gordon Holmes is not a sign of cerebellar disease. It is elicited by having the patient attempt to move a limb against resistance. When the resistance is suddenly removed, the limb normally moves a short distance in the desired direction and then rebounds (jerks back in the opposite direction). Gordon Holmes pointed out that the rebound phenomenon is (1) present in normal libs, (2) exaggreated in spastic limbs, and (3) absent in limbs affected by cerebellar disease. An awareness of Holmes's observations may be helpful in the diagnosis of both cerebellar disease and spasticity.

Shortening reaction in normal and parkinsonian subjects.

During passive extension of the elbow, the triceps shows a shortening reaction (SR), which is manifested by a burst of EMG activity. The SR and the velocity of passive movement (VPM) were measured in parkinsonian patients and control subjects. The mean SR was larger and the mean VPM was smaller in the parkinsonian group. An unexpected finding was that "reinforcement" caused an increase of the SR in normal subjects but not in the patients. The VPM is considered to be a measure of rigidity, and the SR provides a quantitative approach to the pathophysiology of muscle tone.

Efference copy in the control of movement.

On a two-choice tracking test of normal subjects, numerous false moves were induced when the directional relation between movement of the hand and the response marker was changed. The mean error-correction times were not consistently less than simple reaction times. When the center of the display was screened to eliminate visual feedback, numerous moves were reversed before the marker was visible. The probability of reversing an error was much greater than that of reversing a correct move. The findings are best explained in terms of a central mechanism that uses efference copy to amend errors of movement.

Cerebral evoked potentials and somatosensory perception.

In normal subjects, somatosensory evoked potentials (SEPs) were produced by increases or decreases of the load on the biceps muscle during voluntary contraction. The stimuli lasted only 20 msec and caused less than 2 degrees of elbow flexion or extension. When the stimulus was applied during voluntary movement of the elbow, the SEP was attenuated, and the subject was less able to discriminate between loading and unloading pulses. In each of eight subjects, there was a positive correlation between the percentage of correct responses and the size of the SEP. The measurement of both SEPs and perceptual accuracy under various test conditions provides a refined technique for studying the relations between electrical events and sensory processes.

Axial versus distal motor impairment in Parkinson's disease.

We measured axial (head rotation) and distal (wrist flexion and extension) movements in parkinsonian patients with varying stages of disability, before and after administration of L-dopa. Velocities for both movements were proportionately reduced in all stages of disease. L-Dopa administration provided a small but consistent increase in distal movement velocity for most patients, whereas in patients with advanced disease (stages III to V), axial movement velocity actually declined after administration of L-dopa. This decline may be partially responsible for the failure of L-dopa administration to reverse the loss of "righting reflexes" in these patients. Measurement of axial motor control may be a useful tool in evaluating therapeutics for Parkinson's disease patients.

Understanding and diagnosing senile dementia.

Dementia is one of the most common syndromes afflicting the aged, and it should be ranked as a major cause of death. Senile dementia and Alzheimer's disease should now be viewed as one and the same. Familiarity with the cardinal signs of dementia enables the physician to differentiate it from various "functional" disorders. Before making a diagnosis of senile dementia, it is important to exclude all forms of treatable disease, including toxic, metabolic, infectious, neoplastic, and traumatic disorders. Most older patients with dementia will be found to have Alzheimer's disease, for which no definitive treatment is available.

Unloading reflex of a hand muscle.

The unloading reflex of abductor hallucis brevis was elicited by removal of the external load during voluntary contraction. The duration of the unloading pulse was varied experimentally from 1 to 32 msec. With all stimulus durations, the response was a measurable decrease in the level of EMG activity. Expressed as a percentage change from baseline, the mean size of the unloading reflex was a logarithmic function of the unloading pulse duration. The results demonstrate that the hand muscles are sensitive to very brief mechanical stimuli. Although the motoneurons of the intrinsic hand muscles receive strong projections from the cerebral cortex, they exhibit reflex behavior similar to that of the large, postural muscles.

Barognosis in a patient with hemiataxia.

Barognosis was tested in a patient who had a lesion of the right cerebellar hemisphere. While blindfolded, he used each hand to estimate the mass of given test loads, alternating hands between trials. He moved each load sinusoidally, comparing it with the previous one. The period of oscillation was found to be a linear function of the mass. With each load, the period of oscillation was longer when he used the ataxic hand. On 23 of 59 comparisons between loads, the patient reported incorrectly. Ninety-one percent of the errors were in the direction of loads feeling heavier when the ataxic hand was used. To explain these results, it is proposed that (1) the perceived magnitude of a load depends on the corollary discharge, and (2) cerebellar damage may reduce the accuracy of the corollary discharge.