Michael S. Myslobodsky

Auditory inattention in right-hemisphere-damaged patients with and without visual neglect

Fifteen right-hemisphere-damaged patients, eight with- and seven without visual neglect (N+ and N-, respectively), were assessed for the presence of auditory neglect using free-field bilateral simultaneous stimulation (BSS) and pseudorandom unilateral stimulation. Eight healthy subjects served as controls. Both N+ and N- groups extinguished left-sided sound stimuli in the BSS condition. N+ (but not N-) patients showed a right-side advantage in sound localization and were inferior, compared to normal individuals, in their ability to localize unilaterally administered sounds on the left side. Blindfolding significantly improved the localization performance. In a task demanding stimulus identification, both N+ and N- groups performed abnormally when auditory stimuli came from the left. Free-field stimulation is thus an adequate technique for the detection of auditory neglect. The results are consistent with the notion that left-sided neglect reflects a pathologically exaggerated attentional bias towards the right in normal individuals.

Postural asymmetry and directionality of rotation in rats.

The hypothesis [12] that the direction of postural asymmetry can predict rotational side preferences caused by amphetamine, was tested. Postural asymmetry of male and female Wistar rats was assessed using four tests: (a) tail suspension, (b) tail holding, (c) tail pinch, and (d) walking on a narrow path. The tests were conducted prior to and after (+)-amphetamine (1 mg/kg, IP) administration. Rotational directionality was assessed in a rotometer. None of the tests predicted the direction of circling. The findings suggest that there is a multitude of systems contributing to asymmetric posture.

Rotational swimming tendencies in the dolphin (Tursiops truncatus).

Anecdotal evidence suggests that dolphins placed in a pool exhibit stereotypic swimming in circles. The present study confirmed these observations in a sample of thirteen dolphins. The majority of dolphins (84.6%) showed highly consistent directional swimming in counterclockwise circles. The latter directionality held throughout the circadian cycle and resisted environmental manipulations. Only social interaction was capable of altering the directionality of circumnavigation. The consistency of unidirectional swimming is considered paradoxical in view of the existing evidence regarding the alternating of hemispheric activity in sleeping dolphins.

Bilateral electrodermal activity in waking man

Abstract Skin conductance responses were examined bilaterally in a group of 14 normal subjects. Twelve of them were right-handed and two were left-handed. All right-handed subjects exhibited asymmetry in skin conductance level and in skin conductance response during verbal-numerical and visual-imagery tasks. With the visual activity, larger responses were found in the left hand, while during the verbal task, larger responses were recorded from the right hand. The results were interpreted as evidence of hemispheric asymmetry of the electrodermal activity orienting response control mechanisms. More ipsilateral control for the right hand is predicted.

Changes of brain anatomy in patients with posttraumatic stress disorder: A pilot magnetic resonance imaging study

No abnormalities in magnetic resonance images were recorded in patients with posttraumatic stress disorder other than an increased incidence (50%) of a small cleft in the callosal-septal interface, a cavum of the septum pellucidum. A similar grade of cavum was obtained in 14% of normal volunteers matched for age, socioeconomic background, and military experience. The cavum is believed to have antedated the disorder and is conceived to be a neurodevelopmental aberration. The possibility that the cavum is a marker of vulnerability to stress in psychopathology is discussed.

Convulsant-Speciflc Architecture of the Postictal Behavior Syndrome in the Rat

Summary: The postictal immobility syndrome was examined in five experimental grand mal epilepsy models in an attempt to analyze separately the behavioral and underlying neurochemical aspects of the rigid‐catatonic and flaccid‐cataleptic states. Catalepsy and analgesia were found in varying degrees after maximal electroshock (MES), metrazol, picrotoxin, and Ro 5–3663 activated seizures. Signs of rigidity were noticed after the MES and picrotoxin seizures. Kindled seizures were followed by explosive behavior without signs of rigidity, catalepsy, and analgesia. Naloxone reduced the duration but not the score (intensity) of catalepsy and failed to selectively antagonize analgesia. The relative representation of the tonic stage of convulsions seemed to be the major determinant of the development of catatonic‐cataleptic symptomatology. It is suggested that more than a single neurotransmitter system is involved in the postictal immobility syndrome and each epilepsy model has its unique neurochemical profile.

Asymmetry of electrodermal activity in man

Skin conductance responses were examined bilaterally in a group of 12 normal subjects. Ten of them were right-handed and two were left-handed. All right-handed subjects exhibited asymmetry in skin conductance response during verbal-numerical and visual-imagery tasks. With the visual activity, larger responses were found in the left hand; while during the verbal task, larger responses were recorded from the right hand. The results were interpreted as evidence of hemispheric asymmetry of the electrodermal activity orienting response control mechanisms.

EEG asymmetries may be affected by cranial and brain parenchymal asymmetries.

SummaryThe plagiocephaly index, an index that reflects an underlying anatomic asymmetry of the brain, was assessed in ten schizophrenic patients and its values were correlated with the lateral distribution of quantitatively evaluated EEG. The correlations between the index and alpha power at F7 were significant, positive for frontal asymmetry (frontal bulging) and negative for occipital flattening. We then studied ten normal subjects in an attempt to illuminate the contribution of several cephalic and cranial variables to the imbalance of alpha-afterdischarges (AD) of VEP recorded at O1–O2. The asymmetry index of AD was computed and correlated with asymmetries of CT-derived measures of occipital bone thickness, occipital lobe width, mastoid area, and sulcal asymmetry (the asymmetry of intraparietal sulcus location from the longitudinal fissure). With the exception of the sulcal variable all measures significantly covaried with alpha AD. These findings caution that it may be important to determine cranial and brain parenchymal asymmetries where brain laterality is pertinent to studies of EEG.

Unilateral dopamine deficit and lateral EEG asymmetry: Sleep abnormalities in hemi-parkinson's patients

The hypothesis was tested that unilateral dopamine deficiency leading to the contralateral extrapyramidal syndrome (hemi-parkinsonism) would cause distinctly asymmetric EEG sleep patterns. In 7 hemi-Parkinsons patients 2 nights of sleep were monitored along with pre-sleep waking periods. No medication was given prior to the first night. The second night followed at least 2 months of L-DOPA medication. Although in all patients sleep architecture was disturbed, no statistically significant asymmetries of sleep patterns were obtained. L-DOPA medication improved the quality of sleep. Delta sleep was most visibly improved. Also, post-treatment enhancement of the mean delta power over the parkinsonian hemisphere was supported statistically. The role of dopamine in slow wave sleep control and mechanisms of contralateral hemisphere involvement are discussed.

Pharmacologic implications of hemispheric asymmetry

Abstract The hemispheric asymmetry of brain activity is well established, and there in increasing evidence of a relationship between phenomena of asymmetry and personality, arousal status, and the existence of mental and emotional disease. Differences in individual sensitivity to drugs may relate to hemispheric asymmetric patterns. Several mechanisms may contribute to the unequal influence of systematically administered drugs on each hemisphere, including effect of hemispheric activity status on 1) speed and degree of local uptake of drug; 2) differential in synaptic sensitivity; 3) degree of competition with local endogenous neurohumors. Adequate knowledge concerning normal and abnormal hemispheric asymmetry, and the effects of spontaneous or manipulative changes in the activity of each hemisphere should lead to more rational and effective choices and patterns of administration of therapeutic agents.