Human Assessment of Signals Modeling Different Directions of the Motion of Sound Images

The characteristics of a subjective sound field formed under conditions of dichotic stimulation were studied in healthy subjects (six females and seven males) with normal auditory sensitivity upon movement of a sound image (SI) in different directions. The character and the trajectory values of the emerging subjective sound image (SSI) were determined depending on the direction of its motion and the initial interaural delay (700, 400, and 200 s). Certain differences in the assessment of the parameters of moving sound images between the groups of male and female subjects were revealed. In female subjects, the averaged trajectory values in the right and left hemispheres were the same when the SSI moved in both directions and shortened uniformly with a decrease in the initial interaural delay. With a 700-s delay, the trajectory values of the male subjects for all directions of motion of the SSI were the same as those of female subjects. With initial 400- and 200-s delays, the trajectory values were significantly greater in the group of male subjects if a SI moved from the right or left ear to the median line of the head. With the method used, no interhemispheric asymmetry was revealed in the process of lateralization of moving sound images, which, under certain conditions, may be of importance for increasing the accuracy of localization of sound sources in the environment.     

Lateralization of saccadic latency during monocular presentation of stimuli to a leading and non-leading eye

Saccadic latencies were studied in ten healthy subjects. Peripheral targets were presented monocularly to a leading and nonleading eyes in the right and left hemifields. SS (single step) and OVERLAP (200 ms) schemes of visual stimulation were used. Under OVERLAP conditions, the saccadic latency was longer by 30-39 ms and the number of long-latency saccades was higher than under SS conditions, especially in subjects with mixed asymmetry profiles. In the majority of subjects with right asymmetry profile, the latencies of saccades during stimulation of the leading eye were by 12 ms shorter than during stimulation of the nonleading eye, and the latencies of right saccades were by 24 ms shorter than that of the left saccades independently of the stimulated eye. The obtained results explain some characteristic features of hemyspheric asymmetry in organization of saccadic movements.     

Hemispheric participation in the shaping of spatial-motor asymmetry in visual recognition in rats

Asymmetry of movement direction was found in Wistar rats at establishing of motor alimentary conditioned reflex to simultaneously presented visual stimuli. In the course of learning the asymmetry weakened on the whole, but some individuals retained right- or left side preference. The analysis of asymmetry change before and after unilateral cortical inactivation revealed a special role of right hemisphere influences for the formation of right-side preference and of the left hemisphere--for the choice of the left direction. The lack of asymmetry was observed at the presence of the influences from the left hemisphere cortex depressing ipsilateral nigro-striate system and activating the contralateral one. Influences of the cortex of both hemispheres reduce the absolute value of the asymmetry coefficient; the left hemisphere has a special significance for manifestation of temporal asymmetry parameters. Photic interference is a factor modulating the asymmetry. It reduces the right hemisphere activity more than that of the left one; it intensifies right hemisphere influences, contributes to the involvement of the transcallosal conduction channel in the formation of spatial-motor asymmetry.     

Features of Psychomotor Responses and Interhemispheric Relationships at Various Stages of Adaptation to a New Time Zone

Motor response precision (MRP) as dependent on the functional asymmetry of the hands was analyzed before and after transmeridian flights across seven time zones. The MRPs of the two hands were relatively balanced under normal conditions and asymmetrical under conditions of immediate or late adaptation to a new time zone. The functions of the right hemisphere were affected mainly by acute desynchronosis, and those of the left hemisphere, by latent desynchronosis. As the functional indices and circadian biorhythms normalized, the initial domination of the left hemisphere strengthened.     

The asymmetry of movement direction in freshwater shrimp (Gammarus oceanicus) in the open-field test

Behaviour of Gammarus oceanicus was studied in the open field test. For the whole except (n = 204) spatial-motor asymmetry was found. It was manifested in significantly greater number of movements clockwise (to the right) than counterclockwise (to the left). Animals with significant asymmetry dominated, forming 93.5% of the except. The asymmetry was characterized by distinct right-sided direction. Motor activity and spatial-motor asymmetry at repeated tests in the main weakened; the changes in "right" and "left" animals were manifested differently. The essential factor which disturbed the behaviour of the animals in the open field test (including the asymmetry of movement direction) proved to be a toxicant (oil pollution) action.     

Application of transcranial magnetic stimulation for monitoring of the motor cortex condition in dynamics in healthy subjects

Transcranial magnetic stimulation (TMS) is used already for sixteen years for studying human central nervous system. The main objective of this work was to study motor thresholds and their hemispheric asymmetry in healthy subjects during TMS. We examined 31 righthanded healthy students. Their motor thresholds were measured in May (before vacations), September (immediately after vacations), and November (two months after vacations). Magnetic stimulator Neurosoft-MS (Ivanovo, Russia) was used for TNS of the motor cortex. It was shown that in the absence of regular active functional loads on the right hand, the motor thresholds in healthy righthanders significantly increased under the TMS of the left hemisphere, and hemispheric asymmetry disappeared under conditions both of muscle relaxation and voluntary contraction. Motor thresholds under the left-side TMS decreased and hemispheric asymmetry recovered with the restart of the regular active functional loads on the right hand.     

Visual illusions induced by electrical stimulation of the labyrinth

In normal subjects, electrical stimulation of the labyrinth with surface electrodes located on the mastoid process induced illusions of shifting of a fixed point of light in darkness similar to the oculogyral illusion induced by rotatory vestibular stimulation. Monoaural anodal stimulation of the right labyrinth induced apparent shift of the target to the left; with cathodal stimulation, it shifted to the right; threshold current was 0.35–0.6 mA. When the current strength increased, the amplitude and rate of apparent movement of the target increased approximately linearly. With binaural, bipolar stimulation, the illusory movement of the target was toward the site of the cathode and the threshold decreased by 1.5–2.5 times. With binaural, monopolar stimulation, the target seemed to shift along the vertical and the threshold current was 1.4–3.0 mA. Eye movement appeared at substantially higher currents than those resulting in apparent movement of the target. It is suggested that visual illusions are linked not to vestibular eye-movement reactions, but to the effect vestibular signals have on the spatial perception system.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 321–327, May–June, 1991.     

Specific features of lateralization of a stationary auditory image by a human under condition of stimulation without interaural differences: a neurophysiological analysis

Analysis of the lateralization phenomena of a fused auditory image (FAI) was performed on the basis of the previously developed model of the binaural directional hearing. It was found earlier that, under conditions of auditory stimulation without interaural differences, the FAI was localized at the head midline only in about a quarter of subjects. In a greater part of the listeners, the FAI was lateralized within the range of -4.6 ... +11.2 degrees from the midline. It was shown that FAI localization with reference to the head midline may be determined by the extent of asymmetry and spatial contrast between the "active" neural zones in the left and right halves of the subjective auditory space. In turn, the asymmetry (or its absence) of these "active" zones fully depends on a distribution of neurons by characteristic time delays in the left and right halves of the subjective auditory field. The model also explains the fact of a decrease in localization precision with the FAI position just at the midline.     

Asymmetry of the cerebral hemispheres during comparison of paired visual stimuli

In conditions of tachistoscopic presentation of visual stimuli, healthy (male and female) right-handed subjects carried out a paired comparison of the stimuli presented unilaterally and in the center of the visual field. In case of recognition of images of words and objects, the number of correct answers and motor reaction time usually did not significantly differ at two interstimuli intervals (1 and 10 s). In comparing images of faces, there also were no differences by the number of reactions, and the reaction time was less at the intervals of 1 s. The left hemisphere dominated at the identification of words and female faces, the right one--at the recognition of male faces. When the right visual field was stimulated images of various classes were recognized more differentially than at the stimulation of the left visual field. The male subjects had more prominent interhemispheric differences than the females. The increase of the interstimuli interval from 1 to 10 s brought to a weakening of the functional interhemispheric asymmetry and decreasing of the differences between the male and female subjects. The obtained data show that in the processes connected with short-time memory, functional interhemispheric asymmetry is basically formed at the initial stages of the information processing.     

The subjective auditory space of epileptic patients with lesions in both the temporal cortical area and the hippocampus

Parameters of the subjective auditory space formed under the conditions of dichotic stimulation during movement of the acoustic image in different directions were studied in 13 epileptic patients with lesions in both the temporal cortex and the hippocampus. The pattern and degree of the movement trajectory of the subjective acoustic image (SAI) were determined in two groups of patients (in seven patients with the right-side focus and six patients with the left-side focus of convulsive activity, depending on the direction of moving and the initial interauricular delay (700, 400, and 200 μs)). A significant decrease in the SAI movement trajectory was observed in patients with right-or the left-side lesions in the temporal cortex and hippocampus as compared to healthy subjects or patients with temporal cortical epilepsy in the cases when the SAI movement stopped at the side of the epileptic focus. The analysis of the parameters of the SAI movement in each hemisphere showed a highly significant difference between the movement trajectories for all values of initial delays as compared to the control group of healthy subjects (p < 0.01) and patients with a relatively isolated lesion of the right temporal cortex (p < 0.05). A significant role of the epileptic lesion of the hippocampus (which is not an auditory structure) in the impairment of spatial hearing was demonstrated. The characteristics of the functional asymmetry because of simultaneous epileptic lesion of the temporal cortex and hippocampus, which led to the impairment of the binaural effect, are discussed.     

Asymmetry of Characteristics of the Background Activity of Neurons of the Medial Vestibular Nucleus in Rats After Long-Term Vibration

Using computer analysis, we compared characteristics of the impulse background activity (BA) generated by neurons in the right and left medial vestibular nuclei (MVN) of the rats under control conditions and on the 5th, 10th, and 15th day with everyday 2-h-long sessions of vibrational stimulation. In the control group, the BA frequency generated by left-side MVN neurons was, on average, higher than that in the right MVN (23.6 ± 1.5 and 16.6 ± 1.7 sec^-1, respectively); other main characteristics of the BA demonstrated no significant internuclear differences. Vibrational influences of different durations induced complex significant laterally specific modifications of the level of regularity and dynamic indices of BA generated by neurons of the right and left MVN, of proportions of the cells with different types of distribution of interspike intervals (ISI), and of coefficients of variations of ISI. The mean frequency of background spiking in the right MVN increased about twofold (to 31.6 ± 2.2 sec^-1) after 10 days with vibration sessions, but dropped on the 15th day to 20.6 ± 1.7 sec^-1. In the left MVN, the mean BA frequency monotonically decreased, to 11.6 ± 1.0 sec^-1 after 15 days with vibration sessions. Therefore, chronic vibrational stimulation results in differential shifts of the characteristics of the BA generated by neurons of two MVN and in the formation of a new significantly asymmetrical pattern of such activity. Possible reasons for lateral asymmetry of the impulsation of MVN neurons and modifications of this asymmetry after long-term vibrational influences are discussed. We suppose that such an asymmetry can be one of the factors responsible for the development of motor and autonomic manifestations of vibration-induced motion sickness.     

Subjective Acoustic Field of Patients with Cortical Temporal Lobe Epilepsy as Revealed Using Signals Simulating Various Directions of Sound Movement

Perception of signals simulating directional movement of a sound source was studied in two groups of patients with cortical temporal lobe epilepsy and epileptic activity foci in the right or left temporal area of the cortex. On dichotic stimulation, the character and length of the trajectories of subjective auditory images (SAIs) were determined as dependent on the direction of SAI movement and the initial interaural delay (700, 400, and 200 s). For any delay or direction examined, SAI trajectories were shorter in the patients of both groups than in healthy subjects. Regardless of the side of an epileptic focus, the shortest trajectories were detected in the hemisphere where SAI movement ended, especially at an interaural delay of 200 s. The narrowest subjective acoustic field was observed in patients with epileptic foci in the right temporal cortex. Possible mechanisms of the changes in spatial hearing are discussed. The changes in SAI perception are assumed to result from distorted binaural interactions, which manifest themselves in functional asymmetry of the two auditory centers and may be caused by a convulsive activity focus present in one temporal lobe.     

Down-regulation of brain muscarinic cholinergic receptor promoted by diacylglycerols and phorbol ester

Sustained agonist stimulation induces an asymmetric down-regulation of brain muscarinic acetylcholine receptor (mAChR): 43±2% in the right and 26±2% in the left cerebral hemisphere, respectively (Ref. 1). In order to determine the possible involvement of endogenous diacylglycerols produced under muscarinic stimulation in the down-regulation phenomenon, here we have studied the effects of synthetic diacylglycerols and a phorbol ester on cells dissociated from rat cerebral cortex. Oleoylacetylglycerol decreased the amount of cell-surface mAChR by 37±2% and 25±2% in right and left cerebral cortex, respectively. Long-term treatment with phorbol dibutyrate also produced internalization of the mAChR (25±1.5% and 33±2% in right and left cortical cells, respectively). These changes occurred without modification of the Kd_app for the selective antagonist pirenzepine. The action of calcium ions was also studied using incubation of cells with the ionophore A23187. No changes were observed in the amount of mAChR detected at the plasma membrane with the ionophore alone, but when used in combination with phorbol dibutyrate and the agonist carbamylcholine a sinergistic decrease in mAChR was apparent. It is concluded that long-term exposure to exogenously added diacyglycerols and phorbol ester significantly reduces the amount of mAChR detected at the plasma membrane and abolishes the asymmetry of the down-regulation phenomenon observed under specific muscarinic stimulation, suggesting that diacylglycerols may be one of the factors responsible for such asymmetry.Abbreviations used A23187 ionophore A23187 - ATRO atropine - CARB carbamoylcholine - DAG diacylglycerol - DMEM Dulbecco's modified Eagle's medium - DMSO dimethylsulfoxide - HEPES 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid) buffer - PZ pirenzepine - LCC left cerebral cortex - mAChR muscarinic acetylcholine receptor - OAG oleoylacetylglycerol - PDB phorbol dibutyrate - RCC right cerebral cortex     

Influence of asymmetric stiffness on the structural and aerodynamic response of synthetic vocal fold models

The influence of asymmetric vocal fold stiffness on voice production was evaluated using life-sized, self-oscillating vocal fold models with an idealized geometry based on the human vocal folds. The models were fabricated using flexible, materially-linear silicone compounds with Young's modulus values comparable to that of vocal fold tissue. The models included a two-layer design to simulate the vocal fold layered structure. The respective Young's moduli of elasticity of the “left” and “right” vocal fold models were varied to create asymmetric conditions. High-speed videokymography was used to measure maximum vocal fold excursion, vibration frequency, and left–right phase shift, all of which were significantly influenced by asymmetry. Onset pressure, a measure of vocal effort, increased with asymmetry. Particle image velocimetry (PIV) analysis showed significantly greater skewing of the glottal jet in the direction of the stiffer vocal fold model. Potential applications to various clinical conditions are mentioned, and suggestions for future related studies are presented.     

Influence of Achilles tendon vibration on the vertical posture during standing with asymmetrical leg loading

The shift of the common center of pressure (CCP) and the center of pressure (CP) of one leg was studied during the Achilles tendon vibration of one or both legs while the subject was standing with symmetrical load on the legs or with the load transferred to one leg. The CP shift of the standing subject during unilateral Achilles tendon vibration depended on both the side of application of vibration and on the distribution of the leg load. During standing with a asymmetrical load on the legs, the shift of the CCP was larger than when the vibration was applied to the loaded leg. The CP shift of one leg was greater if both vibration and the load were applied to it. Vibration of the unloaded leg caused a CP shift in the loaded contralateral leg. In this case, vibration of the left unloaded leg did not cause any noticeable CP shift of the left leg, while vibration of the unloaded right leg caused a CP shift of the right leg. Under the similar conditions of loading and vibration, the displacement of the CP of the right leg was larger than the displacement of the CP of the left leg. It may be suggested that postural asymmetry and unilateral vibration of the leg muscles change the internal representation of the position of the body axis in relation to the vertical, which affects the displacement of the CP of one leg in response to afferent stimulation of the leg muscles.     

Change in Auditory Image Movement Trajectories under Conditions of Direct Nonsimultaneous Masking

The authors studied fused auditory image (FAI) movement trajectories under conditions of direct nonsimultaneous masking. This movement was created by a gradual change in a dichotically presented series of clicks with interaural differences in stimulation from 0 to ±700 s or from ±700 to 0 s. Binaurally presented transmissions of wide-band noise served as maskers. The location and length of the trajectories were evaluated without a masker and with five values of the time lag between the signal beginning and masker end. When the test signal duration was 200 ms, the length of the trajectories was 33–44° without a masker. In the first test group, this trajectory lay close to the median line of the head without a masker (irrespective of the movement direction) and moved away from it under masking conditions. When the FAI moved from the median line towards the right or left ear, the initial part of the trajectory was masked; when the movement direction was opposite, the final part was masked. In the second group, the trajectories were located near the ears when the FAI moved from either ear and shifted towards the median line as a result of masking. When the movement direction was opposite, they were close to the median line and shifted towards the ear under masking conditions. When the FAI moved along all trajectories, their initial parts were masked.     

Reaction time and interhemispheric interaction

The study was made on healthy adult subjects. The reaction time of the hand (RT) was measured under two conditions: 1) the choice of reaction (right or left hand) is determined by the nature of the warning stimulus; 2) decision on the choice is taken, depending on the second, trigger stimulus. Stimuli are presented at random sequences to different visual fields. The reaction time to the visual signal presented to the visual field ipsilateral to the hand is significantly shorter (by 15 to 26 msec) than to the stimulus in the contralateral visual field. In a simple motor reaction, when no discrimination of trigger stimulus and the decision on the choice of reaction is required, a hemispheric asymmetry of reaction time is manifested: the left hemisphere only responds differently to direct visual stimulation and to that mediated through the contralateral hemisphere.     

Interhemispheric asymmetry of positive emotional reactions in rats

Interhemispheric asymmetry of positive emotional reactions was studied in rats: satisfaction of drinking need and self-stimulation. Successive inactivation of the hemispheres was carried out by potassium spreading depression. Switching off of the right as well as the left hemispheres symmetrically influenced the whole quantity of the water, drunk by the rats to a full thirst satisfaction, i. e. the magnitude of need. However, at different stages of drinking need satisfaction an interhemispheric asymmetry was observed: under a strong drinking motivation the right hemisphere dominated, under a weak motivation--the left one. Switching off of the right hemisphere lowered the frequency of self-stimulation of the lateral hypothalamus and switching off the left one heightened it, testifying to the dominance of the right hemisphere in the reaction of self-stimulation. This reaction was also characterized by asymmetry of the lateral hypothalamus nuclei; reactivity to hemispheres inactivation (decreasing or increasing of self-stimulation frequency) of the right nucleus was more expressed than that of the left one.     

Estimation by humans of signals simulating different sound movement directions and specificity of the perception of these signals by patients with temporal epilepsy

The perception of moving sound stimuli that imitate directional sound source movement was studied in healthy subjects and in patients with temporal lobe lesions, as well as in a group of patients with simultaneous lesions of the temporal cortex and hippocampus. Under the conditions of dichotic stimulation of patients with the rightor left-side foci of convulsive activity, the nature and length of the trajectories of the emerging subjective sound images (SSI) were estimated depending on the direction of movement and interaural time difference (700, 400, 200 μs). The audiograms of all patients did not differ from those of healthy subjects, suggesting that the auditory sensitivity of patients remained unimpaired. However, in the patients, the trajectories were shorter than the trajectories in healthy subjects at all the values of the initial time delay and at all the directions of SSI movements. In patients with the cortical temporal epilepsy, changes of the subjective sound field were the most significant in the case of the right-side localization of foci of the convulsive activity. In patients with simultaneous lesions of the temporal cortex and hippocampus, the averaged trajectories of SSI movement differed significantly from those in the group of healthy subjects (p < 0.01) and in patients with a relatively isolated lesion of the temporal cortex (p < 0.05); these trajectories were independent of the initial delay. The mediobasal structures of the temporal lobe that are involved in the epileptic process proved to play a significant role in the perception and estimation of the moving sound stimuli, although they do not belong to the auditory system proper. The possible mechanisms underlying disorders in patients with temporal epilepsy are discussed.     

Abnormal attentional modulation of retinotopic cortex in parietal patients with spatial neglect

Brain regions beyond visual cortex are thought to be responsible for attention-related modulation of visual processing [1, 2], but most evidence is indirect. Here, we applied functional magnetic resonance imaging (fMRI), including retinotopic mapping of visual areas, to patients with focal right-parietal lesions and left spatial neglect [3, 4]. When attentional load at fixation was minimal, retinotopic areas in right visual cortex showed preserved responses to task-irrelevant checkerboards in the contralateral left hemifield, analogously to left visual cortex for right-hemifield checkerboards, indicating a "symmetric" pattern in both hemispheres with respect to contralateral stimulation under these conditions. But when attentional load at fixation was increased, a functional asymmetry emerged for visual cortex, with contralateral responses in right visual areas being pathologically reduced (even eliminated for right V4/TEO), whereas left visual areas showed no such reduction in their contralateral response. These results reveal attention-dependent abnormalities in visual cortex after lesions in distant (parietal) regions. This may explain otherwise puzzling aspects of neglect [5, 6], as confirmed here by additional behavioral testing.