Sex differences in latencies of bilateral electrodermal responses

The present study examined sex differences in the latencies of bilateral electrodermal responses to stimuli presented in monocular vision. The stimuli were spatial-emotional, verbal-emotional, spatial-neutral and verbal-neutral slides, presented for either 35 ms or 1 s. Subjects were 15 males and 15 females. Bilateral latencies were not influenced by type of stimulus or by right/left hemisphere stimulation, which is in keeping with the most recent findings of bilateral electrodermal activity studies. However, females gave a faster right hand than left hand response and appeared to be more lateralized than males. Males showed shorter latencies on the left hand than on the right. These results confirm the importance of gender in experiments using the bilateral recordings of electrodermal activity.     

Bilateral Asymmetry of Skin Conductance Responses During Auditory and Visual Tasks

Bilateral skin conductance (SC) was recorded while dextral subjects engaged in tasks designed to differentially engage the right (RH) and left (LH) hemispheres. Subjects compared strings of speech sounds (LH) and musical chords (RH). They also decided whether written words rhymed (LH) and viewed pictures of faces in a continuous recognition paradigm (RH). SCRs in the right hand were larger during the chords task than the syllables task. The left hand did not differ for the two stimuli. In the visual experiment a comparable effect was obtained in males only. SCRs in the left hand were larger for rhymes than faces; the right hand did not differentiate between stimuli. Sex differences in laterality are considered. Subjects who were more equally balanced in awareness of the two sides of their bodies and subjects with familial sinistrals were more likely to show task appropriate SC changes. Using rote repetition and visual imagery as mnemonics did not affect SC asymmetries.     

Relative performance of the two hands in simple and choice reaction time tasks

There is evidence that the left hemisphere is more competent for motor control than the right hemisphere. This study investigated whether this hemispheric asymmetry is expressed in the latency/duration of sequential responses performed by the left and/or right hands. Thirty-two right-handed young adults (16 males, 16 females; 18-25 years old) were tested in a simple or choice reaction time task. They responded to a left and/or right visual target by moving their left and/or right middle fingers between two keys on each side of the midline. Right hand reaction time did not differ from left hand reaction time. Submovement times were longer for the right hand than the left hand when the response was bilateral. Pause times were shorter for the right hand than the left hand, both when the responses were unilateral or bilateral. Reaction time results indicate that the putatively more efficient response preparation by the left hemisphere motor mechanisms is not expressed behaviorally. Submovement time and pause time results indicate that the putatively more efficient response execution by the left hemisphere motor mechanisms is expressed behaviorally. In the case of the submovements, the less efficient motor control of the left hand would be compensated by a more intense attention to this hand.     

Bilateral EEG differentiation of stimuli

The EEG of both right and left hemispheres was monitored while subjects were presented with words, music, arithmetical problems and abstract pictures, (15 trials of each treatment, 9 sec per trial). The left side of the brain was most activated during presentation of words and arithmetic, whilst the right side of the brain was most activated during presentation of music. In addition, the right side was more activated during exposure to arithmetic than to words. The pictures were not differentiated by either side of the brain and it is possible that they had the effect of deactivating or relaxing the subjects, since they yielded high abundance values compared with other stimuli. This study confirms earlier findings showing significant between- hemisphere ratios for arithmetic and words. In addition, however, the within-hemisphere analyses show that music affects the right hemisphere (without inducing between-hemisphere changes) and that arithmetic also activates the right hemisphere if compared with the non-activating effects of words.     

Visual evoked response correlates of cerebral specialization after human commissurotomy

Visual evoked responses (VERs) were recorded from commissurotomy patients and normal subjects in order to investigate the electrophysiological correlates of cerebral lateralization and independent hemispheric processing. A verbal task consisted of detecting rhyming words and a spatial task consisted of comparing matching shapes. Stimuli were delivered, by means of a computer graphic display, into the right visual field, the left visual field, or both visual fields. Behavioral results and evoked response waveforms showed lateralization for verbal processing in the left hemisphere for the patient group. Analysis of variance of product moment correlation coefficients between VER waveforms indicated significant differences between unilateral and bilateral stimulation for both patients and normals. Commissurotomy and normal VERs showed similar patterns of correlation when verbal stimuli were delivered to the left hemisphere, but differed during right hemisphere stimulation. The results are discussed in terms of VER correlates of visual-verbal processing.     

Gender differences in lateralization of mismatch negativity in dichotic listening tasks.

OBJECTIVE: With the aim of investigating gender differences in the functional lateralization subserving preattentive processing of language stimuli, we compared auditory mismatch negativities (MMNs) using dichotic listening tasks. METHODS: Forty-four healthy volunteers, including 23 males and 21 females, participated in the study. MMNs generated by pure-tone and phonetic stimuli were compared, to check for the existence of language-specific gender differences in lateralization. Both EEG amplitude and scalp current density (SCD) data were analyzed. RESULTS: With phonetic MMNs, EEG findings revealed significantly larger amplitude in females than males, especially in the right hemisphere, while SCD findings revealed left hemisphere dominance and contralateral dominance in males alone. With pure-tone MMNs, no significant gender differences in hemispheric lateralization appeared in either EEG or SCD findings. CONCLUSION: While males exhibited left-lateralized activation with phonetic MMNs, females exhibited more bilateral activity. Further, the contralateral dominance of the SCD distribution associated with the ear receiving deviant stimuli in males indicated that ipsilateral input as well as interhemispheric transfer across the corpus callosum to the ipsilateral side was more suppressed in males than in females. SIGNIFICANCE: The findings of the present study suggest that functional lateralization subserving preattentive detection of phonetic change differs between the genders. These results underscore the significance of considering the gender differences in the study of MMN, especially when phonetic stimulus is adopted. Moreover, they support the view of Voyer and Flight [Voyer, D., Flight, J., 2001. Gender differences in laterality on a dichotic task: the influence of report strategies. Cortex 37, 345-362.] in that the gender difference in hemispheric lateralization of language function is observed in a well-managed-attention condition, which fits the condition adopted in the MMN measurement; subjects are required to focus attention to a distraction task and thereby ignore the phonetic stimuli that elicit MMN.     

Fluidity theory and neuropsychological impairment in alcoholism.

In order to determine whether the "classic" alcoholic WAIS pattern is the result of right hemisphere damage or the loss of fluid intelligence abilities, right-hemisphere damaged, left-hemisphere damaged, alcoholic, and control groups of 40 subjects each were matched on the variables of age and education. They were administered the WAIS-Revised (WAIS-R) and four sensory and motor measures that were sensitive to lateralized damage but not to fluidity. The alcoholic group showed the "classic" pattern of a lower performance than verbal WAIS IQ. Although the left hand scores on the sensory and motor tests were significantly more impaired than the right hand scores for the right-hemisphere damaged group they were not for the alcoholic group. These results did not support the right hemisphere theory. Rather, as indicated by further analysis, the pattern is most adequately explained by the fluidity theory.     

Asymmetry in visual evoked potentials to gratings registered in the two hemispheres of the human brain.

The study aimed at testing, by a visual evoked potential method, the hypothesis of the hemispheric specialization in processing of high and low-spatial frequencies. Twenty four right-handed subjects (12 males and 12 females) were presented with square-wave vertical gratings of various spatial frequencies (0.67, 0.86, 1.20, 2.00, 2.40, 3.00, 3.30, 6.00 and 7.50 c/deg). Gratings were presented in nine separate blocks each containing 64 exposures. Time of exposure was 30 ms and the interstimulus interval varied from 2 to 3.5 s. VEPs were recorded with electrodes located at O1 and O2 and referred to Cz according to the 10/20 system. Amplitudes and latencies of two VEPs components (N130-150 and P200-240) were analyzed. The results showed larger amplitudes of VEPs registered in the right hemisphere of both males and females. This difference, however, was apparent in the earlier component of VEPs in females and in the later component in males. The observed hemispheric asymmetry did not depend on the spatial frequency of grating. Females demonstrated longer latencies than males for both N and P components. Our data suggest that the right hemisphere predominates in processing grating stimuli, but the dynamics of this process differ in the two sexes. The results do not support Sergent's hypothesis which postulate the right hemisphere specialization for low spatial frequencies and the left hemisphere specialization for high spatial frequencies.     

Hand movements with a phase structure and gestures that depict action stem from a left hemispheric system of conceptualization

The present study addresses the previously discussed controversy on the contribution of the right and left cerebral hemispheres to the production and conceptualization of spontaneous hand movements and gestures. Although it has been shown that each hemisphere contains the ability to produce hand movements, results of left hemispherically lateralized motor functions challenge the view of a contralateral hand movement production system. To examine hemispheric specialization in hand movement and gesture production, ten right-handed participants were tachistoscopically presented pictures of everyday life actions. The participants were asked to demonstrate with their hands, but without speaking what they had seen on the drawing. Two independent blind raters evaluated the videotaped hand movements and gestures employing the Neuropsychological Gesture Coding System. The results showed that the overall frequency of right- and left-hand movements is equal independent of stimulus lateralization. When hand movements were analyzed considering their Structure, the presentation of the action stimuli to the left hemisphere resulted in more hand movements with a phase structure than the presentation to the right hemisphere. Furthermore, the presentation to the left hemisphere resulted in more right and left-hand movements with a phase structure, whereas the presentation to the right hemisphere only increased contralateral left-hand movements with a phase structure as compared to hand movements without a phase structure. Gestures that depict action were primarily displayed in response to stimuli presented in the right visual field than in the left one. The present study shows that both hemispheres possess the faculty to produce hand movements in response to action stimuli. However, the left hemisphere dominates the production of hand movements with a phase structure and gestures that depict action. We therefore conclude that hand movements with a phase structure and gestures that represent action stem from a left hemispheric system of conceptualization.     

Hypnotic susceptibility: a lateral predisposition and altered cerebral asymmetry under hypnosis

Psychophysiological and behavioural evidence is reported of altered cerebral asymmetry under hypnosis in favour of the right hemisphere. This occurred in Susceptible as distinct from Unsusceptible subjects. Measures included bilateral electrodermal responses to tones and bimanual processing times for sorting letters and numbers with eyes closed. Subjects listened to a tape recording of a procedure for inducing relaxation under hypnosis. Susceptible subjects, unlike Unsusceptibles, showed lateral asymmetries in baseline conditions in favour of the left hemisphere. Electrodermal responses were larger on the left than the right hand and haptic processing times were faster with the right than the left hand. Under hypnosis there was a reduction in electrodermal orienting responses coupled with faster habituation and a reversal in lateral asymmetries. Haptic processing revealed a slowing in right hand processing times whereas left hand times were reduced as was the case with bilateral processing times in both Unsusceptible subjects and controls who experienced no hypnosis. Unlike earlier reports left hemisphere dynamic processes were fundamental to the induction of hypnosis. A neuropsychological model is proposed whereby susceptibility is associated both with a left bias prior to hypnosis and left hemisphere inhibition under hypnosis. Unsusceptibles retain a right hemisphere orientation without undergoing left hemisphere inhibition. Thus hypnosis involves an inhibition of left-sided processes which permits the ascendancy of the right hemisphere through the attenuation of left hemisphere control.     

Reduced interhemispheric transmission in schizophrenia patients: evidence from event-related potentials

Interhemispheric transfer was investigated in 14 schizophrenia patients and 15 age- and sex-matched healthy controls in a lateralized lexical decision task. Words and pseudowords were tachistoscopically presented either to the left or to the right visual hemifield. Event-related potentials were determined from a 65-channel electroencephalogram. Information transfer between hemispheres was assessed by the interhemispheric transmission time (IHTT), the N1-latency difference between ipsilateral and contralateral hemisphere.Controls, but not schizophrenia patients showed significantly faster IHTT from the right to the left hemisphere for words, while IHTT from the left to the right hemisphere did not differ between groups and stimuli. These findings are interpreted in terms of a deficit in schizophrenia to transfer verbal information from the right to the left hemisphere via the corpus callosum.     

Hemispheric asymmetry in event related potentials associated with positive and negative emotions.

Event-related potentials from symmetrical points of the left and right frontal and occipital cortex were recorded while subjects experienced positive and negative emotions. The emotions were elicited by either missing or hitting a target with a photoelectric gun. Twenty three right-handers (10 males and 13 females) were tested. Each subject took part in two sessions. In the first session the subjects were informed about their performance (hit or miss) after each shot. In the second, control session, no feedback was given. The amplitudes of P180 potential registered from the occipital cortex were higher in the right than in the left cerebral hemisphere, irrespectively of subjects' performance (i.e. a miss or a hit). No such tendency was observed in potentials registered from the frontal cortex. These regularities emerged only in the feedback situation, i.e. when subjects were informed about their performance, although higher ERPs were registered for hits than for misses. The results support the hypothesis that the posterior region of the right hemisphere is more engaged than the left one in experiencing emotions, irrespectively of their sign.     

Hemispheric asymmetry and emotion: lateralized parietal processing of affect and cognition

The differential cerebral processing of affect and cognition may have important implications for a more general understanding of how these two complex sets of functions differ and how they interact. Building upon recent studies of hemispheric asymmetry in emotion, the present study focused on the differential parietal processing of emotional stimuli under affective and cognitive conditions. Subjects were exposed to neutral and emotional stimuli presented under cognitive and affective instructional sets. Bilateral electroencephalographic (EEG) data showed that the principal differentiation between affective and cognitive conditions occurred in the right hemisphere, whereas the highest overall level of activation during emotional stimulation was in the left hemisphere. It was also found that affective conditions produced higher of levels of both EEG and electrodermal activity than either cognitive or neutral conditions. Finally, significant patterns of gender differentiation suggested greater focal organization for affective arousal in females than males.     

Sex differences and the asymmetry of specific and non-specific electrodermal responses

Phasic electrodermal conductance responses were bilaterally recorded from 30 subjects (15 males and 15 females). After a 5-min adaptation period subjects were presented with two series of ten 80-dB tones each, with a 4-min rest period between the two series. Data from sinistrals, ambidextrous, and from subjects with familial sinistrality were excluded from statistical analysis. Males displayed more asymmetry between hands both in their non-specific and specific responses, with larger skin conductance responses on the left hand. Females showed a less marked asymmetry, with larger skin conductance responses on the right hand. Similar results were found in skin conductance levels. It was concluded that sex differences are an important variable in the study of electrodermal asymmetry.     

Asymmetrical hemispheric EEG activation evoked by stimulus position during the Simon task

The Simon effect has been previously shown to be asymmetric at both the behavioral and electrophysiological levels. The present investigation was aimed to clarify whether, during a Simon task, hemispheric asymmetry is also observed in the early phases of stimulus processing. In a group of healthy subjects performing the Simon task, we analyzed scalp potentials evoked by the first lateralized cue (left or right), instead of the classical readiness potential preceding the motor response. ERP results showed a significant left cortical activation to stimuli presented in the right visual field at the 140–160 ms time window. Instead, left stimuli elicited a significant activation of the right versus left hemisphere starting at the next 160–180 ms time interval. We linked this asymmetry to that observed in behavioral data: the Simon effect recorded with left stimuli is smaller than the Simon effect recorded with right stimuli. Results confirm the hypothesis that in right handed subjects, left hemisphere is specialized for motor response selection and is able to process right stimuli faster than the right hemisphere does for left stimuli.     

Hemispheric specialization in the co-ordination of arm and trunk movements during pointing in patients with unilateral brain damage

During pointing movements involving trunk displacement, healthy subjects perform stereotypically, selecting a strategy in which the movement is initiated with either the hand or trunk, and where the trunk continues after the end of the hand movement. In a previous study, such temporal co-ordination was not found in patients with left-hemispheric brain lesions reaching with either their dominant paretic or with their non-dominant non-paretic arm. This co-ordination deficit may be associated in part with the presence of a lesion in the dominant left hemisphere. If so, then no deficit should be observed in patients with stroke-related damage in their non-dominant right hemisphere moving with their ipsilesional arm. To verify this, 21 right-hand dominant adults (7 who had had a stroke in the right hemisphere, 7 who had had a stroke in the left hemisphere and 7 healthy subjects) pointed to two targets located on a table in front of them in the ipsilateral and contralateral workspace. Pointing was done under three movement conditions: while not moving the trunk, while bending the trunk forward and while bending the trunk backwards. The experiment was repeated with the non-paretic arm of patients with stroke and for the right and left arms of healthy subjects. Kinematic data were recorded (Optotrak). Results showed that, compared to healthy subjects, arm-trunk timing was disrupted in patients with stroke for some conditions. As in patients with lesions in the dominant hemisphere, arm-trunk timing in those with lesions in the non-dominant hemisphere was equally more variable than movements in healthy subjects. However, patients with dominant hemisphere lesions used significantly less trunk displacement than those with non-dominant hemisphere lesions to accomplish the task. The deficit in trunk displacement was not due to problems of trunk control or sitting balance since, in control experiments, all subjects were able to move the trunk the required distance, with and without the added weight of the limb. Results support the hypothesis that the temporal co-ordination of trunk and arm recruitment during pointing movements is mediated bilaterally by each hemisphere. However, the difference in the range of trunk displacement between patients with left and right brain lesions suggests that the left (dominant) hemisphere plays a greater role than the right in the control of movements involving complex co-ordination between the arm and trunk. Electronic Publication     

Do Task and Sex Differences Influence the Visual Evoked Potential?

Visual evoked potentials were recorded from each hemisphere of both male and female subjects at a parietal and a central site while concurrent spatial or verbal mental tasks were performed. The data were analyzed by means of an automated procedure for peak identification and each component's latency and amplitude was submitted to analysis of variance. No convincing taskhemisphere interactions were found, although several components, particularly the later ones, showed either task or hemisphere related effects. At both sites, females showed greater amplitude of the N2 component for both hemispheres and both cognitive tasks. Sex differences also emerged on components P6 and N6 which were consistent with the idea that females show differential hemisphere involvement in spatial tasks.     

Verbal versus visuospatial abilities in relatives of autistic females

Parents and siblings of 26 autistic females and 26 Down's syndrome females were compared on a battery of verbal and visuospatial tasks to test the possibility of familial aggregation of a particular cognitive profile. No difference was found between parents of both groups. In contrast, siblings of autistic females showed significantly lower verbal abilities than controls but did not differ in their visuospatial performance. This difference appeared attributable to brothers of autistic females, some of whom showed an especially pronounced discrepant profile at the disadvantage of verbal abilities compared to their visuospatial abilities. Results are discussed in terms of genetic and/or environ mental factors that may account for an aggregation of cognitive features ranging from left‐hemisphere impairments to enhanced right‐hemisphere abilities.     

Cross-sectional data on soft tissue morphometry of the growing hand and fingers of dextral individuals 5-65 years old

This study examines both hands of right-handed (dextral) subjects 5-65 years old in order to define the separate growth trajectories of digit lengths (2D-5D) and hand widths; to assess how 2D : 4D and other digit ratios also vary with age; and to test whether lengths are influenced by gender dimorphism and lateral (right/left) asymmetry. Calliper measurements were made from hand photocopies. Growth patterns were analysed by linear regression and correlation, main and interaction effects of age and gender were resolved by analysis of variance, and lateral asymmetries were identified by paired tests. All digits, and hand width, grew in a biphasic pattern in both hands, and inflection points between phases showed gender dimorphism. In the early fast-growing phase, male digits grew over a longer period than those in females, before switching to a slower growth phase during which gender dimorphism became more exaggerated. In right hands, age differences in digit ratios were confined to 2D : 4D and, except for 4D : 5D, females tended to show larger ratios than males. In left hands, all ratios (except 3D : 5D) varied with age and gender influenced only 2D : 4D, 2D : 5D and 3D : 5D. Again, ratios were greater in females. In females, 2D was longer in the right hand of older subjects, whilst 3D, 4D and 5D tended to be shorter in the right hand of younger subjects. No asymmetries were seen in 2D, 3D or 4D in males, but 5D tended to be shorter on the right in the group 9-12 years old. Finally, hand width tended to be greater in females on the right at 9-65 years old, and in males on the right at 18-23 years old. A further novel finding was that certain relationships (inflection points, correlation coefficients and gender differences in digit lengths) seemed to follow gradients running from 2D to 5D. It is tempting to speculate that these are manifestations of the antero-posterior gradients established by signalling events that control digit development and patterning in utero.     

Hemispheric sensitivity to body stimuli in simple reaction time

Previous research indicates that people respond fastest when the motor response is (spatially, functionally, anatomically, or otherwise) congruent to the visual stimulus. This effect, called ideomotor compatibility, is thought to be expressed in motor areas. Congruence occurs when the stimulus and response share some dimensions in their internal representations. If the ideomotor compatibility hypothesis were true, we would expect facilitation when right hand stimuli are presented to the left hemisphere, or left hand stimuli are presented to the right hemisphere. To address this issue, we conducted a simple reaction time experiment with lateralized targets. Participants were instructed to press a button as soon as a target was observed. The target stimulus was a left hand, a right hand, or a neutral control. Each hemisphere showed faster responses to contralateral hand stimuli as compared with ipsilateral hand stimuli, consistent with the ideomotor compatibility hypothesis. The results support an automatic and implicit processing of visual stimuli within motor representations even when no recognition of, or decision about, the stimulus is necessary.