Sex Differences in Task-Dependent EEG Asymmetries

Different patterns of lateralization of hemispheric function in the male and female brain have been proposed to account for sex differences in performance of linguistic and visuo-spatial tasks. The present experiment was designed to determine whether task-related asymmetries in suppression of the alpha rhythm differed between the sexes. Bilateral EEGs were recorded from 5 male and 5 female subjects while they performed 3 verbal-numeric and 3 visuo-spatial tasks. The proportion of right hemisphere alpha activity differed between these tasks for the male group but not for the female group. This result suggests a sex-related difference in degree of lateralization of hemispheric function, with males having a more strict segregation of function.     

Heart Beat Perception and Emotional Experience

The main assumption of the present study is that emotional experience is coupled to perception of bodily processes. From this it is deduced that individuals who show good perception of heart activity tend to exhibit higher levels of a momentarily experienced emotion (in this case anxiety) and to score higher on the personality trait “Emotional Lability.” The aspect of cardiac awareness considered here is perception of heart beats. Subjects were instructed to count heart beats (only by concentrating on their body but not by taking their pulse) during a signalled time interval and the reported number of beats was then compared to the actual number of beats as extracted from the EKG. Additionally, skin conductance and respiration were recorded. During the experimental task (i.e., counting heart beats) increases in heart rate, respiration rate and number of spontaneous fluctuations in skin conductance were recorded. Groups of good and poor perceivers were formed on the basis of accuracy on the perception task. The two groups did not differ in heart rate; however, in State Anxiety and Emotional Lability, the group of good perceivers had significantly higher scores. The importance of visceroception for emotional experience is pointed out and the relevance for clinical psychology is discussed.     

Startle and Emotion: Lateral Acoustic Probes and the Bilateral Blink

The affect-startle effect describes the modulation of the reflexive eyeblink response to a probe startle stimulus as a function of foreground emotional valence. Larger blinks occur during viewing of unpleasant slide foregrounds, relative to positive foregrounds. This effect has been obtained repeatedly using binaural acoustic startle probes. The current study examines this phenomenon for monaural probes administered to the left and right ears in separate blocks. Startle probes were presented during and between exposures to pleasant, neutral, and unpleasant slides, with the ear of presentation counterbalanced across subjects. Left monaural probes produced blink magnitudes that increased linearly from pleasant to unpleasant slide foregrounds, and appeared to be independent of attention or interest. Right monaural probes did not vary with foreground valence. These findings suggest that the startle probe indexes emotional processing that is lateralized in the central nervous system.     

The Effect of Lateral Visual Fixation and the Direction of Eye Movements on Heartbeat Discrimination

This study was undertaken to determine whether the asymmetrical activation of the two cerebral hemispheres affects the accuracy of heartbeat perception. Hemispheric preference--the tendency to activate one hemisphere rather than the other--was assessed by the directionality of conjugate lateral eye movements. Actual differential hemispheric activation was achieved by contralateral visual fixation. The results of 44 right-handed male subjects showed that right hemisphere preferent subjects ("left-movers") performed better on a heartbeat discrimination task than left hemisphere preferent subjects ("right-movers"). The direction of lateral visual fixation also influenced heartbeat discrimination: subjects fixating to the left were more accurate than those fixating to the right.     

Laterality, Emotionality, and Heartbeat Perception

Recent research on visceral perception has indicated that hemispheric specialization and emotionality may account for individual differences among subjects. The present study was designed to examine the nature of the relationship between hemispheric specialization and emotionality, and the manner in which these variables influence individual differences in visceral perception (i.e., detection of cardiac activity). Male subjects were given 20 questions used to test lateral eye movements. Following the completion of the State-Trait Anxiety Inventory (STAI), Form X-1 (State Anxiety), cardiac awareness was assessed using the Whitehead heartbeat discrimination procedure. Subjects then completed the STAI, Form X-2 (Trait Anxiety), and the Eysenck Personality Inventory. Results indicated that good heartbeat perceivers made significantly more left lateral eye movements (i.e., right hemisphere preferent) than poor perceivers on any of the emotional indicators. It was found, however, that subjects with high scores on two of the three emotional indicators made significantly more left lateral eye movements than subjects with low scores. Additional analyses indicate that respiration rate and subject obesity may affect the ability to detect feedback of cardiovascular function.     

Evaluation of Cortical Connectivity During Real and Imagined Rhythmic Finger Tapping

Accumulating evidence suggests the existence of a shared neural substrate between imagined and executed movements. However, a better understanding of the mechanisms involved in the motor execution and motor imagery requires knowledge of the way the co-activated brain regions interact to each other during the particular (real or imagined) motor task. Within this general framework, the aim of the present study is to investigate the cortical activation and connectivity sub-serving real and imaginary rhythmic finger tapping, from the analysis of multi-channel electroencephalogram (EEG) scalp recordings. A sequence of 250 auditory pacing stimuli has been used for both the real and imagined right finger tapping task, with a constant inter-stimulus interval of 1.5 s length. During the motor execution, healthy subjects were asked to tap in synchrony with the regular sequence of stimulus events, whereas in the imagery condition subjects imagined themselves tapping in time with the auditory cue. To improve the spatial resolution of the scalp fields and suppress unwanted interferences, the EEG data have been spatially filtered. Further, event related synchronization and desynchronization phenomena and phase synchronization analysis have been employed for the study of functionally active brain areas and their connectivity during real and imagery finger tapping. Our results show a fronto-parietal co-activation during both real and imagined movements and similar connectivity patterns among contralateral brain areas. The results support the hypothesis that functional connectivity over the contralateral hemisphere during finger tapping is preserved in imagery. The approach and results can be regarded as indicative evidences of a new strategy for recognizing imagined movements in EEG-based brain computer interface research.     

Upper limb asymmetries in the utilization of proprioceptive feedback

Despite the importance of proprioception during upper limb movement, the extent to which arm/hemisphere asymmetries exist in the utilization of proprioceptive feedback remains unclear. In the present study, movement accuracy and arm dynamics were examined in 20 right-handed adults during a proprioceptive matching task that required subjects to actively match remembered target positions of the elbow with the contralateral arm. As hypothesized, the results indicated an accuracy advantage in favor of the non-preferred left arm reflected by smaller absolute matching errors when compared to the preferred right arm. This advantage was most pronounced for larger amplitude movements and was not associated with any limb-specific difference in movement strategy as indicated by the dynamics of the matching movement. These results extend current theories of handedness by demonstrating that, in right-handed individuals, the non-preferred arm/hemisphere system is more adept at utilizing position-related proprioceptive information than the preferred arm/hemisphere system.     

Task-dependent asymmetries in the utilization of proprioceptive feedback for goal-directed movement

Whereas the majority of studies regarding upper limb asymmetries in motor performance have focused on preferred arm dominance for producing motor output, studies exploring the role of sensory feedback have suggested that the preferred and non-preferred arms are specialized for different aspects of movement. A recent study by Goble et al. (2006) found evidence of a non-preferred left arm (and presumably right hemisphere) proprioceptive dominance for a target matching task that required subjects to both memorize and transfer across hemispheres proprioceptive target information. This paradigm contrasted previous studies of proprioceptive matching asymmetry that explored only memory-based matching and produced equivocal results. The purpose of the present study, therefore, was to examine task-dependent asymmetries in proprioceptive matching performance, including differences related to active versus passive presentation of the matching target. It was found that the non-preferred left arm of right handers matched target elbow angles more accurately than the preferred arm, but only in the matching condition that required both memory and interhemispheric transfer. Task-dependent asymmetries were not affected by the mode of target presentation and assessment of matching kinematics revealed differences in strategy for both the speed and smoothness of targeted movements. Taken together, these results suggest that the non-preferred arm/hemisphere system is specialized for the processing of movement-related proprioceptive feedback.     

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     

The Symmetry of Emotional and Deliberate Facial Actions

Asymmetries of the smiling facial movement were more frequent in deliberate imitations than spontaneous emotional expressions. When asymmetries did occur they were usually stronger on the left side of the face if the smile was deliberate. Asymmetrical emotional expressions, however, were about equally divided between those stronger on the left side of the face and those stronger on the right. Similar findings were obtained for the actions involved in negative emotions, but a small data base made these results tentative.     

The role of the right hemisphere in the physiological and cognitive components of emotional processing

Right hemisphere specialization for emotional processing was investigated using behavioral and psychophysiological methods, Fifty undergraduates were shown slides depicting negative emotional and neutral scenes briefly lateralized to the right or left cerebral hemispheres and asked to categorize each as emotional or neutral. Pulse volume and heart rate (HR) measured physiological processing and reaction time measured cognitive processing. The largest vasoconstriction responses and HR deceleration were obtained for emotional items in the right hemisphere. However, reaction time failed to show right hemisphere superiority in perceptual/cognitive processing, demonstrating instead slowest responses to emotional stimuli presented to the right hemisphere together with evidence for left hemisphere competence. Selective right hemispheric activation in autonomic responses, combined with the lack of right hemisphere specialization in the cognitive task, suggests that the physiological response system rather than the perceptual/cognitive system is the locus of the right hemisphere superiority for emotion.     

Lateralized startle probes in the study of emotion

Two experiments are reported in which affective modulation of the startle reflex elicited by monaurally presented acoustic probes was further examined. An earlier study in our laboratory obtained significant modulation by effect for probes presented to the left ear, but no significant effect for probes presented to the right ear Experiment 1 replicated the procedures used in that experiment and obtained the same pattern of effects. Experiment 2 changed the presentation of monaural probes from a blocked to a mixed presentation and again obtained a similar pattern. Modulatory differences in reflex magnitude between pleasant and unpleasant stimuli were consistently large and reliable for reflexes elicited by left ear probes but weak and unreliable for reflexes elicited by right ear probes.     

Abnormal Purkinje cell activity in vivo in experimental allergic encephalomyelitis

It has been shown that learning visuomotor rotations with multiple target directions, compared with a single target direction, leads to greater generalization to untrained targets within the same limb. This implies that multiple direction learning results in a more complete internal model of the visuomotor transform. It has also been documented that the extent of transfer of movement information regarding visuomotor adaptations between the limbs is limited, relative to that between different configurations of the same limb. The present study thus investigated the origin of this restriction in interlimb transfer, by comparing the effects of eight-direction and one-direction training conditions with one arm on the subsequent performance with the other arm. It was hypothesized that if multiple direction learning leads to a more complete model of the novel visuomotor transform, interlimb transfer should be enhanced relative to that following single direction training. However, if no differences are observed between single and multiple direction training conditions, this would suggest that such learning is effector dependent. We also tested the hypothesis that interlimb transfer of visuomotor adaptation is not obligatory, by examining the effects of visual rotation direction (same or oppositely directed visuomotor rotations for the two arms). All subjects first adapted to a 30° rotation, either clockwise or counterclockwise, in the visual display during reaching movements. Following this, they adapted to a 30° rotation in either the same or opposing direction with the other arm. Results showed that initial training with the non-dominant arm facilitated subsequent performance with the dominant arm in terms of initial direction control, but only under the same rotation condition. Both single and eight direction training conditions led to substantial transfer in subsequent performance with the other arm, but multiple direction training was no more beneficial than single direction training. This finding suggests that the previously reported intralimb advantages of multiple direction learning are effector specific. Our findings are discussed in the context of hierarchical models of motor control to explain the intralimb advantages of multiple direction training.     

Hemispheric Asymmetry and Bilateral Electrodermal Recordings: A Review of the Evidence

Bilateral electrodermal recordings are often used in psychophysiological research as a measure of functional hemispheric asymmetry. Although significant differences between left and right hand recordings are reported in the literature, the obtained differences are often in different directions. The purpose of the present paper was to review empirical evidence related to the issue of bilateral electrodermal recordings in research on hemispheric asymmetry. Special reference is made to the current controversy concerning contralateral inhibition vs. excitation or facilitation as the underlying mechanism for reported differences in performance of typical hemisphere-specific tasks. After reviewing the evidence, which is contradictory concerning several of the more critical parameters, the conclusion is that bilateral electrodermal recordings have not been unambiguously related to hemispheric asymmetry. However, when asymmetry between the hands is clearly demonstrated, this reflects an asymmetry in the functioning of the cerebral hemispheres.     

Ictal hallucination and hemispheric specialization: Findings from 217 cases with a unilateral epileptic focus

Epileptic populations are generally considered inappropriate to investigate hemispheric specialization. However, (1) because hallucination occurs in the early stage of the ictus during which activation is observed in and around the focus, the former could be a direct result of the latter (hypothesis 1), and (2) the type of psychological content of ictal hallucination could depend on which hemisphere is ictally activated (hypothesis 2). It was predicted that, on the basis of quantitative analysis of previously published singles case reports, unilateral ictal hallucinations should occur in the visual field, ear or hemibody contralateral to the side of the ictal focus (test of hypothesis 1). It was also predicted that verbal ictal auditory hallucinations should result more often from left hemisphere foci, and non-verbal auditory ictal hallucinations from right hemisphere foci (test of hypothesis 2). Previously published cases (N = 217) of ictal hallucination from a unilateral epileptic focus were reviewed and analyzed with multivariate statistics. Both predictions were strongly supported.     

Effects of Task Difficulty on Regional Cerebral Blood Flow: Relationships with Anxiety and Performance

Associations have been described between task difficulty and autonomic arousal. This study addresses task difficulty effects on regional cerebral blood flow (rCBF), a measure of cortical activity. Earlier work suggested that in contrast to a positive association between anxiety and autonomic arousal, there is a curvilinear, inverted-U relationship between anxiety and cortical activity. A sample of 26 normal volunteers (14 men, 12 women) was administered the 133-Xenon inhalation technique for measuring rCBF. Measurements were taken under three conditions: Resting baseline, and Easy and Hard verbal analogy tasks. Subjects were grouped into three anxiety levels on the basis of their average score on a self-report measure. The rCBF was higher during task performance than at rest, but did not differ between the two difficulty conditions. There were Task × Hemisphere interactions showing the expected asymmetry of activation, with higher left hemispheric increase for the verbal task. Anxiety had an inverted-U relationship with both performance and rCBF, which were themselves positively related. These results with measures of central nervous system activity differ from those reported for autonomic responses. They indicate that anxiety effects on cortical activity may mediate the relation between anxiety and performance.     

Interlimb transfer of visuomotor rotations: independence of direction and final position information

Previous findings from our laboratory support the idea that the dominant arm is more proficient than the non-dominant arm in coordinating intersegmental dynamics for specifying trajectory direction and shape during multijoint reaching movements. We also showed that adaptation of right and left arms to novel visuomotor rotations was equivalent, suggesting that this process occurs upstream to processes that distinguish dominant and non-dominant arm performance. Because of this, we speculate that such visuomotor adaptations might transfer to subsequent performance during adaptation with the other arm. We now examine whether opposite arm training to novel visuomotor rotations transfers to affect adaptation using the right and left arms. Two subject groups, RL and LR, each comprising seven right-handed subjects, adapted to a 30 degrees counterclockwise rotation in the visual display during a center-out reaching task performed in eight directions. Each group first adapted using either the right (RL) or left (LR) arm, followed by opposite arm adaptation. In order to assess transfer, we compared the same side arm movements (either right or left) following opposite arm adaptation to those performed prior to opposite arm adaptation. Our findings indicate unambiguous transfer of learning across the arms. Different features of movement transferred in different directions: Opposite arm training improved the initial direction of right arm movements under the rotated visual condition, whereas opposite arm training improved the final position accuracy, but not the direction of left arm movements. These findings confirm that transfer of training was not due to a general cognitive strategy, since such an effect should influence either hand equally. These findings support the hypothesis that each arm controller has access to information learned during opposite arm training. We suggest that each controller uses this information differently, depending on its proficiency for specifying particular features of movement. We discuss evidence that these two aspects of control are differentially mediated by the right and left cerebral hemispheres.     

Tonic and Phasic Relationships Between Heart Rate and Somato-motor Activity in Monkeys

Heart rate (HR) and somato-motor activity were measured in monkeys (Macaca mulatto) during sessions when the animals were operantly conditioned to slow and to speed HR. Tonic (baseline) levels of HR were independent of somato-motor activity. Phasic changes of HR during conditioning were variably coupled with phasic chants in activity. The discriminative cues which signaled the operant contingencies reliably elicited cardiac operants and somato-motor responses. Monotonic trends in cardiac phasic activity generally were independent of phasic responses in somato-motor activity. Short term phasic responses in HR often were correlated with short term phasic responses in somato-motor responses. The findings indicate that the relationship of HR to somato-motor activity) depends upon temporal adjustments within given conditions and stages of training, and upon particular adjustments within each animal. The main conclusion of this study is that HR and somato-motor activity are variably coupled hut that conditioned HR responses are not necessarily caused by somato-motor responses.     

Lateralization effects on the cardiac modulation of acoustic startle eye blink

Cardiac modulation of startle eye blink has been introduced as a methodology to reflect baro-afferent signal transmission. Recent studies showed that affective startle modulation is specific to left-ear presentation that may be due to hemispheric specificity in processing emotional-relevant stimuli, similar to the processing of visceral- and baro-afferent stimuli. To explore whether cardiac modulation of startle eye blink is lateralized as well, 37 healthy volunteers received 160 unilateral acoustic startle probes of 105 dB(A) intensity presented to both ears, one at a time. They were elicited 0, 100, 230, and 530 ms after the R-wave of the cardiac cycle. Startle response magnitude was significantly diminished at a latency of 230 ms, which may be due to the baro-afferent neural feedback at this temporal location, but only for left-ear presentation. This lateralization effect in the cardiac modulation of startle eye blink may reflect the previously described advantages of right-hemispheric brain structures in relaying viscero- and baro-afferent signal transmission.     

P300: The Similarities and Differences in the Scalp Distribution of Visual and Auditory Modality

To examine the topographic relationship of P3(00) between the visual and auditory modalities, especially to examine whether there are any modality-specific hemispheric differences of P3 in normal adults. Methods: The P3s were recorded from the same 41 normal right-handed males between the ages of 20 and 33 in both a typical auditory oddball task and a visual oddball paradigm with novel stimuli, with an extensive set of 61 scalp electrodes. In addition to the visual comparison and quantitative assessment of current source density (CSD) maps between the two modalities, canonical correlation analyses on the P3 raw amplitudes and examination of interaction effects of modality × location on both raw and normalized P3 data were performed. Results: The canonical correlation between modalities was generally high, especially at the left parietal brain region. There were no significant hemispheric effects in anterior brain but significant left-greater- than-right hemispheric effects in posterior brain regions in both modalities; modality-specific hemispheric effect was observed only at the parietal region. Strong surface current density activities were observed in the midline parietal-occipital area, and left and right boundary areas of temporal and inferior frontal region. Conclusions: The topographic similarities between P3s recorded in the visual and auditory modality outnumber the differences. Combining data from CSD assessments and profile analysis of P3 topography support the hypothesis of multiple generators of P3 that are differentially active in processing stimuli from different sensory modalities and are not symmetrically distributed between the two hemispheres.