Electroencephalographic and reaction time asymmetries to musical chord stimuli

EEG was recorded over left and right hemispheres at temporal leads (T3, T4) referred to the vertex (Cz) in 16 right-handed male subjects. Musical chords were presented randomly in monaural sequence, during a task which required a selective motor response to stimuli presented to one ear. The integrated amplitude of the 8-13 Hz alpha rhythm was measured when subjects listened passively. Under all conditions, a lower mean alpha amplitude was recorded over the right hemisphere than the left, regardless of which ear was stimulated. Alpha suppression over the right temporal area was accentuated when the performance task directed attention to the stimulus. Reaction time to left ear stimulation was shorter than that for the right ear. With monaural stimulus presentation behavioral asymmetry, and various EEG asymmetries can be observed. There is hemispheric asymmetry associated with attention to task relevant stimuli indicated by reduction in the alpha rhythm over the right temporal area and asymmetry in reaction time with greater efficiency of the left ear to muscial chords.     

Reaction Time in a Visual 4-Choice Reaction Time Task: ERP Effects of Motor Preparation and Hemispheric Involvement

Reaction time (RT), the most common measure of CNS efficiency, shows intra- and inter-individual variability. This may be accounted for by hemispheric specialization, individual neuroanatomy, and transient functional fluctuations between trials. To explore RT on these three levels, ERPs were measured in a visual 4-choice RT task with lateralized stimuli (left lateral, left middle, right middle, and right lateral) in 28 healthy right-handed subjects. We analyzed behavioral data, ERP microstates (MS), N1 and P3 components, and trial-by-trial variance. Across subjects, the N1 component was contralateral to the stimulation side. N1-MSs were stronger over the left hemisphere, and middle stimulation evoked stronger activation than lateral stimulation in both hemispheres. The P3 was larger for the right visual field stimulation. RTs were shorter for the right visual hemifield stimulation/right hand responses. Within subjects, covariance analysis of single trial ERPs with RTs showed consistent lateralized predictors of RT over the motor cortex (MC) in the 112–248 ms interval. Decreased RTs were related to negativity over the MC contralateral to the stimulation side, an effect that could be interpreted as the lateralized readiness potential (LRP), and which was strongest for right side stimulation. The covariance analysis linking individual mean RTs and individual mean ERPs showed a frontal negativity and an occipital positivity correlating with decreased RTs in the 212–232 ms interval. We concluded that a particular RT is a composite measure that depends on the appropriateness of the motor preparation to a particular response and on stimulus lateralization that selectively involves a particular hemisphere.     

Retroactive interference in normal aging: A magnetoencephalography study

Biomagnetic responses were recorded from healthy elderly subjects (55–67 years) performing a working memory task during recognition. The objective was to identify differential spatio-temporal brain activity patterns with magnetoencephalography by the presentation of two types of retroactive interference, active and passive. We obtained increased activity in the left medial temporal lobe and the left anterior ventral prefrontal cortex at early (100–200 ms) and medium latencies (300–400 ms) for the active interference group, and left anterior ventral prefrontal cortex showed greater activity at late latencies (700–800 ms) for the passive interference group. A time-modulated ventral prefrontal activation was shown for the active and passive interference conditions indicating that executive control mechanisms were necessary in both groups.     

Activation of the human posterior parietal cortex by median nerve stimulation

We recorded somatosensory evoked magnetic fields from ten healthy, right-handed subjects with a 122-channel whole-scalp SQUID magnetometer. The stimuli, exceeding the motor threshold, were delivered alternately to the left and right median nerves at the wrists, with interstimulus intervals of 1, 3, and 5 s. The first responses, peaking around 20 and 35 ms, were explained by activation of the contralateral primary somatosensory cortex (SI) hand area. All subjects showed additional deflections which peaked after 85 ms; the source locations agreed with the sites of the secondary somatosensory cortices (SII) in both hemispheres. The SII responses were typically stronger in the left than the right hemisphere. All subjects had an additional source, not previously reported in human evoked response data, in the contralateral parietal cortex. This source was posterior and medial to the SI hand area, and evidently in the wall of the postcentral sulcus. It was most active at 70–110 ms.     

Anticipatory attention to verbal and non-verbal stimuli is reflected in a modality-specific SPN

The time estimation paradigm allows the recording of anticipatory attention for an upcoming stimulus unconfounded by any anticipatory motor activity. Three seconds after a warning signal (WS) subjects have to press a button. A button press within a time window from 2,850 ms to 3,150 ms after the WS is considered ‘correct’, a movement prior to 2,850 ms after the WS is labelled ‘too early’ and a movement after 3,150 ms is labelled ‘too late’. Two seconds after the button press a Knowledge of Results (KR) stimulus is presented, informing the subject about the correctness of the response. Stimulus Preceding Negativity (SPN) is a slow wave which is recorded prior to the presentation of the KR stimulus. The SPN has a right hemisphere preponderance and is based upon activity in a network in which prefrontal cortex, the insula Reili and the parietal cortex are crucial. In the present study we asked two questions: (1) does the SPN show modality specificity and (2) does the use of verbal KR stimuli influence the right hemisphere preponderance? Auditory and visual stimuli were presented, in a verbal mode and in a non-verbal mode. SPN amplitudes prior to visual stimuli were larger over the visual cortex than prior to auditory stimuli. SPN amplitudes prior to auditory stimuli were larger over the frontal areas than prior to visual stimuli. The use of verbal stimuli did not influence the right hemisphere preponderance. We concluded that apart from the supramodal effect of KR stimuli in general, there is (first) a modality-specific activation of the relevant sensory cortical areas. The supramodal network underlying the attention for and the use of KR information is activated either from different sensory areas or from language processing cortical areas.     

Interhemisphere differences during tasks involving attention and selection of lateralized stimuli

The state of cortical activation in the parietal and temporal areas of the right and left hemispheres was evaluated using evoked potentials (EP) during tasks consisting of selection of visual stimuli lateralized in the right and left visual fields and needing three different types of attention: to stimulus shape, to stimulus position, and simultaneously to stimulus shape and position. EP were recorded in 15 young healthy experimental subjects using six cortical leads: P3, P4, T3, T4, T5, and T6; the following endogenous EP components (in standard terminology) were analyzed: contingent negative variation (CNV), N1, P3, and the N1-P3 complex. Asymmetry in evoked potentials was assessed in terms of differences to contra-and ipsilateral stimuli in the right and left hemispheres. EP asymmetry was detected in the right hemisphere in all types of selection of lateralized stimuli. The magnitude of asymmetry in the right hemisphere depended on the level (or intensity) of attention: the degree of asymmetry increased with increases in the need for attention to analyze the stimuli. There was a significant relationship between the magnitude of asymmetry and the latent periods of the subjects’ responses. The functional significance of these data demonstrating asymmetry may be that it provides better spatial differentiation of visual signals in the right hemisphere, along with dominance of the right hemisphere in attention tasks. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 92, No. 6, pp. 709–722, June, 2006.     

Perspective taking modulates event-related potentials to perceived pain

Recent event-related brain potential (ERP) study disentangled an early automatic component and a late top-down controlled component of neural activities to perceived pain of others. This study assessed the hypothesis that perspective taking modulates the top-down controlled component but not the automatic component of empathy for pain by recording ERPs from 24 subjects who performed pain judgments of pictures of hands in painful or non-painful situations from either self-perspective or other-perspective. We found that, relative to non-painful stimuli, painful stimuli induced positive shifts of ERPs at frontal–central electrodes as early as 160 ms after sensory stimulation and this effect lasted until 700 ms. The amplitudes of ERPs at 230–250 ms elicited by painful stimuli negatively correlated with both subjective ratings of others’ pain and self-unpleasantness in both self-perspective and other-perspective conditions. Neural response to perceived pain over the central–parietal area was significantly reduced at 370–420 ms when performing the pain judgment task from other-perspective compared to self-perspective. The results suggest that shifting between self-perspectives and other-perspectives modulates the late controlled component but not the early automatic component of neural responses to perceived pain.     

The course of visual searching to a target in a fixed location: Electrophysiological evidence from an emotional flanker task

The present study investigated the course of visual searching to a target in a fixed location, using an emotional flanker task. Event-related potentials (ERPs) were recorded while participants performed the task. Emotional facial expressions were used as emotion-eliciting triggers. The course of visual searching was analyzed through the emotional effects arising from these emotion-eliciting stimuli. The flanker stimuli showed effects at about 150–250 ms following the stimulus onset, while the effect of target stimuli showed effects at about 300–400 ms. The visual search sequence in an emotional flanker task moved from a whole overview to a specific target, even if the target always appeared at a known location. The processing sequence was “parallel” in this task. The results supported the feature integration theory of visual search.     

Response priming in the Simon paradigm

The Simon effect refers to the finding of faster responses when stimulus and response locations correspond than when they do not, although a nonspatial stimulus feature is task-relevant. These performance differences are usually accounted for by response priming processes directly induced by the task-irrelevant stimulus location. The present study investigated neural mechanisms of response priming in a Simon task at the level of the motor cortex with the help of transcranial magnetic stimulation (TMS) and motor evoked potentials (MEPs) in both arms. A single TMS was applied contralateral or ipsilateral to the requested response at the time point where response priming was at a maximum. The MEP effects depended on the stimulated hemisphere. Over the left hemisphere, MEP areas were larger when TMS was applied over the primed motor cortex. However, reduced MEPs for the nonprimed hemisphere fell short of significance. Over the right hemisphere, only a MEP reduction for nonprimed left-hand responses was present. Therefore, we conclude that mainly excitatory activation underlies response priming in a Simon task, whereas the role of inhibitory processes is tentative.     

Theta oscillation during auditory change detection: An MEG study

To study the phase and power characteristics of brain oscillations during the preattentive detection of auditory deviance, we recorded magnetoencephalographic responses in 10 healthy subjects with an oddball paradigm. As the subject was watching a silent movie, standard tones (1000-Hz frequency, 100-ms duration) and their duration deviants (50-ms duration, probability of 15%) were randomly delivered binaurally. In addition to localizing the magnetic counterpart of mismatch negativity (MMNm) with equivalent current dipole modeling, we also measured the phase-locking value (PLV) and power change of the oscillatory responses to standard and deviant stimuli by employing the Morlet wavelet-based analysis. The MMNm signals peaking at 150-200 ms after the onset of deviant were localized in bilateral temporal regions with larger amplitudes in the right hemisphere. Then 50 ms after the onset of either standard or deviant stimuli, we observed an increase of PLV and power of theta and alpha oscillations in bilateral temporal regions. PLVs of theta and alpha activities to deviant stimuli were significantly larger in the right than left hemisphere (P < 0.001). Compared with standard stimuli, deviants elicited a larger theta PLV (P < 0.001) at 150-300 ms and a larger theta power change (P < 0.05) at 50-300 ms for the responses in the right temporal region. In addition, a prominent theta phase-locking of deviant-elicited responses was found in the right frontal area at 110-250 ms (P < 0.01). Our current data suggest that a pronounced phase and power modulation on sound-elicited theta oscillations might characterize the change detection processing in the temporo-frontal network as reflected by the mismatch negativity.     

Electrophysiological analysis of a sensorimotor integration task

The present experiment aimed at investigating electrophysiologic changes observed as beta band asymmetry, by Quantitative Electroencephalography (qEEG), when individuals performed a reaching motor task (catching a ball in free fall). The sample was composed of 23 healthy individuals, of both sexes, with ages varying between 25 and 40 years old. All the subjects were right handed. A two-way ANOVA was applied for the statistical analysis, to verify the interaction between task moment (i.e., 2 s before and 2 s after ball's fall) and electrode (i.e., frontal, central and temporal regions). The first analysis compared electrodes placed over the somatosensory cortex. Central sites (C3–C4) were compared with temporal regions (T3–T4). The results showed a main effect for moment and position. The second analysis was focused over the premotor cortex, which was represented by the electrodes placed on the frontal sites (F3–F4 versus F7–F8), and a main effect was observed for position. Taken together, these results show a pattern of asymmetry in the somatosensory cortex, associated with a preparatory mechanism when individuals have to catch an object during free fall. With respect to task moment, after the ball's fall, the asymmetry was reduced. Moreover, the difference in asymmetry between the observed regions were related to a supposed specialization of areas (i.e., temporal and central). The temporal region was associated with cognitive processes involved in the motor action (i.e., explicit knowledge). On the other hand, the central sites were related to the motor control mechanisms per se (i.e., implicit knowledge). The premotor cortex, represented by two frontal regions (i.e., F3–F4 versus F7–F8), showed a decrease on neural activity in the contralateral hemisphere (i.e., to the right hand). This result is in agreement with other experiments suggesting a participation of the frontal cortex in the planning of the apprehension task. This sensorimotor paradigm may contribute to the repertoire of tasks used to study clinical conditions such as depression, alzheimer and Parkinson diseases.     

Activation of the Human Premotor Cortex During Motor Preparation in Visuomotor Tasks

Functional brain mapping studies in humans suggest that both motor and premotor cortices interact during movement execution. The aim of this study was to investigate whether the premotor cortex also participates in motor planning. We measured movement-related cerebral fields (MRCFs) using magnetoencephalography from the left hemisphere of 12 healthy right-handed participants during two simple visuomotor tasks cued by two visual stimuli S1 and S2. Participants performed a unilateral task in which they always extended the right index finger after S2 presentation regardless of the color of S1 and a bilateral task in which they extended either the right or left index finger after S2 presentation according to the color of S1. Significantly higher MRCF activity was observed during the 500 ms S1 to S2 interval in the bilateral task than in the unilateral task. In the bilateral task trials, the latency of the peak MRCF during the S1 to S2 interval was 343.9 ± 73.5 ms after S1 presentation and that of the peak of movement-evoked field 1 was 33.4 ± 3.9 ms after movement onset in the bilateral task. Equivalent current dipoles at the peak MRCF were significantly medial (9.2 ± 12.1 mm) and anterior (19.8 ± 6.9 mm) to the reference location in the somatosensory cortex (area 3b) established by median nerve stimulation. This location corresponds to the dorsal premotor cortex. These findings suggest that activation of the premotor cortex observed during the interstimulus interval may represent a neurophysiological marker of response selection.     

Correspondence between brain ERP and behavioral asymmetries in a dichotic complex tone test

Electrophysiologic correlates of perceptual asymmetry for dichotic pitch discrimination were investigated in 20 normal subjects. Brain event-related potentials (ERPs) elicited by dichotic pairs and binaural probe tones in the Complex Tone Test (Sidtis, 1981) were recorded from homologous scalp locations over left and right hemispheres (F3, F4; C3, C4; P3, P4; O1, O2). Baseline-to-peak amplitudes were measured for N100, P200, and a late positive complex consisting of P350, P550, and slow wave. A left ear advantage (LEA) was evident in 70% of the subjects, and hemispheric asymmetries related to this behavioral asymmetry were found for P350 and P550 amplitudes to probe stimuli. Subjects with a strong LEA had greater amplitudes over the right hemisphere than the left, whereas subjects with little or no LEA showed a nonsignificant trend toward the opposite hemispheric asymmetry. Hemispheric asymmetry of these late ERPs at parietal and occipital sites was highly correlated with behavioral asymmetry. These findings suggest the utility of electrophysiological measures in assessing hemispheric asymmetries for processing complex pitch information.     

Automatic processing of valence differences in emotionally negative stimuli: Evidence from an ERP study

The present study investigated the influence of attention on the human sensitivity to valence differences in emotionally negative stimuli. Event-related potentials were recorded for unattended highly negative (EN), moderately negative (MN) and neutral pictures in Experiment 1 which engaged subjects in an auditory discrimination task; and for EN, MN and neutral pictures in Experiment 2 that required visual classification of pictures. Results of both experiments displayed increased negative deflections during EN than during MN and neutral conditions at 150–250, 250–350, and 350–450 ms intervals post-stimulus. Moreover, MN stimuli elicited larger negativity than did neutral stimuli during 250–350 ms interval in either experiment. This developed our understanding of the human sensitivity to valence differences in negative stimuli, by revealing that the brain sensitivity to the valence strength of negative stimuli exists stably, unaffected by attention access to some extent.     

Hemispheric differences in the relationship between corticomotor excitability changes following a fine-motor task and motor learning

Motor performance induces a postexercise increase in corticomotor excitability that may be associated with motor learning. We investigated whether there are hemispheric differences in the extent and/or time course of changes in corticomotor excitability following a manipulation task (Purdue pegboard) and their relationship with motor performance. Single- and paired-pulse (3 ms) transcranial magnetic stimulation (TMS) was used to assess task-induced facilitation of the muscle evoked potential (MEP) and intracortical inhibition (ICI) for three intrinsic hand muscles acting on digits 1, 2, and 5. Fifteen right-handed subjects performed three 30-s pegboard trials with left or right hand in separate sessions. TMS was applied to contralateral motor cortex before and after performance. Number of pegs placed was higher with the right hand, and performance improved (motor learning) with both hands over the three trials. MEP facilitation following performance was short-lasting (<15 min), selective for muscles engaged in gripping the pegs, and of similar magnitude in left and right hands. ICI was reduced immediately following performance with the right hand, but not the left. The extent of MEP facilitation was positively correlated with motor learning for the right hand only. We conclude that the pegboard task induces a selective, short-lasting change in excitability of corticospinal neurons controlling intrinsic hand muscles engaged in the task. Only left hemisphere changes were related to motor learning. This asymmetry may reflect different behavioral strategies for performance improvement with left and right upper limb in this task or hemispheric differences in the control of skilled hand movements.     

TMS stimulus–response asymmetry in left- and right-handed individuals

There have been inconsistencies in the literature regarding asymmetrical neural control and results of experiments using TMS techniques. Therefore, the aim of this study was to further our understanding of the neural relationships that may underlie performance asymmetry with respect to the distal muscles of the hand using a TMS stimulus–response curve technique. Twenty-four male subjects (12 right handed, 12 left handed) participated in a TMS stimulus–response (S–R) curve trial. Focal TMS was applied over the motor cortex to find the optimal position for the first dorsal interossei muscle and to determine rest threshold (RTh). Seven TMS intensities ranging from 90 to 150 % of RTh were delivered in 10 % increments. One single TMS block consisted of 16 stimuli at each intensity. Peak-to-peak amplitudes were measured and the S–R curve generated. In right-handed subjects, the mean difference in slopes between the right and left hand was ?0.011 ± 0.03, while the mean difference between hands in left-handed subjects was ?0.049 ± 0.08. Left-handed normalized data in right handers displayed a mean of 1.616 ± 1.019 (two-tailed t test p < 0.05). The left-handed group showed a significant change in the normalized slope as indicated by a mean of 1.693 ± 0.149 (two-tailed t test p < 0.00006). The results found in this study reinforce previous work which suggests that there is an asymmetry in neural drive that exists in both left- and right-handed individuals. However, the results show that the non-dominant motor hemisphere displays a greater amount of excitability than the dominant, which goes against the conventional dogma. This asymmetry indicates that the non-dominant hemisphere may have a higher level of excitation or a lower level of inhibition for both groups of participants.     

Motor sequence learning with the nondominant left hand

Whereas the human right hemisphere is active during execution of contralateral hand movements, the left hemisphere is engaged for both contra- and ipsilateral movements, at least for right-handed subjects. Whether this asymmetry is also found during motor learning remains unknown. Implicit sequence learning by the nondominant left hand was examined with the serial reaction time (SRT) task during functional brain imaging. As learning progressed, increases in brain activity were observed in left lateral premotor cortex (PMC) and bilaterally in supplementary motor areas (SMA), with the increase significantly greater in the left hemisphere. The left SMA site was similar to one previously identified with right-hand learning, suggesting that this region is critical for representing a sequence independent of effector. Learning with the left hand also recruited a widespread set of temporal and frontal regions, suggesting that motor skill learning with the nondominant hand develops within both cognitive and motor-related functional networks. After skill acquisition, subjects performed the SRT task with their right hands, and sequence transfer was tested with the original and a mirror-ordered sequence. With the original sequence, the stimulus sequence and series of response locations remained unchanged, but the finger movements were different. With the mirror-ordered sequence, the response sequence involved finger movements homologous to those used during training. Performance of the original and mirror sequence by the right hand was significantly better than with random stimuli. Mirror transformation of the sequence by the right hand was associated with a marked increase in regional activity in the left motor cortex, consistent with a role for sequential transformation at this level of the motor output pathway.     

Expectation decreases brain susceptibility to fearful stimuli: ERP evidence from a modified emotion evaluation task

Expectation decreased the susceptibility to fearful stimuli in prior studies using distracting tasks. The present study tests whether expectation remains effective in decreasing this susceptibility, when subjects focus attention on emotional properties. Event-related potentials were recorded for fearful and neutral faces, while subjects performed a modified emotion evaluation task during unpredictable and predictable conditions. Behavioral data showed faster response latencies during predictable versus unpredictable conditions. ERP data showed prolonged peak latencies in N1 (80–130 ms) and larger amplitudes in P2 (130–180 ms) and N200-300 components, for unpredictable fearful versus neutral faces. Conversely, all these components showed similar responses to predictable fearful and neutral faces. Source analysis suggested that medial temporal lobe mediated ERPs elicited by unpredictable fearful faces, while ventromedial prefrontal cortex mediated those elicited by predictable fearful faces, in the 130–180 ms interval. Thus, we propose emotional expectation as a cognitive regulation strategy that reliably dampens human susceptibility to fearful stimuli.     

Integration of cortical areas during performance of a catching ball task

The study aimed to elucidate electrophysiological and cortical mechanisms involved in anticipatory actions when healthy subjects had to catch balls in free drop; specifically through quantitative electroencephalography (qEEG) alpha absolute power changes. Our hypothesis is that during the preparation of motor action (i.e., 2 s before ball’s drop) occurred integration among left medial frontal, left primary somatomotor and left posterior parietal cortices, showing a differentiated activity involving expectation, planning and preparedness. This hypothesis supports a lateralization of motor function. Although we contend that in right-handers the left hemisphere takes on a dominant role for the regulation of motor behavior. The sample was composed of 23 healthy subjects (13 male and 10 female), right handed, with ages varying between 25 and 40 years old (32.5 ± 7.5), absence of mental and physical illness, right handed, and do not make use of any psychoactive or psychotropic substance at the time of the study. The experiment consisted of a task of catching balls in free drop. The three-way ANOVA analysis demonstrated an interaction between moment and position in left medial frontal cortex (F3 electrode), somatomotor cortex (C3 electrode) and posterior parietal cortex (P3 electrode; p < 0.001). Summarizing, through experimental task employed, it was possible to observe integration among frontal, central and parietal regions. This integration appears to be more predominant in expectation, planning and motor preparation. In this way, it established an absolute predominance of this mechanism under the left hemisphere.     

Dyslexics show a deviant lateralization of attentional control: a brain potential study

The present study compared performance and event-related brain potentials between dyslexic subjects and control subjects while they performed a spatial selective attention-shifting task. The subjects received a prestimulus cue on each trial, which indicated whether the subjects should attend to a position to the left of fixation or to the position at the opposite right of fixation. Thereafter a stimulus was presented either at the cued position or at the other position. In this paper we report on the brain activity in the cue-stimulus interval, which is supposed to reflect processes involved in controlling spatial attention shifting. The dyslexics performed much poorer on this task than the control subjects. The ERP-effects of cue direction closely resembled earlier reports, and consisted of an early (onset at about 200 ms) posterior contralateral negativity, a later (onset at about 350 ms) posterior contralateral positivity, and a later (onset at about 350 ms) frontal positivity. Dyslexics and controls differed with respect to the frontal attention effect. Whereas the controls showed this effect almost exclusively over the right hemisphere, the dyslexics showed both left and right hemispheric effects. We propose that this might support the idea that in dyslexia the development of interhemispheric asymmetry is disregulated.