Hemispheric asymmetry of the auditory evoked N100m response in relation to the crossing point between the central sulcus and Sylvian fissure

The positions of the bilateral N100m sources of the auditory evoked magnetic fields (AEFs) were measured in relation to the central sulcus (CS) using an MRI-linked whole head magnetoencephalography system in 20 right-handed normal male subjects. The location of the N20m source of the median nerve-stimulated somatosensory evoked magnetic fields (SEFs), in the left hemisphere was 3.9±5.4 mm (mean±SD) posterior to that in the right hemisphere (P<0.005). The crossing point (CP) between the CS and Sylvian fissure in the left hemisphere was 4.3±4.8 mm posterior to that in the right hemisphere (P<0.001). The N100m sources were posterior to the CP in both hemispheres. The left hemispheric N100m source was 9.4±6.4 mm posterior to that on the right (P<0.0001) in absolute position. The relative distance between CP and the N100m source was 22.7±8.5 mm in the left hemisphere and 17.7±5.3 mm in the right hemisphere (P<0.01). Comparison of positions of the AEF sources and the CS as defined by the SEF demonstrated functional asymmetry of the human temporal lobe and possible source extension of the AEF-N100m beyond the Heschl gyrus over the planum temporale.     

Subcortical and limbic structures and <Emphasis Type="Italic">P</Emphasis>300 in schizophrenia

The correlations between the volumes of the caudate nucleus, putamen, amygdala, and hippocampus, on the one hand, and the P300 amplitude and latency of auditory evoked potentials, on the other hand, were studied in 14 schizophrenics. Significant positive correlations were found between the parameters of the late cognitive potential P300 (predominantly in the left hemisphere) and the caudate nucleus and putamen volumes, as well as between the right amygdala volume and the P300 amplitude in the left temporal region. The results testify again to the role of changes in the left hemisphere in the pathogenesis of schizophrenia and pose the question of the structural and functional features of left frontosubcortical communications.Translated from Fiziologiya Cheloveka, Vol. 31, No. 2, 2005, pp. 18–23.Original Russian Text Copyright © 2005 by Voronkova, Lebedeva, Gubsky, Orlova, Voscresenskaya, Kupriyanov, Anisimov, Solokhina.     

Dipole source analysis of auditory P300 response in depressive and anxiety disorders

This paper is to study auditory event-related potential P300 in patients with anxiety and depressive disorders using dipole source analysis. Auditory P300 using 2-stimulus oddball paradigm was collected from 35 patients with anxiety disorder, 32 patients with depressive disorder, and 30 healthy controls. P300 dipole sources and peak amplitude of dipole activities were analyzed. The source analysis resulted in a 4-dipole configuration, where temporal dipoles displayed greater P300 amplitude than that of frontal dipoles. In addition, a right-greater-than-left hemispheric asymmetry of dipole magnitude was found in patients with anxiety disorder, whereas a left-greater-than-right hemispheric asymmetry of dipole magnitude was observed in depressed patients. Results indicated that the asymmetry was more prominent over the temporal dipole than that of frontal dipoles in patients. Patients with anxiety disorder may increase their efforts to enhance temporal dipole activity to compensate for a deficit in frontal cortex processing, while depressed patients show dominating reduction of right temporal activity. The opposite nature of results observed with hemispheric asymmetry in depressive and anxiety disorders could serve to be valuable information for psychiatric studies.     

The AEP T-complex to synthesised musical tones: left-right asymmetry in relation to handedness and hemisphere dominance

Auditory evoked potentials were recorded to onset and offset of synthesised instrumental tones in 40 normal subjects, 20 right-handed for writing and 20 left-handed. The majority of both groups showed a T-complex which was larger at the right temporal electrode (T4) than the left (T3). In the T4-T3 difference waveforms, the mean potential between latencies of 130 and 165 ms was negative in all right-handed subjects except two for whom the waveforms were marginally positive-going. Amongst the left-handers, however, this converse asymmetry was seen in 7 subjects, 5 of them more than 2 standard deviations from the mean of the right-handed group. The degree of asymmetry was not significantly correlated with the degree of left-handedness according to the Edinburgh Handedness Inventory. Asymmetry of the T-complex to instrumental tones appears to reflect the lateralisation of auditory `musical' processing in the temporal cortex, confirming evidence from other sources including PET that this is predominantly right-sided in the majority of individuals. The proportion of left-handers showing the converse laterality is roughly in accordance with those likely to be right-hemisphere-dominant for language. If linguistic and `musical' processes are consistently located in opposite hemispheres, AEPs to complex tones may prove a useful tool in establishing functional lateralisation.     

Functional Changes in the Human Auditory Cortex in Ageing

Hearing loss, presbycusis, is one of the most common sensory declines in the ageing population. Presbycusis is characterised by a deterioration in the processing of temporal sound features as well as a decline in speech perception, thus indicating a possible central component. With the aim to explore the central component of presbycusis, we studied the function of the auditory cortex by functional MRI in two groups of elderly subjects (>65 years) and compared the results with young subjects (<lt;30 years). The elderly group with expressed presbycusis (EP) differed from the elderly group with mild presbycusis (MP) in hearing thresholds measured by pure tone audiometry, presence and amplitudes of transient otoacoustic emissions (TEOAE) and distortion-product oto-acoustic emissions (DPOAE), as well as in speech-understanding under noisy conditions. Acoustically evoked activity (pink noise centered around 350 Hz, 700 Hz, 1.5 kHz, 3 kHz, 8 kHz), recorded by BOLD fMRI from an area centered on Heschl’s gyrus, was used to determine age-related changes at the level of the auditory cortex. The fMRI showed only minimal activation in response to the 8 kHz stimulation, despite the fact that all subjects heard the stimulus. Both elderly groups showed greater activation in response to acoustical stimuli in the temporal lobes in comparison with young subjects. In addition, activation in the right temporal lobe was more expressed than in the left temporal lobe in both elderly groups, whereas in the young control subjects (YC) leftward lateralization was present. No statistically significant differences in activation of the auditory cortex were found between the MP and EP groups. The greater extent of cortical activation in elderly subjects in comparison with young subjects, with an asymmetry towards the right side, may serve as a compensatory mechanism for the impaired processing of auditory information appearing as a consequence of ageing.     

A topographical ERP study of healthy premature 5 year old children in the auditory and visual modalities

The aim of this research is to study the impact of extreme prematurity on the cognitive development of the child as assessed at age 5 years 9 months. Our samples include 15 healthy prematures born between 25 and 28 weeks of gestational age carefully matched with 15 full-term controls. In the first experiment, two different auditory stimuli were presented to the subjects who listened passively without instruction. The second experiment consisted of a standard visual oddball task in which the subjects were instructed to `catch' two different animals, by pushing a left or right button for a moose (n=120) or a raccoon (n=40), respectively. In the auditory task, 3 ERP peaks were analyzed (frontal N100 and P3a, temporal P2). All premature children demonstrated normal early frontal N100 and temporal P2 responses. The group differences were apparent in the late positivity (P3a) where controls showed a larger amplitude to the rare tones applied evenly to both ears. In contrast, the prematures did not show sensitivity to rare tones but showed a larger P3a upon left ear stimulation, when compared to the right. Also, the ERPs to the visual oddball task showed normal early positivities (P250–300) in the premature group. Once again, deviations from the normal were evident in late waves. The ERPs recorded from prematures showed a more diffuse topography especially between 500 and 600 ms post-stimulus and around the posterior area (P550). The succeeding negativity (SW) was not altered in the premature group. The ERP data suggest that premature children, even without clinically apparent problems, convey specific ERP singularity when engaged in a task that involves complex processing.     

The Characteristic and Changes of the Event-Related Potentials (ERP) and Brain Topographic Maps before and after Treatment with rTMS in Subjective Tinnitus Patients

Objectives

To compare the event-related potentials (ERPs) and brain topographic maps characteristic and change in normal controls and subjective tinnitus patients before and after repetitive transcranial magnetic stimulation (rTMS) treatment.

Methods and Participants

The ERPs and brain topographic maps elicited by target stimulus were compared before and after 1-week treatment with rTMS in 20 subjective tinnitus patients and 16 healthy controls.

Results

Before rTMS, target stimulus elicited a larger N1 component than the standard stimuli (repeating sounds)in control group but not in tinnitus patients. Instead, the tinnitus group pre-treatment exhibited larger amplitude of N1 in response to standard stimuli than to deviant stimuli. Furthermore tinnitus patients had smaller mismatch negativity (MMN) and late discriminative negativity (LDN)component at Fz compared with the control group. After rTMS treatment, tinnitus patients showed increased N1 response to deviant stimuli and larger MMN and LDN compared with pre-treatment. The topographic maps for the tinnitus group before rTMS -treatment demonstrated global asymmetry between the left and right cerebral hemispheres with more negative activities in left side and more positive activities in right side. In contrast, the brain topographic maps for patients after rTMS-treatment and controls seem roughly symmetrical. The ERP amplitudes and brain topographic maps in post-treatment patient group showed no significant difference with those in controls.

Conclusions

The characterical changes in ERP and brain topographic maps in tinnitus patients maybe related with the electrophysiological mechanism of tinnitus induction and development. It can be used as an objective biomarker for the evaluation of auditory central in subjective tinnitus patients. These findings support the notion that rTMS treatment in tinnitus patients may exert a beneficial effect.     

The Right Planum Temporale Is Involved in Stimulus-Driven,Auditory Attention – Evidence from Transcranial Magnetic Stimulation

It is well known that the planum temporale (PT) area in the posterior temporal lobe carries out spectro-temporal analysis of auditory stimuli, which is crucial for speech, for example. There are suggestions that the PT is also involved in auditory attention, specifically in the discrimination and selection of stimuli from the left and right ear. However, direct evidence is missing so far. To examine the role of the PT in auditory attention we asked fourteen participants to complete the Bergen Dichotic Listening Test. In this test two different consonant-vowel syllables (e.g., “ba” and “da”) are presented simultaneously, one to each ear, and participants are asked to verbally report the syllable they heard best or most clearly. Thus attentional selection of a syllable is stimulus-driven. Each participant completed the test three times: after their left and right PT (located with anatomical brain scans) had been stimulated with repetitive transcranial magnetic stimulation (rTMS), which transiently interferes with normal brain functioning in the stimulated sites, and after sham stimulation, where participants were led to believe they had been stimulated but no rTMS was applied (control). After sham stimulation the typical right ear advantage emerged, that is, participants reported relatively more right than left ear syllables, reflecting a left-hemispheric dominance for language. rTMS over the right but not left PT significantly reduced the right ear advantage. This was the result of participants reporting more left and fewer right ear syllables after right PT stimulation, suggesting there was a leftward shift in stimulus selection. Taken together, our findings point to a new function of the PT in addition to auditory perception: particularly the right PT is involved in stimulus selection and (stimulus-driven), auditory attention.     

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.     

Temporal lobe volume in disorders with psychotic features

Since early neuropathological findings, temporal lobe has been related to the pathophysiology of some disorders with psychotic features. The aim of this study was to compare temporal lobe volumes and asymmetry differences in patients with schizophrenia, schizoaffective and bipolar disorders, disorders that cover the whole psychotic spectrum. Temporal lobe volumes were estimated using high resolution magnetic resonance imaging in 60 subjects, 15 subjects in each patient and one healthy volunteer (control) group. There are no statistically significant differences in temporal lobe volumes among patient and control groups. Comparison of left and right temporal lobes shows that left temporal lobes are smaller than right temporal lobes, however this difference reaches statistical significance only in groups of patients with schizoaffective and bipolar disorders. Overall temporal lobe volume may be less informative in respect to neuropathology of disorders with psychotic features than volumes of specific temporal lobe structures, in particular medial temporal lobe structures.     

Hemispheric interaction in man during perception of visual stimuli]

Averaged evoked potentials (AEP) to verbal (letters) and nonverbal (random shapes) stimuli exposed in the left and right visual fields were registered in healthy subjects with normal vision. Analysis of the later AEP latencies pointed to asymmetry in the temporal parameters of the interhemispheric interaction. The late AEP latency is shorter in the right hemisphere than in the left hemisphere. The difference is more pronounced in responses to nonverbal stimuli. The earlier development of the evoked potential in the right hemisphere (or the later one in the left hemisphere) accounts for the interhemispheric difference in the temporal parameters of the late AEP components. Comparison of the latency of the component P300 to verbal and nonverbal stimuli presented in the ipsilateral or the contralateral visual fields reveals a transfer of the results of the cortical processing of visual information in the course of interhemispheric interaction.     

带状疱疹后遗神经痛患者脑基础活动改变的功能核磁共振研究

带状疱疹后遗神经痛(postherpetic neuralgia,PHN)是临床上一种慢性顽固性神经病理性疼痛,然而,对于其潜在的中枢机制还知之甚少.为了进一步探讨带状疱疹后遗神经痛患者的相关脑区活动,利用功能核磁共振成像低频振幅振荡(ALFF)技术观察带状疱疹后遗神经痛患者的基础脑区活动.8名带状疱疹后遗神经痛患者与8名性别、年龄相匹配的健康者行静息态功能磁共振(f MRI)成像扫描,用SPM8中的多重回归分析,在控制被试年龄、性别、教育年限的影响下,将每个体素的ALFF值同每个被试的病程、视觉模拟评分(visual analog scale,VAS)进行相关分析.与健康志愿者相比,PHN组与VAS评分相关的ALFF值增高的脑区有:右侧小脑后叶、前额叶背外侧区域(BA11/46/47)、右侧顶叶(BA40)、右侧舌回(BA17/18/19);与VAS评分相关的ALFF值降低的脑区有:右侧颞中回(BA21)、左侧舌回(BA17/18)、右侧小脑前叶、左侧后扣带回(BA30/19)和右侧中央前回(BA3/4/6);PHN组与病程相关的ALFF值增高的脑区有:右侧小脑后叶、前额叶背外侧区域(BA9/10/11/47)、左侧颞上回(BA38)、右侧顶叶和右侧舌回(BA17/18/19);与病程相关ALFF值降低的脑区有:左侧海马旁回(BA28)、右侧小脑前叶、左侧扣带回(BA24)、右侧颞上回(BA13)、左侧中央前回和右侧顶下小叶(BA39/40).研究结果提示,涉及疼痛的情绪、警觉行为、注意的脑区在带状疱疹后遗痛慢性疼痛的产生和维持中发挥重要作用.     

Human middle-latency auditory evoked potentials: vertex and temporal components

We recorded middle-latency (20–70 msec) auditory evoked potentials (MLAEPs) to monaural and binaural clicks in 30 normal adults (ages 20–49 years) at 32 scalp locations all referred to a balanced non-cephalic reference. Our goal was to define the MLAEP components that were present at comparable latencies and comparable locations across the subject population. Group and individual data were evaluated both as topographic maps and as MLAEPs at selected electrode locations.Three major components occurred between 20 and 70 msec, two well-known peaks centered at the vertex, and one previously undefined peak focused over the posterior temporal area. Pa is a 29 msec positive peak centered at the vertex and present with both monaural and binaural stimulation, Pb is a 53 msec positive peak also centered at the vertex but seen consistently only with binaural and right ear stimulation. TP41 is a 41 msec positive peak focused over both temporal areas. TP41 has not been identified in previous MLAEP studies that concentrated on central scalp locations and/or used active reference electrode sites such as ears or mastoids.Available topographic, intracranial, pharmacologic, and lesion studies indicate that Pa, Pb and TP41 are of neural origin. Whether Pa and/or Pb are produced in Heschl's gyrus, primary auditory cortex, remains unclear. TP41 is probably produced by auditory cortex on the posterior lateral surface of the temporal lobe. It should prove of considerable value in experimental and clinical evaluation of higher level auditory function in particular and of cortical function in general.     

Temporal characteristics of triggering dipole sources of the auditory <Emphasis Type="Italic">P</Emphasis>300 in tasks varying in complexity

The localization and the order of triggering of the equivalent dipole sources of the auditory evoked potential (AEP) P300 component were analyzed in healthy subjects performing tasks that required different degrees of concentration. The AEP P300 was isolated and analyzed in 12 subjects aged 18–23 years. The P300 was recorded via 19 channels in mono- and bimodal tasks using two- and three-stimulus methods of the oddball paradigm. Analysis of the equivalent dipole sources of the P300 component upon hearing sounds showed simultaneous activity of dipole sources located in the temporal areas of both hemispheres and in the right frontal area, as well as in the brainstem, irrespective of the task’s complexity. The counting of sounds in the monomodal task was accompanied by consecutive involvement of the left temporal, right temporal, and left frontal sources in the P300 generation; in the bimodal task, these were, respectively, the left parietal, right temporal and hippocampal, and left frontal sources.     

Arcuate fasciculus abnormalities and their relationship with psychotic symptoms in schizophrenia

Disruption of fronto-temporal connections involving the arcuate fasciculus (AF) may underlie language processing anomalies and psychotic features such as auditory hallucinations in schizophrenia. No study to date has specifically investigated abnormalities of white matter integrity at particular loci along the AF as well as its regional lateralization in schizophrenia. We examined white matter changes (fractional anisotropy (FA), axial diffusivity (AD), asymmetry indices) along the whole extent of the AF and their relationship with psychotic symptoms in 32 males with schizophrenia and 44 healthy males. Large deformation diffeomorphic metric mapping and Fiber Assignment Continuous Tracking were employed to characterize FA and AD along the geometric curve of the AF. Our results showed that patients with schizophrenia had lower FA in the frontal aspects of the left AF compared with healthy controls. Greater left FA and AD lateralization in the temporal segment of AF were associated with more severe positive psychotic symptoms such as delusions and hallucinations in patients with schizophrenia. Disruption of white matter integrity of the left frontal AF and accentuation of normal left greater than right asymmetry of FA/AD in the temporal AF further support the notion of aberrant fronto-temporal connectivity in schizophrenia. AF pathology can affect corollary discharge of neural signals from frontal speech/motor initiation areas to suppress activity of auditory cortex that may influence psychotic phenomena such as auditory hallucinations and facilitate elaboration of delusional content.     

Hemispheric asymmetry of visual evoked potentials during human recognition of facial emotional expressions

Visual evoked potentials (VEP) in standard 16 EEG derivations were recorded in 26 young men and 20 women during recognition of facial emotional expressions and geometric figures. The stimuli were presented on a computer screen in the center of the visual field or randomly in the right or left vision hemifields. Peak VEP latency and mean amplitude in 50-ms epochs were measured; spatiotemporal VEP dynamics was analyzed in a series of topographic maps. The right hemisphere was shown to be more important in processing emotional faces. The character of the asymmetry was dynamic: at earlier stages of emotion processing the electrical activity was higher in the right inferior temporal region compared to the left symmetrical site. Later on the activity was higher in the right frontal and central areas. The dynamic mapping of "face-selective" component N180 of VEPs revealed the onset of activation over the right frontal areas that was followed by the fast activation of symmetrical left zones. Notably, this dynamics didn't correlate with the hemifield of stimuli exposition. The degree of asymmetry was lower during presentation of figures, especially in the inferior temporal and frontal regions. The prominent asymmetry of information processes in the inferior temporal and frontal areas was suggested to be specific for recognition of facial expression.     

Hemispheric dominance of cortical activity evoked by focal electrogustatory stimuli.

Functional magnetic resonance imaging was used to observe cortical hemodynamic responses to electric taste stimuli applied separately to the right and left sides of the tongue tip. In 11 right-handed normal adults activation occurred primarily in the insular cortex, superior temporal lobe, inferior frontal lobe, including premotor regions, and in inferior parts of the postcentral gyrus. Unexpectedly, the location and laterality of activation were largely identical regardless of the side of the tongue stimulated. Activation in the superior insula, the presumed location of primary gustatory cortex, was predominantly, but not exclusively, in the right hemisphere, whereas central (more inferior) insular activations were more evenly bilateral. Right hemispheric dominance of activation also occurred in premotor regions (Brodmann areas 6 and 44), whereas left hemispheric dominance occurred only in the superior temporal cortex (Brodmann areas 22/42). The electric taste-evoked hemodynamic response pattern was more consistent with activation of the gustatory system than activation of somatosensory systems. The results suggest that the sites for cortical processing of electric taste information are dependent on hemispheric specialization.     

Endogenous cortical rhythms determine cerebral specialization for speech perception and production

Across multiple timescales, acoustic regularities of speech match rhythmic properties of both the auditory and motor systems. Syllabic rate corresponds to natural jaw-associated oscillatory rhythms, and phonemic length could reflect endogenous oscillatory auditory cortical properties. Hemispheric lateralization for speech could result from an asymmetry of cortical tuning, with left and right auditory areas differentially sensitive to spectro-temporal features of speech. Using simultaneous electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) recordings from humans, we show that spontaneous EEG power variations within the gamma range (phonemic rate) correlate best with left auditory cortical synaptic activity, while fluctuations within the theta range correlate best with that in the right. Power fluctuations in both ranges correlate with activity in the mouth premotor region, indicating coupling between temporal properties of speech perception and production. These data show that endogenous cortical rhythms provide temporal and spatial constraints on the neuronal mechanisms underlying speech perception and production.     

Hemispheric asymmetries in cortical electrical activity during sleep. I

The hypothesis of a predominance of the right hemisphere in stage REM as compared to NREM has been tested through a spectral analysis of the EEG recorded from left (T3) and right (T4) temporal sites in 5 young healthy right-handed male subjects. Variations in the asymmetry coefficient R - L/R + L in different sleep stages have been analyzed by one way ANOVAs and Sheffé's tests. The hypothesis of a progressive increase in left hemisphere activity throughout different REM cycles as one approaches final awakenings have been investigated by comparing variations in the asymmetry coefficient for epochs of REM and stage 2 NREM sampled in different phases of the REM cycle. EEG results do not support either the hypothesized stage dependent or cycle dependent variation in EEG activity during sleep. We question whether variations in EEG amplitude and synchronization can be used as indices of hemispheric asymmetries during sleep.     

Right or left ear reference changes the voltage of frontal and parietal somatosensory evoked potentials

Short-latency cortical somatosensory evoked potentials (SEPs) to left median nerve stimulation were recorded with either the left or right earlobe as reference. With a right earlobe reference the voltage of the parietal N20 and P27 was reduced while the voltage of the frontal P20 and N30 was enhanced. The effects were consistent, but their size varied with the SEP component considered and also among the subjects. Analysis of SEPs at different scalp sites and at either earlobe suggested that the ear contralateral to the side stimulated picked up transient potential differences, depending a.o. on side asymmetry and geometry of the neural generators as disclosed in topographic mapping. For example, the right ear potential can be shifted negatively by the right N20 field evoked by left median nerve stimulation. The changes involve the absolute potential values, but not the time features of the gradients of potential fields. Scalp current density (SCD) maps are not affected. The results are pertinent for current discussions about which reference to use and document the practical recommendation of recording short-latency cortical SEPs with a reference at the ear ipsilateral (not contralateral) to the side of stimulation.