RESUMO
OBJECTIVE: Patients with mesial temporal lobe epilepsy (mTLE) often exhibit central auditory processing (CAP) dysfunction. Monaural 40-Hz auditory steady-state magnetic responses (ASSRs) were recorded to explore the pathophysiology of mTLE. METHODS: Eighteen left mTLE patients, 11 right mTLE patients and 16 healthy controls (HCs) were examined. Monaural clicks were presented at a rate of 40â¯Hz. Phase-locking factor (PLF) and power values were analyzed within bilateral Heschl's gyri. RESULTS: Monaural 40-Hz ASSR demonstrated temporal frequency dynamics in both PLF and power data. Symmetrical hemispheric contralaterality was revealed in HCs. However, predominant contralaterality was absent in mTLE patients. Specifically, right mTLE patients exhibited a lack of contralaterality in response to left ear but not right ear stimulation, and vice versa in left mTLE patients. CONCLUSION: This is the first study to use monaural 40-Hz ASSR with unilateral mTLE patients to clarify the relationship between CAP and epileptic focus. CAP dysfunction was characterized by a lack of contralaterality corresponding to epileptic focus. SIGNIFICANCE: Monaural 40-Hz ASSR can provide useful information for localizing epileptic focus in mTLE patients.
Assuntos
Epilepsia do Lobo Temporal/fisiopatologia , Magnetoencefalografia , Lobo Temporal/fisiopatologia , Estimulação Acústica , Adolescente , Adulto , Idoso , Epilepsia do Lobo Temporal/diagnóstico por imagem , Potenciais Evocados Auditivos/fisiologia , Feminino , Lateralidade Funcional/fisiologia , Humanos , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Lobo Temporal/diagnóstico por imagem , Adulto JovemRESUMO
OBJECTIVE: Our previous study of monaural auditory evoked magnetic fields (AEFs) demonstrated that hippocampal sclerosis significantly modulated auditory processing in patients with mesial temporal lobe epilepsy (mTLE). However, the small sample size (nâ¯=â¯17) and focus on the M100 response were insufficient to elucidate the lateralization of the epileptic focus. Therefore, we increased the number of patients with mTLE (nâ¯=â¯39) to examine whether neural synchronization induced by monaural pure tone stimulation provides useful diagnostic information about epileptic foci in patients with unilateral mTLE. METHODS: Twenty-five patients with left mTLE, 14 patients with right mTLE, and 32 healthy controls (HCs) were recruited. Auditory stimuli of 500-Hz tone burst were monaurally presented to subjects. The AEF data were analyzed with source estimation of M100 responses in bilateral auditory cortices (ACs). Neural synchronization within ACs and between ACs was evaluated with phase-locking factor (PLF) and phase-locking value (PLV), respectively. Linear discriminant analysis was performed for diagnosis and lateralization of epileptic focus. RESULTS: The M100 amplitude revealed that patients with right mTLE exhibited smaller M100 amplitude than patients with left mTLE and HCs. Interestingly, PLF was able to differentiate the groups with mTLE, with decreased PLFs in the alpha band observed in patients with right mTLE compared with those (PLFs) in patients with left mTLE. Right hemispheric predominance was confirmed in both HCs and patients with left mTLE while patients with right mTLE showed a lack of right hemispheric predominance. Functional connectivity between bilateral ACs (PLV) was reduced in both patients with right and left mTLE compared with that of HCs. The accuracy of diagnosis and lateralization was 80%-90%. CONCLUSION: Auditory cortex subnormal function was more pronounced in patients with right mTLE compared with that in patients with left mTLE as well as HCs. Monaural AEFs can be used to reveal the pathophysiology of mTLE. Overall, our results indicate that altered neural synchronization may provide useful information about possible functional deterioration in patients with unilateral mTLE.
Assuntos
Estimulação Acústica , Córtex Auditivo/fisiopatologia , Sincronização Cortical , Epilepsia do Lobo Temporal/fisiopatologia , Potenciais Evocados Auditivos , Adulto , Idoso , Córtex Auditivo/diagnóstico por imagem , Estudos de Casos e Controles , Epilepsia do Lobo Temporal/diagnóstico por imagem , Feminino , Humanos , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-IdadeRESUMO
Time is a fundamental dimension, but millisecond-level judgments sometimes lead to perceptual illusions. We previously introduced a "time-shrinking illusion" using a psychological paradigm that induces auditory temporal assimilation (ATA). In ATA, the duration of two successive intervals (T1 and T2), marked by three auditory stimuli, can be perceived as equal when they are not. Here, we investigate the spatiotemporal profile of human temporal judgments using magnetoencephalography (MEG). Behavioural results showed typical ATA: participants judged T1 and T2 as equal when T2 - T1 ≤ +80 ms. MEG source-localisation analysis demonstrated that regional activity differences between judgment and no-judgment conditions emerged in the temporoparietal junction (TPJ) during T2. This observation in the TPJ may indicate its involvement in the encoding process when T1 ≠ T2. Activation in the inferior frontal gyrus (IFG) was enhanced irrespective of the stimulus patterns when participants engaged in temporal judgment. Furthermore, just after the final marker, activity in the IFG was enhanced specifically for the time-shrinking pattern. This indicates that activity in the IFG is also related to the illusory perception of time-interval equality. Based on these observations, we propose neural signatures for judgments of temporal equality in the human brain.
Assuntos
Percepção Auditiva , Encéfalo/fisiologia , Estimulação Acústica , Análise de Variância , Mapeamento Encefálico , Humanos , Imageamento por Ressonância Magnética , Magnetoencefalografia/métodosRESUMO
In a previous magnetoencephalographic study, we showed both functional and structural reorganization of the right auditory cortex and impaired left auditory cortex function in people who stutter (PWS). In the present work, we reevaluated the same dataset to further investigate how the right and left auditory cortices interact to compensate for stuttering. We evaluated bilateral N100m latencies as well as indices of local and inter-hemispheric phase synchronization of the auditory cortices. The left N100m latency was significantly prolonged relative to the right N100m latency in PWS, while healthy control participants did not show any inter-hemispheric differences in latency. A phase-locking factor (PLF) analysis, which indicates the degree of local phase synchronization, demonstrated enhanced alpha-band synchrony in the right auditory area of PWS. A phase-locking value (PLV) analysis of inter-hemispheric synchronization demonstrated significant elevations in the beta band between the right and left auditory cortices in PWS. In addition, right PLF and PLVs were positively correlated with stuttering frequency in PWS. Taken together, our data suggest that increased right hemispheric local phase synchronization and increased inter-hemispheric phase synchronization are electrophysiological correlates of a compensatory mechanism for impaired left auditory processing in PWS.
Assuntos
Córtex Auditivo/fisiopatologia , Percepção Auditiva , Mapeamento Encefálico/métodos , Sincronização Cortical , Magnetoencefalografia , Gagueira/fisiopatologia , Estimulação Acústica , Adulto , Estudos de Casos e Controles , Potenciais Evocados Auditivos , Lateralidade Funcional , Humanos , Masculino , Tempo de Reação , Gagueira/diagnóstico , Gagueira/psicologia , Fatores de Tempo , Adulto JovemRESUMO
The hippocampus is well known to be involved in memory, as well as in perceptual processing. To date, the electrophysiological process by which unilateral hippocampal lesions, such as hippocampal sclerosis (HS), modulate the auditory processing remains unknown. Auditory-evoked magnetic fields (AEFs) are valuable for evaluating auditory functions, because M100, a major component of AEFs, originates from auditory areas. Therefore, AEFs of mesial temporal lobe epilepsy (mTLE, n=17) with unilateral HS were compared with those of healthy (HC, n=17) and disease controls (n=9), thereby determining whether AEFs were indicative of hippocampal influences on the auditory processing. Monaural tone-burst stimuli were presented for each side, followed by analysis of M100 and a previously less characterized exogenous component (M400: 300-500ms). The frequency of acceptable M100 dipoles was significantly decreased in the HS side. Beam-forming-based source localization analysis also showed decreased activity of the auditory area, which corresponded to the inadequately estimated dipoles. M400 was found to be related to the medial temporal structure on the HS side. Volumetric analysis was also performed, focusing on the auditory-related areas (planum temporale, Heschl's gyrus, and superior temporal gyrus), as well as the hippocampus. M100 amplitudes positively correlated with hippocampal and planum temporale volumes in the HC group, whereas they negatively correlated with Heschl's gyrus volume in the mTLE group. Interestingly, significantly enhanced M400 component was observed in the HS side of the mTLE patients. In addition, the M400 component positively correlated with Heschl's gyrus volume and tended to positively correlate with disease duration. M400 was markedly diminished after hippocampal resection. Although volumetric analysis showed decreased hippocampal volume in the HS side, the planum temporale and Heschl's gyrus, the two major sources of M100, were preserved. These results suggested that HS significantly influenced AEFs. Therefore, we concluded that the hippocampus modulates auditory processing differently under normal conditions and in HS.
Assuntos
Córtex Auditivo/fisiopatologia , Percepção Auditiva/fisiologia , Epilepsia do Lobo Temporal/fisiopatologia , Hipocampo/fisiopatologia , Estimulação Acústica , Adulto , Idoso , Epilepsia do Lobo Temporal/patologia , Epilepsia do Lobo Temporal/cirurgia , Potenciais Evocados Auditivos , Feminino , Lateralidade Funcional/fisiologia , Hipocampo/patologia , Hipocampo/cirurgia , Humanos , Imageamento por Ressonância Magnética , Magnetoencefalografia , Masculino , Pessoa de Meia-Idade , Esclerose , Adulto JovemRESUMO
People who stutter (PWS) can reduce their stuttering rates under masking noise and altered auditory feedback; such a response can be attributed to altered auditory input, which suggests that abnormal speech processing in PWS results from abnormal processing of auditory input. However, the details of this abnormal processing of basic auditory information remain unclear. In order to characterize such abnormalities, we examined the functional and structural changes in the auditory cortices of PWS by using a 306-channel magnetoencephalography system to assess auditory sensory gating (P50m suppression) and tonotopic organization. Additionally, we employed voxel-based morphometry to compare cortical gray matter (GM) volumes on structural MR images. PWS exhibited impaired left auditory sensory gating. The tonotopic organization in the right hemisphere of PWS is expanded compared with that of the controls. Furthermore, PWS showed a significant increase in the GM volume of the right superior temporal gyrus, consistent with the right tonotopic expansion. Accordingly, we suggest that PWS have impaired left auditory sensory gating during basic auditory input processing and that some error signals in the auditory cortex could result in abnormal speech processing. Functional and structural reorganization of the right auditory cortex appears to be a compensatory mechanism for impaired left auditory cortex function in PWS.
Assuntos
Vias Auditivas/fisiopatologia , Gagueira/fisiopatologia , Estimulação Acústica , Adulto , Mapeamento Encefálico , Fenômenos Eletrofisiológicos , Potenciais Evocados Auditivos/fisiologia , Feminino , Lateralidade Funcional/fisiologia , Humanos , Processamento de Imagem Assistida por Computador , Magnetoencefalografia , Masculino , Filtro Sensorial/fisiologia , Adulto JovemRESUMO
The aim of this study was to test the hypothesis that visual mismatch negativity (vMMN) is based on memory trace formation. Special care was taken to distinguish between memory mismatch and rareness effect. Subjects were seated in front of a monitor and asked to listen to a story. The standard sequence block consisted of nine consecutive 24-vane windmill patterns with an 800-ms inter-stimulus interval. The deviant sequence block consisted of one 24-vane pattern with eight six-vane patterns. Inter-train intervals (ITIs) varied among 1, 6, and 12s in the changing ITI experiment, while the deviant stimulus occupied the eighth position in the sequence. In the changing order experiment, the position of the deviant stimulus was varied among the second, fourth and eighth position with a 12-s constant ITI. vMMN was ascertained from the difference in responses to standard and deviant stimulus. vMMN appeared in the occipital region 150-300 ms after stimulus onset. It was significantly modulated by the ITI, and more than four preceding stimuli were needed to reinstate the implicit memory trace. These results suggest that memory-based change detection underlies vMMN. Therefore, vMMN is useful to study visual sensory memory function.
Assuntos
Memória de Curto Prazo/fisiologia , Estimulação Acústica , Adulto , Atenção , Eletroencefalografia , Potenciais Evocados Auditivos/fisiologia , Potenciais Evocados Visuais/fisiologia , Feminino , Humanos , Masculino , Estimulação Luminosa , Desempenho PsicomotorRESUMO
To investigate the relationship between neuronal activity and hemodynamics, we carried out a near-infrared spectroscopy (NIRS) study to measure the regional changes of hemoglobin concentration associated with cortical activation in the human sensorimotor cortex (SMI) to both voluntary and nonvoluntary tasks. We measured the hemodynamic evoked responses to voluntary finger movement and nonvoluntary electrical stimulation applied on the fingers (thumb and ring finger, respectively). Measurements were performed on 6 healthy right-handed volunteers using block paradigms and we analyzed both the spatial/temporal features and the magnitude of the optical signal induced by cerebral activation during these protocols. We constantly observed an increase in the cerebral concentration of oxygenated hemoglobin at the cortical side contralateral to the stimulated side. Our findings are in agreement with results in positron emission tomography (PET), functional magnetic resonance imaging (fMRI) and EEG (Electroencephalogram).
Assuntos
Encéfalo/patologia , Córtex Cerebral/anatomia & histologia , Hemodinâmica , Adulto , Mapeamento Encefálico , Córtex Cerebral/patologia , Circulação Cerebrovascular , Estimulação Elétrica , Terapia por Estimulação Elétrica , Desenho de Equipamento , Feminino , Hemoglobinas/metabolismo , Humanos , Masculino , Oxigênio/metabolismo , Fatores de TempoRESUMO
Aging may alter the motor functions of the basal ganglia and cerebellum; however, no previous neuroimaging study has investigated the effect of aging on the functional connectivity of the motor loops involving these structures. Recently, using fMRI with a parametric approach and structural equation modeling (SEM), we demonstrated a significant functional interaction within the basal ganglia-thalamo-motor (BGTM) loop during self-initiated (SI) finger movement in young normal subjects, whereas cerebro-cerebellar (CC) loop was mainly involved during externally triggered (ET) movement. We applied this method to 12 normal aged subjects (53-72 years old) in order to study the effect of age on BGTM and CC loops. Compared with the functional connectivity seen in young subjects, SEM showed decreased connectivity in BGTM loops during SI task, decreased interaction in the CC loop during ET task, and increased connectivity within motor cortices and between hemispheres during both types of tasks. These results suggest an age-related decline of cortico-subcortical connectivity with increased interactions between motor cortices. Aging effects on SI and ET movements are probably caused by functional alterations within BGTM and CC loops.
Assuntos
Envelhecimento/fisiologia , Gânglios da Base/fisiologia , Cerebelo/fisiologia , Imageamento por Ressonância Magnética , Atividade Motora/fisiologia , Córtex Motor/fisiologia , Rede Nervosa/fisiologia , Adulto , Idoso , Mapeamento Encefálico , Dominância Cerebral/fisiologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Modelos Estatísticos , Tálamo/fisiologiaRESUMO
The importance of the basal ganglia in controlling motor function is well known. However, neuroimaging studies have failed to show either movement-rate dependence or different activation patterns caused by self-initiated (SI) and externally triggered (ET) movements in the basal ganglia-thalamo-motor loop. We herein report the functional magnetic resonance image (fMRI) mapping of sequential left-hand finger movements at five different rates under SI and ET conditions. Significant movement-rate dependence was found in the whole right basal ganglia-thalamo-motor loop only during the SI task. Network analysis also showed strong interactions within this loop during SI movement, whereas interactions were present only from the premotor cortex to the putamen via the sensorimotor cortex during the ET task. Furthermore, psychophysiological interaction analysis confirmed the different modulation between the two tasks in the putamen. fMRI provides evidence that the basal ganglia-thalamo-motor loop plays a key role in controlling the rate of sequential finger movements in SI movement but not in ET movement.