Time course of gamma‐band oscillation associated with face processing in the inferior occipital gyrus and fusiform gyrus: A combined fMRI and MEG study

Debate continues over whether the inferior occipital gyrus (IOG) or the fusiform gyrus (FG) represents the first stage of face processing and what role these brain regions play. We investigated this issue by combining functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) in normal adults. Participants passively observed upright and inverted faces and houses. First, we identified the IOG and FG as face‐specific regions using fMRI. We applied beamforming source reconstruction and time–frequency analysis to MEG source signals to reveal the time course of gamma‐band activations in these regions. The results revealed that the right IOG showed higher gamma‐band activation in response to upright faces than to upright houses at 100 ms from the stimulus onset. Subsequently, the right FG showed greater gamma‐band response to upright faces versus upright houses at around 170 ms. The gamma‐band activation in the right IOG and right FG was larger in response to inverted faces than to upright faces at the later time window. These results suggest that (1) the gamma‐band activities occurs rapidly first in the IOG and next in the FG and (2) the gamma‐band activity in the right IOG at later time stages is involved in configuration processing for faces. Hum Brain Mapp 38:2067–2079, 2017. © 2017 Wiley Periodicals, Inc.     

Inter‐subject alignment of MEG datasets in a common representational space

Pooling neural imaging data across subjects requires aligning recordings from different subjects. In magnetoencephalography (MEG) recordings, sensors across subjects are poorly correlated both because of differences in the exact location of the sensors, and structural and functional differences in the brains. It is possible to achieve alignment by assuming that the same regions of different brains correspond across subjects. However, this relies on both the assumption that brain anatomy and function are well correlated, and the strong assumptions that go into solving the under‐determined inverse problem given the high‐dimensional source space. In this article, we investigated an alternative method that bypasses source‐localization. Instead, it analyzes the sensor recordings themselves and aligns their temporal signatures across subjects. We used a multivariate approach, multiset canonical correlation analysis (M‐CCA), to transform individual subject data to a low‐dimensional common representational space. We evaluated the robustness of this approach over a synthetic dataset, by examining the effect of different factors that add to the noise and individual differences in the data. On an MEG dataset, we demonstrated that M‐CCA performs better than a method that assumes perfect sensor correspondence and a method that applies source localization. Last, we described how the standard M‐CCA algorithm could be further improved with a regularization term that incorporates spatial sensor information. Hum Brain Mapp 38:4287–4301, 2017. © 2017 Wiley Periodicals, Inc.     

MEG biomarker of Alzheimer's disease: Absence of a prefrontal generator during auditory sensory gating

Magnetoencephalography (MEG), a direct measure of neuronal activity, is an underexplored tool in the search for biomarkers of Alzheimer's disease (AD). In this study, we used MEG source estimates of auditory gating generators, nonlinear correlations with neuropsychological results, and multivariate analyses to examine the sensitivity and specificity of gating topology modulation to detect AD. Our results demonstrated the use of MEG localization of a medial prefrontal (mPFC) gating generator as a discrete (binary) detector of AD at the individual level and resulted in recategorizing the participant categories in: (1) controls with mPFC generator localized in response to both the standard and deviant tones; (2) a possible preclinical stage of AD participants (a lower functioning group of controls) in which mPFC activation was localized to the deviant tone only; and (3) symptomatic AD in which mPFC activation was not localized to either the deviant or standard tones. This approach showed a large effect size (0.9) and high accuracy, sensitivity, and specificity (100%) in identifying symptomatic AD patients within a limited research sample. The present results demonstrate high potential of mPFC activation as a noninvasive biomarker of AD pathology during putative preclinical and clinical stages. Hum Brain Mapp 38:5180–5194, 2017. © 2017 Wiley Periodicals, Inc.     

Epileptogenic high-frequency oscillations skip the motor area in children with multilobar drug-resistant epilepsy

Objective

Subtotal hemispherectomy involves the resection of multiple lobes in children with drug-resistant epilepsy, skipping the motor area (MA). We determined epileptogenicity using the occurrence rate (OR) of high-frequency oscillations (HFOs) and the modulation index (MI), demonstrating strength of coupling between HFO and slow wave. We hypothesized that epileptogenicity increased over the multiple lobes but skipped the MA.

脑磁图功能定位在脑功能区肿瘤手术中的应用

目的 评价脑磁图(MEG)功能定位在脑功能区肿瘤手术的应用价值.方法 回顾性分析24例肿瘤位于功能区及其附近病人的临床资料.术前行MEG功能定位,术中结合神经导航系统实时定位肿瘤及功能区,指导肿瘤切除和功能保护.结果 肿瘤位于功能区6例,与功能区部分重叠6例,功能区边缘5例,功能区外1-2cm7例.肿瘤全切除20例,次全切除4例.术后出现一过性神经功能障碍加重6例,持久性功能障碍加重4例.结论 MEG功能定位是术前无创功能定位技术,能够明确肿瘤与功能区位置关系,应用于功能区及附近肿瘤手术,可减少神经功能障碍的发生,提高病人术后生活质量.     

Speech perception in the child brain: cortical timing and its relevance to literacy acquisition

Speech processing skills go through intensive development during mid-childhood, providing basis also for literacy acquisition. The sequence of auditory cortical processing of speech has been characterized in adults, but very little is known about the neural representation of speech sound perception in the developing brain. We used whole-head magnetoencephalography (MEG) to record neural responses to speech and nonspeech sounds in first-graders (7-8-year-old) and compared the activation sequence to that in adults. In children, the general location of neural activity in the superior temporal cortex was similar to that in adults, but in the time domain the sequence of activation was strikingly different. Cortical differentiation between sound types emerged in a prolonged response pattern at about 250 ms after sound onset, in both hemispheres, clearly later than the corresponding effect at about 100 ms in adults that was detected specifically in the left hemisphere. Better reading skills were linked with shorter-lasting neural activation, speaking for interdependence of the maturing neural processes of auditory perception and developing linguistic skills. This study uniquely utilized the potential of MEG in comparing both spatial and temporal characteristics of neural activation between adults and children. Besides depicting the group-typical features in cortical auditory processing, the results revealed marked interindividual variability in children.     

Effects of DBS on auditory and somatosensory processing in Parkinson's disease

Motor symptoms of Parkinson's disease (PD) can be relieved by deep brain stimulation (DBS). The mechanism of action of DBS is largely unclear. Magnetoencephalography (MEG) studies on DBS patients have been unfeasible because of strong magnetic artifacts. An artifact suppression method known as spatiotemporal signal space separation (tSSS) has mainly overcome these difficulties. We wanted to clarify whether tSSS enables noninvasive measurement of the modulation of cortical activity caused by DBS. We have studied auditory and somatosensory‐evoked fields (AEFs and SEFs) of advanced PD patients with bilateral subthalamic nucleus (STN) DBS using MEG. AEFs were elicited by 1‐kHz tones and SEFs by electrical pulses to the median nerve with DBS on and off. Data could be successfully acquired and analyzed from 12 out of 16 measured patients. The motor symptoms were significantly relieved by DBS, which clearly enhanced the ipsilateral auditory N100m responses in the right hemisphere. Contralateral N100m responses and somatosensory P60m responses also had a tendency to increase when bilateral DBS was on. MEG with tSSS offers a novel and powerful tool to investigate DBS modulation of the evoked cortical activity in PD with high temporal and spatial resolution. The results suggest that STN‐DBS modulates auditory processing in advanced PD. Hum Brain Mapp, 2011. © 2010 Wiley‐Liss, Inc.     

Psychopathology and working memory-induced activation of the prefrontal cortex in schizophrenia-like psychosis of epilepsy: Evidence from magnetoencephalography

Aim: The aim of this study was to investigate whether magnetoencephalographic oscillations underlying working memory dysfunction in the dorsolateral prefrontal cortex (DLPFC) are related to psychopathological disturbance in patients with schizophrenia‐like psychosis of epilepsy (SLPE). Methods: Twelve patients with SLPE and 14 non‐psychotic epilepsy controls participated in this study. Magnetoencephalography was recorded while patients performed a visual working memory (WM) task. Psychopathology was assessed using a four‐factor structure of the Brief Psychiatric Rating Scale, and regression analyses were carried out to examine the relative impact of severity of psychopathology on WM‐induced activation of the DLPFC. Results: We found that activation of the WM‐compromising DLPFC, as indicated by increased alpha desynchronization in patients with SLPE compared with their non‐psychotic counterparts, showed a positive linear correlation with disorganization symptom scores. This association remained significant after controlling for confounding factors, including age, task performance, IQ, and duration of psychosis. Conclusion: Our results indicate that abnormal activation in prefrontal areas engaged during working memory may be critical to domains of psychopathology, in particular disorganized thought‐processing in patients with SLPE.     

Importance of the left auditory areas in chord discrimination in music experts as demonstrated by MEG

The brain basis behind musical competence in its various forms is not yet known. To determine the pattern of hemispheric lateralization during sound‐change discrimination, we recorded the magnetic counterpart of the electrical mismatch negativity (MMNm) responses in professional musicians, musical participants (with high scores in the musicality tests but without professional training in music) and non‐musicians. While watching a silenced video, they were presented with short sounds with frequency and duration deviants and C major chords with C minor chords as deviants. MMNm to chord deviants was stronger in both musicians and musical participants than in non‐musicians, particularly in their left hemisphere. No group differences were obtained in the MMNm strength in the right hemisphere in any of the conditions or in the left hemisphere in the case of frequency or duration deviants. Thus, in addition to professional training in music, musical aptitude (combined with lower‐level musical training) is also reflected in brain functioning related to sound discrimination. The present magnetoencephalographic evidence therefore indicates that the sound discrimination abilities may be differentially distributed in the brain in musically competent and naïve participants, especially in a musical context established by chord stimuli: the higher forms of musical competence engage both auditory cortices in an integrative manner.     

Preattentive dysfunction in bipolar disorder: A MEG study using auditory mismatch negativity

Background

Neuropsychological studies have demonstrated that cognitive dysfunction represents pathophysiological mechanisms underlying bipolar disorder. However, information processing deficits in bipolar disorder have not often been examined electrophysiologically. Here, we examined preattentive processing and sensory information processing using mismatch field (MMNm) and P1m components, respectively, using magnetoencephalography.

Methods

Ten patients with bipolar disorder and 20 healthy volunteers participated in the study. The participants were presented with auditory stimuli sequences comprising standard and deviant stimuli. MMNm was elicited in response to changes in duration and frequency of pure-tone stimuli and a vowel across-category change.

Results

The magnetic global field power of MMNm in the right hemisphere under the pure-tone condition was significantly delayed in patients with bipolar disorder compared to healthy volunteers, and that of P1m did not differ between the two groups. The MMNm dipole in the left hemisphere was located inferior in patients with bipolar disorder than in healthy volunteers. This finding did not correlate with clinical symptoms.

Conclusions

Information processing at the preattentive level is impaired in patients with bipolar disorder irrespective of clinical symptoms, and this dysfunction is not due to sensory level dysfunction. The quality of preattentive information processing impairment is different between patients with bipolar disorder and patients with major depressive disorder, as shown by the MMNm latency and power differences.