It has been found in numerous electroencephalographic (EEG) studies that a negative potential arises following an erroneous response (so-called Error-Related Negativity, ERN). This typical component ...of the EEG has, however, proven more difficult to identify when transferring analogous paradigms to magnetoencephalography (MEG). The aim of this study was to devise and apply a paradigm to elicit erroneous responses and using MEG to measure both the error-related evoked brain activity (mERN) as well as accompanying induced oscillatory activity. Results clearly demonstrate that it is possible to measure the mERN and to identify cortical sources associated with it. Using distributed source modeling, it is possible to identify the mERN in source space and corroborate EEG findings, with the mERN generated in the anterior cingulate cortex (ACC). This supports notions regarding the role of the ACC in error monitoring and cognitive control of motor behavior. Furthermore, changes in induced oscillatory activity were observed in the theta and beta bands. This extends previous studies, which show that evoked theta activity could underlie the generation of the ERN.
Abstract Objective Dysfunctional emotion processing has been discussed as a contributing factor to functional neurological symptoms (FNS) in the context of conversion disorder, and refers to blunted ...recognition and the expression of one
'
s own feelings. However, the emotion processing components characteristic for FNS and/or relevant for conversion remain to be specified. With this goal, the present study targeted the initial, automatic discrimination of emotionally salient stimuli. Methods The magnetoencephalogram (MEG) was monitored in 21 patients with functional weakness and/or sensory disturbance subtypes of FNS and 21 healthy comparison participants (HC) while they passively watched 600 emotionally arousing, pleasant, unpleasant or neutral stimuli in a rapid serial visual presentation (RSVP) design. Neuromagnetic activity was analyzed 110
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330 ms following picture onset in source space for prior defined posterior and central regions of interest. Results As early as 110 ms and across presentation interval, posterior neural activity modulation by picture category was similar in both groups, despite smaller initial (110
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150 ms) overall and posterior power in patients with FNS. The initial activity modulation by picture category was also evident in the left sensorimotor area in patients with FNS, but not significant in HC. Conclusions Similar activity modulation by emotional picture category in patients with FNS and HC suggests that the fast, automatic detection of emotional salience is unchanged in patients with FNS, but involves an emotion-processing network spanning posterior and sensorimotor areas.
We used the 40-Hz auditory steady-state response (SSR) to compare for the first time tonotopic frequency representations in the region of primary auditory cortex (PAC) between subjects with chronic ...tinnitus and hearing impairment and normal hearing controls. Frequency representations were measured in normal hearing (
n
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17) and tinnitus (
n
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28) subjects using eight carrier frequencies between 384 and 6561 Hz, each amplitude modulated (AM) at 40-Hz on trials of 3 min duration under passive attention. In normal hearing subjects, frequency gradients were observed in the medial–lateral, anterior–posterior, and inferior–superior axes, which were consistent with the orientation of Heschl’s gyrus and with functional organization revealed by fMRI investigations. The frequency representation in the right hemisphere was ∼
5 mm anterior and ∼
7 mm lateral to that in the left hemisphere, corroborating with MEG measurements hemispheric asymmetries reported by cytoarchitectonic studies of the PAC and by MRI morphometry. In the left hemisphere, frequency gradients were inflected near 2 kHz in normal hearing subjects. These SSR frequency gradients were attenuated in both hemispheres in tinnitus subjects. Dipole power was also elevated in tinnitus, suggesting that more neurons were entrained synchronously by the AM envelope. These findings are consistent with animal experiments reporting altered tonotopy and changes in the response properties of auditory cortical neurons after hearing loss induced by noise exposure. Degraded frequency representations in tinnitus may reflect a loss of intracortical inhibition in deafferented frequency regions of the PAC after hearing injury.
Animal studies show that following damage to inner-ear receptors, central representations of intact lesion-edge (LE) frequencies become enlarged (map reorganization). One theory of tinnitus holds ...that this process could be related to the tinnitus sensation. To test this hypothesis, neuromagnetic evoked fields of tinnitus participants with high-frequency hearing loss and normal hearing controls were measured, while subjects listened to monaurally presented LE or control (CO; an octave below LE) tones. The predictions made based on the map reorganization hypothesis of tinnitus were that neuronal responses to LE frequencies would be enhanced, and that source localizations for LE would be distorted. N1m equivalent dipole moments for LE were not supranormal in the tinnitus group, whereas responses to CO of tinnitus patients compared to controls were enlarged in the right hemisphere. This effect was positively associated with tinnitus-related distress. Abnormal source locations were found for generators activated by LE tones in the right hemisphere of the tinnitus group. This right-hemispheric map distortion was not associated with subjective variables of tinnitus. A positive correlation with tinnitus distress was found for the left hemisphere with more anterior sources being associated with enhanced distress. However, this result was independent of the frequency of the stimulus. Overall, the present study suggests that mechanisms of map reorganization, although present in the data, cannot satisfactorily explain the emergence of tinnitus and that differential hemispheric involvement must be considered.
New perspectives in neurorehabilitation suggest that behavioral treatments of movement disorders may modify the functional organization of central somatosensory neural networks. On the basis of the ...assumption that use-dependent reorganization in these networks contributes to the fundamental abnormalities seen in focal dystonia, we treated 10 affected musicians and measured the concomitant somatosensory changes by using whole-head magnetoencephalography. We found that effective treatment, using the method of sensory motor retuning, leads to alterations in the functional organization of the somatosensory cortex. Specifically, before treatment, somatosensory relationships of the individual fingers differ between the affected and unaffected hands, whereas after treatment, finger representations contralateral to the dystonic side become more similar to the less-affected side. Further, somatosensory finger representations are ordered more according to homuncular principles after treatment. In addition, the observed physiologic changes correlated with behavioral data. These results confirm that plastic changes in parallel with emergent neurological dysfunction may be reversed by context-specific, intensive training-based remediation.
Repetitive transcranial magnetic stimulation (rTMS) holds promise as a non-invasive therapy for the treatment of neurological disorders such as depression, schizophrenia, tinnitus, and epilepsy. ...Complex interdependencies between stimulus duration, frequency and intensity obscure the exact effects of rTMS stimulation on neural activity in the cortex, making evaluation of and comparison between rTMS studies difficult. To explain the influence of rTMS on neural activity (e.g. in the motor cortex), we use a neuronal network model. The results demonstrate that the model adequately explains experimentally observed short term effects of rTMS on the band power in common frequency bands used in electroencephalography (EEG). We show that the equivalent local field potential (eLFP) band power depends on stimulation intensity rather than on stimulation frequency. Additionally, our model resolves contradictions in experiments.
Objective: The present study aimed at examining the time course and topography of oscillatory brain activity and event-related potentials (ERPs) in response to laterally presented affective pictures.
...Methods: Electroencephalography was recorded from 129 electrodes in 10 healthy university students during presentation of pictures from the international affective picture system. Frequency measures and ERPs were obtained for pleasant, neutral, and unpleasant pictures.
Results: In accordance with previous reports, a modulation of the late positive ERP wave at parietal recording sites was found as a function of emotional arousal. Early mid gamma band activity (GBA; 30–45 Hz) at 80 ms post-stimulus was enhanced in response to aversive stimuli only, whereas the higher GBA (46–65 Hz) at 500 ms showed an enhancement of arousing, compared to neutral pictures. ERP and late gamma effects showed a pronounced right-hemisphere preponderance, but differed in terms of topographical distribution.
Conclusions: Late gamma activity may represent a correlate of widespread cortical networks processing different aspects of emotionally arousing visual objects. In contrast, differences between affective categories in early gamma activity might reflect fast detection of aversive stimulus features.
Magnetic source imaging revealed that the cortical representation of the digits of the left hand of string players was larger than that in controls. The effect was smallest for the left thumb, and no ...such differences were observed for the representations of the right hand digits. The amount of cortical reorganization in the representation of the fingering digits was correlated with the age at which the person had begun to play. These results suggest that the representation of different parts of the body in the primary somatosensory cortex of humans depends on use and changes to conform to the current needs and experiences of the individual.
Focal clusters of slow wave activity in the delta frequency range (1-4 Hz), as measured by magnetencephalography (MEG), are usually located in the vicinity of structural damage in the brain. Such ...oscillations are usually considered pathological and indicative of areas incapable of normal functioning owing to deafferentation from relevant input sources. In the present study we investigated the change in Delta Dipole Density in 28 patients with chronic aphasia (>12 months post onset) following cerebrovascular stroke of the left hemisphere before and after intensive speech and language therapy (3 hours/day over 2 weeks).
Neuropsychologically assessed language functions improved significantly after training. Perilesional delta activity decreased after therapy in 16 of the 28 patients, while an increase was evident in 12 patients. The magnitude of change of delta activity in these areas correlated with the amount of change in language functions as measured by standardized language tests.
These results emphasize the significance of perilesional areas in the rehabilitation of aphasia even years after the stroke, and might reflect reorganisation of the language network that provides the basis for improved language functions after intensive training.
Background: Patients suffering from Alzheimer’s disease exhibit more activity in the conventional electroencephalographic delta and theta bands. This activity concurs with atrophy and reduced ...metabolic and perfusion rates, particularly in temporoparietal structures.
Methods: Whole-head magnetoencephalographic recordings were obtained from 15 patients diagnosed with Alzheimer’s disease and 19 healthy control subjects during a resting condition. The generators of focal magnetic slow waves were located employing a single moving dipole model.
Results: Dipole density in the delta and theta bands was enhanced in the Alzheimer’s disease group compared with healthy control subjects. Slow-wave activity differed significantly between groups in temporoparietal regions of both hemispheres. Right temporoparietal slow-wave activity covaried with cognitive performance, whereas left temporal delta activity varied with a functional status scale.
Conclusions: Our results support the predominant role of the temporoparietal areas in the diagnosis of Alzheimer’s disease. Magnetoencephalography and the source analysis of focal slow activity in particular provide interesting and potentially clinically useful tools to assess functional modifications of patients’ brain and to evaluate its relationship with the cognitive status.
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