Electroencephalography

Mitochondrial DNA depletion syndromes (MDSs) form a group of autosomal recessive disorders characterized by profoundly decreased mitochondrial DNA copy numbers in affected tissues. Three main clinical presentations are known: myopathic, encephalomyopathic and hepatocerebral. The first is associated with mutations in thymidine kinase 2 (TK2) and p53-induced ribonucleotide reductase B subunit (RRM2B); the second with mutations in succinate synthase A (SUCLA2) and B (SUCLG1); the third with mutations in Twinkle (PEO1), pol-γA (POLG1), deoxyguanosine kinase (DGUOK) and MPV17 (MPV17). In this work, we review the MDS-associated phenotypes and present our own experience of 32 MDS patients, with the aim of defining the mutation frequency of the known genes, the clinical spectrum of the diseases, and the genotype–phenotype correlations. Five of our patients carried previously unreported mutations in one of the eight MDS genes.

Recent findings regarding differences in tinnitus-related neural activity according to onset age have raised a question on possible onset age-related differences in neural substrates of distress. Hence we collected quantitative electroencephalography (qEEG) findings of 28 late-onset tinnitus (LOT) and 29 early-onset tinnitus (EOT) (mean onset age 52.3 and 29.0 years, respectively) participants. According to the tinnitus questionnaire (TQ) score grade, LOTs were then subdivided into 13 high distress (HD; TQ grade 3 or 4) and 15 low distress (LD; TQ grade 1 or 2), while EOTs into 14 HD and 15 LD. Compared to the EOT group, the LOT group demonstrated increased qEEG source-localized activity and functional connectivity primarily in the anterior cingulate cortex (ACC) and parahippocampus. In subgroup comparisons, the ACC was activated more in HD-LOT participants than in LD-LOT participants for the beta 1, beta 2 and gamma frequency bands, while the left orbitofrontal cortex and left dors...

Joshi SN, Fathalla M, Koul R, Al. Maney M, Bayoumi R. Biotin responsive seizures and encephalopathy due to biotinidase deficiency. Neurol India [serial online] 2010 [cited 2011 Oct 13]; 58: 323-4. Available from: http://www. neurologyindia. com/text. asp? 2010/58/2/ ...

Previous experiments have demonstrated that auditory (AS) and/or somatosensory (SS) stimulation can increase the duration of REM sleep periods in rats, cats and humans. The objectives of this study were to determine whether repeated AS stimulation causes habituation to the stimulus and whether any additive effects could be obtained with the simultaneous application of AS and SS. Three experimental procedures were used in this study. In experiment 1, animals were recorded for 4 consecutive days with AS, followed by a post-stimulus session. In experiment 2, they were recorded for 24 hours with AS applied at each REM period, followed by a subsequent 24-hours-post-stimulus recording. In experiment 3, animals underwent AS, SS stimulation, or simultaneous application of both in a random fashion at each REM period. The results of all experiments confirm previous findings showing that auditory or somatosensory stimuli significantly increase REM sleep period duration. In addition, AS--applie...

The precise neural mechanisms underlying transitions between consciousness and anesthetic-induced unconsciousness remain unclear. Here, we studied intracortical neuronal dynamics leading to propofol-induced unconsciousness by recording single-neuron activity and local field potentials directly in the functionally interconnecting somatosensory (S1) and frontal ventral premotor (PMv) network during a gradual behavioral transition from full alertness to loss of consciousness (LOC) and on through a deeper anesthetic level. Macaque monkeys were trained for a behavioral task designed to determine the trial-by-trial alertness and neuronal response to tactile and auditory stimulation. We show that disruption of coherent beta oscillations between S1 and PMv preceded, but did not coincide with, the LOC. LOC appeared to correspond to pronounced but brief gamma-/high-beta-band oscillations (lasting ∼3 min) in PMv, followed by a gamma peak in S1. We also demonstrate that the slow oscillations ap...

The relationship of task relevance and stimulus probability to P300 morphology, latency and distribution was assessed. Eight year olds and adults completed visual oddball tasks of recognition memory with frequent non-target (60%), infrequent target (20%), and infrequent novel (20%) stimuli. Stimuli consisted of 2 female faces posing neutral expressions, and 40 trial unique novel photographs depicting scenes, animals, objects or abstract patterns. Event-related potentials were recorded from 17 electrodes over frontal, central and parietal scalp, including lateral temporal sites. All stimuli elicited P300 responses at parietal electrodes, with the largest responses to the target stimuli (relevant and infrequent). The P300 responses of adults and children were morphologically dissimilar, with children showing broader peaks and latency shifts across electrodes. In addition, the eight year olds displayed a frontal negativity to novel stimuli which was absent in the responses of adult par...

In this paper multivariate spontaneous EEG signals from three broad groups of human subjects--control, seizure, and mania--were studied with the aim of investigating the possible effect of these pathologies on the degree of phase synchronization between cortical areas. The degree of phase synchrony was measured by two recently developed measures which are more suitable than classical indices like correlation or coherence when dealing with nonlinear and non-stationary signals like the EEG. Signals were reduced to seven frequency bands (delta, theta, alpha-1, alpha-2, beta-1, beta-2 and gamma) which were statistically compared between the normal and the other two groups. It was found that the degree of long-range synchrony was significantly reduced for both pathological groups as compared with the control group. No clear differences were found in the degrees of short-range synchrony.

A general conceptual framework for large-scale neocortical dynamics based on data from many laboratories is applied to a variety of experimental designs, spatial scales, and brain states. Partly distinct, but interacting local processes (e.g., neural networks) arise from functional segregation. Global processes arise from functional integration and can facilitate (top down) synchronous activity in remote cell groups that function simultaneously at several different spatial scales. Simultaneous local processes may help drive (bottom up) macroscopic global dynamics observed with electroencephalography (EEG) or magnetoencephalography (MEG).A local/global dynamic theory that is consistent with EEG data and the proposed conceptual framework is outlined. This theory is neutral about properties of neural networks embedded in macroscopic fields, but its global component makes several qualitative and semiquantitative predictions about EEG measures of traveling and standing wave phenomena. A ...

Reliabilities of quantitative measures of absolute and relative EEG amplitudes were assessed in healthy older adults under the eyes closed (n = 46) and eyes opened (n = 45) conditions. For the theta, alpha, beta 1, and beta 2 bands, reliabilities of 28 scalp derivations were stable over the 4.5 month test interval. Reliabilities of delta were lower. When appropriate transformations were applied, the reliabilities of absolute EEG amplitude measures tended to exceed those of relative measures. There were not, however, striking differences in reliabilities under the eyes closed, as compared to eyes opened condition. We concluded that when coupled with the criterion of interpretability, the generally higher reliabilities of absolute, as opposed to relative, amplitude measures render them preferable in clinical research.

Two questions were addressed in the present study: (1) Do autistic and normally developing children exhibit regionally specific differences in electroencephalographic (EEG) activity? (2) Do subgroups of autistic children classified according to Wing and Gould's (1979) system which emphasizes degree of social impairment exhibit distinct patterns of EEG activity? Twenty-eight children with autism (5 to 18 years of age) and two groups of normally developing children (one matched on chronological age and the other on receptive language level) participated. EEG was recorded from left and right frontal, temporal, and parietal regions during an alert baseline condition. Compared to normally developing children, autistic children exhibited reduced EEG power in the frontal and temporal regions, but not in the parietal region. Differences were more prominent in the left than the right hemisphere. Furthermore, subgroups of autistic children based on Wing and Gould's system displayed distinct patterns of brain activity. Compared to autistic children classified as “active-but-odd,” “passive” autistic children displayed reduced alpha EEG power in the frontal region.

Summary: Rasmussen encephalitis is a chronic, progres- sive inflammation of the brain of unknown origin. Early diagnosis and treatment with immunoactive agents and/or hemispherectomy are sought to prevent the progressive cognitive decline that accompanies this disease. Combined anatomic and functional neuroimaging may serve to focus the diagnostic workup and to hasten brain biopsy for de- finitive diagnosis. Two biopsy proved