Forty Hertz EEG activity in dementia of the Alzheimer type and multi-infarct dementia

EEG measures for clinical research in major vascular cognitive impairment: recommendations by an expert panel

Vascular contribution to cognitive impairment (VCI) and dementia is related to etiologies that may affect the neurophysiological mechanisms regulating brain arousal and generating electroencephalographic (EEG) activity. A multidisciplinary expert panel reviewed the clinical literature and reached consensus about the EEG measures consistently found as abnormal in VCI patients with dementia. As compared to cognitively unimpaired individuals, those VCI patients showed (1) smaller amplitude of resting state alpha (8-12 Hz) rhythms dominant in posterior regions; (2) widespread increases in amplitude of delta (< 4 Hz) and theta (4-8 Hz) rhythms; and (3) delayed N200/P300 peak latencies in averaged event-related potentials, especially during the detection of auditory rare target stimuli requiring participants' responses in "oddball" paradigms. The expert panel formulated the following recommendations: (1) the above EEG measures are not specific for VCI and should not be used for its diagnosis; (2) they may be considered as "neural synchronization" biomarkers to enlighten the relationships between features of the VCI-related cerebrovascular lesions and abnormalities in neurophysiological brain mechanisms; and (3) they may be tested in future clinical trials as prognostic biomarkers and endpoints of interventions aimed at normalizing background brain excitability and vigilance in wakefulness.

A Case Study of Gamma Waves in a Woman with Recent Psychotic Symptoms

Reported here is the case of a 41-year-old female who developed paranoia and delusions. Physical examination, laboratory studies, and neuroimaging were unremarkable. She was diagnosed with schizophrenia and treated with risperidone, ultimately at a dose of 3 mg daily, with improvement. Her EEG showed bursts of 30-40 Hz gamma activity in the frontal regions, a finding sometimes noted on the resting EEGs of patients with schizophrenia. This report discusses gamma activity as well as other EEG abnormalities that may occur on the resting EEG of patients with schizophrenia. Additionally discussed is recent research suggesting that 35-45 Hz gamma activity associated with active information processing and cognition may be decreased in patients with schizophrenia compared to normal individuals. The role of gamma activity, both in the resting state and during cognitive activity, could be an area of importance for future research in schizophrenia and possibly other disorders.

Cellular and network mechanisms of genetically-determined absence seizures

The absence epilepsies are characterized by recurrent episodes of loss of consciousness associated with generalized spike-and-wave discharges, with an abrupt onset and offset, in the thalamocortical system. In the absence of detailed neurophysiological studies in humans, many of the concepts regarding the pathophysiological basis of absence seizures are based on studies in animal models. Each of these models has its particular strengths and limitations, and the validity of findings from these models for the human condition cannot be assumed. Consequently, studies in different models have produced some conflicting findings and conclusions. A long-standing concept, based primarily from studies in vivo in cats and in vitro brain slices, is that these paroxysmal electrical events develop suddenly from sleep-related spindle oscillations. More specifically, it is proposed that the initial mechanisms that underlie absence-related spike-and-wave discharges are located in the thalamus, involving especially the thalamic reticular nucleus. By contrast, more recent studies in well-established, genetic models of absence epilepsy in rats demonstrate that spike-and-wave discharges originate in a cortical focus and develop from a wake-related natural corticothalamic sensorimotor rhythm. In this review we integrate recent findings showing that, in both the thalamus and the neocortex, genetically-determined, absence-related spike-and-wave discharges are the manifestation of hypersynchronized, cellular, rhythmic excitations and inhibitions that result from a combination of complex, intrinsic, synaptic mechanisms. Arguments are put forward supporting the hypothesis that layer VI corticothalamic neurons act as 'drivers' in the generation of spike-and-wave discharges in the somatosensory thalamocortical system that result in corticothalamic resonances particularly initially involving the thalamic reticular nucleus. However an important unresolved question is: what are the cellular and network mechanisms responsible for the switch from physiological, wake-related, natural oscillations into pathological spike-and-wave discharges? We speculate on possible answers to this, building particularly on recent findings from genetic models in rats.

Suppression of early evoked gamma band response in male alcoholics during a visual oddball task

We investigated the early evoked gamma frequency band activity in alcoholics (n=122) and normal controls (n=72) during a visual oddball task. A time-frequency representation method was applied to EEG data in order to obtain phase-locked gamma band activity (29-45 Hz) and was analyzed within a 0-150 ms time window range. Significant reduction of the gamma band response in the frontal region during target stimulus processing was observed in alcoholic compared to control subjects. In contrast, significantly higher gamma band response for the non-target stimulus was observed in alcoholics compared to controls. It is suggested that the reduction in early evoked frontal gamma band response to targets may be associated with frontal lobe dysfunction commonly observed in alcoholics. This perhaps can be characterized by a deficient top-down processing mechanism.

Synchronous gamma activity: a review and contribution to an integrative neuroscience model of schizophrenia

Synchronous high frequency (Gamma band) activity has been proposed as a candidate mechanism for the integration or 'binding' of distributed brain activities. Since the first descriptions of schizophrenia, attempts to characterize this disorder have focused on disturbances in such integrative processing. Here, we review both micro- and macroscopic neuroscience research into Gamma synchrony, and its application to understanding schizophrenia. The review encompasses evidence from both animal and human studies for the functional significance of Gamma activity, the association between Gamma dysfunction and information processing disturbances, and the relevance of specific Gamma dysfunctions to the integration and extension of previous disconnection models of schizophrenia. Attention is given to the relationship between Gamma activity and the heterogeneous symptoms of schizophrenia. Existing studies show that measures of Gamma activity have the potential to explain far more of the variance in schizophrenia performance than previous neurophysiological measures. It is concluded that measures of Gamma synchrony offer a valuable window into the core integrative disturbance in schizophrenia cognition.

An integration of 40 Hz Gamma and phasic arousal: novelty and routinization processing in schizophrenia

OBJECTIVES

Frontal and lateralized schizophrenia disturbances were examined in terms of arousal-modulated changes in 40 Hz Gamma activity.

METHODS

Forty patients with schizophrenia and 40 age- and gender-matched controls were studied in a conventional auditory ERP oddball paradigm. We investigated sub-averaged Gamma activity based upon a simultaneous measure of electrodemal skin conductance response (phasic arousal) to differentiate novelty (large responses) from routinization (small or no responses). Both early Gamma (Gamma 1) and later induced Gamma (Gamma 2) activities were examined.

RESULTS

Patients with schizophrenia (compared with controls) had significantly reduced Gamma 1 amplitude in the right hemisphere for novelty processing and delayed Gamma 2 latency in the left hemisphere for both novelty and routinization. Overall, reduced Gamma 1 amplitude in patients with schizophrenia was also evident.

CONCLUSIONS

These findings indicate that the normal laterality of Gamma activity is specifically disturbed in schizophrenia in response to novel, but not routine (familiar) stimuli. The distinct pattern of findings suggests a dysregulation of activation across left and right hemispheres during initial attention and preparatory phases of information processing, in particular, in patients with schizophrenia.

Beta activity in aging and dementia

Considerable variation remains in the reported effects of disease, age and gender on high frequency electroencephalographic activity. We examined the topographic differences in relative and absolute beta power in the 14-54 Hz range in 49 subjects with dementia of the Alzheimer's type (DAT), 25 subjects with multi-infarct dementia (MID), and 62 normal control subjects (CON). Associations of these spectral parameters with age, gender and cognitive status were assessed. Normal control subjects showed modest positive correlations in frontal, central and parietal regions across the age range of 24-90 years but not across a narrower 60-90 year range. Women, particularly women over 60 years of age, showed increased relative and absolute beta power compared to men. Subjects with dementia showed global decreases particularly in relative power. Decreases were most prominent in central and parietal regions for DAT subjects, with MID subjects additionally showing prominent frontal decreases. DAT and MID subjects differed in their correlations of power with age, Folstein Mini Mental State Exam (MMSE) and gender across frontal, central, parietal and temporal regions. Differences in the regional attenuation of absolute and relative beta power within specific high frequency bands may reflect the disparate neuropathologic processes of DAT and MID, as well as the extent of brain dysfunction and the effects of gender.