The spectral properties of hippocampal EEG related to behaviour in man

In an epileptic patient with depth electrodes placed in the hippocampal formation we observed the following: (1) There existed a significant peak in the theta band of the hippocampal EEG of this subject under a number of behavioural circumstances. (2) Four different behaviours were performed at two degrees of intensity. Whenever the values of a certain spectral parameter associated with a low or a high intensity behaviour showed a significant difference, the higher value corresponded with the more intense version of the behaviour. (3) The frequency and rhythmicity of the hippocampal theta component during writing was consistently higher than during sitting or walking. The amplitude was smaller. (4) In a word association task the amplitude, frequency and rhythmicity showed a significant rise during the period of silence immediately following the question and preceding the answer.     

Connectivity changes underlying spectral EEG changes during propofol-induced loss of consciousness

The mechanisms underlying anesthesia-induced loss of consciousness remain a matter of debate. Recent electrophysiological reports suggest that while initial propofol infusion provokes an increase in fast rhythms (from beta to gamma range), slow activity (from delta to alpha range) rises selectively during loss of consciousness. Dynamic causal modeling was used to investigate the neural mechanisms mediating these changes in spectral power in humans. We analyzed source-reconstructed data from frontal and parietal cortices during normal wakefulness, propofol-induced mild sedation, and loss of consciousness. Bayesian model selection revealed that the best model for explaining spectral changes across the three states involved changes in corticothalamic interactions. Compared with wakefulness, mild sedation was accounted for by an increase in thalamic excitability, which did not further increase during loss of consciousness. In contrast, loss of consciousness per se was accompanied by a decrease in backward corticocortical connectivity from frontal to parietal cortices, while thalamocortical connectivity remained unchanged. These results emphasize the importance of recurrent corticocortical communication in the maintenance of consciousness and suggest a direct effect of propofol on cortical dynamics.     

EEG epileptiform abnormalities at admission to a rehabilitation department predict the risk of seizures in disorders of consciousness following a coma

BackgroundSeizures affect about a quarter of patients with disorders of consciousness (DOC) after a coma.AimsWe investigated whether the presence of epileptiform abnormalities (EAs) in the electroencephalogram (EEG) of patients with DOC may predict the occurrence of seizures. Moreover, we evaluated whether EAs have a prognostic role in these patients.MethodsThis was a retrospective single-center cohort study of patients hospitalized between January 2005 and December 2014 in a rehabilitation department (mean time from acute brain injury: 46.1 days). We analyzed 30-minute EEGs at admittance for 112 patients with unresponsive wakefulness syndrome (UWS) or in a minimally conscious state (MCS), then compared occurrence of seizures over the following three months across patients with absent, unilateral, and bilateral EAs (generalized or bilateral independent). Outcomes at three months were assessed in the same groups using the Coma Recovery Scale Revised.ResultsEpileptiform abnormalities were observed in 38 patients (33.9%). Of these, 25 were unilateral, and 13 were bilateral. Seizures occurred in 84.6% of patients with bilateral EAs, which was significantly higher than in patients without EAs (10.8%, p < 0.001) or with unilateral EAs (24%, p = 0.001). The presence of EAs was not related to etiology or different DOC and did not significantly affect outcomes at three months.ConclusionsPatients with EAs at admission to a rehabilitation department have an increased risk of seizures. Specifically, most patients with bilateral EAs had seizures within the following 3 months. Evaluation of EAs in EEGs of patients with DOC may give valuable information in the management of antiepileptic drug treatment.     

How to select epochs of the EEG at rest for quantitative analysis

Before performing a quantitative analysis of the EEG at rest, it has to be specified how many seconds are to be used later on, and a criterion has to be set down according to which data are selected for further analysis. In this paper it is investigated which duration is appropriate for an analysis of background, non-transient activity. Furthermore, different criteria for automatically selecting such epochs for quantitative analysis are compared with respect to broad-band parameters of a sample of 42 children. A length of 20 sec turned out to be sufficient, since using 40 sec or 60 sec did not improve the statistical variability. Moreover, a criterion based on minimizing EOG power from 1.5 to 7.5 Hz was mildly superior to other criteria considered. The particular choice of epoch was, however, less crucial than anticipated.     

In vivo synaptic density relates to glucose metabolism at rest in healthy subjects,but is strongly modulated by regional differences

Preclinical and postmortem studies have suggested that regional synaptic density and glucose consumption (CMRGlc) are strongly related. However, the relation between synaptic density and cerebral glucose metabolism in the human brain has not directly been assessed in vivo. Using [¹¹C]UCB-J binding to synaptic vesicle glycoprotein 2 A (SV2A) as indicator for synaptic density and [¹⁸F]FDG for measuring cerebral glucose consumption, we studied twenty healthy female subjects (age 29.6 ± 9.9 yrs) who underwent a single-day dual-tracer protocol (GE Signa PET-MR). Global measures of absolute and relative CMRGlc and specific binding of [¹¹C]UCB-J were indeed highly significantly correlated (r > 0.47, p < 0.001). However, regional differences in relative [¹⁸F]FDG and [¹¹C]UCB-J uptake were observed, with up to 19% higher [¹¹C]UCB-J uptake in the medial temporal lobe (MTL) and up to 17% higher glucose metabolism in frontal and motor-related areas and thalamus. This pattern has a considerable overlap with the brain regions showing different levels of aerobic glycolysis. Regionally varying energy demands of inhibitory and excitatory synapses at rest may also contribute to this difference. Being unaffected by astroglial and/or microglial energy demands, changes in synaptic density in the MTL may therefore be more sensitive to early detection of pathological conditions compared to changes in glucose metabolism.     

Prognostic value of standard EEG in traumatic and non-traumatic disorders of consciousness following coma

ObjectiveTo investigate the prognostic value of standard electroencephalogram (EEG) in predicting the improvement of the level of consciousness in patients suffering from severe disturbances of consciousness following coma caused by acute brain injuries.MethodsA standard EEG was recorded at admission in our rehabilitation department in a total of 46 patients with impaired consciousness states following coma (22 patients with traumatic brain injuries, 24 patients with non-traumatic brain injuries). We quantified the EEG abnormalities using the scale of Synek (1988) and correlated them with the basal level of cognitive functioning (LCF) scale score and with its variation after three months.ResultsEEG scores correlated with LCF scores at admission (p < 0.01) and with LCF scores’ variation after three months (p < 0.01) in patients with traumatic brain injury; EEG scores correlated only with LCF scores variation after three months (p < 0.01) in patients with non-traumatic brain injury.ConclusionsStandard EEG, analysed using the Synek scale, has a good prognostic value in both groups of patients with disorders of consciousness.SignificanceThis work may have implications for clinical care, rehabilitative programs and medical–legal decisions in patients with impaired consciousness states following coma due to acute brain injuries.     

Cognitive processes in disorders of consciousness as revealed by EEG time–frequency analyses

Objective

Although behavioral evaluation of awareness in disorders of consciousness is difficult it remains the clinical standard. We believe that the refinement of EEG and analyses techniques would improve our characterization of those patients.

Methods

We focused on cognitive processing in a sample of 12 control subjects, eight vegetative-state patients, and 13 patients in the minimally consciousness state using EEG. We used an ‘active paradigm’ which asks subjects to follow instructions, specifically to actively count own or other names as compared to passively listening to them. EEG data was then analyzed using an advanced EEG analysis technique.

Results

Results revealed that all groups exhibit a stronger theta-synchronization to their own names when forced to count them. We also observed a delay in theta power in response to targets relative to non-targets when participants were instructed to count their own name.

Conclusion

Active paradigms are able to induce a different oscillatory activity compared to passive paradigms. Differences between controls and the pathologic groups are prominent in the theta- and alpha-band.

Significance

Time–frequency analyses allow to focus on distinct cognitive processes in patients with disorders of consciousness and thereby contribute to a refined understanding of severely brain-injured patients.     

A deviant EEG brain microstate in acute, neuroleptic-naive schizophrenics at rest

Momentary brain electric field configurations are manifestations of momentary global functional states of the brain. Field configurations tend to persist over some time in the sub-second range (“microstates”) and concentrate within few classes of configurations. Accordingly, brain field data can be reduced efficiently into sequences of re-occurring classes of brain microstates, not overlapping in time. Different configurations must have been caused by different active neural ensembles, and thus different microstates assumedly implement different functions. The question arises whether the aberrant schizophrenic mentation is associated with specific changes in the repertory of microstates. Continuous sequences of brain electric field maps (multichannel EEG resting data) from 9 neuroleptic-naive, first-episode, acute schizophrenics and from 18 matched controls were analyzed. The map series were assigned to four individual microstate classes; these were tested for differences between groups. One microstate class displayed significantly different field configurations and shorter durations in patients than controls; degree of shortening correlated with severity of paranoid symptomatology. The three other microstate classes showed no group differences related to psychopathology. Schizophrenic thinking apparently is not a continuous bias in brain functions, but consists of intermittent occurrences of inappropriate brain microstates that open access to inadequate processing strategies and context information Received: 4 November 1998 / Accepted: 20 May 1999     

EEG alpha synchronization is related to top-down processing in convergent and divergent thinking

Synchronization of EEG alpha activity has been referred to as being indicative of cortical idling, but according to more recent evidence it has also been associated with active internal processing and creative thinking. The main objective of this study was to investigate to what extent EEG alpha synchronization is related to internal processing demands and to specific cognitive process involved in creative thinking. To this end, EEG was measured during a convergent and a divergent thinking task (i.e., creativity-related task) which once were processed involving low and once involving high internal processing demands. High internal processing demands were established by masking the stimulus (after encoding) and thus preventing further bottom-up processing. Frontal alpha synchronization was observed during convergent and divergent thinking only under exclusive top-down control (high internal processing demands), but not when bottom-up processing was allowed (low internal processing demands). We conclude that frontal alpha synchronization is related to top-down control rather than to specific creativity-related cognitive processes. Frontal alpha synchronization, which has been observed in a variety of different creativity tasks, thus may not reflect a brain state that is specific for creative cognition but can probably be attributed to high internal processing demands which are typically involved in creative thinking.     

Elevated platelet MAO is related to impulsivity in disruptive behavior disorders

Platelet monoamine oxidase (MAO) activity was measured in 32 drug-free prepubertal boys with externalizing symptoms of disruptive behavior disorders and 47 boys with no DSM-III-R diagnoses, and correlated to questionnaire and laboratory performance measures of impulsivity. A subgroup of boys with high MAO activity exhibited significantly poorer performance (i.e., more impulsivity) than a subgroup of low MAO activity on laboratory tasks requiring response inhibition. High MAO patients were more impulsive than high MAO controls on some performance tasks and elevated platelet MAO was unrelated to personality questionnaire measures of impulsivity or to patient status. These data suggest that biological markers such as MAO activity may correlate better with performance than clinical questionnaire measures. Abnormally high platelet MAO activity may not be sufficient to produce externalizing symptoms in children, perhaps interacting with an underlying behavioral dimension of impulsivity.     

EEG coherence at rest and during a visual task in two groups of children

EEG coherence was studied in a group of n = 31 normal children (NG) and in a group of n = 25 mildly mentally retarded children (EG), 10-13 years old. This was done for a recording at rest, eyes closed, and one during which a visual matching task was presented. Coherence showed little structure across frequency, apart from a slow decline towards higher frequencies. For the EEG at rest, coherence was higher for the EG and a slight increase with age was found. The visual task changed the coherence pattern in a complex way, and differently for the two groups. Coherence decreased in the fronto-central region (about the same in both groups) and increased in occipito-parietal central combinations (more so for the NG). The delta band showed predominantly an increase for the NG.     

How does upper extremity Fugl-Meyer motor score relate to resting-state EEG in chronic stroke? A power spectral density analysis

ObjectiveWe investigated the potential added value of high-density resting-state EEG by addressing differences with healthy individuals and associations with Fugl-Meyer motor assessment of the upper extremity (FM-UE) scores in chronic stroke.MethodsTwenty-one chronic stroke survivors with initial upper limb paresis and eleven matched controls were included. Group differences regarding resting-state EEG parameters (Delta Alpha ratio (DAR) and pairwise-derived Brain Symmetry Index (BSI)) and associations with FM-UE were investigated, as well as lateralization of BSI and the value of different frequency bands.ResultsChronic stroke survivors showed higher BSI compared to controls (p < 0.001), most pronounced in delta and theta frequency bands (p < 0.0001; p < 0.001). In the delta and theta band, BSI was significantly negatively associated with FM-UE (both p = 0.008) corrected for confounding factors. DAR showed no differences between groups nor association with FM-UE. Directional BSI showed increased power in the affected versus the unaffected hemisphere.ConclusionsAsymmetry in spectral power between hemispheres was present in chronic stroke, most pronounced in low frequencies and related to upper extremity motor function deficit.SignificanceBSI is related to motor impairment and higher in chronic stroke patients compared to healthy controls, suggesting that BSI may be a marker of selective motor control.