15 research outputs found
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 informatio
Functionally aberrant electrophysiological cortical connectivities in first episode medication-naive schizophrenics from three psychiatry centers
Functional dissociation between brain processes is widely hypothesized to
account for aberrations of thought and emotions in schizophrenic patients. The
typically small groups of analyzed schizophrenic patients yielded different
neurophysiological findings, probably because small patient groups are likely
to comprise different schizophrenia subtypes. We analyzed multichannel eyes-
closed resting EEG from three small groups of acutely ill, first episode
productive schizophrenic patients before start of medication (from three
centers: Bern N = 9; Osaka N = 9; Berlin N = 12) and their controls. Low
resolution brain electromagnetic tomography (LORETA) was used to compute
intracortical source model-based lagged functional connectivity not biased by
volume conduction effects between 19 cortical regions of interest (ROIs). The
connectivities were compared between controls and patients of each group.
Conjunction analysis determined six aberrant cortical functional
connectivities that were the same in the three patient groups. Four of these
six concerned the facilitating EEG alpha-1 frequency activity; they were
decreased in the patients. Another two of these six connectivities concerned
the inhibiting EEG delta frequency activity; they were increased in the
patients. The principal orientation of the six aberrant cortical functional
connectivities was sagittal; five of them involved both hemispheres. In sum,
activity in the posterior brain areas of preprocessing functions and the
anterior brain areas of evaluation and behavior control functions were
compromised by either decreased coupled activation or increased coupled
inhibition, common across schizophrenia subtypes in the three patient groups.
These results of the analyzed three independent groups of schizophrenics
support the concept of functional dissociation
Brain electric microstates and momentary conscious mind states as building blocks of spontaneous thinking: I. Visual imagery and abstract thoughts
Prompted reports of recall of spontaneous, conscious experiences were collected in a no-input, no-task, no-response paradigm (30 random prompts to each of 13 healthy volunteers). The mentation reports were classified into visual imagery and abstract thought. Spontaneous 19-channel brain electric activity (EEG) was continuously recorded, viewed as series of momentary spatial distributions (maps) of the brain electric field and segmented into microstates, i.e. into time segments characterized by quasi-stable landscapes of potential distribution maps which showed varying durations in the sub-second range. Microstate segmentation used a data-driven strategy. Different microstates, i.e. different brain electric landscapes must have been generated by activity of different neural assemblies and therefore are hypothesized to constitute different functions. The two types of reported experiences were associated with significantly different microstates (mean duration 121 ms) immediately preceding the prompts; these microstates showed, across subjects, for abstract thought (compared to visual imagery) a shift of the electric gravity center to the left and a clockwise rotation of the field axis. Contrariwise, the microstates 2 s before the prompt did not differ between the two types of experiences. The results support the hypothesis that different microstates of the brain as recognized in its electric field implement different conscious, reportable mind states, i.e. different classes (types) of thoughts (mentations); thus, the microstates might be candidates for the `atoms of thought'
Decreased functional connectivity of EEG theta-frequency activity in first-episode, neuroleptic-naĂŻve patients with schizophrenia: preliminary results
We explored and refined the hypothesis that during a first episode of acute schizophrenia a disorganization of brain functioning is present. A novel EEG measure was introduced, Global Field Synchronization (GFS), that estimates functional connectivity of brain processes in different EEG frequency bands. The measure was applied to EEG's from 11 never-treated, first-episode, young patients with an acute, positive, schizophrenic symptomatology and from 19 controls, residing in Bern, Switzerland. In comparison to age- and sex- matched controls, patients had significantly decreased GFS in the theta EEG frequency band, indicating a loosened functional connectivity of processes in this frequency. The result was confirmed in an independent, comparable patient group from Osaka, Japan (9 patients and 9 controls), thus making a total of 20 analyzed patients. Previous EEG research in healthy, awake subjects indicated a positive correlation of theta activity with memory functions. Thus, our result suggests a loss of mutual interdependence of memory functions in patients with acute schizophrenia, which agrees well with previous reports of working memory dysfunction in schizophrenia