BRAIN ELECTRIC MICROSTATES AND MOMENTARY CONSCIOUS MIND STATES AS BUILDING-BLOCKS OF SPONTANEOUS THINKING - I - VISUAL-IMAGERY AND ABSTRACTTHOUGHTS

Prompted reports of recall of spontaneous, conscious experiences were collected in a no-input, no-task, no-response paradigm (30 random prom pts to each of 13 healthy volunteers). The mentation reports were clas sified into visual imagery and abstract thought. Spontaneous 19-channe l brain electric activity (EEG) was continuously recorded, viewed as s eries of momentary spatial distributions (maps) of the brain electric field and segmented into microstates, i.e. into time segments characte rized by quasi-stable landscapes of potential distribution maps which showed varying durations in the sub-second range. Microstate segmentat ion used a data-driven strategy. Different microstates, i.e. different brain electric landscapes must have been generated by activity of dif ferent neural assemblies and therefore are hypothesized to constitute different functions. The two types of reported experiences were associ ated with significantly different microstates (mean duration 121 ms) i mmediately preceding the prompts; these microstates showed, across sub jects, for abstract thought (compared to visual imagery) a shift of th e electric gravity center to the left and a clockwise rotation of the field axis. Contrariwise, the microstates 2 s before the prompt did no t differ between the two types of experiences. The results support the hypothesis that different microstates of the brain as recognized in i ts electric field implement different conscious, reportable mind state s, i.e. different classes (types) of thoughts (mentations); thus,,the microstates might be candidates for the 'atoms of thought'. (C) 1998 E lsevier Science B.V.