EFFECT OF ENVIRONMENTAL SOUND FAMILIARITY ON DYNAMIC NEURAL ACTIVATION INHIBITION PATTERNS - AN ERD MAPPING STUDY/

The aim of this study was to analyze the timing and topography of brai n activity in relation to the cognitive processing of different types of auditory information. We specifically investigated the effects of f amiliarity on environmental sound identification, an issue which has b een little studied with respect to cognitive processes, neural substra tes, and time course of brain activity. To address this issue, we impl emented and applied an electroencephalographic mapping method named ev ent-related desynchronization, which allows one to assess the dynamics of neuronal activity with high temporal resolution there, 125 ms); we used 19 recording electrodes with standard positioning. We designed a n activation paradigm in which healthy subjects were asked to discrimi nate binaurally heard sounds belonging to one of two distinct categori es, ''familiar'' (i.e., natural environmental sounds) or ''unfamiliar' ' (i.e., altered environmental sounds). The sounds were selected accor ding to strict preexperimental tests so that the former should engage greater semantic, and the latter greater structural, analysis, which w e predicted to preferentially implicate left posterior and right brain regions, respectively. During the stimulations, significant desynchro nizations (thought to reflect neuronal activations) were recorded over left hemisphere regions for familiar sounds and right temporofrontal regions for unfamiliar sounds, but with only few significant differenc es between the two sound categories and a common bilateral activation in the frontal regions. However, strongly significant differences betw een familiar and unfamiliar sounds occurred near the end of and follow ing the stimulations, due to synchronizations (thought to reflect deac tivations) which appeared over the left posterior regions, as well as the vertex and bilateral frontal cortex, only after unfamiliar sounds. These unexpected synchronizations after the unfamiliar stimuli may re flect an awareness of the unfamiliarity of such sounds, which may have induced an inhibition of semantic and episodic representations becaus e the latter could not be associated with meaningless sounds. (C) 1998 Academic Press.