Thalamic asymmetry is related to acoustic signal complexity

Hemispheric asymmetries in response to speech sounds are well documented. H owever, it is not known if these asymmetries reflect only cortical hemisphe ric specialization to language or whether they also reflect pre-conscious e ncoding of signals at lower levels of the auditory pathway. This study exam ined differences in neural representations of signals with acoustic propert ies inherent to speech in the left versus right side of the thalamus. Speci fically, 2000 Hz tone bursts, clicks and synthesized forms of the phoneme / da/ were presented to anesthetized guinea pigs. Evoked responses were recor ded simultaneously from aggregate cell groups in the left and right medial geniculate bodies. Results showed an asymmetric response to complex auditor y stimuli between the left versus right auditory thalamus, but not to the s imple tonal signal. Moreover, asymmetries differed in male versus female an imals. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.