INTENSITY CODING OF AUDITORY-STIMULI - AN FMRI STUDY

The effect of stimulus intensity (sound pressure level, SPL) of audito ry stimuli on the BOLD response in the auditory cortex was investigate d in 14 young and healthy subjects, with no hearing abnormalities, usi ng echo-planar, functional magnetic resonance imaging (fMRI) during a verbal and a non-verbal auditory discrimination task. The stimuli were presented block-wise at three different intensities: 95, 85 and 75 dB (SPL). All subjects showed fMRI signal increases in superior temporal gyrus (STG) covering primary and secondary auditory cortex. Most impo rtantly, the spatial extent of the fMRI response in STG increased with increasing stimulus intensity. It is hypothesized that spreading of e xcitation is associated with the encoding of increasing stimulus inten sity levels. In addition, we found bifrontal activation supposedly evo ked by the auditory-articulary loop of working memory. The results pre sented here should assist in the design of optimal activation strategi es for studying the auditory cortex with fMRI paradigms and may help i n understanding intensity coding of auditory stimuli. (C) 1998 Elsevie r Science Ltd. All rights reserved.