CORTICAL ACTIVATION RESPONSE TO ACOUSTIC ECHO-PLANAR SCANNER NOISE

Purpose: Our goal was to determine the distribution of auditory and la nguage cortex activation in response to acoustic echo planar scanner n oise with functional MRI (fMRI). Method: Acoustic scanner noise and sp oken text, reproduced on high output cassette tape, were separately de livered at equivalent intensities to six normal hearing adult voluntee rs through earphones during fMRI data acquisition. In nine other subje cts, taped scanner noise was delivered in five successive iterations o f the task to assess the consistency of cortical activation to the noi se stimulus. Gyri of the auditory and language system were divided int o 10 different subregions for analysis of cortical activation. The num ber of activated pixels and proportion of volunteers activating each c ortical subregion were determined using a cross-correlation analysis. Results: Cortical activation to taped acoustic scanner noise was prese nt within the transverse temporal gyrus (primary auditory cortex) in a ll subjects, but activation was highly variable between subjects in au ditory association and language relevant cortex. Auditory association cortex activation was seen in the planum polari, planum temporali, and middle temporal gyrus/superior temporal sulcus regions in one-half to two-thirds of the volunteers. There was no significant difference in the distribution of cortical activation within individual subjects acr oss five successive iterations of the scanner noise task. Listening to spoken text consistently activated primary and association auditory c ortex bilaterally as well as language relevant cortex in some cases. T he mean number of activated pixels was significantly greater for text listening than acoustic scanner noise in auditory association and lang uage relevant cortical subregions (p < 0.01), although the distributio n of activity was similar between the two tasks. Conclusion: This prel iminary investigation suggests that the complex sounds produced by the echo planar pulse sequence can activate relatively large regions of a uditory and language cortex bilaterally, with the extent of activation outside the primary auditory cortex being variable between subjects. However, the distribution of activation within individual subjects was relatively constant across several iterations of the scanner noise st imulus.