Cerebral activation with meaningless and meaningful auditory stimuli matched for acoustic parameters : a positron emission tomography study

The purpose of this study was to determine whether there was a difference in localization and amount of cerebral blood flow (CBF) in specific regions of interest (ROIs), as measured by positron emission tomography, in response to meaningless and meaningful auditory stimuli that were matched for acoustic parameters. Twenty-two meaningless and 22 meaningful consonant vowel consonant (CVC) combinations were matched acoustically for overall duration, fundamental frequency contours, and overall intensity. The stimuli were presented to three neurologically normal, age matched, female subjects in the following conditions: 1) resting baseline; 2) stimulation with either meaningless CVCs or meaningful CVCs; 3) resting baseline; 4) stimulation with CVCs not presented in the first activation condition.

This study was a series of single subject experiments. Correlated t-Tests (for related measures) were done to determine whether significant inter- and intra-hemispheric changes in CBF occurred among the conditions. For one subject, significant intra-hemisphere differences, all in the right hemisphere, were found in three instances: 1) meaningless auditory stimuli elicited greater mean CBF than meaningful auditory stimuli; 2) mean CBF in the first resting baseline was greater than in the first activation with meaningful auditory stimuli; and 3) mean CBF in the second activation with meaningless auditory stimuli was greater than the second resting baseline.

These significant findings as well as the lack of significant differences among the other comparisons were discussed in relation to attention factors, presentation order, hemispheric asymmetries for processing meaningless and meaningful auditory stimuli, subject characteristics, and listener strategy. Possible limitations of the study included: habituation, task and stimuli characteristics, image manipulation, and the effect of error inherent in the measurement procedures. The results of this study indicate that differential x responses in CBF to meaningless and meaningful auditory stimuli may be detected with PET, given refinements in the research protocol.