Evidence of Abnormal Processing of Auditory Stimulation
Observed in Cerebral Blood Flow Studies
Several studies have documented abnormal levels of blood flow as a response to auditory stimulation in autistic children. In a study published in Delopmental Brain Dysfunction, Bernard Garreau and his associates (1994, Vol. 7, pp. 119-128) observed changes in regional cerebral blood flow in response to the presentation of a 750 Hertz tone for 200 milliseconds in both autistic (n=14) and non-autistic (n=6) individuals. Cerebral blood flow was measured using single-photon emission computed tomography. The researchers did not observe any differences between the two groups when the tone was not presented. However, in response to the tone, there was an increase in cerebral blood flow in the left temporo-occipital region for those in the control group. In contrast, there was an increase in cerebral blood flow in the right temporo-occipital region with no activation on the left side for those in the autism group. In general, activation in the left hemisphere is considered normal and is thought to indicate retrieval of acoustic information from memory which may be important for language.
The researchers speculate that activation of “the right hemisphere may be of importance in the elaboration of abnormal and often unexplainable behavioral responses to sounds which are among the most pronounced signs in autistic subjects in early childhood” (pp. 126). This same research group conducted two other studies and obtained corroborative results (Biological Psychiatry, 1992, Vol. 32, pp. 691-699; American Journal of Psychiatry, 1992, Vol. 149, pp. 924-930). Given these findings, we encourage researchers to consider examining cerebral blood flow in relation to auditory integration training.
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