AUDITORY FUNCTION IN ALZHEIMERS-DISEASE

The pattern of cerebral degeneration in Alzheimer's disease (AD) patie nts suggests that basic auditory capacities should be normal in AD, wh ereas progressively higher levels of auditory function should be incre asingly impaired. To test this hypothesis, we administered tests of au ditory capacities associated with primary auditory cortex (sound local ization and perception of complex tones) and auditory association cort ex (phoneme discrimination, timbre discrimination, and tonal memory) t o 19 mildly to moderately demented AD patients, 21 elderly control sub jects (ECS), and 14 young control subjects (YCS). The results showed s ignificant differences between YCS and ECS on phoneme discrimination w ith synthetic speech and on tonal memory. The AD group differed from t he ECS group on sound localization, one measure of synthetic speech di scrimination, and timbre discrimination. Performance did not correlate with age, dementia severity, or duration of illness on any test condi tion. These findings indicate that although AD is accompanied by speci fic auditory deficits, the increase in neuropathologic change between primary auditory and auditory association cortices is not reflected in an increased impairment of functions that are mediated by these areas . Degraded aural language comprehension, which is characteristic of AD , likely reflects disruption of language processes rather than dysfunc tion specific to auditory circuits.