Age-related declines in hemispheric asymmetry as revealed in the binaural interaction component

Abstract

The binaural interaction component (BIC) is a physiological index of binaural processing. The BIC is defined as the brain activity resulting from binaural (diotic or dichotic) stimulus presentation minus the brain activity summed across successive monaural stimulus presentations. Smaller binaural-induced activity relative to summed monaural activity is thought to reflect neural inhibition in the central auditory pathway. Since aging is commonly associated with reduced inhibitory processes, we evaluate the hypothesis that the BIC is reduced with increasing age. Furthermore, older listeners typically have reduced hemispheric asymmetry relative to younger listeners, interpreted in terms of compensation or recruitment of neural resources and considered an indication of age-related neural plasticity. Binaural stimuli designed to elicit a lateralized percept generate maximum neural activity in the hemisphere opposite the lateralized position. In this investigation, we evaluated the hypothesis that the BIC resulting from stimuli lateralized to one side (due to interaural time differences) results in less hemispheric asymmetry in older than younger listeners with normal hearing. Behavioral data were obtained to assess the acuity of binaural processing. Data support the interpretation that aging is marked by reduced central auditory inhibition, reduced temporal processing, and broader distribution of activity across hemispheres compared to young adults.