Comparative study of middle-latency responses and auditory brainstem responses in elderly subjects.

Auditory senescence is studied through an electrophysiological investigation of the brainstem, midbrain and thalamocortical tracts of auditory pathways. For this purpose, comparative electrophysiologic studies were carried out by recording middle-latency responses (MLR) and auditory brainstem responses (ABR) in elderly subjects in the 7th-8th and 9th decades of life and in a control group consisting of young subjects in the 3rd decade of life. All these subjects were free of otological, neurological, vascular and metabolic pathologic states. In elderly subjects, the statistical analysis of the results, especially of MLRs, showed a deterioration in the progression of information from the periphery to the center due to changes in morphology, increased latency, reduced amplitude and poorer reproducibility. Furthermore, a different behavior was noticed in females versus males. Indeed, the shorter latency of evoked potentials in the female control group was remarkably reduced in the elderly subjects. MLRs scan a wide tract of auditory pathways and give evident results even by adopting a juxtaliminal stimulation; therefore, they are a more complete and sensitive test than ABRs for the study of involutional processes.