The use of middle latency response in the diagnosis of cortical deafness

Bilateral cortical lesions resulting in true deafness were first reported approximately 100 years ago. A detailed map of the auditory cortex, however, was derived only within the past 50 years, primarily from investigation in the cat and subhuman primate. The few human studies have shown the primary auditory cortex to be located around the posterior two-thirds of the sylvian fissure, especially in the anterior and posterior transverse temporal gyri -or Heschl's gyri- on the superior portion of the temporal lobe. Each organ of Corti has extensive bilateral projections to the primary auditory cortex, although experiments by Celesia have shown larger contralateral than ipsilateral response to auditory stimulation. This bilateral distribution of ascending auditory pathways makes deafness secondary to a single cortical lesion highly unlikely. Before the advent of brainstem evoked responses and computed tomographic (CT) or magnetic resonance imaging (MRI) of the brain, diagnosis of cortical deafness was made only through exhaustive neurologic, speech, hearing, and psychiatric evaluation. The purpose of this article is to present a patient with cortical deafness and illustrate the use of auditory middle latency responses as an aid to diagnosis.