Auditory Processing Following Consecutive Right Temporal Lobe Resections: A Prospective Case Study

Abstract

Background: The role of the right temporal lobe in processing speech is not well understood. Although the left temporal lobe has long been recognized as critical for speech perception, there is growing evidence for right hemisphere involvement. To investigate whether the right temporal lobe is critical for auditory speech processing, we studied prospectively a normal-hearing patient who underwent consecutive right temporal lobe resections for treatment of medically intractable seizures. Purpose: To test the hypothesis that the right temporal lobe is critical for auditory speech processing. Research Design: We used a prospective, repeated-measure, single-case design. Auditory processing was evaluated using behavioral tests of speech recognition (words, sentences) under multiple listening conditions (e.g., quiet, background noise, etc.). Auditory processing of nonspeech sounds was measured by pitch pattern sequencing and environmental sound recognition tasks. Data Collection: Repeat behavioral testing was performed at four time points over a 2 yr period: before and after consecutive right temporal lobe resection surgeries. Results: Before surgery, the patient demonstrated normal speech recognition in quiet and under real-world listening conditions (background noise, filtered speech). After the initial right anterior temporal resection, speech recognition scores declined under adverse listening conditions, especially for the left ear, but remained largely within normal limits. Following resection of the right superior temporal gyrus 1 yr later, speech recognition in quiet and nonspeech sound processing (pitch patterns, environmental sounds) remained intact. However, speech recognition under adverse listening conditions was severely impaired. Conclusions: The right superior temporal gyrus appears to be critical for auditory processing of speech under real-world listening conditions.