Processing of rapid auditory information in epileptic patients with left temporal lobe damage

The role of the temporal lobes in processing time-related (temporal) information was tested in a task of anisochrony (or irregularity) discrimination assessing the temporal processing of sequential auditory information according to different presentation rates or tempos (between 80 and 1000 ms inter-onset intervals, IOI). Epileptic patients with either left (LHA, n=8) or right (RHA, n=10) hippocampal atrophy participated in this study as well as six normal control subjects (NC). For all the subjects, an effect of tempo was obtained, thresholds deteriorating for the 80 ms IOI as compared to longer IOI (the latter conforming to Weber's law). Furthermore, there was a specific impairment of rapid anisochrony discrimination (80 ms IOI) for patients with LHA as compared to patients with a RHA and NC, whereas no significant deficit was observed in these patients for longer IOI. These findings are in agreement with studies carried out in patients with left-hemisphere damage associated with massive language disorders and suggest the specialisation of left medial temporal lobe structures in processing rapid sequential auditory information. However, these results might also be explained by an auditory memory deficit in the presence of left temporal lobe dysfunction, as opposed to a specific impairment of fast sequential temporal processing.