A cortical map for tempo

Abstract

Tonotopy is a well-known property of the brain which consists of a linearly organized representation of the tonal frequencies on the auditory cortex. A similar organization for the rate of auditory events (tempo) is demonstrated. Subjects listened to isochronous, isotonic sequences of pure tones varying in tempo (100-, 200-, 250-, 300-, 400-, 800-, and 1600-ms IOI) and frequency (400, 1000, and 2500 Hz). Brain magnetic activity (MEG) was recorded over the whole skull with a 150-sensor array. For slow tempi (above 300-ms IOI), sources of brain magnetic activity occurring 100 ms after stimulus onset (M100) were localized in the auditory cortex of both hemispheres. Source position varied systematically as a function of tempo and frequency: (1) on a transverse line for different tempi, more laterally in both hemispheres for the slower tempi (‘‘tempotopy’’), and (2) on an anteroposterior line for different frequencies, more anterior for the higher frequencies (tonotopy). For fast tempi, the main observed MEG response occurred at 70 ms. The presence of these two distinct neural activation patterns corroborates previous psychophysical data.