TONOTOPIC ORGANIZATION OF HUMAN AUDITORY ASSOCIATION CORTEX

Neuromagnetic studies of responses in human auditory association corte x for tone burst stimuli provide evidence for a tonotopic organization . The magnetic source image for the 100 ms component evoked by the ons et of a tone is qualitatively similar to that of primary cortex, with responses lying deeper beneath the scalp for progressively higher tone frequencies. However, the tonotopic sequence of association cortex in three subjects is found largely within the superior temporal sulcus, although in the right hemisphere of one subject some sources may be cl oser to the inferior temporal sulcus. The locus of responses for indiv idual subjects suggests a progression across the cortical surface that is approximately proportional to the logarithm of the tone frequency, as observed previously for primary cortex, with the span of 10 mm for each decade in frequency being comparable for the two areas.