Sustained fields of tones and glides reflect tonotopy of the auditory cortex.

Cortical activation in response to two types of auditory stimuli, constant-frequency tones and frequency glides, was studied by measuring the magnetic field outside the head using a whole-head 122-channel magnetometer. Both the magnetic N1m and sustained responses were located in the supratemporal plane of the primary auditory cortex. The sustained responses both to constant-frequency tones and frequency glides reflect tonotopic organization of the auditory cortex both in depth and direction, thus revealing the underlying neuroanatomical structure of the auditory cortex.