Neuromagnetic auditory evoked responses after a stroke in the right temporal lobe

Auditory evoked magnetic fields were recorded with a 24-SQUID magnetometer on a patient with a vascular lesion in the right auditory cortex and its vicinity. The contralateral transient 100 ms response (N100m) was absent over the damaged side, with no recovery within 16 months. Responses were normal over the healthy side. The responses to a binaural click train where interaural delays caused the perception of a shifting sound source; responses were again normal over the left side. Ipsilateral tones elicited N100m over the normal hemisphere but with smaller amplitude and longer latency than in healthy subjects. We suggest that ipsilateral responses are triggered by ipsilateral afferents but are significantly modified by excitatory callosal connections which did not work in our patient.