Multiple supratemporal sources of magnetic and electric auditory evoked middle latency components in humans

The supratemporal sources of the earliest auditory cortical responses (20-8 0 ms) were identified using simultaneously recorded electroencephalographic (EEG) and magnetoencephalographic (MEG) data. Both hemispheres of six subj ects were recorded two or three times in different sessions in response to 8000 right-ear 1 kHz pure tones stimuli. Four components were identified: P a (28 ms), Nb (40 ms), and two subcomponents of the Pb complex, termed Pbl (52 ms) and Pb2 (74 ms). Based on MEG data, the corresponding sources were localized on the anatomy using individual realistic head models: Pa in the medial portion of Heschl's gyri (H1/H2); Nb/Pb1 in the lateral aspect of th e supratemporal gyrus (STG); and Pb2 in the antero-lateral portion of Hesch l's gyri. All sources were oriented antero-superiorly. This pattern was dea rest in the contralateral hemisphere, where these three activities could be statistically dissociated. Results agree with previous invasive human intr acerebral recordings, with animal studies reporting secondary areas involve d in the generation of middle latency auditory-evoked components, and with positron emission tomography and functional magnetic resonance imaging stud ies often reporting these three active areas although without temporal info rmation. The early STG activity may be attributed to parallel thalamo-corti cal connections, or to cortico-cortical connections between the primary aud itory cortex and the STG, as recently described in humans.