Face-selective spectral changes in the human fusiform gyrus.

OBJECTIVE

To characterize ventral occipitotemporal and prefrontal EEG during cognitive processing.

METHODS

Depth probes were implanted for seizure localization in 16 pharmaco-resistant epileptics. Probes penetrated from middle temporal through fusiform to lingual gyrus, and from inferior frontal to anterior cingulate gyrus. Event-related potentials (ERPs) and event-related spectral power (ERSP) were calculated during delayed recognition for faces or words.

RESULTS

Face stimuli evoked a broadband fusiform ERSP increase from 5 to 45 Hz at 150-210 ms after stimulus onset. This ERSP increase was immediately followed by an ERSP decrease in the same region from 300 to 1000 ms. Both the early increased ERSP and the late decreased ERSP, were greater for faces than words. Simultaneous with the late temporal ERSP decrease, the prefrontal depth EEG displayed a low frequency (5-12 Hz) ERSP increase to face and word stimuli.

CONCLUSION

Early temporal ERSP increases occur at a time when the fusiform gyrus is thought to contribute to face processing. This increase is also reflected in spectral analysis of the ERP, but the late temporal ERSP decrease and frontal ERSP increase are not. Thus, intracranial recordings in humans demonstrate event-related fluctuations in EEG spectral power with clear anatomical, temporal and cognitive specificity.