Abstract
Invasive recordings of local field potentials (LFPs) have been used to โread the mindโ of monkeys in real time. Here we investigated whether noninvasive field potentials estimated from the scalpโrecorded electroencephalogram (EEG) using the ELECTRA source localization algorithm could provide realโtime decoding of mental states in healthy humans. By means of pattern recognition techniques on 500โms EEG epochs, we were able to discriminate accurately from single trials which of four categories of visual stimuli the subjects were viewing. Our results show that it is possible to reproduce the decoding accuracy previously obtained in animals with invasive recordings. A comparison between the decoding results and the subjects' behavioral performance indicates that oscillatory activity (OA), elicited in specific brain regions) codes better for the visual stimulus category presented than the subjects' actual response, i.e., is insensitive to voluntary or involuntary errors. The identification of brain regions participating in the decoding process allowed us to construct 3Dโfunctional images of the taskโrelated OA. These images revealed the activation of brain regions known for their involvement in the processing of this type of visual stimuli. Electrical neuroimaging therefore appears to have the potential to establish what the brain is processing while the stimuli are being seen or categorized, i.e., concurrently with sensoryโperceptual processes. Hum Brain Mapp 2006. ยฉ 2006 WileyโLiss, Inc.