Cerebral Cortex Advance Access originally published online on March 30, 2005
Cerebral Cortex 2006 16(1):37-46; doi:10.1093/cercor/bhi082
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Visuo-spatial Consciousness and Parieto-occipital Areas: A High-resolution EEG Study
1 Dip. Fisiologia Umana e Farmacologia, Università ‘La Sapienza’, Rome, Italy, 2 IRCCS ‘S. Giovanni di Dio-FBF’, AFaR, Brescia, Italy, 3 AFaR Dip Neuroscienze, Osp. FBF, Isola Tiberina, Italy, 4 Dipartimento di Scienze Cliniche e Bioimmagini, Università G. D'Annunzio, Chieti, Italy, 5 ITAB, Fondazione ‘Università G D'Annunzio’, Chieti, Italy and 6 Clinica Neurologica, Campus Biomedico, Università di Roma, Rome, Italy
Address correspondence to Dr Claudio Babiloni, Dipartimento di Fisiologia Umana e Farmacologia, Università degli Studi di Roma ‘La Sapienza’, Piazzale Aldo Moro 5, 00185 Rome, Italy. Email: claudio.babiloni{at}uniroma1.it.
Conscious and unconscious visuo-spatial processes are mainly related to parieto-occipital cortical activation. In this study, the working hypothesis was that a specific pattern of parieto-occipital activation is induced by conscious, as opposed to unconscious, visuo-spatial processes. Electroencephalographic data (128 channels) were recorded in 12 normal adults during a visuo-spatial task. A cue stimulus appeared on the right or the left (equal probability) monitor side for a ‘threshold time’ inducing 
50% of correct recognitions. It was followed (after 2 s) by visual go stimuli at spatially congruent or incongruent positions with reference to the cue location. The left (right) mouse button was clicked if the go stimulus appeared on the left (right) monitor side. Subjects were required to say ‘seen’ if they had detected the cue stimulus or ‘not seen’ if they missed it (self-report). ‘Seen’ and ‘not seen’ electroencephalographic trials were averaged separately to form visual evoked potentials. Sources of these potentials were estimated by LORETA software. Reaction time to go stimuli was shorter during spatially congruent than incongruent ‘seen’ trials, possibly due to covert attention on cue for self-report. It was also shorter during spatially congruent than incongruent ‘not seen’ trials, as an objective sign of unconscious processes. Cue stimulus evoked parieto-occipital potentials which has the same peak latencies in the ‘seen’ and ‘not seen’ cases. Sources of these potentials were located in occipital area 19 and parietal area 7. Source strength was significantly stronger in ‘seen’ than ‘not seen’ cases at +300 ms post-stimulus. These results may unveil features of parieto-occipital activation accompanying visuo-spatial consciousness.
Key Words: awareness • human cortex • LORETA • subliminal stimuli • visual evoked potentials (VEPs)
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