Cerebral Cortex Advance Access originally published online on December 28, 2005
Cerebral Cortex 2006 16(12):1690-1700; doi:10.1093/cercor/bhj104
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Pre- and Poststimulus Alpha Rhythms Are Related to Conscious Visual Perception: A High-Resolution EEG Study
1 Dipartimento di Fisiologia Umana e Farmacologia, Università degli Studi di Roma La Sapienza, Rome, Italy, 2 Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) S. Giovanni di Dio-Fatebenefratelli (FBF), Association Fatebenefratelli for Research, Brescia, Italy, 3 Association Fatebenefratelli for Research (AFaR), Dipartimento di Neuroscienze, FBF Hopsital, Isola Tiberina, Italy, 4 Dipartimento di Scienze Cliniche e Bioimmagini, Università G. D'Annunzio, Chieti, Italy, 5 Istituto di Tecnologie Biomediche Avanzate (ITAB) Fondazione Università G. D'Annunzio, Chieti, Italy, 6 Clinica Neurologica, Campus Biomedico, Univesità di Roma, Rome, Italy
Address correspondence to Dr Claudio Babiloni, Dipartimento di Fisiologia Umana e Farmacologia, Università degli Studi di Roma La Sapienza, Piazzale le Aldo Moro 5, 00185 Rome, Italy. Email: claudio.babiloni{at}uniroma1.it.
Conscious and unconscious visuospatial processes have been related to parietooccipital cortical activation as revealed by late visual-evoked potentials. Here the working hypothesis was that a specific pattern of pre- and poststimulus theta (about 4–6 Hz) and alpha (about 6–12 Hz) rhythms is differently represented during conscious compared with unconscious visuospatial processes. Electroencephalographic (EEG) data (128 channels) were recorded in normal adults during a visuospatial task. A cue stimulus appeared at the right or left (equal probability) monitor side for a "threshold time" inducing about 50% of correct recognitions. It was followed (2 s) by visual go stimuli at spatially congruent or incongruent position with reference to the cue location. Left (right) mouse button was clicked if the go stimulus appeared at the left (right) monitor side. Then, subjects said "seen" if they had detected the cue stimulus or "not seen" if missed (self-report). Sources of theta and alpha rhythms during seen and not seen EEG epochs were estimated by low-resolution electromagnetic brain topography software. Results showed that the prestimulus "low-band" (about 6–10 Hz) alpha rhythms in frontal, parietal, and occipital areas were stronger in power in the seen than in the not seen trials. After the visual stimulation, the power of the "high-band" (about 10–12 Hz) alpha rhythms in parietal and occipital areas decreased more in the seen than in the not seen trials. The present results suggest that visuospatial consciousness covary—presumably with a facilitatory effect—with the power of both pre- and poststimulus alpha rhythms.
Key Words: awareness • event-related desynchronization/synchronization (ERD/ERS) • high-resolution EEG • human cortex • LORETA • subliminal stimuli • theta and alpha rhythms
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