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Cerebral Cortex Advance Access originally published online on October 27, 2006
Cerebral Cortex 2007 17(8):1970-1978; doi:10.1093/cercor/bhl106
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© The Author 2006. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Directional Information Flows between Brain Hemispheres during Presleep Wake and Early Sleep Stages

Mario Bertini1, Michele Ferrara1,2, Luigi De Gennaro1, Giuseppe Curcio1,3, Fabio Moroni1, Fabrizio Vecchio4,5, Marco De Gasperis5, Paolo Maria Rossini3,4,6 and Claudio Babiloni4,5,6

1 Dipartimento di Psicologia, Università degli Studi di Roma "La Sapienza," Roma, Italy, 2 Dipartimento di Medicina Interna e Sanità Pubblica, Università di L'Aquila, L'Aquila, Italy, 3 Clinica Neurologica, Università di Roma "Campus Bio-medico," Roma, Italy, 4 AFaR, Dip. Neuroscienze, Ospedale San Giovanni Calibita Fatebenefratelli, Roma, Italy, 5 Dipartimento di Fisiologia Umana e Farmacologia, Università di Roma "La Sapienza," Roma, Italy, 6 IRCCS Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy

Address correspondence to Dr Mario Bertini, MD, PhD, Dipartimento di Psicologia, Università degli Studi di Roma "La Sapienza," Via dei Marsi, 78, 00185 Rome, Italy. Email: mario.bertini{at}uniroma1.it.

Neuroscientists' efforts to better understand the underlying processes of human consciousness are growing in a variety of multidisciplinary approaches. Relevant within these are the studies aimed at exploring the physiological substratum of the propagation and reduction of cerebral—namely, corticocortical—communication flows. However, the preferential direction of the information flow between brain hemispheres is as yet largely unknown. It is the aim of the present research to study the communication flows between brain hemispheres, their directionality, and their regional variations across wake–sleep states. A second aim is to investigate the possibility of an association between different brain rhythms and different preferred directions of the information flow. Scalp electroencephalograms (EEGs) were recorded in 10 normal volunteers from wakefulness to early sleep stages (viz., resting wakefulness, sleep stages 2 and 4, and rapid eye movement [REM] of the first sleep cycle). EEG rhythms of interest were delta (1–4 Hz), theta (5–7 Hz), alpha (8–11 Hz), sigma (12–15 Hz), and beta (16–30 Hz). The direction of the interhemispheric information flow was evaluated by computing directed transformation function from these EEG rhythms. Interhemispheric directional flows varied as a function of the state of consciousness (wake and early sleep stages) and in relation to different cerebral areas. Across wake to sleep states, we found that delta and beta rhythms convey interhemispheric signals with opposite directions: preferred right to left hemisphere direction for delta and left to right for beta rhythms. A log correlation confirmed that the trend of low to high EEG frequencies—traditionally associated with an increasing state of vigilance—was significantly related to the direction of the communication flow from the left to right hemisphere. This evidence might open the way for a variety of research lines on different psychophysiological and pathological conditions.

Key Words: cerebral hemispheres • corpus callosum • quantitative electroencephalography (qEEG) • wake–sleep transition


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