Research Report Location of brain rhythms and their modulation by preparatory attention estimated by current density C.M. Gómez a , J. Marco-Pallarés b,c,d , C. Grau b, ⁎ a Psychobiology Laboratory, Department of Experimental Psychology, University of Sevilla, Spain b Neurodynamics Laboratory, Department of Psychiatry and Clinical Psychobiology, University of Barcelona, Passeig de la Vall d'Hebron 171, 08035 Barcelona, Catalonia, Spain c Starlab Barcelona SL, Spain d Department of Neuropsychology, Otto-von-Guericke Universität, Magdeburg, Germany ARTICLE INFO ABSTRACT Article history: Accepted 1 June 2006 Available online 27 July 2006 To test the hypothesis that there is a functional modulation of conventional EEG bands associated with preparatory attention, putative changes in the spontaneous brain rhythms and their associated cerebral sources were addressed. The goals of the present report were, first, to find the brain areas with maximal rhythmic activity before warning and imperative stimuli in a classic contingent negative variation (CNV) paradigm, and, second, to study the modulation of the EEG rhythms of these areas during the preparatory attention interval which precedes the S2 (imperative) stimulus. Trial by trial LORETA analysis found similar brain rhythm generators during both pre-S1 and pre-S2 intervals. Each theta, alpha and beta traditional EEG rhythm originates in several anatomically distinct brain structures. Preparatory attention is associated with a decrease in power in alpha (right and left occipital and temporal areas) and low-beta (left frontal, bilateral occipital and middle frontal areas) EEG bands. In these structures power changes associated with preparatory attention modulated either a dominant or a non-dominant oscillatory band, suggesting that non- dominant rhythms of a cerebral area have some functional relevance. Our results imply distributed regional sources for brain rhythms and support the view that during preparatory attention there is a modulation of the brain sources generating alpha and beta brain rhythms. Moreover, the proposed combined approach makes it possible to explore the definition of a given brain area not only anatomically, but also by the frequency content and the functional reactivity of the electrical rhythms that it generates. © 2006 Elsevier B.V. All rights reserved. Keywords: Contingent negative variation Brain rhythm LORETA Preparatory attention 1. Introduction In the last decade, interest in the role of EEG rhythms in cortical information processing has increased (Rodriguez et al., 1999; Singer and Gray, 1995; Varela et al., 2001), particularly their function in preparatory attention, working memory and other brain processes (Pfurtscheller and Klimesch, 1992). Although this is a major topic in cognitive neuroscience, several methodological issues complicate the performance and interpretation of these studies, for instance: (i) the ever- changing nature of the time evolution of the spontaneous EEG signal (non-stationarity); (ii) the difficulties in establishing BRAIN RESEARCH 1107 (2006) 151 – 160 ⁎ Corresponding author. Neurodynamics Laboratory, Department of Psychiatry and Clinical Psychobiology, University of Barcelona, Passeig de la Vall d'Hebron 171, 08035 Barcelona, Catalonia, Spain. Fax: +34 934034424. E-mail address: carlesgrau@ub.edu (C. Grau). 0006-8993/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2006.06.019 available at www.sciencedirect.com www.elsevier.com/locate/brainres