Basic mechanisms of central rhythms reactivity to preparation and execution of a voluntary movement: a stereoelectroencephalographic study William Szurhaj a , Philippe Derambure a, * , Etienne Labyt a , Franc ¸ois Cassim a , Jean-Louis Bourriez a , Jean Isnard b , Jean-Daniel Guieu a , Franc ¸ois Mauguie `re b a EA HU6, Department of Clinical Neurophysiology, Ho ˆpital Salengro, CHRU, 59037 Lille Cedex, France b Department of Functional Neurology and Epilepsy, Neurological Hospital, Lyon, France Accepted 15 October 2002 Abstract Objective: To localize the sources of mu, beta and gamma rhythms and to explore the functional significance of their reactivity. Methods: We used the method of quantification of event-related desynchronization (ERD) and synchronization (ERS) to analyze the reactivity of intracerebral rhythms recorded in stereoelectroencephalography within the sensorimotor areas during the preparation and the execution of a simple self-paced hand movement. We recorded 3 epileptic subjects who were explored before a surgical treatment. Results: An ERD of mu and beta rhythms has been recorded before the movement onset in the precentral gyrus, spreading then to the postcentral gyrus and to the frontal medial cortex. The frontal lateral cortex was inconstantly involved during the movement. The movement offset was followed by an important and focused beta ERS which was found within the pre- and post-central gyrus and the frontal medial cortex. Within the beta band, we observed several narrower bands with different reactivities and locations. Focused gamma reactivity was also found in the precentral and postcentral gyri. Conclusions: The reactivities of mu and beta rhythms are different but their locations overlap. Mu ERD is a diffuse phenomenon that reflects the activation of all the sensorimotor areas during a simple movement. Beta band is likely to be composed of different rhythms with different functional significance. The primary motor area seems to contain two distinct areas with different reactivity to the movement preparation and execution. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Event related desynchronization; Event related synchronization; Self paced movement; Stereoelectroencephalography; Mu rhythm; Beta rhythms 1. Introduction The reactivity of electroencephalogram (EEG) consisting of a change in the amplitude of rhythms within specific frequency bands is known since Berger’s first description of the decreasing alpha activity in eyes opening (Berger, 1929). EEG rhythms specifically reactive to a sensorimotor task have then been demonstrated. Jasper and Andrew (1938) described the EEG rolandic beta activity attenuation during a tactile stimulation. Jasper and Penfield (1949) reported in electrocorticographic recordings (ECoG) the suppression of beta activity after a voluntary hand move- ment. In 1952, Gastaut characterized a precentral EEG rhythm within the alpha band: the rolandic mu rhythm, which was blocked by a contralateral voluntary movement, a somatosensory stimulation or a passive movement. The relationships between mu rhythm and central beta rhythm and their meaning are still a matter of controversy. The quantification of the reactivity of the EEG rhythms by using the method of event-related desynchronization (ERD) (Pfurtscheller and Aranibar, 1977) made possible to demon- strate that mu and beta rhythms have a different reactivity related to the movement onset (Pfurtscheller, 1981). Both mu and beta rhythms desynchronize before a voluntary self- paced movement, and the desynchronization is maximal over the contralateral central region (Pfurtscheller, 1981; Pfurtscheller and Bergold, 1989; Derambure et al., 1993). However, after the movement, the temporal evolutions of both rhythms are different: mu ERD is followed by a slow return to the baseline, and sometimes by a slight synchro- nization, while beta rhythms synchronize rapidly after the movement offset. More recently, an event-related synchro- Clinical Neurophysiology 114 (2003) 107–119 1388-2457/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S1388-2457(02)00333-4 www.elsevier.com/locate/clinph CLINPH 2001687 * Corresponding author. Tel.: 133-320-446-461; fax: 133-320-446-355. E-mail address: p-derambure@chru-lille.fr (P. Derambure).