DO CHANGES IN COHERENCE ALWAYS REFLECT CHANGES IN FUNCTIONAL COUPLING

It is well known that the rhythmic activity within the alpha band in t he central area may be composed of two different types of rhythms: (i) the Rolandic mu rhythm, representing the intrinsic activity of the se nsorimotor area, and (ii) rhythmic activity believed to be generated w ithin parieto-occipital areas and to extend into central regions throu gh volume conduction (the;classical alpha rhythm'). In this paper we c learly demonstrate that this second type of rhythmic activity is not d ue to volume conduction from parieto-occipital areas. We also demonstr ate the significant impact of the coexistence of these two types of rh ythms on the interpretation of interhemispheric coherence measurements . (C) 1998 Elsevier Science Ireland Ltd.