The specificity of intrahemispheric EEG alpha coherence asymmetry related to psychological task

Male right handed subjects performed two parallel verbal and nonverbal memory tasks, known to be associated with the anterior temporal lobe, while EEG was recorded from temporal sites referred to either FZ or to linked mastoids. Intrahemispheric coherence and power in the alpha band were calculated. Coherence effects were observed, independent of reference site, which associated the right hemisphere and nonverbal tasks with increased coherence. These effects appear to be relatively specific to more anterior temporal electrode pairs, and confirm previous findings. Power effects demonstrated the difficulty of assessing task-dependent changes independent of reference site, and suggested that specific alpha enhancement may be observed with task involvement. The contribution of coherence analysis to the study of cerebral organisation is discussed.