EEG Alpha: Lateral Asymmetry Related to Task, and Hypnotizability

Occipital EEG alpha (8‐13 Hz) was recorded separately from the right and left hemispheres of 26 right‐handed subjects during analytic (verbal and numerical) tasks, spatial (imagery) tasks, a music task, and a hypnotic susceptibility scale. An alpha laterality score was derived by computing the percent difference in the amplitude of alpha in the two hemispheres. This laterality score was significantly different between the analytic and spatial tasks, and between an eyes‐open baseline and an eyes‐open measurement during hypnotic amnesia. Because the spatial tasks used in this study are considered “easier” than the analytic or music tasks, the role of task difficulty provides some ambiguity in interpretation. Highly hypnotizable subjects showed significantly more alpha activity (compared to low hypnotizables) in all conditions (both outside hypnosis and within it) except for the eyes‐open baseline and the eyes‐open measurement following the release of amnesia. No differences were found between low‐ and high‐hypnotizables in the laterality measure. This suggests that the lateral asymmetry of alpha is a function of task rather than of any particular cognitive style that may characterize the hypnotically susceptible. That high hypnotizables showed higher amplitudes of alpha, however, suggests that the overall production of alpha may be positively related to the particular cognitive style that characterizes the person who is able to experience hypnotic phenomena.