Alexithymia and the split brain. V. EEG alpha-band interhemispheric coherence analysis

Electroencephalographic (EEG) recordings were obtained while 6 completely commissurotomized patients, 2 partially commissurotomized patients, and 8 precision-matched normal control subjects watched 4 times a film symbolically depicting death. Our hypothesis was that alexithymia--a diminished capability to verbally express moods, symbols, and feelings--would be greater for patients because loss of cerebral commissures reduces interhemispheric communication, separating right-hemisphere-dependent affective understanding and left-hemisphere-dependent verbalization. Path and covariance structure analyses confirmed that callosotomy decreased alpha-band EEG coherences (after adjustment for mean intrahemispheric coherence) between pairs of scalp electrode channels placed homologously over frontal, parietal, and temporal lobes of the brain. This result occurred both for an index of interhemispheric coherence and for a latent variable indicated by the 3 adjusted coherences. Reduced levels of interhemispheric coherence in turn increased alexithymia, for an overall index and for a latent variable indicated by lexical-level content-analytic measures of verbal responses to the filmic stimulus.