Hemispheric specialization and the perception of pain: a task-related EEG power spectrum analysis in chronic pain patients.

At EEG power spectrum analysis, chronic pain patients showed less alpha asymmetry than normal subjects during resting conditions, independently of the aetiology of pain. This 'quasi-symmetry' remained substantially unchanged across discrete task conditions differently from normal subjects showing left hemisphere activation during verbal-mathematic tasks and right hemisphere activation during visuo-spatial tasks. When descriptive diagnosis was considered as related to alpha asymmetry, significant differences were found between 'somatogenic' and 'psychogenic' pain patients. Specifically, somatogenic pain patients conformed to normal subjects, whereas psychogenic pain patients exhibited a trend towards a reduced left hemisphere dominance or a relative right hemisphere activation during both experimental conditions. These EEG findings seem congruent with a more frequent lateralization of psychogenic pain on the left side of the body.