‘Handedness’ as an expression of cerebral lateralisation is valuable in analysis of hemispheric asymmetries, carrying implications for implementation (as well as interpretation) of complex cognitive functions. In recent decades it has become possible to categorise handedness in a reproducible manner and, independently, to estimate accurately the degree of language lateralisation of the brain. These advances have re-focussed attention on cerebral organisation and hemispheric asymmetries, and there is now considerable interest in the neuropsychology of left-handedness. Because of procedural and ethical constraints there are relatively few large scale studies on language dominance, whereas handedness has been studied extensively in recent decades. Language is represented in the left hemisphere in all but 1% of right-handers, and in 60% of left-handers; in 15% of right-handers speech representation was bilateral.

Precise determination of handedness or lateralisation does not appear to have been assessed in major studies of electroconvulsive therapy (ECT). Results in 29 reports, when the electrodes were placed over either the non-dominant or both hemispheres, were tabulated and briefly discussed by d'Elia and Raotma, but the criterion of lateral dominance assignment was not clearly specified; the unilateral and bilateral placements were equally efficacious in their antidepressant effect. d'Elia, who introduced unilateral therapy in 1970, accepted the assumption that the left hemisphere was ‘dominant’, but later workers were more circumspect.