Split-Brain Patients

The expression “split-brain” was first used in the 1960s by Roger W. Sperry of the California Institute of Technology (Sperry 1961), referring to those animals who had undergone the surgical resection of the corpus callosum (CC), the largest nerve bundle connecting the left and right cerebral hemispheres (the surgery is called callosotomy). In some cases, the expression is specifically used to refer to the resection of all of the cortical commissures (commissurotomy; here both callosotomy and commissurotomy are used without further distinctions; for a deeper differentiation, see Corballis 1995). Thus, the expression “split-brain patients” is used to refer to such patients who usually suffer a very disabling form of epilepsy which does not respond to pharmacological treatment, so much so that the surgical resection of the callosal fibers is performed to prevent the spreading of seizures across the two sides of the brain. Sometimes, the callosal fibers are sectioned in the presence of a brain tumor. The hemispheric disconnection can be complete (involving all of the callosal portions) or partial (involving only a portion of the CC; Fig. 1). A difference has to be underlined between splitbrain patients, who receive the surgical resection of the CC, and acallosal patients, in whom the callosal fibers are absent from birth.