Frontal callosal disconnection syndromes.

The interhemispheric connections of the cortical areas of the human brain are distributed within the corpus callosum according to a topographic order which is being studied in detail by novel imaging techniques. Total section of the corpus callosum is followed by a variety of interhemispheric disconnection symptoms each of which can be attributed to the interruption of fibers in a specific callosal sector. Disconnection symptoms deriving from posterior callosal sections, disconnecting parietal, temporal and occipital lobes across the midline, are more apparent than those following anterior callosal sections disconnecting the frontal lobes. In spite of the massive bulk of the frontal callosal connections in man, ascertained consequences of their interruption are limited to disorders of motor control, with particular regard to bimanual coordination. Technical advances in brain imaging and the design of appropriate tests are expected to reveal so far undetected deficits in the domain of executive and higher cognitive functions, resulting from callosal disconnection of the prefrontal cortices.