Selective impairment of memory and visual perception in splenial tumours.

The neuropsychological abnormalities found in 9 patients with tumours involving the splenium of the corpus callosum are described. The outstanding features of their cognitive deficits were a severe memory deficit and visual perception impairment in the presence of relatively intact intellect. It is argued that (1) the amnesia is due to damage to the fornix where that structure is closely applied to the splenium and that it is the result of a disconnection between the frontal and temporal lobes, although the possibility that damage to more than one structure, for example, retrosplenial cortex and fornix, cannot be excluded; (2) there is a dual pathway for visual object recognition, one of which passes directly to the dominant hemisphere for semantic analysis and the other via the nondominant hemisphere for prior perceptual analysis. Further, it is postulated that there is a subcortical as well as a callosal route between the hemispheres that is important for visual object recognition.