Retrograde episodic and semantic memory impairment correlates with side of temporal lobe damage

Patients with damage to the mesial and anterior portions of the temporal lobes suffer from a memory impairment involving both anterograde and retrograde amnesia. In the retrograde domain, it has been suggested that the relative severity of autobiographical and nonautobiographical memory impairment may depend on the prevalent side of the temporal damage. Here we present two patients suffering from damage to the mesial and anterior portions of the temporal lobes (hippocampal formation, parahippocampal gyrus and polar cortex) as a result of herpes encephalitis. In the first case, A.S., damage predominantly affected the right temporal lobe, whereas in the second patient, R.S., the damage was bilateral but more severe on the left side. A detailed investigation of the retrograde memory deficit demonstrated a partial double dissociation between the two patients, with A.S. almost exclusively impaired in the autobiographical domain (both episodic and semantic) and R.S. with poor performances in all domains, but much more severe in the nonautobiographical (both public events and general semantic knowledge) than in the autobiographical one. These findings reinforce the view of specialization of right and left temporal lobes in the retrieval of retrograde autobiographical and nonautobiographical memories, respectively.