Verbal encoding deficits in a patient with a left retrosplenial lesion

Over the past decade, memory impairments associated with retrosplenial damage have received increased attention among neuroscientists, although the exact role of the retrosplenial region in memory has not been clearly defined. Evidence from lesion studies and functional neuroimaging has implicated the retrosplenial region in verbal episodic memory, temporal ordering of information, and topographical memory. In addition, recent positron emission tomography studies have shown increased activation of the retrosplenial cortex during tasks involving both the encoding and retrieval of episodic information. The objective of this study was to define more clearly the nature of memory impairments observed in retrosplenial amnesia. A 47-year-old amnesic male with a left retrosplenial arteriovenous malformation was examined on neurocognitive tasks of automatic and directed encoding, temporal ordering of information, and remote memory. Despite normal performance on frontal cognitive tasks, intact memory for remote information, and a superior IQ, this individual exhibited a profound deficit in the encoding of information, evidenced by poor release from proactive interference, poor category clustering on word list recall, poor semantic encoding on a levels of processing task, and mild impairments in temporal ordering. These results imply that the retrosplenial region plays a role in the verbal encoding of information, which contributes to the profound verbal memory impairment reported in previous case studies of patients with retrosplenial damage.