A role for the thalamus in memory for unique entities

Recent case studies of amnesic patients have yielded patterns of impairment that challenge Tulving's (1972) division of retrograde memory into two categories (namely, episodic and semantic memory). Here we describe a patient (JG) who developed partially blocked access to previously stored knowledge following the onset of a medial thalamic infarction. Having previously demonstrated that JG has a dense, pervasive amnesia for autobiographical material, famous people and famous events (Miller et al., 2001), in this study, we show that he is unable to access information about unique entities across a range of domains. In contrast, his memory for more general semantic knowledge (such as word meanings) is intact. JG's memory impairment is discussed in the context of a model of neural functioning put forward by Damasio (1990), in which it was proposed that recall of unique entities depends on many cortical regions being activated in synchrony. This activity, thought to be triggered and coordinated by anterior temporal and frontal lobe regions is, in turn, modulated by projections from the thalamus. We propose that JG's thalamic lesion has disrupted the coordination of the diffuse cortical networks necessary to generate highly specific memories from the past, be they episodic or semantic.