Right medial thalamic lesion causes isolated retrograde amnesia

Pervasive retrograde amnesia without anterograde memory impairment has rare ly been described as a consequence of circumscribed brain damage. We report this phenomenon in a 33 yr-old, right-handed man (JG) in association with the extension in the right thalamus of a previously small, bilateral thalam ic lesion. JG presented with a dense amnesia for autobiographical material more than a few years old, with some sparing of recent memories. Furthermor e, he was completely unable to recognise famous people or world events. Man y other aspects of semantic knowledge were intact and there was no evidence of general intellectual impairment, executive dysfunction or loss of visua l imagery. Magnetic resonance imaging revealed an acute lesion in the right thalamus and two small, symmetrical, bilateral non-acute thalamic lesions. Follow-up neuropsychological assessment indicated a stable pattern of impa ired retrograde and spared anterograde memory over 18 months and psychiatri c assessments yielded no evidence of confabulation, malingering or other sy mptoms to suggest psychogenic amnesia. JG's profile indicates that the divi sion of declarative memory into just two categories - episodic and semantic - is inadequate. Rather, his case adds to the growing body evidence to sug gest that world knowledge pertaining to people and events is stored or acce ssed similarly to autobiographical information and differently from other t ypes of more general factual knowledge. We hypothesize that the right medio dorsal thalamic nucleus and immediately surrounding regions comprise the ce ntral processing mechanism referred to by McClelland (Revue Neurologique, 1 50 (1994) 570) and Markowitsch (Brain Research Review, 21 (1995) 117) as re sponsible for inducing and co-ordinating the recall of these sorts of corti cally stored memory engrams. (C) 2001 Elsevier Science Ltd. All rights rese rved.