Amnesia in a patient with lesions limited to the dorsomedial thalamic nucleus

We describe a patient who suffered a thalamic stroke, MRI revealed bilateral lesions confined to the dorsomedial nucleus (DM), more extensive on the left than on the right. The only other damage evident was some slight atrophy of the mammillary bodies bilaterally. Neuropsychological tests revealed a long-lasting and severe deficit of both recall and recognition and some indication of frontal robe dysfunction. Retrograde amnesia was thought to extend similar to 3 years premorbidly. This case provides strong evidence of a crucial role for the DM in normal memory functioning. The findings are discussed in relation to an hypothesis which postulates that the DM forms part of a memory system which plays an important role in item recognition in contrast to the hippocampal system (hippocampus, fornix, mammillary bodies and anterior thalamus) which is thought to be crucial for free recall and recognition of associative information.