Normal memory after damage to medial thalamus
M. Kritchevsky, N. R. Graff-Radford and A. R. Damasio
We studied two patients with nonhemorrhagic infarcts of the thalamus and
assessed their cognitive functions comprehensively using standardized
neuropsychological probes. Neither patient had any discernible memory
impairment for verbal or nonverbal material. Analysis of magnetic resonance
images with a stereotaxic method revealed that one subject had a
right-sided lesion involving about 15% of the dorsomedial nucleus (DM). The
other had bilateral lesions that affected about 15% of the left DM and less
than 5% of the right DM. The mamillothalamic tract appeared intact in both
patients. Considering that medial thalamic lesions commonly cause amnesia
in human beings as well as nonhuman primates, there are two possible
reasons, alone or in combination, that may explain why these patients
failed to have amnesia: the amount of DM damage was less than required to
cause amnesia; or the amnesia related to thalamic lesions requires damage
to a second structure, such as the mamillothalamic tract or the anterior
nucleus.
