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Abstract:
Retrosplenial amnesia is relatively rare and one of the least
well-characterized human amnestic syndromes. The goal of this study
was to better characterize retrosplenial amnesia by evaluating a
41-year-old male with memory deficits secondary to a glioblastoma
of the splenium of the corpus callosum invading the retrosplenial
region. This individual had marked impairments of verbal and
nonverbal learning and recall, as well as difficulty estimating
temporal relations among recent events. Despite the localization of
his tumor to posterior structures, this patient also manifested
symptoms of dysfunction in frontal systems, including
perseveration, increased susceptibility to interference, and
decreased phonemic verbal fluency. Functional Magnetic Resonance
Imaging (fMRI) using paired-associate and contextual verbal fluency
paradigms demonstrated hippocampal and parahippocampal activation,
suggesting retained functional capacity in these structures.
Positron Emission Tomography using fluorodeoxyglucose revealed
hypometabolism in the anterior thalamic nuclei bilaterally. These
findings suggest that disturbances of retrosplenial function may
disrupt frontal pathways via trans-synaptic mechanisms mediated
through the anterior thalamic nuclei. The results are consistent
with the hypothesis that lesions in the posterior cingulate and/or
retrosplenial region cause amnesia by disrupting midline components
of Papez' circuit {1}. Reference: 1. Valenstein, E. et al., Brain,
1987, 110: 1631-1646 Supported by the Charles A. Dana Foundation
(JH), Cancer Center Support Grant NCI (JH), the Hoyt Foundation
(NR).
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