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Abstract:
Transient global amnesia (TGA) is a condition characterized
by sudden memory loss that typically resolves within 24 hrs. The
etiology varies and is not always linked to a focal lesion,
although previous studies have implicated dysfunction in
temporolimbic regions. We used fMRI to compare changes in temporal
lobe activity during the acute state and following recovery from
TGA. Patient M.W. was admitted to NMH because of an acute
development of disorientation to time, place and recent events, and
anterograde memory loss. His clinical diagnosis was TGA. He
underwent a fMRI session which involved the encoding of complex
visual scenes. The following day, M.W.'s condition resolved, but he
exhibited residual memory loss for events surrounding his
hospitalization. Several months later, M.W. repeated the fMRI
study. Activation to the scenes was compared in the recovery vs.
amnesic state. Following recovery, M.W. showed increased activity
in the medial and anterior temporal lobe and retrosplenial cortex.
In the amnesic state, M.W. showed increased activity in dorsal
frontoparietal regions. These patterns were not observed in 3
healthy control subjects tested in a similar manner. Extrastriate
cortex responses habituated across testing sessions in both M.W.
and controls. These results support the involvement of
temporolimbic regions in TGA. M.W.'s frontoparietal activation
during the amnesic state may reflect compensatory changes toward a
visuospatial encoding strategy.
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