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Abstract:
Abstract: Temporally-graded retrograde memory loss, with a
disproportionate impairment of recent relative to remote memories,
is considered a hallmark of medial temporal lobe amnesia. According
to consolidation theory, the hippocampal complex plays a
time-limited role in memory, needed only until consolidation in
long-term memory is complete (Squire, 1992). Recent support for
this theory comes from findings of a reverse gradient in semantic
dementia ( Hodges & Graham, 1998), a neurodegenerative disorder
characterized by temporal neocortical atrophy with hippocampal
sparing. Consolidation theory, however, is challenged by evidence
that remote autobiographical and semantic memory are not always
spared in amnesia (Nadel & Moscovitch, 1997). We investigated
the role of the hippocampal complex in recent and remote
autobiographical and memory by contrasting the memory of a semantic
dementia patient, D.K., and an amnesic patient, K.C., using family
photographs as recall cues. Semantic memory was tested by
recognition and reading speed of words that entered the language at
different times. K.C. demonstrated a complete loss of
autobiographical episodes with a sparing of autobiographical facts
and temporally-graded loss of semantics, whereas D.K. demonstrated
preserved autobiographical episodes with a reverse temporal
gradient for personally-relevant names and semantics. These
findings suggest that the hippocampal complex plays a permanent
role in the storage and retrieval of autobiographical episodes, but
not semantics, and challenge the notion that episodic memory is
dependent upon an intact semantic system.
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