Current views of long-term memory presume that
both the hippocampal complex and the neocortex play interactive,
but separate, roles in the storage of memories. While the
neocortex is considered the eventual and permanent store
for our memories, the encoding of recently experienced
events is thought to be initially dependent upon the hippocampus
and closely related structures. Neuropsychological studies
have demonstrated that damage to the medial temporal lobe
results in a retrograde amnesia extending back in time,
with better preservation of older memories. The converse
pattern has been shown in patients with semantic dementia,
who have focal atrophy of the inferolateral temporal neocortex,
but relative sparing of the hippocampal complex (Graham
& Hodges, 1997). Here we demonstrate that such patients
can show relatively preserved new learning on a forced-choice
recognition memory test (based on real and chimeric animals),
while patients in the early amnestic phase of Alzheimer's
disease show severely impaired learning on the same test.
This result provides support for the view that new learning
is primarily dependent upon the hippocampus and related
structures. (JINS, 1997, 3, 534–544.)