|dc.description.abstract||A consensus on how to characterise the anterograde and retrograde memory processes
that are lost or spared after hippocampal damage has not been reached. In
this thesis, I critically re-examine the empirical literature and the assumptions behind
current theories. I formulate a coherent view of what makes a task hippocampally dependent
at acquisition and how this relates to its long-term fate. Findings from a
neural net simulation indicate the plausibility of my proposals.
My proposals both extend and constrain current views on the role of the hippocampus
in the rapid acquisition of information and in learning complex associations.
In general, tasks are most likely to require the hippocampus for acquisition if
they involve rapid, associative learning about unfamiliar, complex, low salience stimuli.
However, none of these factors alone is sufficient to obligatorily implicate the
hippocampus in acquisition. With the exception of associations with supra-modal information
that are always dependent on the hippocampus, it is the combination of
factors that is important.
Detailed, complex information that is obligatorily hippocampally-dependent at
acquisition remains so for its lifetime. However, all memories are semanticised as
they age through the loss of detailed context-specific information and because generic
cortically-represented information starts to dominate recall. Initially hippocampally dependent
memories may appear to become independent of the hippocampus over
time, but recall changes qualitatively. Multi-stage, lifelong post-acquisition memory
processes produce semanticised re-representations of memories of differing specificity
and complexity, that can serve different purposes.
The model simulates hippocampal and cortical interactions in the acquisition and
maintenance of episodic and semantic events, and behaves in accordance with my
proposals. In particular, conceptualising episodic and semantic memory as representing
points on a continuum of memory types appears viable. Support is also found for
proposals on the relative importance of the hippocampus and cortex in the rapid acquisition
of information and the acquisition of complex multi-model information; and
the effect of existing knowledge on new learning. Furthermore, episodic and semantic
events become differentially dependent on cortical and hippocampal components.
Finally, as a memory ages, it is automatically semanticised and becomes cortically dependent.||en