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Abstract:
A great deal of information is available about hippocampal
function: the theta and gamma frequency oscillations that occur in
this structure, the properties of place cells and the detailed
wiring diagram of the region. We have been attempting to put this
information into a coherent framework, and I will describe several
efforts in this direction. First, new ideas will be presented about
how the reciprocally connected recurrent networks found in the
dentate and CA3 regions of the hippocampus mediate the storage and
recall of memory
sequences.
It will be argued that such sequences are recalled at gamma
frequency during individual theta cycles and that the phase-advance
described by O'Keefe and Recce
(Hippocampus
3:317, 1993) can be understood in these terms. A new analysis of
place coding in ensembles of neurons provides the strongest
evidence to date for the importance of theta phase coding. It will
be argued that theta/gamma coding may be used in different brain
processes and explain psychophysical short-term memory experiments
that point to serial brain processing. Finally, evidence for theta
oscillations in humans will be presented. These oscillations were
observed during intracranial recordings and show a clear linkage to
memory processes.
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