Memory networks are formed in the cerebral cortex by associative processes,
following Hebbian principles of synaptic modulation. Sensory and motor mem
ory networks are made of elementary representations in cell assemblies of p
rimary sensory and motor cortex (phyletic memory). Higher-order individual
memories, e.g. episodic, semantic, conceptual - are represented in hierarch
ically organized neuronal networks of the cortex of association. Perceptual
memories are organized in posterior (post-rolandic) cortex, motor (executi
ve) memories in cortex of the frontal lobe. Memory networks overlap and int
eract profusely with one another, such that a cellular assembly can be part
of many memories or networks. Working memory essentially consists in the t
emporary activation of a memory network, as needed for the execution of suc
cessive acts in a temporal structure of behavior. That activation of the ne
twork is maintained by recurrent excitation through reentrant circuits. The
recurrent reentry may occur within local circuits as well as between separ
ate cortical areas. In either case. recurrence binds together the associate
d components of the network and thus of the memory it represents. (C) 2000
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