The Journal of Neuroscience, November 15, 2001, 21(22):9053-9067
Self-Organized Synaptic Plasticity Contributes to the Shaping of
and 
Oscillations In Vitro
Andrea
Bibbig1, 4,
Howard J.
Faulkner2,
Miles
A.
Whittington3, and
Roger D.
Traub1, 4
1 Department of Pharmacology, University of Birmingham
School of Medicine, Edgbaston, Birmingham B15 2TT, United Kingdom,
2 Imperial College School of Medicine, London SW7 2AZ,
United Kingdom, 3 School of Biomedical Sciences, University
of Leeds, Leeds LS2 9NQ, United Kingdom, and 4 Department
of Physiology and Pharmacology, State University of New York Health
Science Center, Brooklyn, New York 11203
(30-70 Hz) followed by 
(10-30 Hz) oscillations are evoked
in humans by sensory stimuli and may be involved in working memory.
Phenomenologically similar 
oscillations can be evoked in
hippocampal slices by strong two-site tetanic stimulation. Weaker
stimulation leads only to two-site synchronized . In
vitro oscillations have memory-like features: (1) EPSPs
increase during ; (2) after a strong one-site stimulus,
two-site stimulation produces desynchronized ; and (3) a single
synchronized epoch allows a subsequent weak stimulus to
induce synchronized . Features 2 and 3 last >50 min and so
are unlikely to be caused by presynaptic effects. A previous
model replicated the transition when it was assumed that
K+ conductance(s) increases and there is an ad hoc
increase in pyramidal EPSCs. Here, we have refined the model, so that
both pyramidalpyramidal and pyramidalinterneuron synapses are
modifiable. This model, in a self-organized way, replicates the
transition, along with features 1 and 2 above. Feature 3 is
replicated if learning rates, or the time course of
K+ current block, are graded with stimulus
intensity. Synaptic plasticity allows simulated oscillations to
synchronize between sites separated by axon conduction delays over 10 msec. Our data suggest that one function of oscillations is to
permit synaptic plasticity, which is then expressed in the form of oscillations. We propose that the period of oscillations, ~25
msec, is "designed" to match the time course of
[Ca2+]i fluctuations in dendrites,
thus facilitating learning.
Key words:
Hebbian synapses; 40 Hz; synchronization; EEG; learning; memory
Copyright © 2001 Society for Neuroscience 0270-6474/01/21229053-15$05.00/0
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