Self-organized synaptic plasticity contributes to the shaping of gamma and beta oscillations in vitro.
gamma (30-70 Hz) followed by beta (10-30 Hz) oscillations are evoked in humans by sensory stimuli and may be involved in working memory. Phenomenologically similar gamma-->beta oscillations can be evoked in hippocampal slices by strong two-site tetanic stimulation. Weaker stimulation leads only to two-site synchronized gamma. In vitro oscillations have memory-like features: (1) EPSPs increase during gamma-->beta; (2) after a strong one-site stimulus, two-site stimulation produces desynchronized gamma; and (3) a single synchronized gamma-->beta epoch allows a subsequent weak stimulus to induce synchronized gamma-->beta. Features 2 and 3 last >50 min and so are unlikely to be caused by presynaptic effects. A previous model replicated the gamma-->beta 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 pyramidal-->pyramidal and pyramidal-->interneuron synapses are modifiable. This model, in a self-organized way, replicates the gamma-->beta 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 gamma oscillations is to permit synaptic plasticity, which is then expressed in the form of beta oscillations. We propose that the period of gamma oscillations, approximately 25 msec, is "designed" to match the time course of [Ca(2+)](i) fluctuations in dendrites, thus facilitating learning.
Bibbig
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A
Department of Pharmacology, University of Birmingham School of Medicine, Edgbaston, Birmingham B15 2TT, United Kingdom. abibbig@netmail.hscbklyn.edu
Faulkner
H J
HJ
Whittington
M A
MA
Traub
R D
RD
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation / Q000379:methods; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects / Q000502:physiology; D007858:Learning / Q000187:drug effects / Q000502:physiology; D009020:Morphine / Q000494:pharmacology; D009433:Neural Inhibition / Q000502:physiology; D016571:Neural Networks, Computer; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000502:physiology; D015203:Reproducibility of Results; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D000701:Analgesics, Opioid; D018690:Excitatory Amino Acid Agonists; D009020:Morphine; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D011188:Potassium; D002118:Calcium