Cholinergic modulation of cortical oscillatory dynamics.
Liljenstrom, Hans.
SANS - Studies of artificial Neural Systems, Dept. of Numerical Analysis
and Computing Science, Royal Institute of Technology, S-100 44 Stockholm,
Sweden, hali@sans.kth.se.
APStracts 2:0076N, 1995.
SUMMARY AND CONCLUSIONS
1. The effect of cholinergic modulation on cortical oscillatory dynamics was
studied in a computational model of the piriform (olfactory) cortex. The model
included the cholinergic suppression of neuronal adaptation, the cholinergic
suppression of intrinsic fiber synaptic transmission, the cholinergic
enhancement of interneuron activity, and the cholinergic suppression of
inhibitory synaptic transmission. 2. Electroencephalographic (EEG) recordings
and field potential recordings from the piriform cortex were modeled with a
simplified network in which cortical pyramidal cells were represented by
excitatory input/output functions with gain parameters dependent on previous
activity. The model incorporated distributed excitatory afferent input and
excitatory connections between units. In addition, the model contained two
sets of inhibitory units mediating inhibition with different time constants,
and different reversal potentials. This model can effectively match the
patterns of cortical EEG and field potentials, showing oscillatory dynamics in
both the gamma (30-80 Hz) and theta (3-10 Hz) frequency range. 3. Cholinergic
suppression of neuronal adaptation was modeled by reducing the change in gain
associated with previous activity. This caused an increased number of
oscillations within the network in response to shock stimulation of the LOT,
effectively replicating the effect of carbachol on the field potential
response in physiological experiments. 4. Cholinergic suppression of intrinsic
excitatory synaptic transmission decreased the prominence of gamma
oscillations within the network, allowing theta oscillations to predominate.
Coupled with the cholinergic suppression of neuronal adaptation, this caused
the network to shift from a non-oscillatory state into an oscillatory state of
predominant theta oscillations. This replicates the longer term effect of
carbachol in experimental preparations on the EEG potential recorded from the
cortex in vivo and from brain slice preparations of the hippocampus in vitro.
Analysis of the model suggests that these oscillations depend upon the time
constant of neuronal adaptation rather than the time constant of inhibition or
the activity of bursting neurons. 5. Cholinergic modulation may be involved in
switching the dynamics of this cortical region between those appropriate for
learning and those appropriate for recall. During recall, the spread of
activity along intrinsic excitatory connections allows associative memory
function, while neuronal adaptation prevents the spread of activity between
different patterns. During learning, the recall of previously stored patterns
is prevented by suppression of intrinsic excitatory connections, while the
response to the new patterns is enhanced by suppression of neuronal
adaptation.
Received 13 October 1994; accepted in final form 21 February 1995.
APS Manuscript Number J636-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.