Networks with lateral connectivity I: Dynamic properties mediated by the
balance of intrinsic excitation and inhibition.
Xing, Jing and George L. Gerstein.
Department of Neuroscience, University of Pennsylvania, Philadelphia, PA-
19104.
APStracts 2:0275N, 1995.
SUMMARY AND CONCLUSIONS
1. We studied the rapid dynamic changes of neuron response properties in the
somatosensory cortex by use of computer simulations. The model consists of
three feed-forward layers of spiking neurons, corresponding to skin, subcortex
and cortex structures. Measurements and analysis of model activity throughout
this work are similar to those used in neurophysiological experiments. 2. The
effects of various parameters on response properties of model neurons were
investigated. The most important parameters were the lateral excitation (E)
and inhibition (I) in the simulated cortical network. 3. The balance between
excitation and inhibition is a key factor in determining the stability of the
network model. There is a large E-I parameter region within which the model
can stably respond to inputs. 4. The input-output relations and receptive
field (RF) sizes of simulated neurons are modifiable by the E-I balance. The
shapes of receptive fields are determined by both feedforward projections and
the spatial distribution of lateral connections. 5. We simulated changes in
temporal and spatial properties of neurons in response to manipulations which
mimic BMI (bicuculine methiodide) or glutamate application to the cortex.
Simulation results agreed well with experimental data, suggesting that
cortical transmitter levels play an important role in the dynamic responses of
the neural net through their effects on E-I balance. 6. With parameters of the
model set to an inhibition-dominant scheme, the model was able to reproduce
experimentally observed rapid RF expansions that follow cortical lesion or
input denervation. Simulation results also suggested that spontaneous inputs
to a sensory system can serve as a source of tonic inhibition in the cortex.
7. We concluded that lateral connections could produce and maintain a cortical
network having dynamic properties without the need to invoke synaptic
plasticity. Individual neuron properties could be modified by changing the
balance of cortical layer excitation and inhibition. In a real brain, this
could be achieved either by changing cortical transmitter level (GABA for
example) or by changing tonic background input to the cortical network.
Received 18 July 1994; accepted in final form 23 August 1995.
APS Manuscript Number J440-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.