Networks with lateral connectivity II: Development of neuronal grouping and
corresponding receptive field changes.
Xing, Jing and George L. Gerstein.
Department of Neuroscience, University of Pennsylvania, Philadelphia, PA-
19104.
APStracts 2:0276N, 1995.
SUMMARY AND CONCLUSIONS
1. Using a three-layered network model defined in the previous paper, we
studied the basic features of neurons in the cortical layer while the synaptic
strengths of lateral excitatory connections were made modifiable by a Hebbian
learning rule and a normalization process. 2. We found that neurons in the
cortical layer formed groups through their lateral excitatory connections
after the network was trained with sequential random dot stimulations. Neurons
within a group connected tightly; neurons in different groups connected
weakly. 3. The effects of model parameters and input parameters on the
formation of neuronal groups were investigated. Results showed that the
average size and rough shapes of groups were mainly determined by the spatial
distribution of lateral connections within the cortical layer, irrespective of
input parameters and training methods. Thus groups are structure-dependent.
4. Lateral inhibition in the network is the only key factor that affects the
grouping of neurons. Without an appropriate amount of distant inhibition,
group formation does not occur. Group formation is very robust to all other
parameters we tested. On the other hand, group locations are very easily
disturbed by inputs or changes of parameters, suggesting that such neuronal
groups are dynamically maintained. 5. With the development of neuronal groups,
neurons can be divided into two response types. TN-I neurons respond weakly to
inputs and have small receptive fields or do not respond at all (silent); TN-
II neurons, about 30-40% of all, respond strongly to inputs and have large
receptive fields. The two types of neuron also differ with respect to response
threshold and temporal firing patterns. After groups formed, receptive fields
of TN-II neurons within the same group clustered spatially with high overlap,
while receptive fields of TN-I neurons with detectable responses shifted
systematically with the neuron's spatial location. 6. The two types of neurons
are homogeneously distributed across the cortical layer. The population of
each type of neuron produces a full representation of the input layer with
respectively weak or strong responses. 7. We concluded that neurons in the
cortical network naturally assembled into functional groups. Such groups are
dynamic and amenable to change by input stimuli. A fraction of neurons (30-
40%) within the same group share a similar receptive field and strongly
respond together to stimuli, so that the network has more robust response to
inputs. On the other hand, the responses of a large portion (60-70%) of
neurons become weak or silent: these neurons are available for other (unknown)
functional purposes.
Received 18 July 1994; accepted in final form 23 August 1995.
APS Manuscript Number J441-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.