Networks with lateral connectivity III: Plasticity and reorganization of somatosensory cortex. Xing, Jing and George L. Gerstein. Department of Neuroscience, University of Pennsylvania, Philadelphia, PA- 19104.
APStracts 2:0277N, 1995.
SUMMARY AND CONCLUSIONS
1. Mechanisms underlying cortical reorganizations were studied using a three- layered neural network model with neuronal groups already formed in the cortical layer. 2. Dynamic changes induced in cortex by behavioral training or intracortical microstimulation (ICMS) were simulated. Both manipulations resulted in reassembly of neuronal groups and formation of stimulus-dependent assemblies. RFs of neurons and cortical representation of inputs also changed. Many neurons that had been weakly responsive or silent became active. 3. Several types of learning model were examined in simulating behavioral training, ICMS-induced dynamic changes, deafferentation or cortical lesion. Each learning model most accurately reproduced features of experimental data from different manipulations, suggesting that more than one plasticity mechanism might be be able to induce dynamic changes in cortex. 4. After skin or cortical stimulation ceased, as spontaneous activity continued, the stimulus-dependent assemblies gradually reverted into structure-dependent neuronal groups. However, relationships among individual neurons and identities of many neurons did not return to their original states. Thus a different set of neurons would be recruited by the same training stimulus sequence upon its next presentation. 5. We also reproduced several typical long term reorganizations caused by pathological manipulations such as cortical lesions, input loss and digit fusion. 6. In summary, with Hebbian plasticity rules on lateral connections, the network model is capable of reproducing most characteristics of experiments on cortical reorganization. We propose that an important mechanism underlying cortical plastic changes is formation of temporary assemblies which are related to receipt of strongly synchronized localized input. Such stimulus-dependent assemblies can be dissolved by spontaneous activity after removal of the stimuli. 

Received 18 July 1994; accepted in final form 23 August 1995.
APS Manuscript Number J442-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.