Past models of somatosensory cortex have successfully demonstrated map formation and subsequent map reorganization following localized repetitive stimuli or deafferentation. They provide an impressive demonstration that fairly simple assumptions about cortical connectivity and synaptic plasticity can account for several observations concerning cortical maps. However, past models have not successfully demonstrated spontaneous map reorganization following cortical lesions. Recently, an assumption universally used in these and other cortex models, that peristimulus inhibition is due solely to horizontal intracortical inhibitory connections, has been questioned and an additional mechanism, the competitive distribution of activity, has been proposed. We implemented a computational model of somatosensory cortex based on competitive distribution of activity. This model exhibits spontaneous map reorganization in response to a cortical lesion, going through a two-phase reorganization process. These results make a testable prediction that can be used to experimentally support or refute part of the competitive distribution hypothesis, and may lead to practically useful computational models of recovery following stroke.
Peristimulus inhibition in sensory pathways is generally attributed to lateral inhibitory connections. However, in the neocortex circuitry is incompletely understood at present, and in some cases there is an apparent mismatch between observed inhibitory effects and intracortical inhibitory connections. This paper studies the hypothesis that an additional mechanism, competitive distribution of activation, underlies some inhibitory effects in cortex. Analysis of a mathematical model based on this hypothesis predicts that per stimulus inhibitory effects can be caused by competitive distribution of activation, and computer simulations confirm these predictions by demonstrating Mexican Hat patterns of lateral interactions, transformation of initially diffuse activity patterns into tightly focused "islands" of activation, and edge enhancement. The amount of inhibition can be adjusted by varying the intensity of the underlying competitive process. The concept of competitive distribution of activation provides an important perspective for interpreting neocortical and thalamocortical circuitry and can serve as a guide for further morphological and physiological studies. For example, it provides an explanation for the existence of recurrent cortex-to-thalamus connections that perform a logical AND-operation, and predicts the existence of analogous neocortical circuitry.