Elsevier

Neurocomputing

Volumes 32–33, June 2000, Pages 685-691
Neurocomputing

A biologically plausible computational model of classical conditioning induced reorganization of tonotopic maps in the auditory cortex

https://doi.org/10.1016/S0925-2312(00)00233-2Get rights and content

Abstract

A model of the auditory system with realistic biophysical traits based on experimental data has been constructed with the neurosimulator GENESIS, aiming at producing formation and reorganization of tonotopic cortical maps in a simulation of area AI of the auditory cortex which comprises 2256 pyramidal and 1128 basket cells and receives inputs from a 47-receptor model cochlea and from a source of excitatory stimulus which represents an unconditioned stimulus (US) in simulations of classical conditioning. The simulations performed with the model yielded tonotopic cortical representations, which presented reorganization in simulations of classical conditioning. The reorganization observed favored the processing of the frequency chosen as conditioned stimulus (CS).

Introduction

The study of the mechanisms of formation and reorganization of cortical maps has shown to be a very fruitful approach in the investigation of the processes involved in the formation of a representation of the external world in the brain. In the auditory system, the tonotopic cortical representations have been shown to present reorganization as a consequence of cochlear lesions and classical conditioning [1], [2]. Computational models have been constructed which were able to reproduce processes of formation and reorganization of tonotopic organization in the auditory system [3], [4].

In a previous effort to construct a more realistic model of the auditory system, we have observed the formation of cortical tonotopic representations which presented variability from one simulation to another [5]. The aim of the present work is to study the behavior of a modified version of this computational model in simulations of classical conditioning.

Section snippets

The model

The model presented here is a modification of a model we have described previously [5]. The modified model and the simulations were performed in the simulator GENESIS running under LINUX in a Pentium-II 300.

The original model comprised a simulated primary auditory cortical area which received inputs from a simplified simulated cochlea. The cortical area was a network of 2256 interconnected pyramidal and 1128 basket cells based on physiologic and histologic data about cells of the auditory

Simulations

Before the execution of every simulation, a specific frequency — frequency number 5 in the example described here — was chosen to be the CS and the pyramidal cells received model electrodes so that their activity levels could be monitored throughout the experiments.

In order to obtain formation and reorganization of cortical representations, a stimulation protocol comprising two phases was used. In the first phase, all the cochlear regions were stimulated in non-sequential order, the cochlea as

Results

As a result of the first phase of the stimulation protocol, tonotopically ordered cortical representations of the 16 frequencies applied were obtained [5].

The second phase of the stimulation protocol yielded the following results: increased excitability in the area of cortical representation of the CS (frequency number 5) (Fig. 1), increase in the conductance of the NMDA receptors of this same area (Fig. 2), and reorganization in the sensitivity of the pyramidal cells which responded to the CS

Discussion and conclusions

The formation of tonotopic representations in the simulated cortical area, the presence of variability from one simulation to another [5], and the reorganization in the sensitivities of the pyramidal neurons which favored response to the CS are all in accordance with findings obtained in experimental studies with mammals [6], [7], [8]. These results support the biological plausibility of the model.

The formation of tonotopic cortical representations in the model can be attributed to the

Marilene de Pinho is a psychiatrist and writer born in Teresina, PI, Brazil, where she graduated in Medicine in 1993 and concluded Medical Residence in 1996. She is currently working on her Ph.D., developing biologically plausible simulations involving the auditory system and fear conditioning. Her research interests involve the application of computer simulations to the understanding of emotion, consciousness auditory perception and psychiatric disorders.

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Marilene de Pinho is a psychiatrist and writer born in Teresina, PI, Brazil, where she graduated in Medicine in 1993 and concluded Medical Residence in 1996. She is currently working on her Ph.D., developing biologically plausible simulations involving the auditory system and fear conditioning. Her research interests involve the application of computer simulations to the understanding of emotion, consciousness auditory perception and psychiatric disorders.

Marcelo B. Mazza was born in Teresina, PI, Brazil, where he graduated in Physics. He received his M.Sc. degree in Physics from the University of São Paulo in Ribeirão Preto, Brazil, in 1997, where he is currently working on his Ph.D., developing biologically plausible simulations of the somatosensory system. His research interests involve simulations of cortical functions and applications of neural networks to the study of cognitive functions and psychiatric disorders.

Antônio C. Roque was born in São Paulo, SP, Brazil. He received his BS degree in physics from the State University of Campinas, Brazil, in 1985, and his Ph.D. degree in cognitive science and artificial intelligence from the University of Sussex, Brighton, UK, in 1992. He joined the faculty of the Department of Physics and Mathematics of the University of São Paulo at Ribeirão Preto, Brazil, in June, 1993, where he founded and is the current coordinator of the Laboratory of Neural Networks and Computational Neuroscience. His research interests are computational neuroscience and neural networks applications in medicine.

This work was supported by FAPESP.

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