Brain Inspired Cognitive Systems

A nonlinear electrical circuit is proposed as a basic cell for modeling FitzHugh-Nagumo neurons with a modified excitability. Depending on initial conditions and parameters experiments show various dynamics including stability with excitation, bistability and oscillations. Moreover, we present an electrical circuit which will be used to realize a unidirectional coupling between two cells, mimicking chemical synaptic coupling. Finally, we characterize the frequency-doubling and the chaotic dynamics depending on the coupling strength in a master-slave configuration. In all experiments, we stress the influence of the coupling strength on the control of the slave neuron. INTRODUCTION Research on neural communication is based on a strong synergy between neuroscience discipline and engineering science [1, 2]. As a consequence, electrical circuits are developed including features observed in real neural systems in order to have a flexible, very fast processing and experimental medium mimicking neural activity. Famous illustrations and starting-points of electrical realizations are the Nagumo's lattice [3] and Neuristor device [1], modeling he FitzHugh-Nagumo (FHN) equation . In this case, oscillations rise from AndronovHopf bifurcations: Pulses can propagate with well-defined non zero minimum frequency, as observed for most axons. However, numerous nervous fibers, such as pyramidal cells in cortex or barnacle muscle fibers, are governed by a different mechanism leading to saddle homoclinic loop bifurcations [4] so that the minimum frequency of traveling waves can be close to zero [2,5]. In this paper, in the first part, we propose a nonlinear electrical circuit based on the FitzHugh-Nagumo equation with a modified excitability leading to complex dynamics of traveling waves [6, 7] emerging from saddle homoclinic loop bifurcations. Then, experimental conditions for stability with excitation threshold, bistability and oscillations are discussed. In the second part, we use this circuit as a basic cell to realize a master-slave configuration. Two cells are coupled in a unidirectional manner, which would correspond to two neurons coupled synaptically. We present the electronic circuit giving this coupling. Then, we discuss the experimental conditions for which the master dynamics controls the excitability of the slave neuron leading to a shift of bifurcation curves, a variation of an eigen interspike frequency or a chaotic behaviour. EXPERIMENTAL DESCRIPTION OF ONE CELL