Ying-Yang Competitive Harmony between Direct and Indirect Pathways in A Spiking Neural Network of The Basal Ganglia

Abstract

The basal ganglia (BG) in the brain exhibit a variety of functions for motor and cognition. There are two competing pathways in the BG; direct pathway (DP), facilitating movement and indirect pathway (IP), suppressing movement. It is well known that diverse functions of the BG could be done via “balance” between DP and IP. But, to the best of our knowledge, no quantitative analysis for such balance was done. In this paper, we consider a spiking neural network of the BG and make quantitative analysis for competitive harmony (i.e., competition and cooperative interplay) between DP and IP by introducing their competition degree 𝒞d, given by the ratio of strength of DP 𝒮DP) to strength of IP (𝒮IP) (i.e.,𝒞d= 𝒮DP/𝒮IP). We first consider the case of normal dopamine DA) level ofϕ*= 0.3. In the case of phasic cortical input (10 Hz) in the phasically-active state, a healthy state with(i.e., DP is 2.82 times stronger than IP) appears. In this case, normal movement occurs via harmony between DP and IP. Next, we consider the case of decreased DA level,ϕ=ϕ*(= 0.3)xDA(1> xDA≥0). With decreasingxDAfrom 1, the competition degree 𝒞dbetween DP and IP decreases monotonically from, which results in appearance of a pathological state (e.g., Parkinson’s disease) with decreased competition degree. In this pathological state, strength of IP (𝒮IP) is much increased than that in the case of normal healthy state, leading to disharmony between DP and IP. Due to such break-up of harmony between DP and IP, impaired movement occurs. Finally, we also study treatment of the pathological state via recovery of harmony between DP and IP.PACS numbers87.19.lj, 87.19.lu, 87.19.rs