The model extended a cortico-BG-SC model for threshold detection and modulation by including the indirect pathway of the basal ganglia. This model reproduces the ramping of CD activity during evidence accumulation in perceptual decision making. When the indirect pathway balances the direct pathway, the decision threshold can be modulated over a wide range, which leads to a flexible tuning in decision threshold. The saturation of CD activity during evidence accumulation is also reproduced in the model.
Sensory input (Nx2 matrix) - Defined as sensory input induced by the leftward and rightward moving dots, fed into left-preferring and right-preferring cortical modules Cx_L and Cx_R, respectively.
Saccade burst (Nx2 matrix) - Defined as saccade burst SC_L and SC_R corresponding to the population that becomes active.
Decision threshold (scalar) - Defined as the firing rate of the cortical population Cx_e that projects to the active SCe unit at the onset time of SCe activity.
Figure 1: Schematic circuit model with three interconnected structures: the cortex, BG, and SC.
"Schematic circuit model with three interconnected structures: the cortex, BG, and SC. The two selective excitatory populations in the cortical circuit exhibit ramping activity reflecting integration of sensory input and compete with each other through shared inhibition. Sensory evidence accumulated in the cortical network is sent to the SC (a command center for eye movement) and through the BG. The SC sends feedback signals to the cortex. Inset, The structure of the BG used in our model. Signals to the CD are transmitted to the output nucleus (SNr) through two pathways: the direct pathway (Direct) from the CD directly to the SNr and the indirect pathway (Indirect) from the CD through the GPe, STN to the SNr."
The model is focused on indirect pathway of the basal ganglia system based on spiking network model. The mechanism of adjusting the decision threshold by plasticity of the corticostriatal connection is effective, provided that the indirect pathway counterbalances the direct pathway in the projections to the output nucleus. Abnormal enhancement of the interactions between STN and GPe in the indirect pathway, with an oscillation frequency that depends on the excitatory cortical input to the STN and the inhibitory striatal input to the GPe, would lead to a parkinsonism. Characterized as a state of Parkinsonism, the reduction of mean reaction time and range of threshold variation in beta oscillation is due to a specific circuit mechanism for impairments of perceptual decision making.
Summaries of Experimental Data (SEDs) and Simulation Results (SSRs) (Show)