The basic basal ganglia circuit. StrD1 and D2 are straital inputs for D1 and D2 dopamine receptrs, STN is the subthalamic nucleus, and GPe and GPi are the globus palidus externus and internus respectively.
This video shows a simulation of the basal ganglia circuit, whose network structure is shown here on the right.
The input can be thought of as cortex and the output is going to thalamus. This graph shows the output and the input is controlled by these 5 sliders
Let me start the simulation. When a given cortical state has a high value its corresponding action should be selected by thalamus.
This can be seen in the graph below.
Here, selection means decreasing the activity of the corresponding action because basal ganglia is known to release thalamus from inhibition.
Notably there is little response of the circuit to negative values or values below about .3.
Nevertheless the circuit can select the most valuable state as soon as one of the actions goes significantly higher than .3 regardless of the value of the other states.
In addition, the bigger the difference, the more clear the selected activity is
Notice that when several competing states have high, near threshold values the dynamics of the circuit still allow it to make fine distinctions.
For instance here it can distinguish a difference of only .06, selecting the highest action appropriately .
As I move the slider back to near the threshold value the corresponding action quickly becomes indistinguishable from other possible actions
Critically the specific dynamics we see here, while looking something like a winner take all circuit, are much more sophisticated than the dynamics we would get by merely inhibitorily connecting cells
Specifically, this network responds particularly quickly, and over a wider range of possible network inputs.