Reservoir Computing Properties of Neural Dynamics in Prefrontal Cortex
Fig 8
Continuous phase readout from reservoir and dACC activity.
A. Example stimuli sequence, corresponding reservoir activity and model output during test showing the stability of phase readout. Upper panel shows a selection within the stimuli input sequence fed to the reservoir during test. Colored blocks represent activity of the reservoir input neurons simulating the different features of the task. Middle graph shows the activity of 20 randomly picked reservoir neurons illustrating the dynamic nature of activity in the reservoir. Lower graph shows the evolution of the readout neurons that represent target fixation (dashed lines) and hand touch (solid lines) along with the activity of a unit reading out the task phase (brown line). This special readout unit was not connected back to the reservoir and could not rely on the attractors created with a feedback connection. This portion of stimuli sequence starts with the last trial of a problem. After the signal to change is given to the model (grey block) the phase readout unit activates and fires steadily during the following three trials corresponding to the search phase showing the stable output that can be obtained from the dynamic reservoir activity. The third target exploration is rewarded (COR1 trial) and ends the search phase. At COR1 trial, when the reward neuron activates, the phase readout unit shuts off thereby signaling the start of the repeat phase. The rewarded target choice (red lines) is then repeated in subsequent trials. B. Upper graph illustrates the average readout output across all COR4 trials. Shaded area corresponds to the standard deviation. Correct readout is inferior to 0.5 for time bins before the signal to change, and the opposite for the following time bins. Lower graph is the average decoding accuracy and 95% confidence interval as computed from a 10,000 permutation test. C. Same as B for COR1 trials. Correct readout is superior to 0.5 for time bins before the first correct feedback, and the opposite for the following time bins. Transition from repetition to search was slower than the transition from search to repetition.