Figure 6.

The effects of ketamine on signal and noise, visualized in a single ensemble. A, An example of a dimension-reduced MSUA space constructed from the standardized firing rates of 61 dorsolateral PFC neurons recorded during a single session, before ketamine injection. Each dot reflects the activities of all 61 neurons in the delay period of a single trial. Trials with the same rule (blue, prosaccade rule; red, antisaccade rule) are associated with similar ensemble activities, reflected as a relatively compact cluster that is distinct from the other cluster. B, Averaged activities from each neuron in prosaccade (blue) and antisaccade (red) trials (in z-scores) before injection. Each bar represents the mean and SEM of activities from a single neuron. Gray boxes highlight neurons showing great difference in their responses to the two rules. C, The MSUA space for the same ensemble after ketamine injection, dimension reduced together with activities shown in A. Ketamine administration increased noise, or greater variance in ensemble activity across trials associated with the same rule, which is reflected as greater dispersion among dots of the same color. D, Averaged activities from each neuron in prosaccade (blue) and antisaccade (red) trials (in z-scores) after ketamine injection. The same neurons highlighted in A (gray boxes) now show reduced difference in their responses to the two rules. Hence, in these neurons, ketamine resulted in a reduction in the signal strength for task rules.