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. Author manuscript; available in PMC: 2023 Oct 11.
Published in final edited form as: Neuron. 2023 Jun 22;111(16):2601–2613.e5. doi: 10.1016/j.neuron.2023.05.028

Figure 7. Hypothesized circuit mechanism.

Figure 7.

(A) Macrocircuit. SC receives direct excitatory input from LIP and the FEF. It receives tonic inhibitory input from the SNr, an output nucleus of the basal ganglia. SC projects indirectly to the FEF and LIP via thalamic nuclei medio-dorsalis (MD) and pulvinar (Pulv.), respectively. LIP and FEF are reciprocally connected. FEF and LIP inhibit SNr by exciting neurons in the caudate nucleus that inhibit SNr.

(B) A possible mechanism that determines termination events in SC. The tonic inhibitory input from SNr to SC prevents bursts caused by LIP upticks to generate a saccade. The first uptick shown in LIP (top dark segment) leads to a non-saccadic burst because SNr activity is still substantial. The second uptick is associated with suppressed activity in SNr, unleashing SC to fire a large saccadic burst. The FEF is not shown in this panel because single-trial firing rates have yet to be elucidated from this structure and the trial-averaged activity is similar to that in both SC and LIP.