Neural Correlates of Saccade Target Selection and Programming in Superior Colliculus
Decision Making , Superior Colliculus , Noise Correlations , Threshold Mechanism , Decoding
Decision-making process involves sequential stages of sensory processing, perceptual selection of a target for the behavior, preparation of an action, and execution of that action. Superior colliculus is at the center of a network which integrates the sensory information into evidence towards decisions about whether, to where and when a saccade should be made, and is therefore a suitable model to explore different aspects of these stages. This work explores the dynamics of interactions of SC populations during a decision that involves selection of a particular stimulus among the alternative options as the target for a future saccade. I show that these interactions evolve in time along with the requirements of the task, and the patterns of this evolution are different among neurons from the same or different SC populations. I further explore the impact of correlations within the activity rates of these neurons on the efficiency of coding this decision variable. I show that while the variability in pairs of neurons seems to increase the available information about the encoded target for the saccade, they decrease the performance of two biologically plausible decoders over simulated large populations. Finally, I explore the role of neuros in intermediate layers of SC in saccade production in a task where the subjects anticipate the possibility of withholding a programmed saccade. I show that while an accumulation of evidence towards a decision to execute a saccade appears to happen in SC, this activity pattern cannot fully account for the behavior of the subject. SC should be mainly considered as the threshold unit that transfers this decision variable from an accumulation unit elsewhere in the brain, such as the frontal eye fields, to the execution unit in the brainstem. This work confirms previous findings on the role of SC in two perceptual and executive stages of a decision process and provides additional insights on the details of how these roles are implemented.