Superior colliculus

The superior colliculus (SC) is the evolutionary expansion of the tectum in mammals, and can be thought of as the subcortical, evolutionarily primary version of the neocortex, by integrating various sensory inputs to drive more complex motor behavior (Isa et al., 2021). Whereas the neocortex is much more strongly shaped by synaptic plasticity (learning), the SC is more strongly shaped by evolution and is thought to be a major locus of innate behavior. Whereas the SC is primarily driven by visual input (i.e., the optic tectum in non-mammalian species), the the inferior colliculus (IC) is primarily driven by auditory input (i.e., the auditory tectum). The two are densely interconnected and the same overall principles apply to both structures.

The SC has massive interconnectivity with every other major network in the brain Benavidez et al., 2021, including the neocortex, basal ganglia, cerebellum and the motor brainstem and spinal cord. It sends sensory signals to the amygdala and acetylcholine (ACh) areas that then drive neuromodulation of the entire brain, consistent with the Rubicon model.

One of the most well-studied aspects of SC functionality is in driving eye movements (saccades) toward spatial targets. The retinotopically organized superficial layers of the SC receive direct input from the retina and visual areas of neocortex, and project into the intermediate and deep layers that contain motor output neurons that directly drive eye movements. These deeper layers receive extensive input from the SNr of the basal ganglia, along with many other subcortical and motor cortical inputs, which can then modulate and contextualize the motor outputs.