Interactions between the Midbrain Superior Colliculus and the Basal Ganglia

Area of Science:

• Neuroscience
• Evolutionary Biology
• Computational Neuroscience

Background:

• Cortico-basal ganglia connections feature parallel, re-entrant loops.
• Phylogenetically older, subcortical loops linking the basal ganglia with brainstem structures are suggested.
• The functional segregation of these subcortical loops requires further investigation.

Purpose of the Study:

• To evaluate the loop hypothesis for subcortical structures using the superior colliculus (SC) as a model.
• To investigate the connectivity and information flow between the SC and basal ganglia.
• To understand the role of SC-basal ganglia interactions in basal ganglia functions.

Main Methods:

• Anatomical tracing of projections between the SC and basal ganglia nuclei.
• Electrophysiological recordings to assess information transmission.
• Analysis of ascending projections from the SC to the thalamus.

Main Results:

• Robust anatomical evidence supports closed-loop connectivity between the SC and basal ganglia.
• The SC projects to key basal ganglia input nuclei: substantia nigra and subthalamic nucleus.
• SC afferent signals convey information about biologically significant event onsets to basal ganglia nuclei.

Conclusions:

• The superior colliculus serves as a model for understanding older, subcortical basal ganglia loops.
• SC projections to the basal ganglia carry critical information for selection and reinforcement learning.
• These findings suggest a significant role for subcortical sensorimotor structures in basal ganglia circuitry evolution.