Crossed Corticostriatal Projections in the Macaque Brain

Area of Science:

• Neuroscience
• Primate Brain Anatomy
• Cortico-striatal Pathways

Background:

• The striatum receives major input from ipsilateral cortex and thalamus in nonhuman primates.
• Crossed corticostriatal (CSt) projections from the contralateral hemisphere to the striatum have been understudied.
• Understanding these pathways is vital for comprehending brain function and recovery mechanisms.

Purpose of the Study:

• To qualitatively and quantitatively analyze the distribution and origin of crossed CSt projections in the macaque brain.
• To compare crossed CSt projections with ipsilateral projections to the striatum.
• To elucidate the functional significance of these bilateral connections.

Main Methods:

• Neural tracer injections into different striatal regions of macaques (both sexes).
• Qualitative and quantitative analysis of labeled CSt cells in both hemispheres.
• Comparison of the origin and density of crossed versus ipsilateral projections.

Main Results:

• Crossed CSt projections to the caudate and putamen can be substantial, accounting for up to 30% of total labeled cells.
• Crossed projections predominantly originate from motor, prefrontal, and cingulate areas, unlike ipsilateral projections.
• In some cases, contralateral input was comparable in strength to ipsilateral input.

Conclusions:

• This study provides the first detailed anatomical description of crossed CSt pathways in the macaque.
• These projections facilitate bilateral distribution of motor, motivational, and cognitive signals.
• They are potentially important for reinforcement learning, action selection, and motor compensation post-stroke.