Uncovering specific changes in network wiring underlying the primate cerebrotype.

Area of Science:

• Neuroscience
• Evolutionary Biology
• Comparative Anatomy

Background:

• Brain evolution is often explained by regular scaling principles.
• Alternative theories propose deviations from scaling are key to primate brain evolution and diverse cerebrotypes.

Purpose of the Study:

• To investigate scaling rules in the deep cerebellar nuclei (DCN), a crucial link between the cerebellum and cerebral cortex.
• To compare axonal and dendritic wiring in rodent and primate DCN to identify evolutionary changes.

Main Methods:

• Comparative analysis of neuronal density, dendritic length per neuron, and Purkinje cell axon length in rodent and primate DCN.
• Examination of scaling rules, specifically in the primate dentate nucleus (LN/dentate).
• Analysis of dendritic diameter distribution and region-of-influence.

Main Results:

• Regular scaling was confirmed for neuronal density, general dendritic length, and Purkinje cell axon length.
• Deviations from regular scaling were observed in the primate LN/dentate, particularly a reduced dendritic length per neuron.
• The LN/dentate showed changes favoring neurons with spatially restricted dendritic branching, suggesting a shift towards accommodating more network modules.

Conclusions:

• Primate brain evolution, particularly in the LN/dentate, involves specific modifications to scaling rules.
• Reduced dendritic fields in the LN/dentate may facilitate a higher number of network modules, explaining primate cerebrotype divergence.
• Connectivity maximization is not the only evolutionary driver; increased network modularity is also crucial for primate brain evolution.