Sensorimotor Complexity and Cognition as Predictors of Primate Brain Size

Area of Science:

• Comparative neurobiology
• Evolutionary biology
• Primate evolution

Background:

• Animal brain size generally correlates with cognitive performance.
• However, brain size also influences somatic regulation, sensory processing, and motor control.
• Recent studies suggest cognitive abilities in fishes rival primates, questioning the brain size-cognition link.

Purpose of the Study:

• To investigate the relationship between primate brain size and its four main functions: somatic regulation, sensory input, motor actions, and cognition.
• To determine if correlations between brain size and cognitive performance are spurious due to other brain functions.
• To analyze the evolutionary pathways linking body size, brain size, and brain functions.

Main Methods:

• Application of multi-response Bayesian phylogenetic mixed models.
• Utilized phylogenetic path analysis to examine causal relationships.
• Treated four main brain functions as dependent variables predicted by brain size.

Main Results:

• Primate brain size strongly predicted somatic functions (body size), with weaker effects on sensory and motor functions.
• Phylogenetic path analysis indicated body size independently influences brain size.
• Brain size, in turn, predicted sensory, motor, and cognitive functions with similar strength.

Conclusions:

• The correlation between body and brain size arises from both correlated evolution and brain size effects on somatic functions.
• Primate cognition is found to be tightly coevolved with sensory and motor functions.
• The study refutes challenges posed by fish cognition data regarding the brain size-cognition relationship.