Neural coding of numerousness.

Area of Science:

• Comparative cognition
• Neuroscience
• Evolutionary biology

Background:

• Numerousness perception, or "number sense," is a widespread cognitive ability found across various animal taxa, including insects, fish, reptiles, birds, and mammals.
• This ability transcends sensory modalities, with animals capable of estimating quantities from visual stimuli, auditory tones, and even self-generated movements.
• The evolutionary divergence in neuroanatomy across these taxa makes a single, conserved neural pathway for number cognition unlikely.

Approach:

• This review synthesizes current research on how numerousness information is processed in the brain, from initial sensory input to the abstract coding in higher-order brain centers.
• It examines the similarities in response properties of "number neurons" found in evolutionarily distant groups like primates and birds.
• The review explores the hypothesis that conserved computational mechanisms, rather than homology, underlie these similarities in neural processing.

Key Points:

• Neurons selectively responding to numerical quantities have been identified in higher-order brain centers of primates and birds.
• Despite evolutionary distance, these "number neurons" exhibit similar response properties, suggesting convergent evolution driven by computational efficiency.
• The processing of numerousness information likely involves conserved computational steps across diverse neural pathways.

Conclusions:

• The study of number cognition in animals highlights convergent computational strategies in neural processing despite divergent evolutionary paths.
• Understanding these conserved mechanisms provides insights into the fundamental principles of numerical information processing in the brain.
• Further research is needed to address key open questions regarding the neural basis and evolutionary trajectory of number cognition.