An evolutionary scaling law for the primate visual system and its basis in cortical function

Area of Science:

• Neuroscience
• Evolutionary Biology
• Comparative Anatomy

Background:

• Mammalian brain evolution is characterized by disproportionate neocortical expansion relative to subcortical structures.
• The visual system, particularly primary visual cortex (V1), serves as a model for studying neocortical evolution due to its well-understood organization.

Purpose of the Study:

• To investigate the relationship between the number of neurons in the lateral geniculate nucleus (LGN) of the visual thalamus and primary visual cortex (V1) across primate species.
• To understand the scaling laws governing the evolutionary expansion of the visual cortex.

Main Methods:

• Comparative analysis of neuron counts in the LGN and V1 across various primate species.
• Mathematical modeling to determine the scaling relationship between LGN and V1 neuron numbers.

Main Results:

• A consistent 3/2 power law relationship was identified between the number of V1 neurons and LGN neurons across primates.
• Humans utilize significantly more V1 neurons per LGN neuron for visual processing compared to other primates like the tarsier, reflecting this scaling law.

Conclusions:

• The 3/2 power scaling law in the primate visual system is likely driven by V1's organization and the need to match spatial resolution with LGN input.
• This organizational principle may extend to other thalamocortical systems, suggesting a general rule for neocortical evolution.