Segregation and convergence of specialised pathways in macaque monkey visual cortex

Area of Science:

• Neuroscience
• Visual Processing
• Primate Brain

Background:

• Cortical area V2 in macaque monkeys exhibits three distinct visual input channels: thick dark stripes, thin dark stripes, and interstripes, defined by cytochrome oxidase architecture.
• The fate of these segregated channels at higher visual processing stages remains unclear, with questions about whether they remain distinct or are combined.

Purpose of the Study:

• To investigate whether the segregated visual processing channels from V2 are maintained in higher visual areas V4 and V5.
• To map the connections of V4 and V5 to understand the integration or segregation of visual information streams.

Main Methods:

• Injection of distinct orthograde tracers into functionally distinct areas V4 and V5 in three macaque monkeys (Macaca fascicularis).
• Analysis of tracer patterns to determine the origins and destinations of connections from V2 and within higher visual areas.

Main Results:

• Area V4 receives input from V2 thin stripes and interstripes, with subcompartments showing differential contributions.
• Despite V4 subcompartments, their projection patterns to downstream areas and subcortical structures are largely similar.
• Area V5 receives input from V2 thick stripes; V4 and V5 show weak interconnections with limited direct convergence, projecting to different subregions of areas like LIP and the superior temporal sulcus.

Conclusions:

• The segregated visual processing channels originating in V2 are largely maintained through at least two subsequent stages of cortical processing (V4 and V5).
• This suggests a predominantly parallel processing architecture for visual information in the primate brain.