The pattern of anatomical connections in visual area V2 of Macaque monkey
In visual area V2, cytochrome oxidase (CO) histochemistry reveals a pattern of alternating densely labeled thick and thin stripes separated by lightly labeled interstripe regions. These stripe-like compartments have been related to three separate cortico-cortical pathways, which may be involved with different aspects of visual processing.In the first experiment, we examined whether the tangential distribution of cells projecting to the superior colliculus bear a relationship with the CO stripes in V2. The cortico-tectal pathway is thought to be functionally specific, extending from magnocellular layers of the lateral geniculate nucleus (LGN). From previous evidence that V2 thick stripes are closely associated with the magnocellular LGN layers, we predicted that V2 neurons projecting to the superior colliculus would preferentially reside in thick stripe regions. Our results bore out this prediction. These data support the idea that the stripe-like compartments in V2 represent separate functional pathways, and extend the notion of segregated cortico-cortical pathways to cortico-subcortical projections.In the second experiment, we compared the distribution of interhemispheric connections in V2 with the pattern of CO stripes. We found that V2 callosal connections tend to accumulate within a continuous band along the V1/V2 border from which callosal cells cluster within finger-like extensions within thin and thick stripe regions in V2 up to 7-8 mm from the V1 border. Our findings extend the notion of segregated cortico-cortical pathways to interhemispheric connections. In addition, different from the pattern of intracortical connections, our results suggest that few cells within interstripe regions in V2 send connections to V2 or other extrastriate areas in the contralateral hemisphere.In the third experiment we examined the pattern of callosal linkages in V2. Based on previous data on the visual field map in V2, callosal connections could link representations of the visual field located away from the vertical meridian. We examined whether the pattern of V2 callosal linkages supports this idea. The results demonstrate that callosal connections preferentially link corresponding regions between areas V2. These data support the hypothesis that V2 callosal connections mediate interactions between visual field representations located away from the vertical meridian.
- Psychology