Abstract
Purpose: :
In the primate, the second visual area (V2) occupies most of the extrastriate cortex. V2 receives its main excitatory input from the primary visual area (V1) and sends axonal projections to most of the other visual areas. The receptive fields (RFs) of the neurons in V2 form the whole visual field, especially the area with eccentricities from 0° to 5°. Knowing the characteristics of the neurons in V2 will help us to get a better understanding of the human visual system, concerning its working pattern and division of labor among different visual areas.
Methods: :
Four healthy adult marmosets were included randomly. After craniotomy in vivo, the neurons in V2 were tested by visual stimuli with different moving orientations,spatial frequencies and temporal frequencies. The information was collected by parylene-coated tungsten microelectrode which was put at different site of V2. After the experiments, the marmosets were killed and after sectioning, the brain tissue slides were stained for Nissl substance, myelin and cytochrome oxidase for reconstruction of the electrodes. The data were analyzed by the Expo Operation System. Then we summaried the characteristics of neurons in V2 and compared our data with that of neurons in V1.
Results: :
Data of 130 neurons in V2 was successfully collected and:1. Most of the neurons (88.18%) were orientation selective, with their optimal orientations from 60° to 90°.2. The neurons having direction selectivity occupied 31.96% of those with orientation selectivity.3. The neurons that had RFs centered between 8° and 15° of eccentricity (the "near peripheral" group) didn’t tune to horizontal, vertical or oblique orientations.4. None of the neurons was speed selective.5. For one marmoset, the optimal spatial frequency and optimal temporal frequency of neurons in V1 and V2 were similar to each other when eccentricities of their RFs were about the same.
Conclusions: :
In the primate, neurons in V2 have many characteristics in common with those in V1.This indicate that the functions of V2 may cover or even beyond that of the V1, playing an important part in one’s vision function, especially in the aspects of image location, image motion and so on. Our findings can also help to get a better understanding of characteristics of neurons in senior central visual system of primate and human.
Keywords: visual cortex • neuro-ophthalmology: cortical function/rehabilitation