The Feedback Modulation On Direction Preference From Visual Cortical Form Area 21a To Area 17 And 18 Of The Cat

In visual cortices of high mammals such as cats and monkeys, there are two major, largely parallel,’feedforward’ processing streams which carry visual information from the primary visual cortices respectively to the parietal and temporal visual cortices.Plenty of the investigation about structure and function for the feedforward processing streams has been widely developed, but the function of the feedback processing streams from high order visual cortices to low order visual cortices are not well understood. Area 21a, a dominant form processing region in the temporal pathway of the cat, is mainly in charge of form information processing. There are mutual and compact synaptic connections between area 21a and low order visual cortex. The purpose of our study is to find out whether area 21a has a feedback modulation on the motion information in area 17 and 18.In the present study, using the optical imaging technique based on intrinsic signals combined with pharmacological methods, we examined the influence of ’feedback’ signals from area 21a on direction selectivity of the visual cortical area 17 and 18.In the study, we found that:(1) the relative amplitude of visual responses of area17 and 18 of primary visual cortex exhibited a significant decrease of around 25% when area 21a was inactivated with 400mM GABA or by cauterizing; (2) the change of response amplitude did not alter the patterns of direction map in the observed areas: there was no change in pin-wheel center positions or preferred directions; (3) the direction selectivity strength of area 17 and 18 was weakened by inactivation of area 21a with a significant decrease of about 15% on average across area 17 and 18; (4) the activation of area 21a with 0.3mM glutamate significantly increased both the response amplitude and direction selectivity strength across area 17 and 18, while no change was found in the pattern of direction maps.This study shows that area 21a has a regulatory and mainly excitatory effect on the response of area 17 and 18. The change of area 21a activity does not affect the pattern of direction maps of area 17 and 18, but significantly alters the direction bias of neurons there, suggesting a positive feedback modulation of area 21a on the direction preference of primary visual cortices.