Functional biases in visual cortex neurons with identified projections to higher cortical targets.

BACKGROUND: Visual perception involves information flow from lower- to higher-order cortical areas, which are known to process different kinds of information. How does this functional specialization arise? As a step toward addressing this question, we combined fluorescent retrograde tracing with in vivo two-photon calcium imaging to simultaneously compare the tuning properties of neighboring neurons in areas 17 and 18 of ferret visual cortex that have different higher cortical projection targets.
RESULTS: Neurons projecting to the posterior suprasylvian sulcus (PSS) were more direction selective and preferred shorter stimuli, higher spatial frequencies, and higher temporal frequencies than neurons projecting to area 21, anticipating key differences between the functional properties of the target areas themselves. These differences could not be explained by a correspondence between anatomical and functional clustering within early visual cortex, and the largest differences were in properties generated within early visual cortex (direction selectivity and length preference) rather than in properties present in its retinogeniculate inputs.
CONCLUSIONS: These projection cell groups, and hence the higher-order visual areas to which they project, likely obtain their functional properties not from biased retinogeniculate inputs but from highly specific circuitry within the cortex. Copyright Â