10 - Long-Range Intrinsic Connections in Cat Primary Visual Cortex

Abstract

This chapter focuses on the detailed layout of long-range horizontal connections in the primary visual cortex of cats, their topographic relation to functional cortical maps, learning and activity-induced modifiability, and possible functions. The majority of long-range intrinsic connections of excitatory cortical neurons in the primary visual cortex of cats link neurons with similar response properties such as orientation preference and possibly also direction preference. The selectivity of the long-range connections may depend on the relative position of a neuron within a functional map such as projections extending from pinwheel centers are less orientation selective than projections originating from linear zones of an orientation preference map. Both the selectivity and maximal lateral extent of long-range connections depend on the layer. There is extensive cross-talk between different orientation domains and clear differences in the layout of long-range excitatory and inhibitory connections. Many different functions have been ascribed to long-range intrinsic connections. In particular, there is growing evidence that they are important for perceptual integration. The outgrowth of new connections, previously thought to be restricted to so-called “critical periods” in early life, also occurs in the adult brain and most probably mediates long-term long-range representational plasticity in the cortex.