Chapter 75 - Attentional Modulation and Changes in Effective Connectivity

Abstract

The nonlinear nature of integration among cortical brain areas renders the effective connectivity between them inherently dynamic and context-sensitive. A compelling example is attentional modulation of responses in functionally specialized sensory areas. The aim of this chapter is to demonstrate that parietal regions may mediate selective attention to motion by modulating the effective connectivity from early visual cortex to the motion-sensitive area V5/hMT. Using functional magnetic resonance imaging, and an analysis of effective connectivity based on regression models and nonlinear system identification, it is shown that backward modulatory influences from the posterior parietal cortex are sufficient to account for a significant component of attentional modulation of V5/hMT responses to inputs from V1/V2. By explicitly modeling interactions among inputs to V5/hMT, we are able to make inferences about the influences of V1/V2 inputs and their concomitant activity dependent modulation by parietal afferents. The latter effects embody dynamic changes in effective connectivity that may underlie attentional mechanisms and provide empirical evidence that attentional effects may be mediated by backward connections, of a modulatory sort, in humans.