Attentional modulation of effective connectivity from V2 to V5/MT in humans

Abstract

The nonlinear nature of integration among cortical brain areas renders the effective connectivity between them inherently dynamic and context-sensitive. One emerging architectural principle of functional brain organization, which rests explicitly on these nonlinear interactions, is that neuronal responses expressed at any level in a sensory hierarchy reflect an interaction between (i) bottom up ''driving'' afferents from lower cortical areas and (ii) backwards ''modulatory'' inputs from higher areas that mediate top-down contextual effects. A compelling example is attentional modulation of responses in functionally specialized sensory areas. The aim of this work was 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 V5͞MT. Using functional magnetic resonance imaging, and an analysis of effective connectivity based on nonlinear system identification, we found that backwards modulatory influences from the posterior parietal cortex are sufficient to account for a significant component of attentional modulation of V5͞MT responses to ''driving'' inputs from V2. By explicitly modeling interactions among inputs to V5͞MT, we were able to make inferences about the influences of 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. These results speak to the context-sensitive nature of functional integration in the brain and provide empirical evidence that attentional effects may be mediated by backwards connections, of a modulatory sort, in humans.

A Blueprint for Target Motion: fMRI Reveals Perceived Sequential Complexity to Modulate Premotor Cortex

“…Although motion was presented under all conditions, target motion differed systematically with regard to its intensity in dependence on number and trend. We therefore suggest that top-down attentional processes modulate neural responses within area MT, as implicated by other studies (Treue and Maunsell, 1996;Treue and Martinez Trujillo, 1999;Friston and Bü chel, 2000).…”

Depression alters “top-down” visual attention: A dynamic causal modeling comparison between depressed and healthy subjects

“…Based on the results from our previous study using the same paradigm and from research showing attentional modulation of networks dynamics (Friston and Buchel, 2000;Friston et al, 2003), we considered 3 main "regions of interest" (ROI) for our DCM analysis: the right early visual region (V1) and the right color responsive area (V4), both likely to process the visual aspects of the colored block stimuli, and the right intraparietal sulcus (P) linked to top-down attentional modulation of visual areas (Corbetta and Shulman, 2002). We chose regions in the right hemisphere because they showed robust activation in all our subjects (at the fixed effect level) and because attentional effects in V4 were also stronger on the right for both populations.…”

“…The selection of these models is based on the paradigm used, neuroanatomy and the literature (Friston and Buchel, 2000;Friston et al, 2003). The endogenous network connecting the 3 areas (V1, V4 and P) is the same for all the models and consists in a cascade of forward and backward connections between V1 and V4, and between V4 and P (Fig.…”

Modelling functional integration: a comparison of structural equation and dynamic causal models

“…In previous work, we have established that attention modulates connectivity in a distributed system of cortical regions mediating visual motion processing (Buchel and Friston, 1997;Friston and Buchel, 2000). These findings were based on data acquired using the following experimental paradigm.…”