Left:
Brain regions and connections comprising an effective connectivity model
formulated in terms of a Volterra series (see ). Right: Characterization of the effects of V2
inputs on V5 and their modulation by posterior parietal cortex (PPC). The broken lines represent estimates of V5
responses when PPC activity is zero, according to a second order Volterra model
of effective connectivity with inputs to V5 from V2, PPC and the pulvinar
(PUL). The solid curves represent the
same response when PPC activity is one standard deviation of its variation over
conditions. It is evident that V2 has an
activating effect on V5 and that PPC increases the responsiveness of V5 to
these inputs. In this study subjects
were studied with fMRI under identical stimulus conditions (visual motion
subtended by radially moving dots) whilst manipulating the attentional
component of the task (detection of velocity changes). The insert shows all the voxels in V5 that
evidenced a modulatory effect (p <
0.05 uncorrected). These voxels were
identified by thresholding a SPM