Functional MRI in Awake Unrestrained Dogs
The same region of activation was observed in both dogs and is identified as the right caudate as indicated on the corresponding slice of each dog's structural image (CD). The structural image has been uniformly scaled to match the size of the brain of the functional images. The underlay of the functional map is the mean of the non-excluded functional images. McKenzie was rotated slightly out of plane, but this was a consistent position in both functional and structural scans. The significance of the peak voxel in this cluster was p<0.01 in Callie and p<0.001 in McKenzie (colorbar indicates t-values and maps are thresholded at p<0.05 to show full spatial extent). The time series of activation was extracted for the cluster (9 voxels in Callie, and 18 voxels in McKenzie after restricting spatial extent with p<0.01), and after adjusting for the other effects in the design matrix (including motion), the average trial response is seen to match a typical hemodynamic response function, which is significantly greater for the “reward” signal than the “no-reward” signal (error bars are +/− 1 s.e.) Bottom: statistical map of the combined model with both dogs, co-registered and overlaid on Callie's structural scan. Activation of the caudate cluster (CD) was significant at p<0.05 after correcting for FDR over the search volume of the ventral brain from olfactory bulb to internal capsule (p<0.01 height and cluster extent>6). Averaged over both dogs, the timecourse of activation in the caudate showed a distinct response to the reward hand signal which differentiates from the no-reward signal (lower right). Scan volumes are 1610 ms apart, indicating a peak in the response 3–5 s after the onset of the reward hand signal.