Overall, the vessel density changes were minimal, except for the control group animal highlighted in Fig. 3 (W87), the animal that appeared to have a significant vessel compression (Fig. 7, W82), and the animal with temporary flow drop-out (Fig. 8, W83), the last two of which were 2-shank A microelectrodes. The perfused capillary density change did increase with depth, with the number of steps that exhibited a change greater than 20% increasing from 23% to 46% to 52%, from slice 1 to 2 to 3, respectively. Seventy five percent of the animals had an increase exceeding 20% in at least one step for slice 3 (300 to ). In terms of the perfused capillary density change as a function of insertion step, the change was generally larger in steps 2 and 3 than step 1 ( to 3 times larger), reaching significance for slice 2 (100 to ) in the electrode animals, where the change in step 3 was 3.6 times larger than in step 1. Part of the reason for this is that the perfused capillary density analysis, unlike the optical flow analysis, was referenced to baseline for each insertion step, therefore some cumulative effect is likely to result. However, another possible explanation is that the lateral and axial extent of the interaction region between electrode and tissue is smallest for the first insertion step. The control animals showed a similar trend but, as expected, no significant differences between steps.