Figure 1

Electrode configuration of tetrapolar probes used in the study. 1a. Sheffield 3 mm probe: pitch circle diameter 2 mm, electrode separation (between centres) 1.41 mm, electrode diameter 0.6 mm, peak current 3.0 μA. 1b. Sheffield 12 mm probe: pitch circle diameter 8.5 mm, electrode separation (between centres) 6.01 mm, electrode diameter 1.50 mm, peak current 12.5 μA.