Figure 3. A series of cortical activation maps from the same animal is shown for different stimulating current levels.

The spike rate was normalized between the base line level (blue) and the maximum activity (dark red). Images were smoothed using a 3 × 3 Gaussian filter with σ = 0.2. Current densities (σ) ranged between 0 μC⋅cm² to 212 μC⋅cm² when seven electrodes, arranged in a hexagonal pattern, were activated simultaneously. The sequence illustrates regions which exhibit a non-monotonic profile such as the area around the centre of each map.