Figure 8 shows the results of a group of HPPD subjects compared to non-drug users. The measure in this study is called electrical coherence. It is a way of assessing the degree to which parts of the brain show connectivity with one another. In HPPD there appears to be excessive connectivity in regions of the brain that process visual information: the posterior lobes of the brain, and the right temporal region. This excess coherence in actively hallucinating patients is noted by the white, yellow and red color bands. They may represent an overreaction of these regions to normal visual stimulation.