Studies by Ko and Ermentrout (2007) and Tiesinga and Sejnowski (2010) use mathematical models that best explain the onset of a phase shift to be initiated by cortico-cortical long distant excitatory dendritic synapses. The mathematical models and experiments fit the physiological facts that local distance connections are exponentially more numerous and exhibit temporal compactness while distant connections are less numerous and exhibit temporal dispersion. Therefore, the ratio of local to distant connections determines the duration of phase shift and this ratio varies as an exponential function of distance between a given Brodmann area. This conclusion is consistent with studies showing anti-phase shifts are related to neural packing density (Li and Zhou, 2011) and with the surface EEG PR where increased local packing density was hypothesized to explain the difference between PR in the posterior-to-anterior direction (e.g., O1-P3) vs. the anterior-to-posterior directions (e.g., Fp1-F3) because of increased packing density in the posterior cortex as compared to frontal cortex (Thatcher et al., 2009a). The results of the present study are also consistent with the hypothesis that phase shift is related to recruitment
