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Optogenetic Stimulation Shifts the Excitability of Cerebral Cortex from Type I to Type II: Oscillation Onset and Wave Propagation

Fig 3

Propagation of LFP waves in one spatial dimension for the model with type II excitability.

A-C: Space-time plots for media with a range of excitatory time constants, τe = {0.4, 0.3, 0.2}. In all cases, steady stimulation (Je = 1.3) was applied focally to the excitatory cells near the origin (−0.25<x<0.25) and the time constant of inhibition was fixed at τi = 4 ms. Absorbing boundary conditions were imposed at |x| = 3 mm (not shown). D: The propagation envelope (shaded region) as a function of the relative time course of inhibition and excitation (τi/τe). The dashed line indicates the boundary of the stimulated region. No waves emitted from the stimulated region for τi/τe<4. Waves propagated a finite distance for 4 < τi/τe ≲ 12.5. Indefinite wave propagation occurred for τi/τe ≳ 12.5. E: Bifurcation diagram for the isolated excitatory-inhibitory model with τi/τe = 12.5. The near-instantaneous rise in the oscillation amplitude at the Hopf bifurcation is markedly different from the slow rise observed in the neurophysiological data.

Fig 3