Fig. 8. Computational modeling: the cortex generates high beta activity which is propagated subcortically and provokes the generation of pathological lower beta frequencies.

A We explore the effect of altering the hyperdirect connection strength (W_ES, left figure), cortical time constants (${\tau }_E$/${\tau }_I$, middle figure), and the cortical delay (T_IE/T_IE, right figure) on the spectra of the STN and GPi. High beta frequency activity generated within the cortex propagates to the STN and GPi. In addition, under certain parameter values, a lower beta frequency (between 10 and 15 Hz) emerges. The left image in B is a bifurcation diagram highlighting that low beta frequency oscillatory activity may be generated in the STN-GPe feedback loop depending on cortical inputs. In the oscillatory region of STN and GPe firing the dominant frequency is color-coded. The right image in B displays the effect on STN and GPi spectra of changing the subcortical delay parameters (T_GeS /T_SGe).