Fig. 2

How modulating arousal may contribute to optimal gait performance in Parkinson’s disease (PD). a Healthy persons. In healthy persons, the primary automatic mode of motor control is intact. Different brain networks are largely segregated, as there is (usually) no need for compensatory input to achieve optimal gait control. b  PD—Suboptimal arousal. Impaired function of the corticostriatal motor network cannot be optimally compensated for by complementary input from other brain networks, as these networks remain largely segregated in this suboptimal state of arousal. c  PD—Optimal arousal. Impaired function of the corticostriatal motor network can be optimally compensated for by complementary input from other brain networks, as these networks are optimally integrated in this optimal state of arousal. d  PD—Supraoptimal arousal. Impaired function of the corticostriatal motor network cannot be optimally compensated for by complementary—but now competing—input from other brain networks, as these networks are engaged in dysfunctionally increased ‘cross-talk’ in this supraoptimal state of arousal. Green circle: intact corticostriatal motor network; Dashed green circle: impaired corticostriatal motor network; Yellow circle: sensory network; Purple circle: limbic network; Blue circle; cognitive network. Black double-sided triangle arrows represent a simplified schematic illustration of the functional integration between the different brain regions (which is presumably much more complex than depicted); Dashed arrows indicate the impaired function of the primary motor circuitry in PD; Thickness of the dark-grey equilateral barb arrows represents the neuromodulatory activity of the locus coeruleus (depicted here in the rostral pons as a small dark-grey ellipse). Figure inspired by Gilat et al. [48]