Cortico-pallidal beta dynamics underlie impaired turning in Parkinson's disease

Turning while walking is one of the most common yet complex human movements, and it is frequently impaired in Parkinson's disease (PD), leading to falls and loss of independence. The neural mechanisms underlying this difficulty remain unclear. Using chronically implanted devices that simultaneously record and stimulate the brain, we repeatedly measured activity in the motor cortex and basal ganglia of five individuals with PD during natural walking and turning. Successful turns were marked by reduced beta-band activity and flexible communication between cortical and pallidal regions, whereas impaired turns showed excessive beta synchrony that rigidly constrained movement. Medication and deep brain stimulation improved turning through distinct circuit mechanisms, dopamine suppressing abnormal pallidal beta activity and its communication with the cortex, and stimulation restoring cortical flexibility. These findings reveal how dynamic cortical-basal ganglia interactions may enable complex movement and establish circuit targets for adaptive brain stimulation to reduce falls in PD.