Freezing of gait in Parkinson's disease: where are we now?

Freezing of gait (FOG) is defined as a brief, episodic absence or marked reduction of forward progression of the feet despite the intention to walk. It is one of the most debilitating motor symptoms in patients with Parkinson's disease (PD) as it may lead to falls and a loss of independence. The pathophysiology of FOG seems to differ from the cardinal features of PD and is still largely unknown. In the present paper, we review the studies that were performed since 2011 on methods to provoke and assess FOG and discuss new insights into behavioral and neural mechanisms underlying this clinical phenomenon. We conclude that most of the work reviewed confirms that gait pattern generation disturbances are central to FOG. The finding that FOG reflects a combined motor and cognitive de-automatization deficit, which may not be sufficiently offset by executive control, probably acts as parallel mechanism.