Thesis defense Katrijn Smulders (Donders Series 157)

21 May 2014

Promotors: Prof.dr. B.R. Bloem, prof.dr. A.C.H. Geurts

Copromotors: dr. R.A.J. Esselink, dr. B.J.M. de Swart

Cognitive control of gait and balance in patients with chronic stroke and Parkinson's disease

One of the challenges of walking is to keep the body in a stable position. To stay upright and maintain a stable walking pattern, balance control mechanisms are needed. This is already true for walking in predictable environments such as in the examination room of the doctor. However, when walking outside, one also needs to pay attention to traffic, to irregularities on the ground, or to the conversation with a friend. Although we may not be aware of it, all these situations call for cognitive control. Nonetheless, we generally do not experience walking to be difficult. This is however different for patients with neurological disorders that impair gait and balance.

In the first part of this thesis, the amount of attention needed to walk in daily life circumstances was tested using a dual task paradigm. In two studies we showed that even well recovered stroke patients rely more heavily on cognitive resources to prevent stumbling when walking and avoiding obstacles. However, the amount of attention needed to negotiate obstacles while walking can be decreased by gait training on an instrumented treadmill.

In the second part of this thesis the focus was on Parkinson’s disease. Dual task deficits are very common in PD patients and have been hypothesized to cause falling. The dual task performance in a large cohort of PD patients could not confirm this hypothesis. Interestingly, impulsive behavior was predictive for fall risk in this cohort. The final chapters of this thesis concern a specific cognitive impairment in PD patients: the ability to flexibly switch between task sets. Deficient switching between motor sets during stepping (i.e. changing the direction of the step) was observed in PD patients with freezing of gait. Such a switching deficit was not observed when the step was made in response to a postural perturbation.