Emotional and cognitive information processing in obstacle negotiation in patient with Parkinson’s disease and freezing

Objective: We used emotional (images from the International Affective Picture System - IAPS)1 and cognitive inputs (visual perturbation in a stepping-over-the-obstacle task) with the aim to investigate the hypothesis of a cognitive and affective processing overload in the genesis of freezing of gait (FoG) in Parkinson’s disease (PD). Background: FoG is one of the most severe symptoms in PD. It appears as an unpredictable stopping phenomenon during gait and locomo- tor tasks. The underlying mechanism of freezing is still largely unknown. An emerging hypothesis explores freezing as an information processing overload problem produced by a basal ganglia faulty output control in cognitive, limbic and motor neural networks2 Methods: We recruited 12 PD patients with FoG, 11 patients without FoG, and 15 healthy elderly controls. Participants underwent neurological, neuropsychological, and affective state assessments. The emotional stimuli were 20 different images taken from the IAPS system (10 with positive valence, 10 with negative valence, all with a medium level of rating in the arousal). The cognitive stimulus was the obstacle with a light placed on the top. Participants were placed at the beginning of a walkway and were asked to look at a screen placed at the other end, where the IAPS images were presented. The obstacle was positioned in the middle of the walkway (set at 10% of participants’ height). The participants were asked to walk and step over the obstacle, and in half of the trials, when the subject began the last step before overcoming the obstacle, the light on the top was turned on randomly. Results: In PD with FoG, the clearance (vertical distance between the foot and the obstacle during the crossing step) was modulated by the valence of the emotional image when the light was off (lower step clear- ance in response to unpleasant images p=0.020), but not when the light was on. Moreover, results showed slower reaction times in response to unpleas- ant images (p=0.028), and longer times to approach (p=0.012) and cross (p=0.023) the obstacle when unpleasant images were presented. A similar slowing is present in the mean velocity of the crossing step in response to unpleasant images ((p=0.044). Conclusions: Our data support the hypothesis that the increase of cog- nitive and emotional information processing3, could be relevant in the gen- esis of freezing episodes during planning and motor control.