Emotional processing in Parkinson's disease: a reaction time study

Background: Clinically, patients with Parkinson's disease (PD) have been often described to suffer from blunted emotional responses. Yet, due to hypomimia and generalized bradykinesia it is difficult to determine whether emotional reactions are indeed blunted in PD.

Objective: The aims of this study were (1.) to obtain measures as to whether PD patients are able to differentiate subjectively between emotional and non-emotional stimuli, (2.) to ascertain whether the emotional modulation of reaction times that is found in intact subjects is preserved in patients with PD, and (3.) to examine the effect of dopaminergic treatment on motor responses to emotional and neutral stimuli.

Methods: 16 non-demented PD patients on and off dopaminergic medication and 16 age-, education-, gender ratio-, and IQ-matched normal controls participated in the study. Upon presentation of either emotional or neutral pictures (IAPS), subjects characterized the emotional experience elicited by the respective stimulus using a rating scale for graded measures of valence (pleasant, neutral, and unpleasant) and arousal (high, low). Reaction times upon presentation of positive, negative and neutral stimuli were measured during a forced-choice recognition task.

Results: As in controls, reaction times in PD patients differed significantly depending on valence and arousal of the presented stimuli. This pattern was not affected by dopaminergic medication. Compatible with this, subjective ratings revealed that both PD patients and controls experientially discriminated between neutral and emotional stimuli.

Conclusion: These findings do not support the notion that basal-ganglia pathology and deficient dopaminergic neurotransmission in moderately advanced non-demented PD patients are associated with “flattened“ responses to emotional stimuli.