Vulnerability to emotionally negative stimuli in Parkinson's disease: an investigation using the Emotional Stroop task.

Objective: The objective of this study was to determine whether the pathophysiological changes associated with Parkinson's disease (PD) lead to an increased vulnerability to react to negative emotional stimuli and hence to depression. It is hypothesized that nondepressed PD patients will demonstrate, associated with particular PD and/or cognitive variables, vulnerability to the interfering effects of negative words on the Emotional (sad) Stroop task (EST).

Background: Depression has been reported to occur frequently in PD, but there is controversy regarding its pathophysiology: psychosocial factors versus neurobiologic ones.

Method: Thirty nondepressed/ nondemented patients with idiopathic PD attending a specialist movement disorders clinic were assessed from their emotional state (Beck's Depression Inventory [BDI], and Hospital Anxiety and Depression Scale) and from their cognitive state (Mini-Mental State Examination, Stroop tasks [including the EST], Modified Card Sorting Test, Word Fluency tasks, Digit Span, and Trail Making tests). In addition, information was gathered on PD-related variables such as severity (Hoehn and Yahr scale), duration of the disease, and type of motor response to dopaminergic drugs. The sample was split into two groups according to the median BDI score to allow for comparisons. One-way ANOVA techniques were used to look for significant differences between variables in the two groups. Bivariate correlations were used to look for significant relationships between variables in each group.

Results: The two groups only differed in parameters measuring emotional state. Only the subjects with higher BDI scores showed significant correlations between EST performance and cognitive and PD-related variables.

Conclusions: Those PD patients with more severe forms of illness and a greater level of prefrontal cognitive dysfunction are more vulnerable to the distracting effects of external negative stimuli. According to the cognitive model of depression, this may ultimately lead to the development of clinical depression.