Objective: This study investigated humor comprehension and appreciation deficits in Parkinson’s disease (PD) as potential non-motor symptoms, and the effect of levodopa on these processes.

Background: Humor is a ubiquitous, but cognitively complex phenomenon that facilitates social interactions and promotes well-being. The processing of humorous stimuli is separable into two components: 1) humor comprehension (i.e., understanding), and 2) humor appreciation (i.e., enjoyment). Humor comprehension involves resolving the incongruities that are inherent in humorous stimuli (e.g., recognizing that a pun contains a play-on word that can be interpreted in more than one way), which requires dopamine. Humor appreciation also relies on dopamine; functional neuroimaging studies demonstrate that the dopamine-mediated reward processing pathways in the brain are activated during feelings of amusement in response to humorous stimuli.

Parkinson’s disease (PD) is often recognized by its characteristic motor symptoms, which are well-treated with levodopa medication. However, PD patients might also experience “dopamine overdose” in the brain regions that are less affected by PD, particularly early in the disease course before neurodegeneration advances. In many cases, levodopa-induced dopamine overdose can exacerbate or even produce non-motor symptoms of PD, which include cognitive and socioemotional difficulties. Surprisingly, few studies have investigated humor processing deficits as a non-motor symptom of PD, and none have considered the effect of levodopa medication.

Method: This study investigated humor comprehension (i.e., categorization as jokes or non-jokes) and appreciation (i.e., funniness ratings) of verbal joke and non-joke statements in PD patients (n=10) and healthy age-matched controls (n=10) while ON and OFF levodopa medication.

Results: Relative to controls, PD patients demonstrated reduced ability to distinguish between jokes and non-jokes. This suggests that PD-related neurodegenerative changes to dopaminergic structures might contribute to problems understanding humor. Furthermore, controls found jokes to be less funny while ON levodopa, suggesting that dopamine overdose might reduce the rewarding nature of humor.

Conclusion: Our results demonstrate that disease-related and medication-induced changes might lead to aberrant humor processing in PD. Deficits in humor processing could have a negative impact on quality of life for PD patients.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/humor-processing-is-affected-by-parkinsons-disease-and-levodopa/