Master of Science
MacDonald, Penny A.
Owen, Adrian M.
Dopamine has a demonstrated role in humor processing. Humor comprehension (i.e., “getting the joke”) relies on dorsal striatum (DS) mediated problem-solving mechanisms, whereas humor appreciation (i.e., “funniness”) relies on ventral striatum (VS) mediated reward processing. Despite this, relatively little research has been conducted on potential deficits in humor processing in Parkinson’s disease (PD). The present study investigated the comprehension (i.e., categorization as jokes or non-jokes) and appreciation (i.e., funniness ratings) of verbal jokes and non-jokes in PD patients and healthy age-matched controls while ON and OFF levodopa medication. Relative to controls, PD patients demonstrated reduced humor comprehension in the form of decreased accuracy identifying non-humorous stimuli. Furthermore, controls found jokes to be less funny while ON medication. This suggests that dopamine hypoactivity in the DS of PD patients could contribute to problems understanding humor, whereas levodopa can reduce the rewarding nature of humor via overdose of the VS.
Summary for Lay Audience
Humor is a ubiquitous and unique human cognitive ability, with two fundamental components. The first, humor comprehension, or “getting the joke”, is associated with part of the brain called the dorsal striatum (DS) that is involved in problem-solving. The second, humor appreciation, refers to subjective amusement experienced in response to funny jokes, and relies on the ventral striatum (VS), an area of the brain responsible for processing pleasurable rewards. The DS and VS are influenced by a neurotransmitter molecule called dopamine. Parkinson’s disease (PD) is a neurodegenerative disease caused by the death of dopamine-producing neurons in the brain, leading to dopamine deficiency in the DS, followed by the VS in later stages of the disease. The frontline treatment for PD is to replace dopamine with a medication called levodopa. However, levodopa can sometimes create an overload of dopamine in the VS, particularly early in the disease, which can cause problems with VS-mediated functions. Surprisingly, humor processing has been relatively understudied in PD, although it is likely that the disease’s dopamine dysfunction can cause problems to DS-mediated humor comprehension, whereas levodopa could cause problems to VS-mediated humor appreciation.
We investigated humor comprehension and appreciation in 10 PD patients and 10 age-matched healthy controls while ON and OFF levodopa. Participants listened to joke and non-joke audio clips and were asked to make judgements about them. The first judgement was to categorize audio clips as jokes or non-jokes. We found that PD patients had more difficulty categorizing non-jokes, which is indicative of a deficit in humor comprehension. The second judgement was to rate how funny each audio clip was. We found that control participants rated jokes as less funny while ON levodopa, suggesting that VS dopamine overdose via levodopa can indeed lead to reduced humor appreciation. However, our patients did not show differences in humor appreciation ON or OFF levodopa, likely due to their relatively later disease stage. Overall, these results suggest that humor comprehension deficits are present in PD, and that treatment with levodopa could cause further problems in the form of reduced humor appreciation for patients early in the disease.
Prenger, Margaret T.M., "Investigating Humor Processing in Parkinson's Disease" (2020). Electronic Thesis and Dissertation Repository. 7002.