Patients with middle-onset Parkinson’s disease have difficulties recognizing negative and neutral emotions, deficits that appear to be even stronger in female patients, a study shows.
The study, “Emotion-Specific Affective Theory of Mind Impairment in Parkinson’s Disease,” was published in the journal Scientific Reports.
Parkinson’s disease is known to affect the frontal-subcortical circuit, an area responsible for motor and behavioral processes.
This region is also responsible for processing the theory of mind (ToM), a complex function that enables the detection and recognition of cognitive and emotional states (thoughts, feelings, beliefs, intentions, or desires) of other people, and thus the anticipation and interpretation of their behaviors. These abilities are crucial in a social situation for successful communication.
ToM can be divided into cognitive ToM, involved in reading the cognitive beliefs of other people, and affective ToM, involved in recognizing and interpreting the emotional states of others.
While Parkinson’s disease is known to impair cognitive ToM, whether it influences affective ToM remains controversial, with several studies reaching varying conclusions.
Researchers in Taiwan evaluated whether affective ToM is affected in Parkinson’s patients with either young-onset (YOPD) or middle-onset (MOPD) disease, and whether impaired affective ToM is associated with Parkinson’s motor symptoms.
Researchers first recruited 30 people with middle-onset Parkinson’s, 30 young-onset Parkinson’s patients, and 30 healthy participants. Young-onset was defined as developing the disease at 49 years of age or younger, while middle-onset was classified as developing the disease between 50 and 70 years old.
Affective ToM was assessed through the validated Reading the Mind in the Eyes Test (RMET), which comprises 36 black-and-white photographs of pairs of eyes that each depict a particular emotion. These photographs are shown to the participant, who must pick the adjective that best fits the emotion.
Results showed that while young-onset Parkinson’s patients and healthy individuals appeared to have comparable abilities to infer emotions in others (similar RMET scores), patients with middle-onset Parkinson’s had significant difficulties recognizing emotions — particularly negative and neutral emotions.
Researchers also found that these deficits were only present in women in the middle-onset group.
“This finding may imply that female patients with MOPD have a vulnerable emotional recognition ability; thus, early detection and appropriate treatment are needed for the female MOPD population,” the researchers wrote.
They noted that these results may explain the variability of previous studies, since Parkinson’s patients with particular disease onsets or genders showed distinct differences in affective ToM.
Next, the team analyzed the data of 107 middle-onset Parkinson’s patients, which included the initial 30 patients, plus an additional 77 participants, to better understand the potential associations between deficits in affective ToM and Parkinson’s motor and non-motor symptoms in these patients.
In this Parkinson’s population, the ability to accurately interpret the emotional state of others decreased with disease duration and with the presence of specific motor symptoms, such as slowness of movement, walking and posture instability, and impaired speech and facial expression.
Additional analysis showed that impaired ability to recognize others’ emotions in these patients was associated with the development of motor symptoms, but not of non-motor symptoms. The same was true for women in this group of patients.
The team noted that the data support an association between affective ToM and motor symptoms, and that additional studies are required to clarify the underlying mechanisms of this link, and to more thoroughly evaluate the potential link between affective ToM and cognitive function.
They also believe the use of a test with both verbal and nonverbal information to assess affective ToM may “provide more comprehensive context that mimics real-life situations.”
“Whether the affective ToM can be used as a biomarker to detect or diagnose PD [Parkinson’s disease] is a noteworthy issue, and the development of a useful diagnostic tool is therefore needed,” they concluded.