Summary: The level of dopamine in the brain may have an impact on emotional recognition in those with Parkinson’s disease and schizophrenia, a new study reports.
Source: University of Birmingham
Emotion recognition among people with disorders such as Parkinson’s disease or schizophrenia may be affected by changes in the levels of dopamine in the brain, say researchers at the University of Birmingham.
Dopamine is a chemical messenger – often known as the ‘happy hormone’ – that carries signals controlling mental and emotional responses in the brain.
Parkinson’s disease and other neurological disorders are known for their links with low or disrupted dopamine levels that cause those affected to struggle with a number of social skills. This is the first time, however, that a positive connection has been made between dopamine and the ability to recognize emotions in others.
In a new study, published in the Journal of Neuroscience, a team in the University’s Centre for Human Brain Health showed that manipulating levels of dopamine affected emotion recognition.
More specifically, the research showed that while people with low baseline levels of the chemical messenger became better at emotion recognition after receiving a dopamine boost, those with higher baseline levels actually became worse.
Lead author Dr Bianca Schuster said: “The ability to recognise emotions in others is fundamental to our everyday social interactions and this is often atypical in people with neurological disorders. Our research shows that dopamine medication – even in small doses – can affect these abilities. That has important implications for fine tuning a patient’s medicine regime to ensure a balance between controlling their symptoms and preserving social functions.”
In the study, the team worked with 33 healthy male and female individuals and assessed their baseline dopamine levels. This was done by testing people’s working memory, a well-recognised proxy for dopamine levels that avoids invasive brain imaging.
Individuals were asked to gauge the emotions of a series of figures in three different video clips in two separate tests. In the first they were given a dose of haloperidol, a drug affecting brain dopamine levels which is commonly used to treat schizophrenia, and in the second they were given a placebo. The figures were seen walking, in outline only, and in three different gaits and postures, denoting angry, happy and sad emotions.
Participants with a lower working memory, and so assumed lower baseline levels of dopamine, improved their emotion recognition under haloperidol, whereas those with a higher working memory became worse at emotion recognition under the drug.
“Individuals with low baseline dopamine also slowed their own walking pace under haloperidol, and so we think the effects of the drug on movement and emotion recognition are connected,” says Dr Schuster. “It is not yet clear, however, why the drug actually impaired emotion recognition in the participants with high baseline dopamine. It’s likely that timing and movement are not the only mechanisms that are important.”
More work needs to be done to confirm whether these results predict the effects of dopamine in other emotion recognition tasks.
Dopaminergic modulation of dynamic emotion perception
Emotion recognition abilities are fundamental to our everyday social interaction. A large number of clinical populations show impairments in this domain, with emotion recognition atypicalities being particularly prevalent among disorders exhibiting a dopamine system disruption (e.g., Parkinson’s disease).
Although this suggests a role for dopamine in emotion recognition, studies employing dopamine manipulation in healthy volunteers have exhibited mixed neural findings and no behavioural modulation. Interestingly, whilst a dependence of dopaminergic drug effects on individual baseline dopamine function has been well established in other cognitive domains, the emotion recognition literature so far has failed to account for these possible interindividual differences.
The present within-subjects study therefore tested the effects of the dopamine D2 antagonist haloperidol on emotion recognition from dynamic, whole-body stimuli while accounting for interindividual differences in baseline dopamine. 33 healthy male and female adults rated emotional point-light walkers (PLWs) once after ingestion of 2.5 mg haloperidol and once after placebo.
To evaluate potential mechanistic pathways of the dopaminergic modulation of emotion recognition, participants also performed motoric and counting-based indices of temporal processing.
Confirming our hypotheses, effects of haloperidol on emotion recognition depended on baseline dopamine function, where individuals with low baseline dopamine showed enhanced, and those with high baseline dopamine decreased emotion recognition.
Drug effects on emotion recognition were related to drug effects on movement-based and explicit timing mechanisms, indicating possible mediating effects of temporal processing.
Results highlight the need for future studies to account for baseline dopamine and suggest putative mechanisms underlying the dopaminergic modulation of emotion recognition.
A high prevalence of emotion recognition difficulties amongst clinical conditions where the dopamine system is affected suggests an involvement of dopamine in emotion recognition processes.
However, previous psychopharmacological studies seeking to confirm this role in healthy volunteers thus far have failed to establish whether dopamine affects emotion recognition and lack mechanistic insights.
The present study uncovered effects of dopamine on emotion recognition in healthy individuals by controlling for interindividual differences in baseline dopamine function and investigated potential mechanistic pathways via which dopamine may modulate emotion recognition.
Our findings suggest that dopamine may influence emotion recognition via its effects on temporal processing, providing new directions for future research on typical and atypical emotion recognition.