Mental Rigidity in PWS Goes Beyond Intellectual Disability

Adults with Prader-Willi syndrome (PWS) have greater mental rigidity than those with matching intellectual disability, but without the disease, and those with normal intellectual level, according to a study from France.

These findings support the presence of PWS-specific mental flexibility deficits, over and above intellectual problems, the researchers said.

Notably, contrary to the scientists’ hypothesis, PWS-associated mental rigidity, assessed through switching-task performance, was not greatly affected by emotional contexts.

Further studies, using stronger emotional contexts, are needed to clarify how emotional difficulties in these patients affect their cognitive function and mental rigidity, the investigators noted.

The study, “The influence of emotional contexts on mental flexibility in Prader–Willi syndrome,” was published in the Journal of Intellectual Disability Research.

PWS is associated with excessive appetite, temper outbursts, compulsion, poor mental flexibility (mental rigidity), mild-to-moderate intellectual disability, and emotional and social difficulties. Mental flexibility is defined as the mental ability to switch between different concepts, tasks, or strategies.

Emotional and social problems are thought to be related to specific deficits in emotion recognition in people’s faces, especially of negative emotions such as sadness and anger, impairing social information processing.

“In PWS, the presence of emotional lability [exaggerated changes in mood], deficits in emotional identification and temper outbursts, partly resulting from impaired switching abilities, suppose a joint influence of cognitive and emotional factors,” the researchers wrote.

However, how these two factors interact in PWS remains largely unclear.

Researchers in France have evaluated whether mental rigidity in adults with PWS is specific to the disease or linked to intellectual disabilities, and whether it is affected by emotional contexts.

The study involved 30 adults with PWS, 30 age- and intellectual disability-matched individuals, and 30 age-matched healthy people.

Mental rigidity was assessed with a voluntary task-switching paradigm comprised of two simple tasks (indicating whether a letter was an “M” or a “W” and whether the current letter was crossed out or not). In two successive trials, participants could either repeat the same task or switch between tasks.

Each participant underwent 384 trials with a total duration of 15 minutes. Indicators of switching performance were switching cost and repetition bias.

Switching cost is the difference in latencies and/or error rates between trials where participants repeat a given task, and trials where they switch between two tasks. Repetition bias, an increased number of repetition trials relative to switching trials, also was observed previously in healthy participants and is thought to represent an attempt to minimize time and effort during the task.

The emotional context in which the task was performed was manipulated with task-irrelevant pictures from daily life, showing either positive, neutral, of negative emotions. The team expected that PWS patients would spend more time “decoding” positive and negative pictures relative to neutral ones, particularly during switches.

Results showed that PWS patients took about 100 milliseconds longer to complete a task after a switch than those in the other two groups, suggesting that intellectual disability is not the sole contributor to the characteristic mental rigidity in PWS.

“These findings add to the previous literature by strengthening the idea that PWS shows specific deficits in task switching, independent of general processing delay,” the researchers wrote.

Contrary to the team’s expectations, adults with PWS — who typically display impulsive and compulsive behaviors — did not show a global increase in error rates or repetition bias, compared with the other two groups.

“A possible explanation … may be that individuals with PWS exhibit more control over acts than previously thought, at least when experiments are conducted in laboratory settings,” the scientists added.

Also, there were no robust changes in global task-switching performance, switching-specific deficits, or repetition bias across emotional contexts.

Still, “negative contexts tended to increase the repetition bias [reflecting poorer mental flexibility] in all three groups while positive contexts slowed down global performance in PWS,” the team wrote, adding that further studies are needed to confirm these results.

The investigators hypothesized that the selected pictures were not strong enough to promote high levels of interference in the tasks and that the fact that each picture was shown eight times during the trials also may have contributed to the participants’ habituation.

Future research is needed to clarify the underlying mechanisms of mental rigidity in PWS patients and better understand the potential influence of emotional context, particularly positive emotions, in patients’ mental flexibility.

“We suggest that further studies could increase the strength of the emotional impact of pictures when everyday scenes are used to operationalize more emotional context,” the researchers wrote.

These findings also “highlight the difficulty of finding clear cognitive specificities in emotional processing in PWS,” they added.