Inhibition, Working Memory Impaired in PWS Patients, Study Finds

Impairments in behavioral and working memory tasks are seen in people with Prader-Willi syndrome (PWS) compared with healthy controls, a new study shows.

The study, “Investigation of the relationship between electrodermal and behavioural responses to executive tasks in Prader-Willi syndrome: An event-related experiment,” was published in the journal Research in Developmental Disabilities.

PWS patients can have a wide range of symptoms, including those affecting the endocrine system and nervous system, and experience changes at the cognitive and behavioral levels.

Previous studies have found that PWS is associated with dysfunctions in the autonomic nervous system, which controls the function of internal organs. According to these studies, PWS patients have abnormal temperature regulation, circadian rhythm, pain perception, and increased heart rate.

The contribution of the autonomic nervous system on attention and memory has become increasingly popular in research on genetic neurodevelopmental disorders, such as PWS.

Previous cognitive studies in PWS patients suggested that impaired executive functions (mechanisms responsible for adaptation to non-routine situations and government of goal-directed actions, such as organizing, planning, prioritizing, and paying attention) may explain the relationship between some PWS-related behavioral and cognitive symptoms.

Still, little is known about executive functions such as behavioral inhibition (suppression of pre-potent responses) and working memory updating (storage of new working memory content). Also, the association between impairments in executive functions and the autonomic nervous system is still inconclusive.

A team of researchers investigated behavioral inhibition and working memory updating in PWS patients, and searched for features that could be associated with these functions.

The study included 30 adults with PWS (mean age 30.4 years), and 30 healthy adults (mean age 22.6 years), and assessed inhibition and working memory functions while simultaneously measuring sympathetic nervous system signals through electrodermal activity (EDA).

The sympathetic nervous system is part of the autonomic nervous system, and is characterized by the body’s fight-or-flight response.

EDA is used in psychological research as a measurement of the autonomic nervous system, more specifically the sympathetic nervous system. In essence, EDA measures the electrical conductance in the skin, and links the output with psychological and physiological arousal. Because a sympathetic feature such as sweating increases electric conductance, increased EDA is thought to be a marker of sympathetic arousal.

Behavioral inhibition was assessed with a time-limited go/no-go task, where participants press a key to a go stimulus (the letter “M”) on a screen, and avoid responding when a no-go stimulus appears (the letter “W”).

Working memory updating was measured using the N-2-Back task, where participants track the order of letters appearing on the screen and their locations on a grid.

Because height and weight can influence EDA outcomes, researchers measured and controlled for body mass index (BMI) of all participants. As expected, PWS participants had a higher BMI (45.7), compared with healthy controls (21.6).

Results showed that PWS patients performed worse than healthy participants in both the behavioral inhibition and working memory updating tasks.

PWS participants had a slight impairment of inhibition, as they committed more errors (3.5%), and a severe working memory updating impairment (29.61%), compared with healthy participants (2.2% and 8.39%, respectively).

Also, task reaction times were significantly slower for PWS participants (inhibition, 448 milliseconds; working memory updating, 1,307 milliseconds), compared with healthy individuals (inhibition, 363 milliseconds; working memory updating, 946 milliseconds).

Sympathetic activation was assessed through EDA variables, including skin conductance levels (SCL; measures slow changes in the autonomic system), and skin conductance response (SCR; measures faster-changing signals).

Researchers found no consistent significant link between EDA results and executive functions in both PWS and healthy groups. However, PWS patients showed higher SCRs, indicating an over-activation of the sympathetic nervous system.

“[O]ur results suggest that overactivation of the sympathetic division in PWS may be related to difficulties during cognitive effort underpinned by less cognitive resource available for task performance,” the researchers stated. “The findings suggest that PWS adults are associated with slightly impaired inhibition and severely impaired working memory updating functions.”