Background and aims
Pain processing changes with aging. Compared to young adults, older individuals show increased pain thresholds, increased temporal summation and decreased pain inhibition. Previous studies suggested that these changes might be associated with an age-related decline in cognitive functions, especially in executive functions. This study aimed to investigate whether – in addition to executive functioning deficits – structural brain changes might also help to explain pain responses in older individuals.

Methods
Pain responsiveness was assessed in forty-six healthy older individuals by verbal and facial responses to phasic pressure pain, pain inhibition (conditioned pain modulation using heat and pressure pain) and temporal summation of heat pain. Executive functioning performance was assessed in three cognitive domains, namely inhibition, shifting and updating. A structural magnetic resonance imaging scan was acquired to assess gray matter volume. 

Results
Multiple regression analyses revealed that pain responses could be significantly predicted by cognitive inhibition (R2=0.248; p=0.038) and shifting (R2=0.337; p=0.005). Voxel-based analysis of the magnetic resonance imaging scans revealed that one type of pain response, pain inhibition measured via facial expression, was positively correlated with gray matter volume in two regions of the ventrolateral prefrontal cortex (p<0.05, corrected).  

Conclusions
The results confirm previous findings of an association between pain responses and executive functions in older individuals. Moreover, this study shows that pain responses in older adults, specifically the loss in endogenous pain inhibition, can be explained by a decrease in gray matter volume in frontal regions of the brain.

STRUCTURAL BRAIN CHANGES AND EXECUTIVE FUNCTIONS CAN EXPLAIN PAIN RESPONSES IN OLDER ADULTS