On the moderating role of age in the relationship between pain and cognition.

BACKGROUND: A relationship between pain perception and cognitive function is evident. However, the directionality of this association is unclear and may be influenced by age. That is, inverse associations between pain and cognition have been reported in young and middle-aged chronic pain patients, whereas higher clinical pain ratings have been associated with better cognitive performance in older chronic pain patients. Therefore, this study examined the possible moderating role of age in the pain-cognition relationship. METHOD: Twenty-two younger and 24 older chronic pain participants completed neuropsychological tests of psychomotor speed, memory and executive function. They also completed the McGill Pain Questionnaire to evaluate clinical pain. RESULTS: Interaction analyses revealed that age indeed moderates the relationship between clinical pain ratings and cognitive functions. In the younger age group, pain ratings were inversely related to memory and executive function. In the older age group, a positive relationship was found between pain ratings and executive function, whereas the inverse association of clinical pain with memory was no longer present. CONCLUSIONS: This study was the first to confirm the hypothesis that age is an important moderator of the relationship between pain and cognition. An important finding is that in older adults, most inverse effects of pain on cognition are either no longer present or may even be reversed. The positive relationship between pain and executive function may indicate age-related reduced integrity of a shared underlying neural substrate.

Chemical characterisation of organic electron donors for sulfate reduction for potential use in acid mine drainage treatment.

The production of acid mine drainage (AMD) containing high amounts of sulfate, heavy metals and low pH is of increasing concern. AMD is highly corrosive and results in economic and environmental problems. Organic electron donors for sulfate reduction were chemically characterised for potential use in AMD treatment. This was done in a process to develop a correlation between chemical composition and the capacity to drive sulfate reduction. Potential organic electron donors for sulfate reduction were chemically characterised in terms of dry matter content, ash content, total Kjeldahl nitrogen, lignin content, cellulose content, crude fat, crude fibre, in vitro digestibility, water-soluble carbohydrates, total non-structural carbohydrates and starch content. The chemical composition of the organic electron donors was then compared to results obtained from pilot plant studies where the organic electron donors for sulfate reduction were evaluated in terms of sulfate reduction. The chemical composition of the carbon source severely impacted its capacity to drive sulfate reduction and may be used to assist in predicting the sulfate reduction capacity of a carbon source. Organic electron donors for sulfate reduction high in protein content and low in lignin content or high in carbohydrate and crude fat content increased the capacity of a carbon source to drive sulfate reduction. The higher the fibre content of a carbon source, the lower the capacity to drive sulfate reduction. No correlation could be drawn between % dry matter, % ash content and sulfate reduction for the organic electron donors tested. Chemical characterisation can be used to assist in predicting sulfate reduction capacity of organic electron donors.