Memory Impairment Means Less Pain for Mice

Acute versus chronic pain treatment in Alzheimer's disease

Several studies have suggested a lower consumption of analgesics in patients with Alzheimer's disease (AD) than in cognitively intact individuals (ND), but little attention has been paid to a distinction in analgesic consumption between acute and chronic pain treatment. The aim of this prospective and longitudinal study is a comparison in AD and ND residents at selection, and one year later, of analgesic consumption for acute and chronic pain, with an assessment of cognitive status (with the Mini Mental State Examination (MMSE)). Three hundred institution residents (150 AD and 150 ND), 20% male and 80% female (84.4 +/- 8.3 years old), were included in this study. Analgesic consumption and MMSE were reassessed at one year's distance (period 1 P1 and 2 (P2)). Analgesic consumption for acute pain was not significantly different for AD and ND at selection time or one year later, while MMSE declined significantly for AD (6 +/- 7 (P1) versus 4 +/- 6 (P2) p < 0.01, and ND individuals 23 +/- 5 (P1) versus 20 +/- 6 (P2), p < 0.01, respectively). Chronic pain analgesic consumption however was significantly lower in AD than in ND (p < 0.01). These findings may suggest a dissociation between sensory-discriminative (lateral pain system) and motivational-affective (medial pain system) aspects of pain in individuals with AD. This dissociation must be further investigated as it may have important consequences for pain evaluation and pain treatment in this vulnerable population.

A novel conditioned nociceptive response in mice

Chronic pain tends to be intractable, regardless of whether the etiology has improved or is persistent. This intractability may be due, in part, to conditioning factors, but studies of the underlying mechanism are limited. We predicted that the body might learn pain sensation during sustained pain. In the present study, we sought to examine the prediction that nociceptive pain could be a conditioned response. After pre-exposing mice to the context box, we assessed hind-paw licking responses(s), an unconditioned nociceptive response (UCR), in the training phase for 30 min following each of two injections (24h apart) of formalin into the hind paws. Forty-eight hours later, in the test phase, we tested for a conditioned nociceptive response (CR) from paw injections of saline, with mice placed in either the same or a different visual context box. The results showed that the CR elicited in the same context box was significantly larger than one elicited in the different box. An audiovisual context, which is used in prototypical Pavlovian conditioning, augmented the CR. The CR diminished to baseline levels during repeated extinction procedures, in which saline alone was given in the same context box. However, the CR in animals injected with saline in their home cages was unchanged. Treatment with scopolamine, which has an antimuscarinic action, and thus induces an amnestic effect, did not affect the UCR, but reduced the CR. These results indicated that repeated nociceptive stimuli were sufficient to produce a CR.

Exploring the relationship between cognition and self-reported pain in residents of homes for the elderly

BACKGROUND

Pain poses a major problem in older adults, specifically for those living in homes for the elderly. Previous research indicates that the presence of pain may be associated with changes in cognitive functions. It is unclear, however, how the reported experience of pain relates to cognitive functioning in elderly people with chronic pain. The present study was intended to examine the relationship between clinical pain experience and neuropsychological status in residents of homes for the elderly.

METHODS

Forty-one residents suffering from arthritis or arthrosis completed tests measuring memory, processing speed, and executive function. The sensory-discriminative and the affective-motivational aspects of clinical pain were measured.

RESULTS

Performance on executive function tests was positively related to self-reported pain experience. No relationship was observed between pain and memory or processing speed performance.

CONCLUSION

The present study shows that executive functioning is related to the severity of subjectively reported pain. Possible explanations for this association are discussed.

Relationship between chronic pain and cognition in cognitively intact older persons and in patients with Alzheimer's disease. The need to control for mood

BACKGROUND

Brain areas that are involved in cognition and mood also play a role in pain processing.

OBJECTIVE

The goal of the present study was to examine the relationship between chronic pain and cognition [executive functions (EF) and memory], while controlling for mood, in cognitively intact older persons and in patients with Alzheimer's disease (AD).

METHODS

Two groups of subjects participated: 20 older persons without dementia and 19 patients in an early stage of probable AD who suffered from arthrosis/arthritis. Pain intensity and pain affect were assessed by the Colored Analogue Scale for Pain Intensity and for Pain Affect, the Faces Pain Scale (FPS) and the Number of Words Chosen-Affective (NWC-A). Level of depression and anxiety were evaluated by questionnaires. EF and memory were assessed by neuropsychological tests.

RESULTS

The results show that significant correlations between specific cognitive functions, pain intensity and pain affect were lacking in the cognitively intact older persons. Cognition, in particular memory, appeared to be related to depressive symptoms. In contrast, a significant positive correlation was observed between EF, pain intensity and pain affect measured by the FPS in the AD group.

CONCLUSIONS

Although older persons with depression were excluded, in studies on pain and cognition one should control for the presence of depressive symptoms in older persons with and without dementia.