Environmental factors and their impact on chronic pain development and maintenance

It is more than recognized and accepted that the environment affects the physiological responses of all living things, from bacteria to superior vertebrates, constituting an important factor in the evolution of all species. Environmental influences range from natural processes such as sunlight, seasons of the year, and rest to complex processes like stress and other mood disorders, infections, and air pollution, being all of them influenced by how each creature deals with them. In this chapter, it will be discussed how some of the environmental elements affect directly or indirectly neuropathic pain, a type of chronic pain caused by a lesion or disease of the somatosensory nervous system. For that, it was considered the edge of knowledge in translational research, thus including data from human and experimental animals as well as the applicability of such findings.

Environmental enrichment for stroke and other non-progressive brain injury

BACKGROUND

Rehabilitation is effective for recovery after stroke and other non-progressive brain injuries but it is unclear if the rehabilitation environment itself, outside of limited therapy hours, is maximally conducive to recovery. Environmental enrichment is a relatively new concept within rehabilitation for humans. In this review, this is defined as an intervention designed to facilitate physical (motor and sensory), cognitive and social activity by the provision of equipment and organisation of a structured, stimulating environment. The environment should be designed to encourage (but not force) activities without additional specialised rehabilitation input.

OBJECTIVES

To assess the effects of environmental enrichment on well-being, functional recovery, activity levels and quality of life in people who have stroke or non-progressive brain injury.

SEARCH METHODS

We conducted the search on 26 October 2020. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library; MEDLINE (from 1950); Embase (from 1980); the Cumulative Index to Nursing and Allied Health Literature (CINAHL; from 1982); the Allied and Complementary Medicine Database (AMED; from 1985); PsycINFO (from 1806); the Physiotherapy Evidence Database (PEDro; from 1999); and 10 additional bibliographic databases and ongoing trial registers.

SELECTION CRITERIA

We planned to include randomised controlled trials (RCTs) that compared environmental enrichment with standard services.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligible studies, extracted data, and assessed study quality. Any disagreements were resolved through discussion with a third review author. We determined the risk of bias for the included study and performed a 'best evidence' synthesis using the GRADE approach.

MAIN RESULTS

We identified one RCT, involving 53 participants with stroke, comparing environmental enrichment (which included physical, cognitive and social activities such as reading material, board and card games, gaming technology, music, artwork, and computer with Internet) with standard services in an inpatient rehabilitation setting. We excluded five studies, found two studies awaiting classification and one ongoing study which described environmental enrichment in their interventions. Of the excluded studies, three were non-RCTs and two described co-interventions with a significant component of rehabilitation. Based on the single small included RCT at high risk of bias, data are insufficient to provide any reliable indication of benefit or risk to guide clinical practice in terms of the provision of environmental enrichment.

AUTHORS' CONCLUSIONS

The gap in current research should not, however, be interpreted as proof that environmental enrichment is ineffective. Further research is needed with robust study designs, such as cluster RCTs, and consistent outcome measurement evaluating the effectiveness of environmental enrichment in different settings (inpatient versus outpatient), the relative effectiveness of various components of environmental enrichment, cost-effectiveness, and safety of the intervention in people following stroke or other non-progressive brain injuries. It should be noted, however, that it is challenging to randomise or double-blind trials of environmental enrichment given the nature of the intervention.

Effect of environmental enrichment and isolation on behavioral and histological indices following focal ischemia in old rats

Stroke is a disease of aging. In stroke patients, the enriched group that received stimulating physical, eating, socializing, and group activities resulted in higher activity levels including spending more time on upper limb, communal socializing, listening and iPad activities. While environmental enrichment has been shown to improve the behavioral outcome of stroke in young animals, the effect of an enriched environment on behavioral recuperation and histological markers of cellular proliferation, neuroinflammation, and neurogenesis in old subjects is not known. We used behavioral testing and immunohistochemistry to assess the effect of environment on post-stroke recovery of young and aged rats kept either in isolation or stimulating social, motor, and sensory environment (( +)Env). We provide evidence that post-stroke animals environmental enrichment ( +)Env had a significant positive effect on recovery on the rotating pole, the inclined plane, and the labyrinth test. Old age exerted a small but significant effect on lesion size, which was independent of the environment. Further, a smaller infarct volume positively correlated with better recovery of spatial learning based on positive reinforcement, working and reference memory of young, and to a lesser extent, old animals kept in ( +)Env. Histologically, isolation/impoverishment was associated with an increased number of proliferating inflammatory cells expressing ED1 cells in the peri-infarcted area of old but not young rats. Further, ( +)Env and young age were associated with an increased number of neuroepithelial cells expressing nestin/BrdU as well as beta III tubulin cells in the damaged brain area which correlated with an increased performance on the inclined plane and rotating pole. Finally, ( +)Env and an increased number of neurons expressing doublecortin/BrdU cells exerted a significant effect on performance for working memory and performance on the rotating pole in both age groups. A stimulating social, motor and sensory environment had a limited beneficial effect on behavioral recovery (working memory and rotating pole) after stroke in old rats by reducing neuroinflammation and increasing the number of neuronal precursors expressing doublecortin. Old age however, exerted a small but significant effect on lesion size, which was independent of the environment.