The enrichment objects can include various ‘toys’ of different find more shapes, sizes, colours, textures and smells, as well as specific facilitators of physical activity, such as tunnels, ladders, ropes and running wheels. This enhancement of sensory, cognitive and motor

activity is thought to stimulate neural activity across a range of central (and peripheral) systems, and a variety of subsequent cellular and molecular changes, which will be discussed below. Environmental enrichment is a relative term, defined in the context of ‘standard housing’, which varies between laboratories. Standard housing for laboratory rodents often includes minimal objects (apart from bedding and nesting material) added to the Smoothened Agonist home cage and might therefore be considered a form of sensorimotor deprivation [1]. This may impact on the ‘environmental construct validity’ of standard-housed preclinical models of brain disorders and have implications for clinical translation, as discussed recently [2,3]. Nevertheless, it is the difference between ‘enriched’ and ‘standard’ conditions which is crucial for such laboratory animal studies, allowing the experimenter to define EE-induced changes to brain structure and function, as well as molecular and cellular correlates. The first description of environmental enrichment of experimental animals

was by the pioneering neuroscientist (-)-p-Bromotetramisole Oxalate Donald Hebb, involving free-roaming rats in a home environment, relative to standard-housed caged controls [4]. Since Hebb’s first description, a wide variety of EE experiments have been performed using laboratory mice and rats. These EE effects on wild-type rodents have been reviewed extensively [1,5,6] and therefore will only be discussed briefly in the present article. However, key aspects of the reproducible effects of EE on wild-type rodents include cognitive enhancement, enhanced synaptic plasticity, adult hippocampal neurogenesis, synaptogenesis and modulation of gene expression [7]. Furthermore, following the

review of EE effects in animal models of brain disorders, I will briefly discuss potential mechanisms suggested by studies in wild-type rodents. The first evidence that EE could be beneficial in a genetic model of a brain disorder was provided using Huntington’s disease transgenic mice [8], as discussed in a later section. This was followed up with EE studies in animal models other neurodegenerative disorders, including Alzheimer’s disease and Parkinson’s disease [9], which will be reviewed in detail below. Furthermore, EE has also been found to induce beneficial effects in animal models of a range of other CNS disorders, including depression [10–12], epilepsy [13–15], stroke [16–18], multiple sclerosis [19], addiction [20,21], schizophrenia [22], autism spectrum disorders [23–25] and other neurodevelopmental disorders [26,27].