One group of mice, however, proved resilient to the stress. For three weeks before the social defeat treatment, all of the mice were subjected to two dramatically different living conditions. Some were confined to spartan cages, while others were treated to enriched environments with running wheels and tubes to explore. Unlike the mice in the bare-bones cages, bullied mice that had been housed in enriched environments showed no signs of rodent depression or anxiety after social defeat ( Journal of Neuroscience , 2011). "Exercise and mental enrichment are buffering how the brain is going to respond to future stressors," Lehmann says.
The areas of the brain where cannabinoid receptors are most prevalently located are consistent with the behavioral effects produced by cannabinoids. Brain regions in which cannabinoid receptors are very abundant are the basal ganglia , associated with movement control; the cerebellum , associated with body movement coordination; the hippocampus , associated with learning , memory, and stress control; the cerebral cortex , associated with higher cognitive functions; and the nucleus accumbens , regarded as the reward center of the brain. Other regions where cannabinoid receptors are moderately concentrated are the hypothalamus , which regulates homeostatic functions; the amygdala , associated with emotional responses and fears ; the spinal cord , associated with peripheral sensations like pain; the brain stem , associated with sleep , arousal , and motor control; and the nucleus of the solitary tract , associated with visceral sensations like nausea and vomiting .