Effects of environmental complexity and deprivation on brain chemistry and physiology: a review

Within the last two decades it has become evident that the brain exhibits a wide range of chemical and physiological responses to its sensory environment. Comparison of the brains of animals reared in relatively complex as opposed to deprived sensory environments has yielded significant insight into the nature of these effects, which are reviewed in this paper. Greater complexity of the sensory environment results in increased total cholinesterase and acetylcholinesterase enzyme activity, while other neurotransmitter related substances, the catecholamines, show more variable responses. RNA concentration is slightly greater as is DNA transcriptional activity, while protein precursor uptake shows a variety of regional and temporal patterns. In general, responses for most substances tend to show regional and temporal specificity with the largest effects most often in the occipital cortex. Electrophysiological measures have revealed shorter visual cortex evoked potential latencies and greater amounts of sleep in the complexity-reared subjects. The wide range of environmentally responsive parameters is consistent with an adaptive functioning of brain chemistry and physiology and with recent models in the physical sciences which view the universe as composed of dynamic webs of relationships rather than isolated independent units.