The influence of complex and threatening environments in early life on brain size and behaviour

The ways in which challenging environments during development shape the brain and behaviour are increasingly being addressed. To date, studies typically consider only single variables, but the real world is more complex. Many factors simultaneously affect the brain and behaviour, and whether these work independently or interact remains untested. To address this, zebrafish (Danio rerio) were reared in a two-by-two design in housing that varied in structural complexity and / or exposure to a stressor. Fish experiencing both complexity (enrichment objects changed over time) and mild stress (daily net chasing) exhibited enhanced learning and were less anxious when tested as juveniles (between 77-90 days). Adults tested aged 1 year, were also less anxious even though fish were kept in standard housing after 3 months of age (i.e. no chasing or enrichment). Volumetric measures of the brain using magnetic resonance imaging (MRI) showed that complexity alone generated fish with a larger brain, b...