Impulsivity is affected by cognitive enrichment and links to brain gene expression in red junglefowl chicks

Abstract

Despite reported findings, explanations for within-species variation in behavioural performance on cognitive tests are still understudied. Cognitive processes are influenced by environmental and genetic differences, where cognitive stimulation and monoaminergic systems are predicted to be important. To explore explanations for individual variation in impulsivity (a behaviour that is negatively correlated with inhibitory control), we experimentally altered the environment of red junglefowl, Gallus gallus , by exposing chicks from newly hatched to 9 weeks old to either (1) both environmental and cognitive enrichment, (2) environmental enrichment without additional cognitive enrichment or (3) neither environmental nor cognitive enrichment. Subsequently, we measured variation in impulsivity and brain gene expression of genes from the dopaminergic system ( DRD1 and DRD2 ) and serotonergic system ( 5HT2A, 5HT1B, 5HT2B, 5HT2C and TPH ). We focused on two aspects of impulsivity, impulsive action and persistence, and their reduction over time. Cognitively enriched chicks tended to have higher initial impulsive action and had higher initial persistence, and our environmentally enriched chicks had slower reduction of impulsive action over time. DRD2 (a dopamine receptor gene) had lower expression in environmentally enriched chicks. Variation in impulsive action tended to correlate with expression of TPH (a gene involved in serotonin synthesis), whereas persistence correlated with both TPH and the dopamine receptor gene DRD1 , and tended to correlate with the dopaminergic gene DRD2 , regardless of rearing treatment. These results indicate that both environment and links to neurobiology could explain initial individual variation in, and reduction of, impulsivity. Further, distinct neurobiological pathways appear to govern impulsive action versus persistence, supporting the suggestion that impulsivity is a heterogenic behaviour. • We studied effects of experimentally altered rearing experiences on impulsivity. • We measured two aspects of impulsivity: impulsive action and persistence. • Cognitive enrichment affected impulsivity and rate of inhibiting impulsivity. • Brain monoaminergic gene expression linked to both aspects of impulsivity. • Thus, both environment and neurobiology contribute to variation in impulsivity.