Does Microplastic Ingestion Affect Cognition and Brain Gene Expression in Zebrafish, Danio rerio?

Cognition exhibits remarkable plasticity and therefore is potentially susceptible to non-adaptive changes caused by anthropogenic disturbances such as pollution. Among the most pervasive pollutants in aquatic environments are microplastics, which can be ingested by fish and other organisms, causing a range of physiological alterations that have been hypothesised to affect cognition. In this study, we conducted the first extended investigation of the cognitive consequences of microplastic ingestion in a teleost fish, the zebrafish Danio rerio. We measured brain activity, visual and spatial learning abilities and cognitive flexibility in both visual and spatial tasks across three experimental groups of zebrafish. One group was fed a diet containing microplastics from a common synthetic polymer, polyethylene (PE); one group a diet containing microplastics from a biodegradable polymer, polybutylene adipate terephthalate (PBAT); and a group received a control diet without microplastics. The treatments were continued over a medium-term period of 20–40 days. We found that PE microplastics significantly reduced brain activity in the zebrafish. However, the three experimental groups showed no differences in learning abilities and cognitive flexibility. Additionally, no detectable changes in individual differences in cognition were observed due to microplastic exposure. We conclude that microplastics derived from synthetic polymers altered brain functioning at the molecular level, although these alterations did not lead to detectable changes in the cognitive abilities in the tasks we investigated.