Storage of experience, including learning and memory, is thought to involve plasticity within pre-existing brain circuits. One model for looking at experience-dependent changes is environmental enrichment (EE), which involves exposing animals to a complex novel environment. Animals exposed to EE have previously been shown to exhibit a variety of behavioural and structural alterations in the brain, including decreased stress, improved learning and memory, altered levels of immediate early genes and synaptic change in the visual cortex. We were interested in understanding what regions of the brain are activated during the initial stages of EE. We used fos-tau-lacZ (FTL) transgenic mice to examine changes in functional activation throughout the brain after a single exposure to EE. We found that there was a significant increase in FTL expression within particular morphologically identified neurons in a series of brain regions in the enriched group compared to control groups, indicating that multiple circuits were activated. These regions include the claustrum, infralimbic cortex, hippocampus, amygdala and the hypothalamus. The data suggest that EE stimulates an initial strong increase in activation of multiple functional circuits. These circuits are presumably involved in the initial response of the animal to the enriched environment.