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Enriched environments elicit brain plasticity in animals. In humans it is unclear which environment is enriching. Living in a city has been associated with increased amygdala activity in a stress paradigm, and being brought up in a city with increased pregenual anterior cingulate cortex (pACC) activity. We set out to identify geographical characteristics that constitute an enriched environment affecting the human brain. We used structural equation modelling on 341 older adults to establish three latent brain factors (amygdala, pACC and dorsolateral prefrontal cortex (DLPFC)) to test the effects of forest, urban green, water and wasteland around the home address. Our results reveal a significant positive association between the coverage of forest and amygdala integrity. We conclude that forests may have salutogenic effects on the integrity of the amygdala. Since cross-sectional data does not allow causal inference it could also be that individuals with high structural integrity choose to live closer to forest.

The anterior cingulate cortex (ACC) is thought to play a major role in executive processes. Studies assessing neuroanatomical attributes of this region report a high degree of morphological variability. Recent theories consider the fissurization of the cortex to be a product of gross mechanical processes related to cortical growth and local cytoarchitectural characteristics. Hence, local sulcal patterning and gray matter volume are supposed to be associated. ACC fissurization was quantified in left- and right-handers of both sexes by recording the presence and extension of the paracingulate sulcus (PCS). Differences between groups regarding local gray matter volume were assessed by means of optimized voxel-based morphometry (oVBM) including additional modulation. Overall, the PCS occurred more often and was more pronounced in the left as compared to the right anterior cingulate region, although hemispheric differences were less pronounced in male left- and female right-handers. These discrepancies between groups seem to stem from variations of cingulate morphology in the left rather than the right hemisphere. The pattern of relevant comparisons in the oVBM analysis indicated a similar interaction. Therefore, evidence was found for discrepancies between groups and hemispheres on the macrostructural level.