Summary
Research on brain plasticity supports the notion that experience can shape brain structure as well as function [1, 2]. In particular, cultural and geographical properties of the environment have been shown to deeply influence cognition and mental health [3, 4]. In rodents, exploring complex environments has a positive impact on hippocampal neurogenesis and cognition [5]. In humans, spatial navigation activates the hippocampus [6], and continuous navigation of a large complex city environment increases posterior hippocampal volume [7]. While living near green spaces has been found to be strongly beneficial, urban residence has been associated with a higher risk of some psychiatric disorders [8–10]. However, how the environment experienced during childhood and early life impacts later cognitive abilities remains poorly understood for two reasons. First, human environments are manifold and much harder to characterize than a rodent’s cage. Second, gathering cognitive testing of large samples from populations living in different environments is very costly. To overcome these limitations, we measured non-verbal spatial navigation ability in 3.9 million people across all countries and examined a subset of this data (442,195 people, in 38 countries). We used a cognitive task embedded in a video game, that is predictive of real-world navigation skill [11, 12]. We focused on spatial navigation due to its universal requirement across cultures, and parallels to rodent studies [13, 14]. We quantified the complexity of participants’ environment with OSMnx, a tool giving access to the street network topology of cities anywhere in the world [15]. We found that on average, people who reported having grown up cities have worse navigation skills than those who reported growing up outside cities, even when controlling for age, gender, and level of education. This effect varied across countries, being for instance more than 6 times larger in the USA than in Romania. To investigate these variations we computed the average Street Network Entropy (SNE) of the biggest cities of 38 countries: grid-like cities (e.g. Chicago) have a small SNE, while more organic cities (e.g. Prague) have a higher one. We find a correlation between the average SNE and the extent to which growing up in a city negatively impacts spatial navigation ability. People growing up in countries with lower average SNE (griddy cities) have comparatively worse spatial abilities than their rural compatriots. This confirms the impact of the environment on human cognition on a global scale, and highlights the importance of urban design on human cognition and brain function.
