This question has long interested psychologists, especially follow­ing Canadian psychologist Donald Hebb’s original discovery that rats who lived in enriched environments were markedly superior intellectual beings than laboratory rats living in more Spartan sur­roundings. Hebb’s enriched rats could solve more complicated maze problems in shorter times than their less-fortunate lab mates. Later work carried out by the University of California–Berkeley’s Mark Rosenzweig showed that such enriched rats were not only superior performers, but that they also had a thicker neocortex with more richly developed synaptic connec­tions between brain cells. Indeed, this finding was the cornerstone of the modern view in neuroscience that the brain, far from being a fully formed and immutable organ by adulthood, could show dramatic physical responses to environmental changes all through the life span.A better benchmark for the effects of environmental deprivation on human behavior and brain function may come from studies devoted to pinpointing the causes of human disorders such as attention deficit hyperactivity disorder, or ADHD. Here, comprehensive studies of the home environment of children have shown that the lack of availability of enrichment in the physical environment of the home, in the form of affordances for play and stimulating wall panels and artwork, is one of the strongest predictors of the symptoms of ADHD. This finding fits intriguingly well with the results of the Merrifield and Danckert study because the psychophysiological signature of boredom that they identified has also been seen in children diagnosed with ADHD. At this point, we simply don’t know the extent to which such effects might be produced by daily exposure to poorly designed urban environments. But based on well-understood principles of neuroplasticity and on what is known of the effects of deprivation and enrichment, there is every reason to believe that these sterile, homogeneous environments are exerting a measurable effect on our behavior, and likely our brains as well. Given this, the prudent design of city streets and buildings, taking optimal levels of factors such as visual complex­ity into account, goes beyond the simple idea of promoting walkabil­ity and active and vibrant downtown neighborhoods. It is a matter of public health—mental health in particular.