When we reach for a cup of coffee or tea in the morning, eat some chocolate, smoke a cigarette or take an herbal supplement, we are using plants and their byproducts to alter our brains and how we feel.
Much is known about how the psychoactive components of these various products have their their way with human brain function, but why they have these effects has been almost totally ignored.
Plants and the Human Brain by David O. Kennedy describes and discusses both how and why phytochemicals affect brain function with respect to the three main groups of secondary metabolites: the alkaloids, the phenolics, and the terpenes.
The answers reside, in part, with the terrestrial world's two dominant life forms, the plants and the insects, and the many ecological roles the 'secondary metabolite' plant chemicals are trying to play; for instance, defending the plant against insect herbivores whilst attracting insect pollinators.
The answers also reside in the intersecting genetic heritage of mammals, plants, and insects and the surprising biological similarities between the three taxa. There is a surprisingly close correspondence between the brains of insects and humans, and the intercellular signaling pathways shared by plants and humans.
