Brain function includes memory, concentration, and overall neurological functioning and regeneration.  In Ayurvedic medicine, attention is placed on the ability to remain focused so that learning is enhanced.  Sometimes this is equated to intelligence, but it involves more than IQ since synaptic responses need to processed and integrated into the perceptual world of individuals.  In most cases, the herbs affect clarity and assimilation of information, but many are also regeneration and have nootropic actions that can alleviate symptoms of neural deterioration.  Brain function can be associated wth toxicity, infection, exposure to EMF and nuclear radiation, and probably much more.  The symptoms are usually associated with vata dosha so some of the herbs reduce anxiety levels whereas others may help with telomere regeneration.  Please think about symptoms and choose accordingly.