Abstract
The human brain is the most complicated structure in the solar system. Astronomical numbers of nerve cells (neurons) and even larger numbers of nerve contacts (synapses) form elaborate networks. Chemical and electrical signals in the neuronal networks of the brain make us feel, move, think, understand, decide, create, remember, ... the brain is who we are. The synapses become more efficient when we use them: we can learn. When we rehearse and exercise, we get better, and we can counteract the deterioration of brain function with age and in disease. Change of synaptic function during learning involves production of 'growth factors' that the nerve cells need in order to thrive. The production of such factors (eg, 'brain derived neurotrophic factor' BDNF) increases also during physical exercise: for the brain to function optimally and keep young, the body must also be active.