Coloured 3D magnetic resonance imaging (MRI) scan of the limbic system of the human brain viewed from below. The limbic system's structures include the caudate nucleus, basal ganglia, thalamus, fornix (yellow), amygdala (light blue), and hippocampus (red). It is a primitive part of the brain involved in emotions, learning and the formation of memories. The optic nerves (yellow) are at top centre. At upper centre is the pituitary gland (green), a hormone secreting gland that regulates several physiological processes including stress, growth, reproduction and lactation.