Limbic system. Artwork of the limbic system of the brain, a network involved in the expression of instinct and mood. The hippocampus (large purple oval, upper right) is involved in memory. It lies next to the amygdala (basal ganglion, red) which controls the emotions. The corpus callosum (green, upper centre to upper right) surrounds the limbic system, its front part covering the hypothalamus (green, only partially seen), which monitors body temperature, thirst and hunger. The hypothalamus is connected to the hippocampus by the fornix (narrow purple tube). The limbic system surrounds the thalamus (brown), a relay station for all sensory messages that enter the brain.