Limbic system. Illustration of the anatomical structures of the limbic system of the brain. The limbic system is represented in blue. At centre is the ovalshaped thalamus; at centre right, beside it are two lobes of the caudate nucleus; around these is the large Cshaped corpus callosum; at lower right are two bulblike olfactory lobes; the reticular formation is the blue structure which extends into the brainstem (lower left). This complex network of nerve pathways is involved with the expression of instinct and mood. Activities governed by the limbic system include expression of fear, rage, pleasure, reproduction, self preservation, and formation of memory patterns.