Hypothalamus

Located below the thalamus in the brain and immediately above the brain stem, the hypothalamus is involved in the control of metabolic processes and control or initiation of a wide variety of behaviors, including eating, drinking, sex, sleep, stress responses, anger and fear reactions, and other behaviors.

Nuclei Clusters of nerve cells in the hypothalamus are linked with the autonomic nervous system (ANS), the limbic system (other brain structures), and the endocrine system (system of glands in the body) by direct nerve connections and neurohormonal secretions.

Through these links, the hypothalamus regulates many behaviors, including those governed by the two branches of the ANS: the sympathetic and parasympathetic nervous systems.

By triggering either the sympathetic (stress) or parasympathetic (vegetative) responses, the hypothalamus attempts to meetthe needs created by changes in the external environment or to maintain a balanced (homeostatic) state. For instance, one’s blood pressure is adjusted depending on whether one’s blood pressure is adjusted depending on whether one is sleeping or jogging.

The hypothalamus synthesizes and secretes hormonal substances that are transmitted to the pituitary gland (the master gland in the body), located directly below the hypothalamus. When the pituitary gland is stimulated, hormones are released into the bloodstream, leading to a variety of bodily changes.

The hypothalamus is involved in emotional behaviors. In a study utilizing cats as subjects, Bard and Macht (1958) detached different parts of the brain and observed the associated behavioral reactions. They concluded that the hypothalamus was the part of the brain that was primarily responsible for organizing rage/attack behaviors; with a detached hypothalamus, cats would still show elemtens of rage behaviors but would not produce the constellation of reactiosn that are called rage.

Wasman and Flynn (1962) demonstrated that different types of emotional behaviors could be produced by electrically stimulating different nuclei within the hypothalamus of cats. Specifically, stimulation to the medial (central) nuclei of the hypothalamus elicited vicious attack behavior in cats, while stimulation to the lateral nuclei of the hypothalamus elicited unemotional quiet-attack behaviors (e.g., a quiet, biting attack).

The hypothalamus is also known for its functions in times of stress. Hess (1954) showed that electrical stimulation of the posterior (rear) hypothalamus produces sympathetic (stress) responses and that electrical stimulation of the anterior (front) hypothalamus produces parasympathetic (relaxed, vegetative) responses. In everyday, stressful situations, the hypothalamus causes the release of stress hormones through the adrenal glands (located above each kidney). The hypothalamus causes this release both through direct neural connections with the adrenal glands and by sending messages to the pituitary gland, causing the pituitary to release hormones into the bloodstream.