In the human brain, the hypothalamus is a structure responsible for several autonomic functions. The autonomic nervous system regulates unconscious processes, such as body temperature, heartbeat, and breathing. One portion of this structure is the anterior hypothalamus, which is involved in several processes.
The preoptic area is a section of the anterior hypothalamus. It plays a role in regulating body temperature. In this region, there are neurons that respond to changes in the temperature of the hypothalamus, also called the core temperature. Other neurons receive input from sensory cells on the skin and in the spinal cord that detect temperature changes.
Having several different input neurons allows the anterior hypothalamus to determine overall body temperature. These send signals to lower areas that can influence temperature. Responses may vary based on whether temperature is due to internal or external conditions. For example, influencing metabolic processes can increase internal temperature. Shivering is an automatic response that can help the body respond to cold exterior temperatures.
Compounds like pyrogens can influence these particular neurons. Pyrogens are created in the body, and increase signals from sensory cells that detect cold. This activity causes the anterior hypothalamus to increase body temperature, resulting in a fever.
Another role of this region of the hypothalamus that is essential to normal functioning involves sleep. The suprachiasmatic nucleus in the hypothalamus responds to the presence of light, causing this structure to send messages to the pineal gland. This in turn causes it to stop producing melatonin. Among other essential functions, melatonin plays a role in inducing sleep. The varied responses to different light levels cause the anterior hypothalamus to help regulate circadian rhythms.
Thirst and hunger perceptions are mediated by a part of this structure. Within the anterior region, the lateral hypothalamus has neurons that respond to lower levels of blood glucose. Lower blood glucose levels create activity in this area, and when these neurons fire, the individual feels a desire for food.
One region in the anterior hypothalamus may help regulate aggressive behavior. The basolateral hypothalamus responds to chemical neurotransmitters like vasopressin and serotonin. Vasopressin activates cells in this area that lead to aggressive behaviors, like biting, in hamsters. Serotonin prevents the activation of these neurons, thereby decreasing aggression.
The medial preoptic nucleus in this region contains size differences between males and females. In males, this structure is larger, and releases hormones that affect the pituitary gland. These hormones are involved in sexual maturation in males. Stimulation of this nucleus has caused sexual behavior in rats involved in animal studies.