Brain

Humans and other vertebrates possess a central nervous system (CNS)—the brain and spinal cord—containing specialized cells called neurons. The nervous system is essential for virtually every aspect of life and, along with the body's other systems (muscular-skeletal, endocrine, etc.), performs the following seven basic, interrelated tasks:

1. Maintenance of vital functions, including control of the cardiovascular system and homeostasis (regulation of temperature, weight, internal milieu in general).
2. Obtaining information via the sensory systems (auditory, visual, somatosensory, olfactory, etc.) and processing that information. Information about ourselves and the world is provided by the sensory portions of the nervous system.
3. Storage and retrieval of information by the processes of learning and memory. Changes occur in the brain every time something new is learned, and the changes often last in the form of memories. Moreover, the brain must be adept at retrieving that information from storage when needed.
4. Production of behavior, including movement, locomotion, autonomic responses, and communicative behavior such as language. The brain's motor systems operate skeletal muscles that move the limbs, facial muscles, mouth, vocal cords, and so on.
5. Integration of information and output: tying things together to make "decisions" ranging from simple reflexes to complex social and cognitive processes (intelligence, language, spatial orientation, etc.).
6. Modulation of the overall activity levels of the brain and body associated with emotion, arousal, and sleep.
7. Carrying out the genetic mandate to pass on one's genes to the next generation, especially with respect to sex, reproductive behavior, parenting, and aggression.

It is evident from our everyday observations that any or all of the seven functions may operate at sub-par levels as people get older. For example, maintaining body temperature may become more difficult under extreme conditions; the eyes, ears, and other senses may not pick up as much as they used to; it can become harder to remember names; athletic skills decline; "intelligence" for new technological concepts seems poorer compared to that of young people; a good night's sleep is often harder to get; and the frequency of sexual activity may change. Because all seven functions are beholden to the nervous system, it follows that age-related changes in the system's components are part and parcel of these problems.

Understanding how the nervous system and its components fare as individuals age, how agerelated neural changes are manifested behaviorally, and how this knowledge may be used to improve the quality of life is an immensely daunting task because, irrespective of aging, the nervous system is bafflingly complex.

Figure 1 Midsagittal view of the human brain, which would be visible if the brain was separated into two halves and viewed from the (inside) cut surface. SOURCE: Suggested by Rosenzweig, Mark R.; Leiman, A. L.; Breedlove, S. M. Biological Psychology. Sunderland, Mass.: Sinauer Associates, 1999.