The four major regions of the brain are

• the brainstem
• the diencephalon
• the cerebellum
• the cerebrum

In the brainstem: Reticular Activating System (RAS) - filters important and unimportant information from sensory input

In the diencephalon:
* thalamus - filters sensory information, senses pain
* hypothalamus - regulates hunger, thirst, body temperature
* epithalamus - secretes melatonin, sets day/night cycle

In the cerebellum: balance, gait, posture

In the cerebrum:
* corpus callosum - transfers information between right and left brains
* frontal lobes - regulates impulses, inhibitions, judgment
* basal ganglia - memory processing

Some of this information was obtained from:
http://www.edb.utexas.edu/syllabus/farrar/lectures/brain.html
More information on the brain can be found at the National Institute of Health's Mind Over Matter web site.