Information processing is a function of the a. medulla b. reticular formation c. hypothalamus d. cerebral cortex

The answer is D. cerebral cortex.

The cerebral cortex is the largest part of the brain. It is responsible for higher functions of the brain, including information processing. It controls memory, sensation, perception, association, thought, voluntary physical actions. 

Reticular formation is responsible for consciousness, medulla is a brain center for respiration and circulation, while the most important function of hypothalamus is linking ot the nervous and endocrine systems.