What controls our behavior?

Behavior is the way a person or an animal reacts to a stimulus from the environment.  A specific type of behavior occur in response to a specific type of stimulus.  For instance, a dog would not wag its tail at and a cat would not purr to a threatening subject.  Since Ancient Mesopotamian and Ancient Egyptian times, people have known that the brain controls one’s behavior.  The brain’s connection to human behavior was increasingly understood after observing behavioral change in subjects who had suffered brain injury.  The most famous and described case of behavior change after brain injury was the case of Phineas P. Gage of the 19th century.  (Picture below shows Gage holding the iron rod that went through his head)

Gage was an American railroad construction foremen, who survived an accident in which a large iron rod went through his head and destroyed most of his left frontal lobe.  Before the accident, Gage was described as a hard-working, responsible, and "a great favorite" with the men in his charge.  His employers had regarded him as "the most efficient and capable” foreman” in their employment.  However, after the accident, his personality changed drastically.  “He is fitful, irreverent, indulging at times in the grossest profanity, manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires, at times pertinacious obstinate, yet capricious and vacillating, devising many plans of future operation, which are no sooner arranged than they are abandoned in turn for others appearing more feasible”, described by Dr. John Martyn Harlow.

Another example was the lobotomy, which was a radical physical therapy for the asylum's patients in the first half of the 20th century.  This psychosurgery cuts the connections to and from the prefrontal cortex, located in the front portion of the brain.  After lobotomy, patients’ behaviors changed dramatically and it appeared as if they were no longer plagued by their “insanity”.  This behavioral change led psychiatrists to believe that "prefrontal lobotomy reduces anxiety feelings and introspective activities; feelings of inadequacy and self-consciousness are thereby lessened.  Lobotomy reduces the emotional tension associated with hallucinations and does away with the catatonic state", as described in the Psychiatric Dictionary in 1970.  It is now known that, in fact, the prefrontal cortex is responsible for the orchestration of thoughts and the actions in accordance with internal goals.

If the brain controls behavior, it begs the question, what then controls the brain?  Scientists have long wondered, whether a person’s genetic makeup dictates behavior.  The relationship between genes and behavior was first investigated through the study of patients with schizophrenia, which is considered as a more complex “behavior”, and their family members.  It was observed that among the family members of a schizophrenic, his or her identical twin (monozygotic twin), who shares the same exact genetic makeup, had the highest risk of developing schizophrenia.  This observation was also made for more complex behaviors such as memory, neuroticism, vocational interests (adolescence), extraversion, spatial reasoning, scholastic achievement(adolescence), processing speed, verbal reasoning, and general intelligence.  [Plomin, et al.,1994].  These twin studies suggest that genes are at least in part, responsible for our behaviors.  Today’s research focuses on the direct relationship between genes and behavior.