Biological Basis of Aggression:

Studies show that mild electrical stimulation of  a specific region of the hypothalamus - produces aggressive behaviour  in animals. When a cat's  hypothalamus was stimulated by implanting electrodes in  the brain and passing an electric current, it's hair stood on end; it hissed and arched it's back and would strike at anything that was placed in its cage. 

In  higher mammals like monkeys this instinctive pattern  is not observed. Their behaviour was seen to be more controlled by  the cerebral cortex rather than mere stimulation of the hypothalamus. The hypothythus may  send a message  to the cerebral cortex that its aggressive centres have bcen stimulated, the cortex then chooses the response considering what is going on in the environment, and what has been  stored in  the memory from past experiences. 

We  too have centres in  thc brain that can make us behave aggressively, but thefactivation  is under cognitive control. Some brain damaged persons may react to stimulation with aggressive behaviour, which would not elicit any response from normal persons. In such cases, it was found  that  the cerebral cortex was the damaged area ot  the brain. In normal persons. we can say  that  aggressive hehaviour  is determined largkly by social influences and personal experiences.