I want to know the effects that xanax has on the brain?

Benzodiazepines (eg Xanax) affect a key neurotransmitter in the brain called gamma-amino butyric acid (GABA). This neurotransmitter has an inhibitory effect on motor neurons, thus the presence of GABA slows or stops neuronal activity. Benzodiazepines enhance the activity of GABA, effectively slowing nerve impulses throughout the body.
As a consequence of the enhancement of GABA's inhibitory activity caused by benzodiazepines, the brain's output of excitatory neurotransmitters, including norepinephrine (noradrenaline), serotonin, acetyl choline and dopamine, is reduced. Such excitatory neurotransmitters are necessary for normal alertness, memory, muscle tone and co-ordination, emotional responses, endocrine gland secretions, heart rate and blood pressure control and a host of other functions, all of which may be impaired by benzodiazepines.