Hereditary aspects to personality aren"t in isolation, they are combined with the environment. Heart rate increase leads to what behavioural change. Saliva is more common since blood needs to be drawn by someone with proper training. Depending on where the electrode is placed it gives off different readings. As muscles react to stimuli electrodes pick up responses. If some people have little reaction to all stimuli it could be due to high scores on psychoticism or high emotional stability. If heart rate reacts different than normal (extreme results) could be due to type a personality. Cognitive behavioural therapy helps deal with phobias by controlling physiological activity like heart rate and sweating. Introverts don"t need to seek as much stimuli because they already have high levels of aras. Both groups are seeking optimal level because too much or too little activity in aras is not good.