German psychologist Hans Eysenck's nervous system model of temperament links temperament traits, particularly introversion and extraversion, to the central nervous system. Introverts are typically quiet, reserved, and shy while extroverts are active, sociable, and outgoing (151). According to Eysenck, introverts have high levels of brain arousal, which is controlled by the ascending reticular activating system (ARAS). Therefore, introverts do not need to seek external excitement which leads them to be more reserved. In contrast, he argues that extroverts have lower levels of brain arousal and are therefore more sensation seeking to compensate. In this article, I will aim to summarize and summarize some of the research regarding introversion and extroversion and their connection to the central nervous system and arousal states. I will summarize this information to support the idea that while introversion and extroversion are at some level linked to states of arousal, Eysenck's arousal hypothesis is not alone sufficient to explain the biological differences between introverted and extroverted individuals and their behaviors in as such. Gerald Matthews, D. Roy Davies, and Jackie L. Lees conducted a series of three experiments to test Eysenck's arousal hypothesis of introversion and extraversion. The first of the experiments, which consisted of two parts (A and B), is the most relevant to this topic. According to Eysenck's hypothesis, extroverts have a low level of arousal and therefore should seek stimulation in the morning. However, according to Matthew's experiment, the opposite actually happens. In part A of this experiment, participants were 50 males and 50 females between the ages of 18 and 36 with normal vision. ...... middle of paper ...... Testing Eysenck's arousal/arousal hypothesis. Journal of Individual Differences, 30(2), 87-99. doi:http://dx.doi.org/10.1027/1614-0001.30.2.87Lindín, M., Zurrón, M., & Díaz, F. (2007). Influences of introverted/extroverted personality types on p300 amplitude across repeated stimulation. Journal of Psychophysiology, 21(2), 75-82. doi: http://dx.doi.org/10.1027/0269-8803.21.2.75Matthews, G., Davies, D. R., & Lees, J. L. (1990). Arousal, extraversion, and individual differences in resource availability. Journal of Personality and Social Psychology, 59(1), 150-168. doi:http://dx.doi.org/10.1037/0022-3514.59.1.150Rammsayer, T. H. (1998). Extraversion and dopamine: Individual differences in response to changes in dopaminergic activity as a possible biological basis of extraversion. European Psychologist, 3(1), 37-50. doi: http://dx.doi.org/10.1027//1016-9040.3.1.37