Association Between Brain Activity And Personality Types

Introduction

The underlying association between brain activities and personality types can be difficult to ascertain given the complexity of the human brain and variance of personality sub-types. For example, introversion and extraversion only represents the polar opposite of a range of personalities. Keeping this in mind, a wide range exist between these polar opposites, thus quantification can be challenging and difficult. With respect to the biological basis of personalities, Eysenck’s hypothesized that introvert personalities has significantly lower thresholds for environmental stimulus, therefore aroused more compared to extroverts (Eysenck, 1967). Introvert personalities tend to exhibit higher baseline alpha 8 to 13 Hz wave frequency, which have been shown to be correlated with being awake, non-focused, relaxed, drowsy or non-vigilant. In contrast, extrovert personalities has been associated with beta wave frequency ranging between 14 to 40 Hz which has been correlated to being awake, alert, focused attention, and problem solving (Kumari et al. , 2004).

The aim of the study, therefore is to tease apart the relationship between the level of arousability and personality type as suggested by Eysenck’s model of personality. In the study, introvert and extrovert personality types were exposed to low and high level of environmental stimulation. The non-invasive electrodes attached to the left and right temporal lobes, and parietal-occipital area were measured in response to varying environmental stimulus as a function of intro-extraversion scale, and reflected in the electroencephalogram (EEG)

Methods

The selected participants for the study were recruited from the University of Northern British Columbia (UNBC), specifically from the biomedical studies and health sciences to represent a well-balance representative for the population. The twenty relatively healthy subjects that participated in the study had an age range of 19 to 25. The cohort were composed of seven females and thirteen males with varying ethnic origins, but mostly born raised in Prince George, BC Canada. Materials/ApparatusAs per the equipment used for the study, each participants were connected to the IX-TA iWire-B3G for the duration of the study. Four electrodes were utilize to detect and measure EEG frequencies and amplitudes generated by the right and left temporal, and right and left occipital lobes. To ensure the brain wave signals were detect by the electrodes, adhesive gels and a headband were used to connect the probe to the scalp.

Procedures

The IX-TA iWire-B3G detected and collect the participants’ alpha and beta wave frequency and amplitude. The detected signals were then recorded, manipulated, and analyzed through LabScribe software version: 3. 017700. Prior to the actual experiment, the subject were instructed to relax for a period of time to minimize artifacts and serve as a base line for the experiment. Recording of the EEG frequencies and amplitude with varying stimulus lasted about couple to a few minutes. That being said, the data were collected on an individual level and each participants were subjected to varying environmental stimulus, for example, low and high stimulus environments. The parameters for low stimulus environment were eyes-closed and high stimulus were eyes-opened while minimizing auditory signals from the environment. While the experiment were being conducted each participants were also instructed to minimize movements, for example, arm and leg movements as these could result in artifacts in the data sets. In addition, the subjects were also discourage not to speak during the experiment, therefore minimizing artifacts during the low and high stimulus phase of the study.

Results

Statistical analysis showed that there is weak linear correlation between the mean alpha and beta frequency as a function of intro-extraversion personality type. As shown in figure 1 and 2, it was found that introverts had a higher alpha and beta frequency compared to extroverts. The value decreases in both low and high environmental stimulus as intro-extraversion scale increases. Additionally, similar trend was also found with the alpha frequency, however the trend was less pronounced with respect to the right temporal lobe. In short, the trends observed for the left and right temporal lobe were similar in that there was higher base-line alpha and beta frequency for introverts, and decreases as extraversion tendency increases. As shown in figure 3, 4, 5, and 6, the male and female responded differently to different level of stimulus with respect to the left and right portion of the temporal lobe.

For the most part the trends were similar, introverts showing high alpha and beta frequency, however the left brain response for the female participants in high intensity stimulus showed a different trends. Female introverts showed a lower alpha frequency and increases as intro-extraversion scale increases as shown in figure 4. Similarly, in the low intensity stimulus male participants showed the recurring trends which was high alpha and beta frequency for introverts and the values decrease as the intro-extraversion scale increases. That being said, this trend were reversed for the female participants in low intensity environment. As shown in figure 6, the left temporal lobe signals for the female participants had a decreasing trend.

Discussion

It was found that there was clustering of data points at the polar opposites of the intro-extraversion scale creating a decreasing trends with respect to the alpha frequencies. The observed trends were expected as introverts are over-stimulated resulting in a high alpha frequency peak at these regions (Gale et al. , 1969). That beings said, the reverse were also observed for the extravert personality type because they are under-stimulated requiring greater threshold for arousability. The less pronounced degree of difference between introverts and extroverts response to low and high intensity stimulus could be the result of subjects mostly scoring in the mid-range of the personality scale. In short, most of the participants were neither introverts and/or extroverts instead they were in the median scale. Keeping this in mind, the trends was still noticeable when all the samples were pooled, however, the trends of introverts having higher base-line alpha wave frequency were reversed as soon as the samples were split into males and females category.

The deviation from the expected trends in the female groups could be the result of insufficient sample size since there were only 7 females in the study. The difference in response to stimulus between male and female brains could be the result of physiology (Rabinowicz et al. , 1999). The basic function of the temporal lobe includes processing visual, auditory, and long-term storage of sensory input, however, there is specialization of the left and right temporal lobes. That being said, the differences in the observed responses in the study between the left and right temporal lobes could be the result of specialization of function.

For example, the wernicke’s area which helps in speech processing and understanding of language is located on the left side of the brain. The auditory instruction provided by the experimenter could have triggered this portion of the brain during the transition of high to low intensity phase, thus leading to a deviation in the expected response from the left temporal brain. This was reflected on figure 6, the female introverts showed a higher alpha wave frequency compared to the extroverts. Moreover, the laboratory settings in which the study was conducted there was a significant amount of other stimulus, for example, noises coming the hallway as well as high intensity light coming from the window. All of which could have introduced artifacts or caused unusual data sets.