Two recent studies have challenged the well-established belief that offending behaviors are inversely related to the personality trait of conscientiousness. Therefore, the aim of this study was to explore prisoners’ levels of traits according to the Five-Factor Model (FFM) of personality compared to control groups, with a focus on conscientiousness. Two separate samples of inmates in Swedish high-security prisons were investigated in three studies. Inmates and non-inmates completed a Swedish-language translation of Goldberg’s (1999) International Personality Item Pool questionnaire (IPIP-NEO, Bäckström, 2007). Male inmates (n = 46) in Studies 1 and 2 scored higher on conscientiousness than non-inmates (norm data based on approximately 800 males, and a students’ sample), which conflicts with previous results. Study 3 further explored the conscientiousness differences on the facet level. Male and female inmates (n = 131) scored higher on order and self-discipline (even after an adjustment for social desirability) than students (n = 136). In conjunction with previous findings, these differences are interpreted as being either temporal or enduring adjustments to the prison environment. It is suggested that researchers and clinical teams should cautiously interpret the FFM factor of conscientiousness (and its facets) when planning the further treatment of inmates.

Amplitude differences between extraverts and introverts in the P300 component of visual event-related potentials were examined in a picture classification task. A set of pictorial stimuli was used with three types of instructions, requiring responses based on colour, semantic category, or a combination of both criteria. Forty university students (22 men, 18 women) served as subjects. Based on their scores on the Eysenck Personality Inventory, they were divided into 3 groups of Low, Medium or High Extraversion. The pictures evoked large late positivities, with higher amplitude in the right hemisphere. P300 amplitude increased with increasing degrees of extraversion. The effect of extraversion on amplitude (High > Medium > Low) was larger for target stimuli in posterior derivations. The extraversion effect was mainly attributable to the impulsivity subtrait. Whereas some earlier studies have found higher P300 amplitudes for introverts in tasks inducing habituation or attention decrement, the present tasks differed by using more varied stimuli and by requiring more processing. The results are discussed in relation to theories on the biological basis of extraversion.

Eysenck's theory asserts that low cortical arousal accompanies extraversion (or the sub-component impulsivity). In Gray's theory, impulsivity is associated with high sensitivity to signals of reward, and anxiety with high sensitivity to signals of punishment. These hypotheses were tested by recording EEG signs of arousal and phasic arousability in emotional imagery, using 17 EEG channels and frequency analysis by Fourier transform. Three conditions were used: a neutral control task, and two emotional conditions involving imagery about pleasant and unpleasant personal memories. Forty subjects participated (23 men, 17 women; median age 23 years). Orthogonal personality dimensions of impulsivity and anxiety were derived from a joint analysis of the EPI and KSP questionnaires. The results showed, as expected, lower arousal, defined by more posterior theta activity, in impulsive subjects than in non-impulsives. These differences extended across all conditions. The EEG responses to the emotional conditions, in relation to the neutral one, consisted primarily of a right-lateralized frontal theta increase and changes in temporal beta activity (an increase in the positive condition, and a decrease in the negative one). These responses were expected to be amplified for impulsive subjects in positive emotion, and for anxious subjects in negative emotion. The right-sided frontal theta activity was stronger in high-anxious subjects than in low-anxious ones across all conditions, suggesting higher overall emotionality. For the temporal beta activity, the expected amplification of the response to negative emotion in the high anxiety group was confirmed, but the corresponding prediction for impulsives and positive emotion was not upheld. It is concluded that anxiety is related to EEG signs of heightened emotionality, especially in negative affect, and that impulsivity is associated with lowered arousal.

Eysenck's hypothesis of higher cortical arousal in introverts was examined using regional cerebral blood flow measurement in 37 healthy subjects . The measurement was made at rest, using the133Xe-inhalation method. Estimates of gray matter flow were obtained for 32 brain regions. There was no significant evidence of personality differences in general arousal, as measured by the mean flow level, averaged over all regions. There were, however, regional differences. An overall test of the blood flow distribution indicated different patterns of activity in introverts and extraverts. Follow-up tests attributed this to higher flow in the temporal lobes for introverts than for extraverts. Higher temporal lobe activity in introverts may be interpreted as increased functional connections between cortex and the limbic system.

Earlier research has shown that extraverts tend to increase their visual evoked potential amplitudes with increasing light intensity (augmenting), while introverts reach their maximum amplitude at lower intensities (reducing). The evoked response has normally been measured from association areas of the brain (at the vertex). The present study measured VEP amplitudes over visual cortex and at the vertex, using four light intensities in two conditions, where attention was either directed towards the light stimuli, or away from them by a concurrent auditory task. Forty subjects were classified as extraverts or introverts based on the Eysenck Personality Inventory. The results show that attention interacted significantly with extraversion. Introverts exhibited a narrower focus of attention, with higher amplitudes and amplitude-intensity functions when attending to the light flashes and lower when distracted. Extraverts showed smaller differences between conditions, indicating a more evenly distributed attention. Higher arousal in introverts is the probable cause of their narrower focus of attention. There were marked differences in the distribution of activity between vertex and occipital cortex. Introverts showed relatively stronger occipital responses and extraverts stronger vertex responses across all intensities and in both conditions. The predisposition for mainly perceptual responses to aversive stimuli in introverts, and for general alerting and motor preparatory responses in extraverts, are interpreted as supportive of Brebner & Cooper's hypothesis that introverts are "geared to inspect" and extraverts are "geared to respond".

Previous studies have indicated a relationship between evoked potential augmenting/reducing and extraversion or sensation seeking. However, the proposed mechanism of protective inhibition can account for this fact only if the relationship generalizes across different modalities and response definitions. The present study was designed to test this, using six intensities of visual and six intensities of auditory stimuli along with the EPI and SSS questionnaires.For the visual stimuli, the slope of the P90-N120 amplitude at the vertex correlated significantly with both the extraversion and the disinhibition scales in the way that augmenting/reducing theory predicts. However, over the primary visual area, no component showed the same personality relationship as the vertex wave, and one early component showed the opposite. This result suggests that personality differences in VEPs may reflect different ways of allocating processing resources between primary and association areas, rather than a generalized tendency to inhibit strong stimuli. In the auditory modality, personality differences were not apparent in the amplitude slopes, possibly due to the confluence from primary and association areas in AEPs in the vertex lead. There was a general tendency for latencies to correalte positively with extraversion and disinhibition, in congruence with Eysenck's theory on the biological basis of extraversion.

Regional cerebral blood flow was examined in a group of 17 subjects (8 men, 9 women, ages 22-35) at rest and during three mental activations, inducing perceptual and spatial processing. The subjects completed two personality questionnaires, the Eysenck Personality Inventory and the Karolinska Scales of Personality. The aim of the study was to examine the relation between rCBF and the extraversion-introversion dimension. Earlier studies of rCBF at rest have found higher blood flow in the temporal lobes for introverts than for extraverts, and a negative correlation between extraversion and global cerebral blood flow among women. Both findings were confirmed in this group. The importance of related personality dimensions, such as impulsivity and anxiety, for rCBF differences between extraverts and introverts were examined, using scales from the KSP questionnaire. It was found that anxiety-proneness aspects of introversion were more important in determining high temporal blood flow than low-impulsivity aspects. Global CBF in women, as a measure of general arousal, was mainly related to the sensation-seeking aspects of extraversion. Results from the spatial processing tasks showed more right-hemispheric activation for introverts than extraverts in a mental rotation task.