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Keywords:

  • brain activation;
  • near-infrared spectroscopy;
  • personality characteristic;
  • subjective motivation

Abstract

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENTS
  7. REFERENCES

Aim:  To examine relationships between personality traits and cerebral cortex reactivity under different motivating conditions.

Methods:  Relationships between personality traits assessed using the NEO Personality Inventory–Revised (NEO-PI-R) and cerebral cortex reactivity during a verbal fluency task monitored using multichannel near-infrared spectroscopy (NIRS) were examined under three different motivational conditions: control, monetary reward, and goal-oriented, in healthy young male volunteers.

Results:  Significant correlations between cerebral cortex reactivity and personality traits were found in the frontopolar region: a positive correlation with agreeableness and a negative correlation with the neuroticism and conscientiousness scores of the NEO-PI-R under the three motivational conditions. Higher scores for agreeableness were more strongly associated with a greater increase in total hemoglobin concentration ([total-Hb]) under the goal-oriented and control conditions than under the monetary reward condition. In addition, higher scores for neuroticism were more strongly associated with a greater increase in deoxygenated hemoglobin concentration ([deoxy-Hb]) under the monetary reward condition than the goal-oriented condition, and higher scores for conscientiousness were more strongly associated with a greater increase in [deoxy-Hb] under control conditions than under the goal-oriented condition.

Conclusion:  Using multichannel NIRS, certain personality traits of the big-five model are related to frontopolar reactivity. These relationships vary depending on the motivational condition when brain functions are monitored: agreeableness, neuroticism, and conscientiousness are all related to frontopolar reactivity depending on the motivational condition.

PERSONALITY IS DEFINED as ingrained patterns of thought, feeling, and behavior characterizing an individual's unique lifestyle and model of adaptation resulting from constitutional factors, development, and social experience. It has conventionally been conceptualized as consisting of several factors or dimensions. Representative examples of hypothesis-driven and empirically based major personality models are the Temperament and Character Inventory and the NEO Personality Inventory–Revised (NEO-PI-R), respectively.1,2

The brain substrates associated with the five dimensions of the NEO-PI-R have been studied in healthy subjects. The neuroticism score of the NEO-PI-R was negatively correlated with the ratio of the brain volume to the remainder of the intracranial volume on magnetic resonance imaging (MRI) and with insula metabolism on positron emission tomography (PET).3,4 The extraversion score was positively correlated with orbitofrontal cortex metabolism on PET and with increased cerebral blood flow in the anterior cingulate gyrus, temporal lobes, and posterior thalamus on single-photon emission computed tomography (SPECT).4,5 Significant correlations have also been observed in patients with psychiatric disorders: the depression score (one of the subscales of neuroticism) was correlated with MRI abnormalities in early-onset Alzheimer's disease,6 the extraversion score was correlated with gray matter volume loss in the right posterior fusiform gyrus in patients with chronic schizophrenia,7 and the agreeableness score was positively correlated with right orbitofrontal lobe volume and negatively correlated with left orbitofrontal lobe volume in frontotemporal dementia patients.8

Near-infrared spectroscopy (NIRS) is a recently available functional brain imaging technique in which cerebral blood volume (CBV) changes are monitored by measuring increases in oxygenated hemoglobin concentration ([oxy-Hb]) and decreases in deoxygenated hemoglobin concentration ([deoxy-Hb]). NIRS is particularly suitable for personality studies because it enables measurement in a natural setting, compared with other functional brain imaging techniques such as PET and functional MRI.9–11 For example, NIRS enables examination of subjects in a sitting position, with their eyes open, and while speaking using a small apparatus by their bedside, with a fine time resolution.12 Due to its technical advantages, NIRS addresses one of the main problems of functional neuroimaging personality studies: lack of a natural setting during neuroimaging.

Here, we examined differential relationships between personality traits assessed using the NEO-PI-R and frontal and temporal lobe activation during a verbal fluency task (VFT) using multichannel NIRS in healthy male subjects. Activation changes in brain functions were able to be monitored in a natural setting. In addition to the usual task-activated condition, frontal lobe and temporal lobe activation was also examined under two motivationally modified versions of the task-activated condition: a monetary reward condition and a goal-oriented condition. These conditions were used because human behaviors are, in general, motivated by reward and social interaction, and because task-induced brain activation is considered to be modified by the motivational state of the subject at the time of examination and hence to be differentially related to personality depending on the type of motivation.13

We hypothesized that the personality dimensions of the NEO-PI-R would be correlated with brain activation, and that these relationships would vary between the monetary reward, goal-oriented, and control conditions.14,15 All of the dimensions of the NEO-PI-R could be correlated with brain activation, because motivation is assumed to consist of various aspects of brain function. For example, personality dimensions reflecting interpersonal relationships such as extraversion and agreeableness could be positively correlated with brain function, especially under the goal-oriented condition, because subjects with high extraversion or agreeableness are assumed to be more motivated in a natural setting with an examiner. Personality dimensions reflecting interpersonal relationships and emotional features such as openness and neuroticism could be positively and negatively correlated with brain function, respectively, particularly under the monetary reward and the goal-oriented conditions, because motivation is considered to be related to openness and to be decreased during high-tension situations such as an examination. In addition, personality dimensions reflecting an effort-related nature such as conscientiousness could be positively correlated with brain function, because motivation is closely correlated with effort.

METHODS

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENTS
  7. REFERENCES

Subjects

Thirty-six healthy volunteers participated in this study. All of the subjects were male (mean age, 23.6 ± 2.75 years; range, 19–29 years) and were scored as right-handed using the Edinburgh Handedness Inventory scale.16 They were medics or medical department students with no history of any major psychiatric disorder, neurological disorder, substance abuse, head injury, or major physical illness, and they were not on any psychotropic medications at the time of the study. The subjects abstained from alcohol for at least 12 h prior to the NIRS measurements. This study was approved by the Institutional Review Board of Gunma University Graduate School of Medicine. Written informed consent was obtained from all of the subjects prior to the study.

Assessment of personality characteristics

The personality characteristics of the subjects were assessed using the Japanese version of the NEO-PI-R (Tokyo Shinri, Tokyo, Japan).2 The NEO-PI-R was undertaken by all subjects after the NIRS measurements using a standardized assessment protocol in which subjects completed a personality characteristics questionnaire.

Verbal fluency task and motivational conditions

A modified letter version of a verbal fluency task was used as the activation task for measurement of CBV changes. Subjects sat in a comfortable chair in a bright room with their eyes open throughout the measurements. The verbal fluency task consisted of a 30-s pre-task baseline, a 60-s verbal fluency period, a 70-s post-task baseline, and 60-s relaxation period.

Each subject underwent three consecutive sessions of the verbal fluency task with different motivational conditions, with a rest of >5 min between sessions: control, monetary reward, and goal-oriented conditions. We measured only one activation period per motivational condition, because repeating the measurement dampens the effect of personality and reward on brain activation. Under the control condition, the subjects were instructed to perform the verbal fluency task without any motivational condition, looking at a plus symbol on the CRT monitor in front of the subject. Under the monetary reward condition, the subjects were instructed before the session that they would be paid 100 yen for each correct word generated. The subjects looked at a plus symbol on the CRT monitor during the session as under the control condition. Under the goal-oriented condition, the subjects were motivated to generate the expected number of words by looking at the CRT monitor: on the CRT monitor, the number of words generated was overtly displayed as the number of accumulated green rectangles, and the expected number of words was shown as a pink line above the accumulated rectangles. The subjects were instructed to continue the task even when they reached the goal line. The order of the three syllable sets (six combinations) and the order of the three motivational conditions (six combinations) were completely counterbalanced among the 36 (6 × 6) subjects.

Assessment of subjective changes induced by motivational condition

Subjective changes induced by the motivational conditions were assessed immediately after each NIRS measurement condition using a questionnaire that the authors developed for this study. The questionnaire consisted of six items: motivation, effort, concentration, tiredness, difficulty, and fatigue, and the subjects were required to score each item from 5 (strongly agree) to 1 (strongly disagree).

NIRS measurements

Changes in [oxy-Hb], [deoxy-Hb], and total hemoglobin ([total-Hb]; the sum of [oxy-Hb] and [deoxy-Hb]) were monitored using a 52-channel NIRS machine based on the continuous wave method of measurement (ETG-4000; Hitachi Medical, Tokyo, Japan). The NIRS probe holders were placed on the subject's frontal and temporal regions. Hemoglobin concentration changes were measured at 52 measurement points, with the lowest probe line positioned along the T3, F7, Fp1, Fp2, F8, and T4 lines in accordance with the international 10/20 system used in electroencephalography. [Oxy-Hb] and [deoxy-Hb] were calculated based on absorption of near-infrared light of two wavelengths (780 and 830 nm) emitted from the emission probe and detected by the detection probe 3 cm away.

We chose the prefrontal cortex as the measured region because previous studies have reported that the prefrontal cortex was related to personality and motivational conditions.4,17–19

Statistical analysis

Task performance and subjective changes induced by the motivational conditions

Task performance and subjective changes induced by the motivational conditions were analyzed using one-way repeated-measures analysis of variance (anova) and the Friedman test, respectively, with ‘condition’ (the control, monetary reward, and goal-directed conditions) as an independent factor, followed by the post-hoc Wilcoxon test. Pearson's correlations of the NEO-PI-R scores with task performance were also examined.

NIRS data

The channels for which the mean [total-Hb] during the task segment divided by the standard deviation of [total-Hb] during the pre-task segment was <5.0 were excluded from further analysis, because such channels tend to have low signal-to-noise ratios due to the limited near-infrared light detected. Based on this criterion, 29 channels (11, 14, 15, 18, 19, 24–29, 32, 34–40, 42, and 44–52) were retained for further analysis. Channels were generally excluded if the signal was low under at least one reinforcement condition.

[Oxy-Hb] and [deoxy-Hb] measured during the task period were analyzed in three steps. First, channels with significant [oxy-Hb] and/or [deoxy-Hb] changes were identified. The individually averaged [oxy-Hb] and [deoxy-Hb] waveforms were divided into the following three time segments: a pre-task segment for 10 s before the verbal fluency period; a task segment for 60 s during the task period; and a post-task segment for 60 s after the task period. The averages of [oxy-Hb], [deoxy-Hb], and [total-Hb] within these three time segments were calculated and analyzed using one-way repeated measures of anova. The channels were considered to be activated by the verbal fluency task when the segment factor showed a significant effect (P < 0.05, anova) and [Hb] during the pre-task and task segments was significantly different, as determined on a post-hoc t-test with Bonferroni correction, because these effects were considered to be independent at each channel.

Next, Pearson's correlations for [oxy-Hb], [deoxy-Hb], and [total-Hb] with task performance were conducted. Finally, the mean [oxy-Hb], [deoxy-Hb], and [total-Hb] during the task segments were analyzed using one-way repeated-measures analysis of covariance (ancova) with ‘condition’ (control, monetary reward, and goal-directed conditions) as an independent factor and the five scores of the NEO-PI-R for ‘personality characteristics’ (neuroticism, extraversion, openness, agreeableness, and conscientiousness) as covariates, followed by a post-hoc t-test. For channels showing statistically significant covariate effects of personality characteristics, the mean [oxy-Hb], [deoxy-Hb], and [total-Hb] during the task segments were analyzed using correlation analysis with the five personality characteristics scores of the NEO-PI-R under each condition. In addition, as a post-hoc test for interaction, for channels showing statistically significant interaction effects for the NEO-PI-R scores with ‘condition’ (the three conditions), the mean [oxy-Hb], [deoxy-Hb], and [total-Hb] during the task segments were analyzed using one-way repeated-measures ancova with ‘condition’ (all pairs of conditions: control–monetary reward, control–goal oriented, and monetary reward–goal oriented) as an independent factor and the five scores of the NEO-PI-R for ‘personality characteristics’ as covariates.

In the second and third steps, channels with significant activation under all three conditions were used for analysis. Correlations and interactions were interpreted as statistically significant only if more than two neighboring channels had significance levels of P < 0.05 to exclude the effects of multiple correlations; the probability that three spatially neighboring channels had a significance level of P < 0.05 was less than 5% of all possible combinations of three channels among all of the channels with significant activation (maximum for [total-Hb]: n = 27).

RESULTS

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENTS
  7. REFERENCES

Comparison of the three conditions

NEO-PI-R scores and subjective changes induced by motivational condition and task performance

The means and SDs for the NEO-PI-R scores were 97.2 ± 19.1 (neuroticism), 103.8 ± 21.1 (extraversion), 116.9 ± 15.0 (openness), 107.8 ± 13.7 (agreeableness), and 102.1 ± 18.5 (consciousness). The means and SDs for task performance and the scores for the subjective changes induced by the motivational conditions were 19.9 ± 5.9 (task performance), 3.6 ± 0.8 (motivation), 3.2 ± 0.9 (effort), 3.5 ± 0.9 (concentration), 2.5 ± 1.1 (tiredness), 3.3 ± 0.6 (difficulty), and 2.2 ± 1.0 (fatigue). Motivation was scored significantly higher under the monetary reward than under the control condition (Z = −2.48, P = 0.013), and was not significantly different between the goal-oriented condition and the control (Z = −1.63, P = 0.103) or monetary reward (Z = −1.03, P = 0.302) conditions. Task performance, however, was not significantly different among the three conditions. The other scores were also not significantly different among the three conditions (F = 0.093, P = 0.911).

NIRS data

The grand averaged waveforms for [oxy-Hb], [deoxy-Hb], and [total-Hb] during the verbal fluency task under the control, monetary reward, and goal-oriented conditions are shown in Figure 1. During the task period, [oxy-Hb] significantly increased in 27 channels (11, 14, 15, 18, 19, 24–29, 32, 34–40, and 44–51; F = 9.0–30.2, P < 0.001) under the control condition; in the same 27 channels (11, 14–15, 18, 19, 24–29, 32, 34–40, 44–51; F = 13.6–49.6, P < 0.001) under the monetary reward condition; and in these 27 channels (11, 14–15, 18, 19, 24–29, 32, 34–40, 44–52; F = 10.4–35.4, P < 0.001) under the goal-oriented condition. During the task period, [deoxy-Hb] significantly decreased in 22 channels (24–29, 32, 34–40, 44–51; F = 5.1–33.1, P < 0.039) under the control condition; in 26 channels (14, 18, 24–29, 32, 34–40, 42, 44–51; F = 4.0–58.9, P < 0.031) under the monetary reward condition; and in 22 channels (24–29, 32, 34–40, 44–46, 48–52; F = 5.3–42.5, P < 0.014) under the goal-oriented condition. During the task period, [total-Hb] significantly increased in 27 channels (11, 14, 15, 18, 19, 24–29, 32, 34–40, 44–51; F = 9.6–30.8, P < 0.001) under the control condition; in 27 channels (11, 14, 15, 18, 19, 24–29, 32, 34–40, 44–52; F = 8.6–33.7, P < 0.003) under the monetary reward condition; and in 28 channels (11, 14, 15, 18, 19, 24–29, 32, 34–40, 44–52; F = 9.9–26.1, P < 0.001) under the goal-oriented condition. One-way ancova demonstrated no significant main effect of the independent variable ‘condition’: [oxy-Hb], [deoxy-Hb], and [total-Hb] changes during the task period were not significantly different among the three conditions (F < 3.86, P > 0.033; F < 4.22, P > 0.025; and F < 5.37, P > 0.010, respectively) in any channel.

image

Figure 1. Grand averaged waveforms of hemoglobin concentration changes during the verbal fluency task under the control, monetary reward, and goal-oriented conditions. Grand averaged waveforms of (red) [oxy-Hb], (blue) [deoxy-Hb], and (green) [total-Hb] changes during the verbal fluency task (between the two vertical dotted lines) measured using frontal and temporal probes. (grey fill) Channels with low signal-to-noise ratios. An example of a grand averaged waveform is enlarged below. The upper figures show the measurement positions of the near-infrared spectroscopy machines, superimposed on a magnetic resonance image of a reconstructed cerebral cortex. Ch, channel number.

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Correlation analysis

Assessment of personality characteristics

None of the NEO-PI-R scores was significantly correlated with task performance under the control, monetary reward, or goal-oriented conditions (P > 0.073, P > 0.095, and P > 0.081, respectively).

NIRS data

[Oxy-Hb] changes were negatively correlated in more than two neighboring channels with task performance under the control condition (ch. 29: r = −0.346, P = 0.039; ch. 39: r = −0.338, P = 0.044; ch. 50: r = −0.346, P = 0.039), but not under the monetary reward condition (r < 0.274, P > 0.107) or the goal-oriented condition (r > −0.314, P > 0.062). [Deoxy-Hb] changes were significantly correlated in more than two neighboring channels with task performance under the goal-oriented condition (ch. 26: r = −0.359, P = 0.032; ch. 27: r = −0.449, P = 0.006; ch. 36: r = −0.426, P = 0.010; ch. 37: r = −0.386, P = 0.020; ch. 38: r = −0.456, P = 0.005; ch. 48: r = −0.363, P = 0.029; ch. 49: r = −0.367, P = 0.028), but not under the control condition (r > −0.237, P > 0.164) or the monetary reward condition (r > −0.379, P > 0.022). [Total-Hb] changes were significantly correlated in more than two neighboring channels with task performance under the control condition (ch. 29: r = −0.356, P = 0.033; ch. 39: r = −0.350, P = 0.036; ch. 40: r = −0.337, P = 0.045; ch. 50: r = −0.371, P = 0.026), but not under the monetary reward condition (r < 0.365, P > 0.029) or the goal-oriented condition (r > −0.317, P > 0.060). Table 1 lists channels showing significant correlations of [oxy-Hb], [deoxy-Hb], and [total-Hb] with task performance under three motivational conditions.

Table 1.  Channels with significant correlations of [oxy-Hb], [deoxy-Hb], and [total-Hb] with task performance
Condition[Oxy-Hb][Deoxy-Hb][Total Hb]
  1. Ch., channel no.; N, negative correlations; P, positive correlations. Bold, significant correlation (P < 0.05).

ControlN (ch. 11, 24, 29, 34, 37, 39, 50: R < 0.332, P < 0.048)R > −0.237, P > 0.164N (ch. 24, 29, 32, 34, 37, 39 40, 50: R < −0.337, P < 0.045)
Monetary rewardR < 0.274, P > 0.107N (ch. 37: R = −379, P = 0.022)P (ch. 15: R = 0.365, P = 0.029)
Goal-orientedR > −0.314, P > 0.062N (ch. 26, 27, 36, 37, 38, 48, 49: R < −0.359, P < 0.032)R > −0.317, P > 0.060

Covariate effects of personality characteristics in the ancova were significant for [oxy-Hb] for neuroticism (ch. 18, 28, 29, 39; F > 4.39, P < 0.045) and agreeableness (ch. 14, 15, 24–26, 35, 39, 40, 50, 51; F > 4.18, P < 0.050), but were not significant for [deoxy-Hb] for any of the five dimensions. Covariate effects were significant for [total-Hb] for neuroticism (ch. 18, 28, 39; F > 4.50, P < 0.042), agreeableness (ch. 14, 24–27, 29, 35, 37–40; F > 4.18, P < 0.050), and conscientiousness (ch. 29, 40, 50; F > 4.28, P < 0.047) in more than two neighboring channels. Table 2 lists channels having significant correlations of [oxy-Hb], [deoxy-Hb], and [total-Hb] with scores in NEO-PI-R, obtained as significant effects of ‘personality’ covariates in ancova.

Table 2.  Channels with significant correlations of [oxy-Hb], [deoxy-Hb], and [total-Hb] vs. NEO-PI-R score
 [Oxy-Hb][Deoxy-Hb][Total Hb]
  • Obtained as significant effects of ‘personality’ covariates in ancova. Bold, significant correlation (P < 0.05). F and P-values are for the significant but the most weak correlation. P and F-values are the largest and smallest, respectively. Ch, channel number; NEO-PI-R, NEO Personality Inventory–Revised.

NeuroticismCh. 18, 28, 29, 39, F > 4.39, P < 0.045F < 3.46, P > 0.073Ch. 18, 28, 39, F > 4.50, P < 0.042
ExtraversionCh. 24, F = 4.60, P = 0.40F < 3.76, P > 0.062F < 3.64, P > 0.066
OpennessCh. 25, 35, 39, F > 4.59, P < 0.040Ch. 25, 45 51, F > 6.43 P < 0.017Ch. 35, 36, 39, F > 4.45, P < 0.043
AgreeablenessCh. 11, 14, 15, 24, 25, 26, 35, 37, 39, 40, 45, 50, 51, F > 4.27, P < 0.048Ch. 34, F = 4.29, P = 0.048Ch. 11, 14, 24, 25, 26, 27, 29, 35, 37, 38, 39, 40, F > 4.18, P < 0.050
ConscientiousnessCh. 40, 44, 50, F > 4.18, P < 0.050Ch. 40, F = 4.33, P = 0.046Ch. 29, 40. 44, 50, F > 4.28, P < 0.047

[Oxy-Hb] was positively correlated with agreeableness under the control condition (r > 0.353, P < 0.035) and the goal-oriented condition (r > 0.344, P < 0.040), and was negatively correlated with neuroticism under the monetary reward condition (ch. 28: r = −0.333, P = 0.047) and the goal-oriented condition (ch. 28: r = −0.388, P = 0.019; ch. 39: r = −0.329, P = 0.050). [Total-Hb] was positively correlated with agreeableness scores under the control condition (r > 0.339, P < 0.043) and the goal-oriented condition (r > 0.399, P < 0.016), and was negatively correlated with neuroticism (ch. 18: r = −0.343, P = 0.041; ch. 28: r = −0.343, P = 0.041) and conscientiousness (ch. 40: r = −0.377, P = 0.023) under the monetary reward condition. Figure 2 shows NIRS channels with significant correlations for [Hb] with NEO-PI-R and significant interactions between NEO-PI-R and ‘condition’.

image

Figure 2. Near-infrared spectroscopy channels with significant correlations for (a) [oxy-Hb] (b) [deoxy-Hb], and (c) [total-Hb] with agreeableness (red arrows), neuroticism scores (blue arrows), and consciousness scores (yellow arrows) on the NEO Personality Inventory–Revised (upward for positive and downward for negative correlations), and those with significant (red outline) interactions between agreeableness and ‘condition’, (blue outline) interactions between neuroticism and ‘condition’, and (yellow outline) interactions between consciousness and ‘condition’ as determined on ancova. (Light blue fill) Channels in which activations of [Hb] were not significant under any of the conditions. Ch., channel number.

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Interaction effects between ‘condition’ and ‘personality characteristic’ were significant in more than two neighboring channels for [deoxy-Hb] for neuroticism (ch. 25, 26, 36; F > 3.45, P < 0.038) and conscientiousness (ch. 28, 38, 39; F > 3.35, P < 0.042), and for [total-Hb] for agreeableness (ch. 19, 27–29, 38–40, 49, 50; F > 3.43, P < 0.039). Post-hoc ancova showed that higher scores for neuroticism were more strongly associated with a greater increase in [deoxy-Hb] under the monetary reward condition than under the goal-oriented condition (F > 6.367, P < 0.017), that higher scores for conscientiousness were more strongly associated with a greater increase in [deoxy-Hb] under the control condition than under the goal-oriented condition (F > 30.0, P < 0.033), and that higher scores for agreeableness were more strongly associated with a greater increase in [total-Hb] under the goal-oriented condition (F > 5.05, P < 0.032) and control condition (F > 4.31, P < 0.047) than under the monetary reward condition. Figure 3 shows relationship between agreeableness score and [total-Hb] under control, monetary reward, and goal-oriented conditions in ch. 39.

image

Figure 3. Relationship between agreeableness score and [total-Hb] under (inline image) control, (inline image) monetary reward, and (inline image) goal-oriented conditions in ch. 39, in which their interactions were significant. Ch, channel number.

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DISCUSSION

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENTS
  7. REFERENCES

In the present study we examined relationships between personality traits assessed using the NEO-PI-R and cerebral cortex reactivity during a verbal fluency task monitored using multichannel NIRS under three different motivational conditions: control, monetary reward, and goal-oriented, in healthy young male volunteers. The results indicate that (i) subjective motivation for the task was enhanced under the monetary reward condition, but without any improvement in task performance or cerebral cortex reactivity, that is, [oxy-Hb], [deoxy-Hb], and [total-Hb] changes during the task were not significantly different among the three conditions; (ii) cerebral cortex reactivity correlated negatively with task performance under the control condition for [oxy-Hb] and [total-Hb] and under the goal-oriented condition for [deoxy-Hb]; (iii) agreeableness was positively correlated with [oxy-Hb] and [total-Hb], neuroticism was negatively correlated with [oxy-Hb] and [total-Hb], and conscientiousness was negatively correlated with [total-Hb]; and (iv) agreeableness was more strongly associated with a greater increase in [total-Hb] under the goal-oriented and control conditions than under the monetary reward condition, neuroticism was more strongly associated with a greater increase in [deoxy-Hb] under the monetary reward condition than under the goal-oriented condition, and conscientiousness was more strongly associated with a greater increase in [deoxy-Hb] under the control condition than under the goal-oriented condition.

These results suggest that (i) several of the personality traits in the big-five model are related to frontopolar reactivity; (ii) such relationships vary depending on the motivational condition when brain functions are monitored; and (iii) agreeableness, neuroticism, and conscientiousness are related to frontopolar reactivity depending on the motivational condition. The present subjects were psychologically motivated under the motivational condition, but not sufficiently to improve task performance. The advantage of the NIRS technique is that it can monitor brain functions as activation changes in a more natural setting than other neuroimaging methods. We hypothesized that personality dimensions reflecting interpersonal relationships such as extraversion and agreeableness might be positively correlated with brain functions, particularly under the goal-oriented condition, because subjects with high extraversion or agreeableness are assumed to be more motivated in a natural setting with an examiner. Agreeableness was found to be positively correlated with brain functions, particularly under the goal-oriented condition. We also hypothesized that personality dimensions reflecting interpersonal relationships and emotional features such as openness and neuroticism might be positively and negatively correlated with brain functions, respectively, particularly under the monetary reward and goal-oriented conditions, because motivation is considered to be related to openness and to be decreased in high-tension situations such as an examination. Neuroticism was found to be negatively correlated with brain functions, particularly under the monetary reward condition. Last, we hypothesized that personality dimensions reflecting an effort-related nature such as conscientiousness might be positively correlated with brain functions, because motivation is closely correlated with effort. Conscientiousness was found to be negatively correlated with brain functions, particularly under the control condition, contrary to our hypothesis.

These findings suggest that subjective motivation may differentially affect brain functions depending on the motivation of the subjects. Such differential brain activation is, in addition, dependent on personality traits, based on the significant interactions between personality characteristics and motivational conditions for [total-Hb] and [deoxy-Hb]. Thus, subjective motivation was observed to be influenced by various factors such as brain function, motivational condition, and personality traits. These findings can be applied to motivational procedures in education and rehabilitation in medicine.

Conclusions

Using multichannel NIRS, several of the personality traits in the big-five model were found to be related to frontopolar reactivity. These relationships vary depending on the motivational condition when brain functions are monitored; agreeableness, neuroticism, and conscientiousness are related to frontopolar reactivity depending on the motivational condition.

ACKNOWLEDGMENTS

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENTS
  7. REFERENCES

This work was supported in part by grants from Japan Society for the Promotion of Science (Grants-in-Aid for Scientific Research (B) (No. 23390286) and for challenging Exploratory Research (No. 22659209) to MF), from the Ministry of Health, Labour and Welfare (Health and Labour Sciences Research Grants, Comprehensive Research on Disability, Health and Welfare, No. H23-Seishin-Ippan-002 to MF), and from the National Center for Neurology and Psychiatry (Intramural Research Grant for Neurological and Psychiatric Disorders, no. 21-1 and 23-10 to MF).

REFERENCES

  1. Top of page
  2. Abstract
  3. METHODS
  4. RESULTS
  5. DISCUSSION
  6. ACKNOWLEDGMENTS
  7. REFERENCES