Regardless of the many studies linking aspects of various diseases with neural meaningful link systems, no single neurotransmitter or hormone system is likely to be responsible for the full array of symptoms in any disease pattern. Instead, a multitude of factors influence how each of these neural systems impact one another, affect other neural systems, modifiers and genomic activational events, and contribute to cognitive and behavioral outcomes. Much further investigation is necessary to establish substantive links between the temperament dimensions of the FTI and specific bio-behavioral illnesses.
The Cronbach’s alpha coefficients for the U.S. sample were: 0.79 for both the Curious/Energetic and Cautious/Social Norm Compliant constellations; 0.80 for the Analytical/Tough-minded subscale; and 0.78 for the Prosocial/Empathetic scale.
Each colored ball is a specific question on the FTI. Yellow, Curious/Energetic; Blue, Cautious/Social Norm Compliant; Red, Analytical/Tough-minded; Green, Prosocial/Empathetic; e = eigenvector. The position of each colored ball (in three-dimensional space) indicates the correlation coefficient calculated by the Eigen analysis for each item on the FTI. The lines connect the questions within each scale. The length of each line is a rough estimate of the covariance between items, or the eigenvector. The four scales are clearly separable.
Mean scale scores for responses to “Sex is an essential part of a successful relationship.” The data describe attitudes about sexual activity and relationships for the four scales. For the Curious/Energetic scale, both men and women showed a positive correlation between their scale scores and level of endorsement for sexual activity in a relationship (men: r = 0.13, p = 3.89 ? 10 -69 ; women: r = 0.16, p -100 ); the correlation for women was significantly higher than the one for men (p = 0.0024). For the Cautious/Social Norm Compliant scale, men showed no effect, while women showed a negative correlation (r = -0.03, p = 3.46 ? 10 7 ), which was significantly different from men (p = 0.0015). For the Analytic/Tough-minded scale, men showed a greater correlation than women (r = 0.11, p = 2.2 ? 10 -48 vs. r = 0.06, p -20 ), and the two sexes were different from each other (p = 2.0 ? 10 -19 ). For the Prosocial/Empathetic scale, women showed a higher correlation than men (r = 0.10, p -54 vs. r = 0.05, p = 2.09 ? 10 -12 ), and the sexes were different from each other (p = 7.2 ? 10 -10 ) N = 39,913. All effects are statistically significant using the FDR multiple comparison test at a 0.05 criterion. For SE (generally too small to see in the figure) and SD, see Results.
These data are consistent with the hypothesis that the Analytic/Tough-minded scale measures some influence by the testosterone system, and the Prosocial/Empathetic scale measures some influence by the estrogen/oxytocin system. These data are also consistent with the results of two fMRI studies using the FTI (Brown et al., 2013). The FTI Analytical/Tough-minded scale co-varied with activity in regions of the occipital and parietal cortices associated with visual acuity and mathematical thinking, attributes linked with testosterone; testosterone also contributes to brain architecture in these areas. Further, the FTI Prosocial/Empathetic scale co-varied with activity in regions of the inferior frontal gyrus, anterior insula, and fusiform gyrus. These are regions associated with mirror neurons or empathy, a trait linked with the estrogen/oxytocin system. The effect sizes in this study were relatively small; but many other influences from biological, cultural and epigenetic forces play a role in temperament and behavior.