Altruistic decisions following penetrating traumatic brain injury

Abstract

The cerebral correlates of altruistic decisions have increasingly attracted the interest of neuroscientists. To date, investigations on the neural underpinnings of altruistic decisions have primarily been conducted in healthy adults undergoing functional neuroimaging as they engaged in decisions to punish third parties. The chief purpose of the present study was to investigate altruistic decisions following focal brain damage with a novel altruistic decision task. In contrast to studies that have focused either on altruistic punishment or donation, the Altruistic Decision Task allows players to anonymously punish or donate to 30 charitable organizations involved with salient societal issues such as abortion, nuclear energy and civil rights. Ninety-four Vietnam War veterans with variable patterns of penetrating traumatic brain injury and 28 healthy veterans who also served in combat participated in the study as normal controls. Participants were asked to invest $1 to punish or reward real societal organizations, or keep the money for themselves. Associations between lesion distribution and performance on the task were analysed with multivariate support vector regression, which enables the assessment of the joint contribution of multiple regions in the determination of a given behaviour of interest. Our main findings were: (i) bilateral dorsomedial prefrontal lesions increased altruistic punishment, whereas lesions of the right perisylvian region and left temporo-insular cortex decreased punishment; (ii) altruistic donations were increased by bilateral lesions of the dorsomedial parietal cortex, whereas lesions of the right posterior superior temporal sulcus and middle temporal gyri decreased donations; (iii) altruistic punishment and donation were only weakly correlated, emphasizing their dissociable neuroanatomical associations; and (iv) altruistic decisions were not related to post-traumatic personality changes. These findings indicate that altruistic punishment and donation are determined by largely non-overlapping cerebral regions, which have previously been implicated in social cognition and moral experience such as evaluations of intentionality and intuitions of justice and morality.10.1093/brain/awy064_video1awy064media15758316955001.

Figure 1

Lesion map illustrating the number of lesion overlap at each voxel across the whole penetrating TBI population (n = 94). The colour bar indicates the number of overlapping lesions at each voxel. Red in the scale indicates a higher number of subjects, and blue indicates a lower number. The maximum overlap occurred in the right rostrolateral prefrontal lobe.

Figure 2

Statistical β-maps of lesions that decreased (red) or increased (blue) punishment on the Altruistic Decision Task. (A–C) Right rostrolateral prefrontal and perisylvian cortices, including the inferior parietal lobule, posterior middle temporal and superior temporal gyri. (D–G) Medial views of the dorsomedial prefrontal cortex and left medial temporal pole.

Figure 3

Statistical β-maps of lesions that decreased (red) or increased (blue) donations on the Altruistic Decision Task. (A) Precuneus, cingulate gyrus, superior parietal lobule, and postcentral gyrus. (B) Precuneus and dorsomedial frontal cortex. (C) Posterior orbitofrontal cortex (gyrus rectus and medial orbitofrontal cortex). (D) Ventrolateral orbital and precentral gyri, and precentral sulcus. (E–G) Dorsolateral occipital lobe/posterior middle temporal gyrus, superior parietal lobule (angular and supramarginal gyri), and posterior superior frontal gyrus.