These results provide strong evidence that when individuals naturally process statements about sacred values, they use neural systems associated with evaluating rights and wrongs (TPJ) and semantic rule retrieval (VLPFC) but not systems associated with utility. The involvement of the TPJ is consistent with the conjecture that moral sentiments exist as context-independent knowledge in temporal cortex [14
]. Both the left and right TPJ have been associated with belief attribution during moral judgements of third parties [17
]. Our results show that it is also involved in the evaluation of personal sacred values without decision constraints. Thus, one explanation for the reduction in morally prohibited judgements when the TPJ is disrupted by transcranial magnetic stimulation [25
] is because disruption impairs access to personal deontic knowledge.
The involvement of the left VLPFC in personal sacred values is also consistent with the conjecture that deontic rules are retrieved and processed as semantic knowledge as opposed to utility calculations. Although the VLPFC has been historically implicated in language function, more recent neuroimaging work has demonstrated that the particular area we identified as processing sacred values is associated with semantic rule retrieval and processing [27
]. Importantly, the function of the left VLPFC is not restricted to verbal or written rules. In a study of road signs, the anterior division of the left VLPFC was found to be most closely associated with rule retrieval [28
]. We observed the same division more active when participants processed sacred values. Similar results were also found in a language-based study of rules, with this region being implicated in top-down retrieval of semantic knowledge [27
Although activation of the left TPJ and VLPFC for sacred values is consistent with a deontic rule retrieval process, it could be explained by properties of the stimuli, as opposed to how participants processed the stimuli. One possibility is that the items deemed sacred (optout), are governed by legal doctrine and thus the left VLPFC activity simply reflected the retrieval and processing of a legal rule (e.g. it is illegal to kill people). To test this, we created another model in which we added a separate category for items governed by a legal doctrine. An item was coded as a legal doctrine if it or its complement were illegal, either by US or international law (Geneva Conventions). The original analysis was then repeated on the remaining items. Using the original ROIs, we found that the effect of optout–bid was still significant in the left VLPFC (t30
= 2.15, p
= 0.040). Thus, even for items not governed by any rule of law (e.g. believing in God), if the individual did not sell it, it was retrieved and processed as a rule. We also tested the possibility that sacred values involve concepts, like God, which have more meanings than mundane concepts such as dogs and cats. SR refers to the amount of semantic information contained in, or associated with, a concept in semantic memory [33
] and has been previously associated with activation in VLPFC [34
]. To test the possibility that SR may be partially confounded with our measures of sacredness, we formulated an alternative model that controlled for the SR of the statements. There was no significant correlation between the SR of the stimulus and the fraction of individuals submitting bids to change their answers (R2
= 0.045, p
= 0.053), and when SR was included as a control variable in the passive phase model, significance remained and changed only slightly for the ROIs. This suggests that sacredness was not confounded with SR. We also tested alternative models that controlled for the length and the syntax of each statement, none of which greatly changed the significance of the activations in the ROIs.
Only the left and right inferior parietal lobules showed the opposite activation pattern, with greater activity to the bid versus optout items, which also coincided with cost/benefit decisions (). This suggests that these regions activate for items that have a measurable utility or value. This is consistent with prior evidence implicating the parietal cortex in utility-based decisions [23
]. The other region most likely to encode utilitarian values is the VMPFC and striatum [18
], but we did not observe a significantly greater activation to bid versus optout items in these regions during the passive phase.
The auction mechanism was a unique aspect of our experiment and suggests a new way to quantify sacred values that is not solely dependent on self-report, but there are assumptions behind its use. First, we assume that individuals take the auction seriously. As noted above, signing a document does not bind one to the action that one is signing. It is therefore somewhat surprising that most people did not sell all of their choices. The fact that participants took money for some items and not others suggests that they were adequately motivated to express their preferences through their choices. The upper limit of $100, however, placed a boundary constraint on the auction, which when averaged over all items, yielded a low value per item in expectation (the framing of the auction explicitly instructed participants to value each item in the $1–100 range, and all participants' questions about the auction pertained to how to earn the most money). Although $100 may have been insufficient to buy some answers, this could be true for any amount of money offered. The distribution of bids, however, suggests that this was not the case (see the electronic supplementary material). Although the distribution was dominated bimodally by $1 and optout, the ask values showed a declining frequency towards the $100 boundary, which could be fit by a gamma distribution. This indicates a decreasing marginal exchange value, and a higher upper limit would not have made a significant difference in items that were not auctioned.
Our experiment dovetails with a large literature on the neural correlates of moral judgement [12
]. However, it differs in that it initially measured the natural mode of processing sacred values in a way that was relatively unconstrained by a choice framework. This is particularly important for the scientific study of sacred values, because one cannot ethically place volunteers in real situations that would test such values. However, recent findings in neuroeconomics have demonstrated that ‘choiceless’ brain responses are predictive of future actions [38
]. Here, we find tantalizing evidence of this for sacred values too. We also found that the difference in VLPFC activation between optout and bid items correlated with the individual's level of involvement in organizations (). This suggests that neural markers for sacredness extend to real-world decisions of group membership. Moreover, when sacred values were contradicted by their opposites, we observed a significant increase in amygdala activation, which suggests the presence of an arousal response and is consistent with the hypothesized role of emotion, especially negative emotions, when sacred values are violated [1
Figure 4. Difference in left ventrolateral prefrontal cortex (VLPFC) activation to sacred items (optout) relative to non-sacred (bid) items as function of each participant's level of involvement in group activities (n = 31). The activist score was calculated as (more ...)
Our results complement existing research in sacred values and may have implications for policymakers [1
], although further research in conditions that emulate policymaking environments will be required to make the case. Economic, foreign and military policies are typically based on utilitarian considerations. More specifically, it is believed that those who challenge a functioning social contract should concede if an adequate trade-off is provided (e.g. sanctions or other incentives). However, when individuals hold some values to be sacred, they fail to make trade-offs, rendering positive or negative incentives ineffective at best. Our results suggest that individuals naturally retrieve sacred values as deontic rules, not as representations of utility, providing the first neurobiological evidence for what has been previously conjectured [3