You are the captain of a military submarine travelling underneath a large iceberg. An onboard explosion has caused you to lose most of your oxygen supply and has injured one of your crew who is quickly losing blood. The injured crew member is going to die from his wounds no matter what happens.
The remaining oxygen is not sufficient for the entire crew to make it to the surface. The only way to save the other crew members is to shoot dead the injured crew member so that there will be just enough oxygen for the rest of the crew to survive.
Would you kill the fatally injured crew member in order to save the lives of the remaining crew members?
What would you do? What would you do!?? If it helps, you can imagine that Dennis Hopper is making you choose...
That scenario is from the New Scientist article by Roxanne Khamsi, covering the paper by Koenig and colleagues about the effects of ventromedial prefrontal cortex lesions on decision-making. She also finds the obvious analogy with the final scenes of Star Trek II: The Wrath of Khan.
The second paragraph of the article itself is the most enlightening, concerning the background of the study:
The basis of our moral judgements has been a long-standing focus of philosophical inquiry and, more recently, active empirical investigation. In a departure from traditional rationalist approaches to moral cognition that emphasize the role of conscious reasoning from explicit principles (15), modern accounts have proposed that emotional processes, conscious or unconscious, may also play an important role (16, 17). Emotion-based accounts draw support from multiple lines of empirical work: studies of clinical populations reveal an association between impaired emotional processing and disturbances in moral behaviour (1, 2, 3, 4); neuroimaging studies consistently show that tasks involving moral judgement activate brain areas known to process emotions (5, 6, 7, 8, 9); and behavioural studies demonstrate that manipulation of affective state can alter moral judgements (10, 11). However, neuroimaging studies do not settle whether putatively 'emotional' activations are a cause or consequence of moral judgement; behavioural studies in healthy individuals do not address the neural basis of moral judgement; and no clinical studies have specifically examined the moral judgements (as opposed to moral reasoning or moral behaviour) of patients with focal brain lesions. In brief, none of the existing studies establishes that brain areas integral to emotional processes are necessary for the generation of normal moral judgements. As a result, there remains a critical gap in the evidence relating moral judgement, emotion and the brain.
This study brings together two interesting subjects -- the role of emotion in decision-making, and the structure of the ventromedial prefrontal cortex (vmPFC). It has long been known that normal emotional cognition is necessary for decision-making -- people with brain injuries that interfere with normal emotional response often exhibit various degrees of inability to make decisions.
Damasio and colleagues have been especially central to this area of neuroscience. My copy of Purves et al. (2004:708) has a nice paragraph summarizing their general idea:
Antonio Damasio and his colleagues at the University of Iowa have suggested that such decision-making entails the rapid evaluation of a set of possible outcomes with respect to the future consequences associated with each course of action. It seems plausible that the generation of conscious or subconscious mental images that represent the consequences of each contingency triggers emotional states that involve either alterations of somatic and visceral motor function, or the activation of neural representations of such activity. Whereas William James proposed that we are "afraid because we tremble," Damasio and his colleagues suggest a vicarious representation of motor action and sensory feedback in the neural circuits of the frontal and parietal lobes. It is these vicarious states, according to Damasio, that give metnal representations of contingencies the emotional valence that helps an individual to identify favorable or unfavorable outcomes.
This isn't the first study to examine decision-making in vmPFC patients. A 2000 paper by Bechara, Tranel, and Damasio described a gambling experiment, in which subjects were given an opportunity to risk high immediate punishment for a high long-term reward, or low punishment for a low long-term reward. They found that vmPFC subjects avoid the high short-term punishment, even after the already-high long-term reward is raised further.
The gambling result complicates matters somewhat, as far as interpreting the "moral quandary" experiments in the new research. Plausibly, the long-term versus short-term punishment factor is an important part of the "moral" decision: do you sacrifice many people immediately for a long-term relationship with a relative? That's backward from the way the question is usually asked, but it poses the same problem.
Tranel, Bechara, and Denberg (2002) found that patients with damage to the right vmPFC in particular had social and emotional deficits, in comparison to patients with left-only damage:
The aim of this study was to begin to parse the relative contributions of the right and left ventromedial prefrontal cortices (VMPC) in regard to social conduct, decision-making, and emotional processing. We hypothesized that the right VMPC is a critical component of the neural systems that subserve such functions, whereas the left VMPC is not. Seven participants with focal, stable unilateral lesions to the right (n = 4) or left (n = 3) VMPC were studied with procedures designed to measure social conduct, decision-making, and emotional processing and personality. The right-sided participants had profound disturbances of social and interpersonal behavior and of the ability to maintain gainful employment; they had defective performance and impaired anticipatory skin conductance responses during the Gambling Task; most had profound abnormalities of emotional processing and personality, and met criteria for "acquired sociopathy." By contrast, the left-sided participants had normal social and interpersonal behavior; they had stable employment; they performed normally and had normal skin conductance responses on the Gambling Task; they had normal emotional processing; and their personalities were unchanged from premorbid status. The marked deficits in social conduct, decision-making, and emotional processing in participants with unilateral right VMPC lesions are reminiscent in kind of those that have been reported in connection with bilateral VMPC lesions, albeit perhaps of lesser severity. The findings provide preliminary evidence that insofar as social, decision-making, and emotional functions are concerned, the right-sided component of the VMPC system may be critical, whereas the left-sided component may be less important.
Research in people without damage to their vmPFC has tried to determine the logical structure that the area uses to make decisions. For example, Alan Hampton and colleagues (2006) scanned people with an fMRI while they made different kinds of decisions. Here's the abstract:
Many real-life decision-making problems incorporate higher-order structure, involving interdependencies between different stimuli, actions, and subsequent rewards. It is not known whether brain regions implicated in decision making, such as the ventromedial prefrontal cortex (vmPFC), use a stored model of the task structure to guide choice (model-based decision making) or merely learn action or state values without assuming higher-order structure as in standard reinforcement learning. To discriminate between these possibilities, we scanned human subjects with functional magnetic resonance imaging while they performed a simple decision-making task with higher-order structure, probabilistic reversal learning. We found that neural activity in a key decision-making region, the vmPFC, was more consistent with a computational model that exploits higher-order structure than with simple reinforcement learning. These results suggest that brain regions, such as the vmPFC, use an abstract model of task structure to guide behavioral choice, computations that may underlie the human capacity for complex social interactions and abstract strategizing.
That paper argues for sophistication in the function of the vmPFC, which makes this area very interesting in the context of human evolution.
There is much more to say, here, but it's a post that has already gone on too long. The discussion at Neurophilosophy is definitely worthwhile. I especially found the comments interesting, where there is some consideration of what counts as "impaired". Considering prior research on VMPC lesions, together with this study, it is not obvious what "impaired" really means. Clearly, people with a brain injury and resulting behavior alterations are not quite the same. But when they become more rational, what does that mean about "normal"?
Koenigs M, Young L, Adolphs R, Tranel D, Cushman F, Hauser M, Damasio A. 2007. Damage to the prefrontal cortex increases utilitarian social judgements. Nature (advance online) doi:10.1038/nature05631
Bechara A, Tranel D, Damasio H. 2000. Characterization of the decision-making deficit of patients with ventromedial prefrontal cortex lesions. Brain 123:2189-2202. Free full text
Tranel D, Bechara A, Denberg NL. 2002. Asymmetric functional roles of right and left ventromedial prefrontal cortices in social conduct, decision-making, and emotional processing. Cortex 38:589-612.
Hampton AN, Bossaerts P, O'Doherty JP. 2006. The role of the ventromedial prefrontal cortex in abstract state-based inference during decision making in humans. J Neurosci 26:8360-8367. doi:10.1523/JNEUROSCI.1010-06.2006
Purves D, Augustine GF, Fitzpatrick D, Hall WC, LaMantia A-S, McNamara JO, Williams SM. 2004. Neuroscience. 3 ed. Sinauer, Sunderland MA.