Sunday, December 16, 2007

Truth may be beauty, and beauty truth,

in more than a metaphorical sense, and false propositions may actually disgust us (Harris et al., 2007).
When old age shall this generation waste,
Thou shalt remain, in midst of other woe
Than ours, a friend to man, to whom thou say'st,
"Beauty is truth, truth beauty," - that is all
Ye know on earth, and all ye need to know.

-- John Keats, Ode on a Grecian Urn

It's easy for the urn to say that, of course, because it doesn't have to bear the bruised ego caused by truthful remarks such as "that's a terrible hairstyle for you" or "wow, you look so poorly endowed in those Speedos" or the classic, "those jeans make you look fat!"

Blogging on Peer-Reviewed ResearchThe latest neuroimaging study in the Annals of Neurology (Harris et al., 2007) didn't really set out to prove Keats, but to determine
The difference between believing and disbelieving a proposition is one of the most potent regulators of human behavior and emotion. When one accepts a statement as true, it becomes the basis for further thought and action; rejected as false, it remains a string of words. The purpose of this study was to differentiate belief, disbelief, and uncertainty at the level of the brain.
The authors expected activation in the prefrontal cortex (PFC) to exert "top-down" control to bias behavior based on beliefs. Participants read statements designed to be clearly true, clearly false, or undecidable. These statements were from a number of different categories:

Mathematical: (2 + 6) + 8 = 16

Geographical: Wisconsin is on the West Coast of the United States.

Semantic: “Gigantic” means “huge.”

Factual: The Dow Jones Industrial Average rose 1.2% last Tuesday.

Autobiographical: You had eggs for breakfast on December 8, 1999.

Ethical: It is bad to take pleasure at another's suffering.

Religious: There is probably no actual Creator God.

That last one might be a bad example... how about "Jesus spoke 2,467 words in the New Testament" instead? Anyway, results from the True Statement minus False Statement contrast is shown bellow:

Figure 1A (from Harris et al., 2007). Ventromedial prefrontal cortex (VMPFC) regions showing positive blood oxygen level dependent (BOLD) signal for judgments of truth (belief) minus judgments of falsity (disbelief) across the seven stimulus categories.

Here we see activation in the VMPFC, which was the only area that showed greater activity for True versus False. HOWEVER, this was due to greater DEactivation during False Statements than during True Statements (when each was compared to an "implicit baseline" condition which wasn't described). The authors suggested that since this emotional processing area often shows decreases in BOLD signal during cognitive tasks, uh, hmmm... I'm not sure what they're getting at here:
The involvement of the VMPFC in belief processing suggests an anatomic link between the purely cognitive aspects of belief and emotion/reward. Even judging the truth and falsity of emotionally neutral propositions activated [NOTE: is less deactivation the same as activation?] brain regions that are strongly connected to the limbic system. It is not clear from these data whether emotional engagement enters directly into the assessment of propositional validity or whether it is a secondary consequence of the cognitive process, but the fact that ethical belief showed a similar pattern of activation to mathematical belief suggests that the physiological difference between belief and disbelief can be independent of a proposition's content and affective associations.
OK. What about the opposite contrast, False Statement minus True Statement?

Figure 2 (from Harris et al., 2007). Axial image shows increased BOLD signal in the inferior frontal gyrus (primarily the left), the right middle frontal gyrus, and the anterior insula (bilateral) when judgments of falsity (disbelief) are compared with judgments of truth (belief) across all stimulus categories. Sagittal image shows increased signal in the superior parietal lobule, the cingulate cortex, and superior frontal gyrus within the same contrast.

Not too surprisingly, the authors wanted to interpret the insula activation as a reflection of disgust at reading false statements. However, most of the false statements don't seem particularly disgusting:
Wisconsin is on the West Coast of the United States.
Devious means friendly.
Oh the horror. Additionally, they noted the similarity in frontal lobe activations for the False Statements here and "no" responses in prior studies of the Sternberg working memory task (e.g., saying "no" when the letter R was not in the study set of T J S Q). Honestly, can we really say anything about conventional notions of "belief" and "disbelief" from the Sternberg task? [I do not "believe" that R was in the study set]. Then we have the mystery activity:
...the rejection condition (disbelief) also showed increased signal in medial regions of superior parietal lobule, bilaterally. This is an area that has strong connectivity with the medial PFC, though its recruitment in the present task is not readily explained based on prior studies.
And what of uncertainty? Uncertainty was associated with greater activity in the anterior cingulate than either of the other two conditions. Also not surprisingly, the authors connected this result to response conflict, such as that observed in the Stroop effect. They concluded with a lovely philosophical discussion...
The human brain is a prolific generator of beliefs. Indeed, personhood is largely the result of the capacity of a brain to evaluate new statements of propositional truth in light of countless others that it already accepts. By recourse to intuitions of truth and falsity, logical necessity and contradiction, human beings are able to knit together private visions of the world that largely cohere. The results of our study suggest that belief, disbelief, and uncertainty are mediated primarily by regions in the medial PFC, the anterior insula, the superior parietal lobule, and the caudate. The acceptance and rejection of propositional truth-claims appear to be governed, in part, by the same regions that judge the pleasantness of tastes and odors.
...although it seems they are overstepping the bounds of their actual data.
He, who knows how to distinguish between true and false, must have an adequate idea of true and false.

-- Spinoza, from Ethics, Part II: On the Nature and Origin of the Mind

Reference

Harris S, Sheth SA, Cohen MS. (2007). Functional neuroimaging of belief, disbelief, and uncertainty. Ann Neurol. Dec 10; [Epub ahead of print].

OBJECTIVE: The difference between believing and disbelieving a proposition is one of the most potent regulators of human behavior and emotion. When one accepts a statement as true, it becomes the basis for further thought and action; rejected as false, it remains a string of words. The purpose of this study was to differentiate belief, disbelief, and uncertainty at the level of the brain. METHODS: We used functional magnetic resonance imaging (fMRI) to study the brains of 14 adults while they judged written statements to be "true" (belief), "false" (disbelief), or "undecidable" (uncertainty). To characterize belief, disbelief, and uncertainty in a content-independent manner, we included statements from a wide range of categories: autobiographical, mathematical, geographical, religious, ethical, semantic, and factual. RESULTS: The states of belief, disbelief, and uncertainty differentially activated distinct regions of the prefrontal and parietal cortices, as well as the basal ganglia. INTERPRETATION: Belief and disbelief differ from uncertainty in that both provide information that can subsequently inform behavior and emotion. The mechanism underlying this difference appears to involve the anterior cingulate cortex and the caudate. Although many areas of higher cognition are likely involved in assessing the truth-value of linguistic propositions, the final acceptance of a statement as "true" or its rejection as "false" appears to rely on more primitive, hedonic processing in the medial prefrontal cortex and the anterior insula. Truth may be beauty, and beauty truth, in more than a metaphorical sense, and false propositions may actually disgust us.

ADDENDUM #1: Until reading What Your Brain Looks Like on Faith (by David Van Biema), The Neurocritic did not know that the first author of the Harris et al. article is Sam Harris, the well-known nonfiction writer (The End of Faith and Letter to A Christian Nation) and highly-discussed atheist. [Oops!! He also happens to be a neuroscience graduate student at UCLA.]

ADDENDUM #2: Vaughan at Mind Hacks has posted The problem of believing in belief. He focuses on the philosophical definition of belief and whether the Harris et al. study really tells us anything about it:
...from what we know about belief it's not clear that this study tells us much more about belief rather than what happens when people respond to questions.
Yes. And deciding if the answer is Yes/No/Don't Know draws on different types of knowledge -- semantic memory, autobiographical memory, calculation -- which are heavily dependent on regions outside of PFC (e.g., temporal lobe, left inferior parietal cortex), and which do not have identical neural substrates. Although Harris would like to say there is no difference between beliefs about ethics and beliefs about mathematical equations, the experimental design is underpowered to detect such differences (which is why I didn't bother mentioning it in the first place).

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