| Subject: The biasing effects of belief and emotion. |
Author:
Baz
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Date Posted: 07/ 6/02 5:24am
I thought you all might like a peek at the neurology of belief and reason.
Affective = emotional
MV = medioventral
fMRI = brain imaging
Project 3: Neurobiology of Belief-Logic Interactions
More recently we have begun probing the relationship between cognitive and affective processing. It is generally accepted that lateral and MV prefrontal cortices are differentially involved in cognitive and affective processing. There is evidence that, whereas affective processing requires activation of MVPFC, logical/rational cognitive processes require activation of lateral and dorsolateral prefrontal cortex (Adolphs et al., 1996; Bechara et al., 1994; Damasio, 1994; Elliott et al., 1999; Koechlin et al., 2000; Stuss et al., in press; Stuss and Levine, in press).
Our own research (Goel and Dolan, 2001) has shown a nice dissociation along these lines in the domain of joke appreciation, a domain with both a cognitive and affective component. Successful jokes involve a cognitive juxtaposition of mental sets, followed by an affective feeling of amusement. Our findings show that while there are modality-specific pathways for processing the juxtaposition of mental sets necessary for the appreciation of jokes (involving lateral prefrontal cortex), the affective appreciation of humor is expressed in activity in medial ventral prefrontal cortex, a region involved in reward processing (Rolls, 2000).
Of particular interest is the interaction between cognitive and affective processing. We are currently undertaking a series of fMRI studies in which normal controls are confronted with a conflict between rational and affective responses within the domain of deductive and inductive reasoning. Deductive reasoning is a closed system, requiring no external information for its operation. However, it is known that oneīs beliefs about the world (belief-bias) influence logical judgments. Consequently, subjects perform better on syllogistic reasoning tasks when the truth value of a conclusion (true or false) coincides with the logical relationship between premises and conclusion (valid or invalid). In other words, if the logical conclusion is consistent with beliefs about the world, the beliefs are facilitory to the logical task. For example, the following valid argument with a believable conclusion, "No cigarettes are inexpensive; Some addictive things are inexpensive; \ Some addictive things are not cigarettes" is accepted as valid 96% of the time. By contrast, a logically identical argument with an unbelievable conclusion, "No addictive things are inexpensive; Some cigarettes are inexpensive; \ Some cigarettes are not addictive" is accepted as valid only 46% of the time.(Evans et al., 1983) Hence if the logical conclusion is inconsistent with beliefs about the world, the beliefs are inhibitory or misleading to the logical task.
We have shown (Goel and Dolan, in review) that within the context of reasoning involving inhibitory or misleading beliefs, the crucial element in the modulation of reasoning by beliefs is the preferential engagement of MVPFC. Where the MVPFC is preferentially engaged, subjects are more likely to generate responses based upon their belief-biases. This contrasts with correct logical reasoning that requires relatively greater activation of lateral prefrontal cortex. The involvement of MVPFC and its strong associations with affective processing indicates that belief-bias effects in reasoning may be a special instance of the modulatory effect of emotion on cognition (Damasio, 1994). The fact that the response of the MVPFC is specific to inhibitory belief trials and is facilitated by its relative deactivation (with respect to facilitory belief trials) during correct inhibitory belief trials leads us to the following hypothesis:
H2: (a) Successful logical processing requires activation of lateral PFC. (b) It may also require inhibition of MVPFC (with respect to a rest baseline). If the MVPFC fails to be inhibited during logical processing, logical/rational responses may be overpowered by emotional responses.
We are addressing H2 in a series of reasoning tasks that allow us to independently manipulate logical and affective components. Given the above result, the next study will address the following questions: How does saliency of content affect the functional neuroanatomy of reasoning? Does the involvement of the MVPFC in incorrect trials covary with emotional saliency of the content? In a subsequent study we will manipulate the emotional content of inductive arguments. We would expect MVPFC and limbic structures to interact with lateral PFC during inference involving emotional content.
Hypothesis H2 not only predicts greater activation of MVPFC when rational responses are overcome by emotional responses, it also predicts inhibition of MVPFC (relative to a rest baseline) when rational responses overcome emotional responses. The latter is difficult to demonstrate. We hope to show it indirectly. With respect to the imaging studies, we will compare the activation of the MVPFC in the relevant trials with that of various low-level baseline trials. We would expect MVPFC to show greater activation in the baseline trials than in the active trials. These tasks will also be carried out on the frontal lobe patient population described above and patients with MVPFC lesions, with similar characteristics and cognitive baselines as above. We expect to show that patients with MVPFC lesions have an advantage (as compared to dorsolateral patients and perhaps even normal controls) in logical reasoning in emotionally-laden contexts, particularly those involving misleading content. There are some clinical reports to suggest that this may be the case (Damasio, 1994).
Basic operating funds for this study are covered by my NSERC grants (Title of Project: Neurology of Belief & Logic) and Premierīs Research Excellence Award (Title of Project: Neurobiology of Rationality).
This project is funded by my NSERC grants (Title of Project: Neurology of Belief & Logic) and Premierīs Research Excellence Award (Title of Project: Neurobiology of Rationality).
Oct. 5, 2001
Baz.
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