Thursday, September 20, 2012

Distinct prefrontal areas regulating cognitive control and value decisions.

A massive study involving workers at five different universities has utilized a dataset on brain lesions accumulated over many decades to reveal two distinct functional-anatomical networks within the prefrontal cortex (PFC), one associated with cognitive control and the other associated with value-based decision-making. They used lesion-symptom mapping in 344 participants who were assessed by using a large battery of standardized neuropsychological tasks. Of these participants, 165 had damage in the frontal lobes that included sectors of the PFC, supplementary motor area (SMA), or premotor cortex (PM). Here is their abstract, followed by some details:
A considerable body of previous research on the prefrontal cortex (PFC) has helped characterize the regional specificity of various cognitive functions, such as cognitive control and decision making. Here we provide definitive findings on this topic, using a neuropsychological approach that takes advantage of a unique dataset accrued over several decades. We applied voxel-based lesion-symptom mapping in 344 individuals with focal lesions (165 involving the PFC) who had been tested on a comprehensive battery of neuropsychological tasks. Two distinct functional-anatomical networks were revealed within the PFC: one associated with cognitive control (response inhibition, conflict monitoring, and switching), which included the dorsolateral prefrontal cortex and anterior cingulate cortex and a second associated with value-based decision-making, which included the orbitofrontal, ventromedial, and frontopolar cortex. Furthermore, cognitive control tasks shared a common performance factor related to set shifting that was linked to the rostral anterior cingulate cortex. By contrast, regions in the ventral PFC were required for decision-making. These findings provide detailed causal evidence for a remarkable functional-anatomical specificity in the human PFC.
Here is a description of the array of tests used (edited to simplify):
The four cognitive control tasks were as follows: the Trail-Making Test (TMT), a measure of executive response switching; the Perseverative Errors score from the Wisconsin Card Sorting Test (WCST), which measures impairments in set switching; the Color-Word Interference score from the Stroop Test (STROOP), a measure of response inhibition; and the Number of Words score from the Controlled Oral Word Association Test (COWA), which measures verbal fluency, divergent thinking, and response creativity. As an index of value-based decision-making and reward learning, we used the Net Score (advantageous minus disadvantageous choices) from the Iowa Gambling Task (IGT). All these tasks have been extensively used and well standardized, and they have been shown to detect impairments reliably in clinical populations such as ours. As expected, the cognitive control-related tasks were all weakly, but positively intercorrelated, whereas their correlation with the IGT was generally lower, a pattern that remained even after the covariates were statistically removed from the data.
And here is a summary graphic:

Results from the lesion overlap analysis of different tests of cognitive control and value-based decision making.

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