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Dorsal Medial Prefrontal Cortex Plays a Necessary Role in.docx

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Andy Lee

Dorsal Medial Prefrontal Cortex Plays a Necessary Role in Rapid Error Prediction in Humans Mandana Modirrousta and Lesley K. Fellows McGill University Literature Review By: Anum Khuzaima Aslam INTRODUCTION The dorsal anterior cingulate cortex (dACC) is activated in tasks that involve selection of incongruent responses. Converging evidence from functional imaging along with electrophysiological studies have shown conflict-related waveforms possibly arising from dACC. Although there is unanimous agreement for dACC role in cognitive control the specific processes monitored and the extent to which this region is responsible remains heavily debated. Modirrousta and Fellows (2008) reason some of this widespread disagreement in scientific literature is due to the lack of standard behavioral measures and the rarity of focal damage to dACC. The purpose of their experiment was to identify if any component of error processing was affected by damage to dACC in humans (Modirrousta et al, 2008). Five patients with damage to dorsal medial prefrontal cortex (mPFC) centered on dACC and 19 healthy subjects performed three versions of Eriksen Flanker task designed to assess post- error slowing, error reporting and error correction respectively. Three of the five patients in mPFC group had lesions limited to the left hemisphere centered in pre-genual and dACC whereas two patients had bilateral mPFC lesions including dACC and regions of frontopolar and orbitofrontal cortex. The first version of flanker task measured post-error slowing which was depicted by mean reaction time (RT) on correct trials followed by correct trials in comparison to correct trials followed by incorrect trials. The second version measured error reporting and the third version measured error correction. The parameters were adjusted for each patient and control group to maintain an error rate of 8% on average. In a second experiment all five patients and 10 control participants performed letter two-back task to assess the likelihood that a given response was an error at the time of response. In the standard flanker task patients were slower on average and portrayed a greater flanker effect, however, only 3 out of 5 patients had flanker effect > 1.5 SD from the control mean. When the effect of error was measured on subsequent trial both mPFC group and controls had comparable post-error slowing of similar magnitude. Four of five patients in mPFC group were able to report errors after an error of commission suggesting that damage to mPFC did not significantly interfere with the ability to report errors (Modirrousta et al, 2008). In the error correction trial mPFC group were equally able to recognize and correct errors although they were notably slower to make the corrective response. Such slowing effect was evident in the performance of all patients and even the fastest patient error correction RT was 1.43 SD from control mean. In the standard online monitoring go-no go task of error likelihood dorsal mPFC group made significantly more errors of commission than controls. This was replicated in previous studies as well where the false alarm rate was > 10-fold in mPFC in comparison to healthy controls and patients with damage elsewhere in frontal lobe. The two groups however did not significantly differ in the level of confidence for correct go responses (Modirrousta et al, 2008). CRITIQUE There is widespread disagreement about the higher cognitive functions of the dACC of which the prominent features include detecting conflict between competing response alternatives and monitoring for errors (Swick & Turken, 2002).The primary purpose of the experiment by Modirrousta et al (2008) aimed to determine if components of error processing, specifically, error reporting, error correction and post-error slowing were affected by dACC damage. They discovered intact post-error slowing, the ability to correctly identify errors and correct errors after commission. The damage to mPFC was however associ
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