Differences in time course activation of dorsolateral prefrontal cortex associated with low or high risk choices in a gambling task

Abstract

Prefrontal cortex plays an important role in decision making (DM), supporting choices in the ordinary uncertainty of everyday life. To assess DM in an unpredictable situation, a playing card task, such as the Iowa Gambling Task (IGT), has been proposed. This task is supposed to specifically test emotion-based learning, linked to the integrity of the ventromedial prefrontal cortex (VMPFC). However, the dorsolateral prefrontal cortex (DLPFC) has demonstrated a role in IGT performance too. Our aim was to study, by multichannel near-infrared spectroscopy, the contribution of DLPFC to the IGT execution over time. We tested the hypothesis that low and high risk choices would differentially activate DLPFC, as IGT execution progressed. We enrolled 11 healthy adults. To identify DLPFC activation associated with IGT choices, we compared regional differences in oxy-hemoglobin variation, from baseline to the event. The time course of task execution was divided in four periods, each one consisting of 25 choices, and DLPFC activation was distinctly analyzed for low and high risk choices in each period. We found different time courses in DLPFC activation, associated with low or high risk choices. During the first period, a significant DLPFC activation emerged with low risk choices, whereas, during the second period, we found a cortical activation with high risk choices. Then, DLPFC activation decreased to non-significant levels during the third and fourth period. This study shows that DLPFC involvement in IGT execution is differentiated over time and according to choice risk level. DLPFC is activated only in the first half of the task, earlier by low risk and later by high risk choices. We speculate that DLPFC may sustain initial and more cognitive functions, such as attention shifting and response inhibition. The lack of DLPFC activation, as the task progresses, may be due to VMPFC activation, not detectable by fNIRS, which takes over the IGT execution in its second half.

Keywords: DLPFC; Iowa Gambling Task; attention shifting; multichannel NIRS; response inhibition; risk.

Figure 1

(A) Schematic representation of fibers holder positioning over the DLPFC. Stripped circles represent near-infrared emitters and dotted circles detectors. Squares are channels and their respective number. Reference points of the international 10–20 electroencephalography system of electrode placement are indicated as well. (B) Channels' projection on DLPFC region of a rendered brain.

Figure 2

Illustration of the experimental procedure concerning the first two choices. Each choice could be made just after the presentation of the green slide, but within 12 s (e.g., the interval between choices we selected to allow the detection of a complete hemodynamic response associated with each decision). The black screen was inserted to fill the 12 s inter-choice interval creating an alternation with the green slide, which had to be again presented to allow the next choice. This was repeated for 100 times.

Figure 3

Cortical location, on a rendered brain, of channels found significantly activated in association with low risk choices (evidence in green), during the first IGT period.

Figure 4

Time courses of HbO2 (in red) and deoxy-hemoglobin (in blue) concentration changes, reported in mM•mm, in channels found significantly activated during the first IGT period, in association with low risk choices. The dark green area shows when the green slide was presented on a computer screen to participants, signaling that the choice could be made.

Figure 5

Cortical location, on a rendered brain, of channels found significantly activated in association with high risk choices (evidence in pink), or in high and low risk choices (evidence in pink/green), during the second task period.

Figure 6

Time courses of HbO2 (in red) and deoxy-hemoglobin (in blue) concentration changes, reported in mM•mm, in channels found significantly activated during the second IGT period, in association with high risk choices (pink background) or low risk choices (green background). The green area shows when the green slide was presented on a computer screen to participants, signaling that the choice could be made.