Differential Neural Correlates in the Prefrontal Cortex during a Delay Discounting Task in Healthy Adults: An fNIRS Study

Figures

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  Figure 1. (a) Example trials of the DD task and control task. The left panel shows an example trial of the DD task. The right panel shows example trial of the control task, which presents two options with consisted fixed amounts of reward delivered after different delays. In the experiment, the options were presented in Japanese. (b) Time course of experimental session. FNIRS measurements were conducted from the starting baseline to the end of control trials after the last block.

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  Figure 2. (a) Positions of the probes and channels as situated on the head of the representative participant. The two probe holders, each equipped with five laser diodes and four photodiodes (cyan dots), were located on the prefrontal regions. Open circles correspond to Fp1 and Fp2. Magenta dots with numbers represent the 24 measurement channels. (b) Channel positions registered to the MNI standard brain space. Red circles represent statistically estimated channel locations. White numbers indicate corresponding channels.

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  Figure 3. (a) Negative correlation between Area Under the Curve and the discounting rate (k-value) (r = −0.488, p = 0.029). (b) Negative correlation between mean reaction time in the DD task and the motor impulsivity (BIS-Im) (r = −0.473, p = 0.035).

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  Figure 4. (a) Mean changes in oxy- and deoxy-Hb concentrations during the DD task relative to the control task. Numbers on the x-axis represent the measurement channel. Error bars represent standard errors. * p < 0.05, ** p < 0.01. (b) Grand-averaged waveforms of oxy- and deoxy-Hb concentrations in representative channels. Red lines represent oxy-Hb changes and blue lines represent deoxy-Hb changes. Gray rectangles on the x-axis represent task period.

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  Figure 5. (a) Positive correlation between oxy-Hb concentration in the left dorsolateral PFC (CH9) and the discounting rate (k-value) (r = 0.528, p = 0.017). (b) Negative correlation between oxy-Hb concentration in the right frontal pole (CH22) and the motor impulsivity (BIS-Im) (r = −0.557, p = 0.011).