Differences in Discounting Behavior and Brain Responses for Food and Money Reward

Most neuroeconomic research seeks to understand how value influences decision-making. The influence of reward type is less well understood. We used functional magnetic resonance imaging (fMRI) to investigate delay discounting of primary (i.e., food) and secondary rewards (i.e., money) in 28 healthy, normal-weighted participants (mean age = 26.77; 18 females). To decipher differences in discounting behavior between reward types, we compared how well-different option-based statistical models (exponential, hyperbolic discounting) and attribute-wise heuristic choice models (intertemporal choice heuristic, dual reasoning and implicit framework theory, trade-off model) captured the reward-specific discounting behavior. Contrary to our hypothesis of different strategies for different rewards, we observed comparable discounting behavior for money and food (i.e., exponential discounting). Higher k values for food discounting suggest that individuals decide more impulsive if confronted with food. The fMRI revealed that money discounting was associated with enhanced activity in the right dorsolateral prefrontal cortex, involved in executive control; the right dorsal striatum, associated with reward processing; and the left hippocampus, involved in memory encoding/retrieval. Food discounting, instead, was associated with higher activity in the left temporoparietal junction suggesting social reinforcement of food decisions. Although our findings do not confirm our hypothesis of different discounting strategies for different reward types, they are in line with the notion that reward types have a significant influence on impulsivity with primary rewards leading to more impulsive choices.

[Timed dose-response relationship analysis of pressor and hypotensive action of drugs]

The graded and timed dose-response relationship (TDRR) of pressor and hypotensive action by i.v. norepinephrine (NE) and sodium nitroprusside (SNP) respectively were studied in 13 male rabbits. The arterial blood pressure was dose-dependently raised by NE 0.98-125 micrograms.kg-1 and lowered by SNP 7.81-500 micrograms.kg-1 (F test, P < 0.01). The comparisons between dose groups showed that the latency and duration of both NE and SNP action were dose-dependent (P < 0.01), and the data were nonlinear least-square fit to the hyperbolic 4-parameter model II (HFPM): Y = cs + 1/(magnitude of ln X - a)s + b, weighting the square error inversely with the square of Sx. In duration data, the regression equation was Y = 462.9906/(6.6924 - ln X) 0.9701 - 24.3335 for NE and Y = 374935.1632/(12.8573 - ln X)3.3975 - 3.139 for SNP action, while in latency, Y = 345.5548/(ln X + 7.8428)2.4056 + 3.9809 and Y = 17.9595/(ln X - 0.4898)0.5763 + 1.4768 for NE and SNP, respectively. Moreover, the positive correlation was found between the peak-reaching time or average rising rate of the drug actions and the dose groups (P < 0.01). The results proved that the hyperbolic type of TDRR existed in the pressor and hypotensive action by iv drugs, and the HFPM was the common mathematical model to fit different TDRR data.

Clonal characteristics of fibrous plaques and fatty streaks from human aortas

Using isoenzymes of glucose-6-phosphate dehydrogenase (G-6-PD) as cellular markers, a study was made of atherosclerotic fibrous plaques and fatty streaks in aortas of black women heterozygous for G-6-PD. Of 29 fibrous plaques, 26 (89.7%) contained only one isoenzyme (17, A; 9, B), the other three containing both A and B. Of 28 fatty streaks, five (17.8%) contained only one isoenzyme (2, A; 3, B), the remaining 23 containing both A and B. Normal uninvolved aorta contained both A and B isoenzymes in 99 of 101 samples. These results confirm the monoclonal character of atherosclerotic fibrous plaques; this strands in contrast to the fatty streaks which most commonly contain the two isoenzymes. The studies on the fatty streaks are inconclusive at this stage in determining whether the streak is the forerunner of the fibrous plaque.