Distinct developmental trajectories for risky and impulsive decision-making in chimpanzees

Abstract

Human adolescence is characterized by a suite of changes in decision-making and emotional regulation that promote risky and impulsive behavior. Accumulating evidence suggests that behavioral and physiological shifts seen in human adolescence are shared by some primates, yet it is unclear if the same cognitive mechanisms are recruited. We examined developmental changes in risky choice, intertemporal choice, and emotional responses to decision outcomes in chimpanzees, our closest-living relatives. We found that adolescent chimpanzees were more risk-seeking than adults, as in humans. However, chimpanzees showed no developmental change in intertemporal choice, unlike humans, although younger chimpanzees did exhibit elevated emotional reactivity to waiting compared to adults. Comparisons of cortisol and testosterone indicated robust age-related variation in these biomarkers, and patterns of individual differences in choices, emotional reactivity, and hormones also supported a developmental dissociation between risk and choice impulsivity. These results show that some but not all core features of human adolescent decision-making are shared with chimpanzees. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Figure 1:. Diagram of the risky and inter-temporal choice tasks.

(a) In the risky choice task, chimpanzees chose between a safe option that reliably provided three pieces of an intermediately-preferred food (peanuts), and a risky option that provided either a preferred food (a slice of banana) or a non-preferred food (a slice of cucumber) with 50% probability. While the safe food option was baited under an overturned container while the chimpanzee watched (and thus the knew what was there with certainty), the risky reward was baited behind an occluder such that they did not know which of the two possible food items had been placed under the container. (b) In the inter-temporal choice task, chimpanzees chose between a larger, delayed reward (three banana slices available after a minute) and a smaller immediate reward (one slice). In both tasks, rewards were placed on a table in front of the chimpanzee, who could indicate their preference by pointing at one of the options. Side assignment of options was counterbalanced across trials in both tasks.

Figure 2:. Choice patterns and emotional responses in the risk task.

(a) Younger chimpanzees showed stronger preferences for risk than adults; ribbon indicates 95% CI from GLMM model estimates of trial-by-trial data accounting for age, sex, trial number, food preference score, and prior reward outcome; scatter plot indicates individuals’ mean proportion choice for the risky option. (b) Younger and adult chimpanzees showed weak proclivities to adjust their choice behavior in response to prior decision outcomes. (c) Both younger and older chimpanzees showed more negative affective responses to bad risk outcomes compared to good risk or safe outcomes. (d) Chimpanzees of all ages showed more attempts to switch their choice in response to bad risk outcomes. Boxplot hinges indicate the lower and upper quartile, the horizontal line represents the median, diamonds indicate the mean, and whiskers indicate the minimum and maximum range of the analyzed data. Outliers are plotted as individual points.

Figure 3:. Choices and emotional responses in the inter-temporal choice task.

(a) Chimpanzees chose the larger reward more in the number pretest without delays, than in the main inter-temporal choice task where the larger reward was delayed. (b) Younger and older chimpanzees showed similar preferences for the larger, delayed reward in the inter-temporal choice task; ribbon indicates 95% CI from GLMM model estimates of trial-by-trial data accounting for age, sex, trial number, and number pretest performance; scatter plot indicates individuals’ mean proportion choice for the delayed option. (c) Emotional responses to immediate rewards were similar regardless of age, but younger chimpanzees showed more intense negative responses to waiting for delayed rewards; ribbons indicate 95% CI from LMM model estimates accounting for choice outcome (immediate or delayed), age, sex, trial number, trial type (exposure or choice trial).

Figure 4:. Physiological changes over development.

(a) Chimpanzees of both sexes showed increasing cortisol levels over the sampled age range. (b) Chimpanzees showed increasing testosterone levels over this age range, a shift exacerbated in males. Error bars indicate SE.

Figure 5:. Relationships between cognitive, affective, and hormonal measures.

(a) Pairwise correlations between choice measures (mean risky choice, mean inter-temporal choice), emotional measures (mean risk affect score, mean inter-temporal affect score), physiological measures (mean log-transformed cortisol, mean log-transformed testosterone), and age; strength of correlation is indicated by color on plot. (b) Contribution of each of the measures to the two distinct dimensions extracted from the principal components analysis.