Sunk costs under stress: Acute stress reduces the impact of past expenses on risky decisions

Rational choice should be guided solely by the prospects of available options. However, our decisions are often influenced by irrecoverable past costs, even when the current course of action turns out to be unfavorable, reflecting a cognitive bias known as the "sunk-cost effect". In everyday life, many decisions are made under stress or elicit stress themselves. Whether and how stress impacts the sunk-cost effect, however, is not known. Based on evidence suggesting that the sunk-cost effect critically depends on the dorsolateral prefrontal cortex, which in turn is highly sensitive to stress, we hypothesized that stress may reduce the influence of past expenses on current decisions. Participants underwent a psychosocial stress manipulation or control procedure, before we assessed their sunk-cost tendency in a monetary investment task. Overall, participants showed a pronounced sunk-cost effect, particularly for options with low expected value. Acute stress reduced this tendency to invest in risky options with low probability of success following high prior investments. Moreover, the strength of this reduction of the sunk-cost effect was predicted by individual cortisol reactivity. These findings show that acute stress may reduce the impact of past expenses on current choice and that this effect may be mediated by glucocorticoid action.

Time-dependent motor memory representations in prefrontal cortex

How memories evolve over time is fundamental for understanding memory. Hippocampus-dependent episodic memories are generally assumed to undergo a time-dependent neural reorganization involving an increased reliance on neocortical areas. Yet, whether other forms of memory undergo a similar reorganization over time remains unclear. Here, we examined whether the neural underpinnings of motor sequence memories change over time. Participants were trained on a motor sequence learning task. Either 1d or 28d later, they performed a retention test for this task in the fMRI scanner. Sequence-specific motor memory was observed both 1d and 28d after initial training. Bayesian second-level fMRI analyses suggested a higher probability for task activity in the middle frontal gyrus and frontal pole 28d compared to 1d after initial motor learning. Searchlight representational similarity analysis indicated that areas in middle and superior frontal cortex were more involved in differentiating between multivariate activity patterns for old motor sequence memories and newly learned motor sequences in the 28d-group compared to the 1d-group. This increased involvement of lateral frontal areas during the task after 28 days was not paralleled by a decrease in those areas that were involved in performing the motor sequence retention task after 1d. These novel findings provide insights into how memories beyond the hippocampus evolve over time.

Stress-induced cortisol hampers memory generalization

Integrative encoding and generalization across past experiences depends largely on the hippocampus, an area known to be particularly sensitive to stress. Yet, whether stress influences the ability to generalize memories is unknown. We exposed volunteers to a stressor or a control manipulation before they completed an acquired equivalence task probing memory generalization. While stress left learning performance intact, it reduced participants' ability to generalize and this deficit was directly linked to the cortisol response to the stressor. These findings show that stress, presumably through the action of glucocorticoids, creates rather rigid memories that are difficult to transfer to novel situations.