How the Brain Translates Money into Force

TLDR: For instance, this article showed that even when subjects cannot report how much money is at stake, they nevertheless deploy more force for higher amounts, underpinned by engagement of a specific basal forebrain region.

Abstract: Unconscious motivation in humans is often inferred but rarely demonstrated empirically. Weimaged motivational processes, implemented in a paradigm that varied the amount andreportability of monetary rewards for which subjects exerted physical effort. We show that, evenwhen subjects cannot report how much money is at stake, they nevertheless deploy more force forhigher amounts. Such a motivational effect is underpinned by engagement of a specific basalforebrain region. Our findings thus reveal this region as a key node in brain circuitry that enablesexpected rewards to energize behavior, without the need for the subjects’ awareness.Humans tend to adapt the degree of effort they expend according to the magnitude of rewardthey expect. Such a process has been proposed as an operant concept of motivation (1-3).Motivational processes may be obvious, as when a prospector spends days in extremeconditions seeking gold. The popular view is that motivation can also be unconscious, suchthat a person may be unable to report the goals or rewards that drive a particular behavior.However, empirical evidence on this issue is lacking, and the potential brain mechanismsinvolved in converting expected rewards into behavioral activation are poorly understood.We developed an experimental paradigm to visualize unconscious motivational processes,using functional magnetic resonance imaging. A classical approach to trigger unconsciousprocessing is subliminal stimulation, which can be implemented by means of maskingprocedures. The terminology we use in this report is based on a recent taxonomy (4), inwhich a process is considered subliminal if it is attended but not reportable. Successful brainimaging studies of subliminal processes have focused so far on processing words (5, 6) aswell as emotional stimuli (7, 8). In our study, the object of masking was an incentivestimulus for a future action, represented by the amount of reward at stake. The question weasked is whether, and how, the human brain energizes behavior in proportion to subliminalincentives.We developed an incentive force task, using money as a reward: a manipulation that isconsistently shown to activate reward circuits in the human brain (9-11). The exact level ofmotivation was manipulated by randomly assigning the amount at stake as one pound or onepenny. Pictures of the corresponding coins were displayed on a computer screen at thebeginning of each trial, between two screenshots of “mask” images (Fig. 1). The reportabiity