By Jan Willem de Gee and Tobias Donner.
When asked to make repeated decisions we will often choose differently each time even when we are given the same information to inform our choice. A stock trader, for example, will typically be more inclined to buy on some days and sell on others even if the financial markets remain unchanged. Fluctuations in the brain’s level of alertness or excitability, otherwise known as its arousal, are thought to contribute to this variability in decision-making.
An area at the base of the brain called the brainstem – and in particular one of its subregions, the locus coeruleus – helps shape arousal levels by releasing chemicals called neuromodulators (Figure 1A). For reasons that remain unknown, activation of the locus coeruleus also causes the pupil of the eye to suddenly increase in size (Figure 1A,D). In the current study, we have exploited this link to unravel how changes in brain arousal lead to systematic changes in decision-making.
Volunteers were asked to judge whether a faint pattern was embedded in flickering noise on a computer screen, and to report their judgment by pressing one of two buttons to indicate “yes” or “no” (Figure 1B). Although the decision was comparatively simple, it did involve evaluating changing information over time before making a choice (Figure 1C) – like when considering the stock market. As the volunteers performed the task, de Gee et al. measured their brain activity and the size of their pupils. Most of the volunteers had a tendency to respond “no” even when the pattern was present. However, whenever their locus coeruleus was particularly active, and their pupils increased in size, their decision process was changed so that this unhelpful choice bias decreased (Figure 1E).
This suggests that by boosting arousal, the locus coeruleus reduces existing biases in our decision-making. Varying levels of locus coeruleus activity may thus explain why we can reach different conclusions when considering the same information on multiple occasions. The next challenge is to identify what it is about the decision-making process that strongly activates the locus coeruleus on some occasions, but not (or less so) on others.
de Gee JW, Colizoli O, Kloosterman NA, Knapen T, Nieuwenhuis S & Donner TH (2017). Dynamic modulation of decision biases by brainstem arousal systems. eLife. 2017 Apr 6;6. pii: e23232. doi: 10.7554/eLife.23232. [Epub ahead of print]