Brainstem Alertness Systems Modulate Decision Biases
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. For reasons that remain unknown, activation of the locus coeruleus also causes the pupil of the eye to suddenly increase in size.
Now, Jan Willem de Gee, of the University of Amsterdam, and colleagues have exploited this link to unravel how changes in brain arousal lead to systematic changes in decision-making.
Locus Coeruleus Activity
!5 volunteer subjects 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”. Although the decision was comparatively simple, it did involve evaluating changing information over time before making a choice – like when considering the stock market.
As the volunteers performed the task, the researchers measured their brain activity and the size of their pupils in several fMRI sessions. Most of the volunteers had a tendency to respond “no” even when the pattern was present.
Cortex-wide fMRI correlates of phasic arousal and stimulus. (A) Functional map of task-evoked fMRI responses computed as the mean across all trials. (B) As panel A, but for the contrast high vs. low TPR trials. (C) As panel A, but for the contrast signal+noise vs. noise. (D) As panel A, but for the interaction between TPR (2 levels) and stimulus (2 levels). All panels: functional maps are expressed as t-scores computed at the group level (N = 14) and presented with cluster-corrected statistical threshold (see Materials and methods). DOI: http://dx.doi.org/10.7554/eLife.23232.021
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.
The result suggest 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 activates the locus coeruleus on some occasions but not others.
The research was supported by the German Research Foundation, the European Union Seventh Framework Programme, and the European Research Council.