Characterizing the Neural Signature of Preferences

Post by Elisa Guma

What's the science?

When we make a decision, typically we identify our options, estimate the value of those options, and compare the values to select the best option. Several neural and computational approaches have been employed to try to understand the valuation process, and the brain networks involved. However, the mechanisms behind decision making remain poorly understood. A few key brain regions have been identified as playing a key role in subjective valuation, also termed ‘brain valuation system’ including the ventromedial prefrontal cortex, ventral striatum, and posterior cingulate cortex, however, several other regions have also been identified as playing a key role. This week in Nature Neuroscience, Lopez-Persem and colleagues use a large dataset of intracranial electrophysiological recordings in humans (being treated with epilepsy) to better identify which brain regions and what type of underlying activity is involved in generating value signals in judgement tasks.

How did they do it?

The authors’ first goal was to identify brain regions in which value signals were detectable during judgement tasks. In other words: to identify the brain valuation system. The authors collected intracranial electroencephalography (iEEG) data from 4,273 intracranial electrodes in the brains of 36 patients being treated for drug-resistant focal epilepsy (across 3 treatment centers). Each participant had between 12-18 electrodes implanted for seizure localization. Participants performed judgments tasks while neural activity was being recorded via electrodes. Some participants performed a short version of the task, and others performed a longer version. The longer version of the task started with a “distracting task” in which participants were asked to estimate the age of faces and paintings, and rate how confident they felt in their guess. In the second phase of the task, participants were asked to rate the likeability of food items as well as faces and paintings, followed by a confidence rating. In a third phase, participants were given a choice of two pictures belonging to the same category (face, food, painting) and asked to choose the one they liked best. In the short version of the task, participants only completed the second and third phases with food item images and were not asked to rate confidence. 

The authors sought to find the time window in which each brain region of interest was most associated with the value signal by investigating the relationship between the subjective value given by participants and parcellated brain activity (77 regions using the Automated Anatomical Labeling atlas). They focused their analyses on high-gamma-band (50-150Hz) activity because it is thought to be a close reflection of local neuron spiking activity. The authors wanted to know if the electrophysiological activity recordings were related to four core properties of subjective valuation. They assessed anticipation with pre-stimulus activity, generality with the inclusion of non-food items, automaticity by including other types of rating (age), and quadratic coding by measuring confidence in ratings.

What did they find?

The authors identified a quadratic, or U-shaped relationship between first-order ratings (age or likeability of an item) and second-order (confidence in those ratings) ratings. This was true for both food and non-food items as well as age and likeability tasks. The authors also observed that the likeability ratings were reliable estimates of subjective value, able to predict choice, reaction time, and confidence. The authors identified 18 regions of interest (among the 77 analyzed) in which a significant subjective value representation was associated. The authors identified several regions belonging to the brain valuation system: the orbitofrontal cortex OFC (comprising the ventromedial prefrontal cortex and lateral orbitofrontal cortex), and parahippocampal complex (PHC) comprising the hippocampus and parahippocampal cortex. They also found significant associations with other regions including the anterior cingulate gyrus, fusiform area, inferior temporal cortex, and inferior frontal opercularis.   

For anticipation (how baseline activity predicts value judgement) they found that OFC pre-stimulus activity was significantly associated with value signaling, but not the PHC activity. In the post-stimulus window, they found a significant association with both food and non-food item likeability rating for all regions, indicative of the generality of the signal. They also found that these regions responded to value in a distractive, or non-value task, reflective of automaticity in subjective valuation. Finally, they found that brain valuation system activity was also associated with a quadratic form of likeability ratings (quadraticity), indicative of a co-representation of confidence.

What's the impact?

This study identified a brain network important for valuation in decision making. Further, these findings indicate this network’s involvement in anticipation, generality, and automaticity in decision making. This work provides important evidence for how the brain assigns value to options during decision making and may help us understand the mechanisms of irrational judgement.

Alizee Lopez-Persem et al. Four core properties of the human brain valuation system demonstrated in intracranial signals. Nature Neuroscience (2020). Access the original scientific publication here