Neuronal substrates underlying the construction of value in humans

California Institute Of Technology, Pasadena CA

Investigators

Abstract

How do our personal preferences arise? We all have a multitude of preferences and a sense of our own individual taste – but why do we come to like some things and not like others? For instance, why might a person like potato chips but not like popcorn, pop music rather than country-western, baseball rather than basketball, or come to like a representational painting by Rembrandt, but dislike abstract, modern art of Jackson Pollock? The major question we are addressing in this project is how are our preferences formed in the brain? The researchers aim to test a theory that the brain relies on “features” of objects which are the elements that make up an object – such as the ingredients in a food item, or the color, shapes and textures in a painting, in order to make a decision about how much something is liked or not. The hypothesis is that the brain cells (neurons) respond to these elementary features of an object, and that other neurons integrate over these features to form an overall preference judgment. To test for this, the responses of neurons are recorded directly from the human brain, while people make simple judgements about how much they like a variety of items including food, visual art and even clothing items. This research is made possible because of safe technological advances in brain surgery, and the generosity of patients who are being treated for intractable epilepsy. Prior to brain surgery to remove the epileptic brain tissue, patients have small electrodes temporarily placed into their brain to locate their seizures as part of their treatment. These patients are often willing to volunteer to take part in research studies, yielding a rare opportunity to measure electrical activity from neurons directly. Understanding how neurons in our brain form our preferences could help us better understand how people make decisions in the real world. While value signals are known to be encoded in the brain, a fundamental question remains about how such signals come to be computed in the first place. The major hypothesis to be tested in this project is that value signals for stimuli ranging from foods to consumer goods through to art, are constructed by the brain in a dynamic fashion by integrating over the component features or attributes of a stimulus. While a number of prior studies have examined value construction using neuroimaging techniques (such as functional magnetic resonance imaging or fMRI), insights can only be gained over the spatiotemporal resolution of the technique, which cannot measure single cells. As a consequence, little is known about how stimulus features are represented by individual cells and integrated to compute an overall stimulus-value. Here, this limitation can be overcome through the use of intracranial recordings in human epilepsy patients while they perform three different tasks probing value construction. The research focuses on neuronal populations in the three key parts of the value network in the brain: the amygdala, lateral orbitofrontal, and ventromedial prefrontal cortex. The spatial resolution of these methods enables insight into how individual features are represented at the neuronal level, while the temporal resolution allows us to identify the temporal dynamics by which features are actively integrated to yield an overall value signal. Features in the amygdala and lateral orbitofrontal cortex are hypothesized to be integrated to yield value signals in the ventromedial prefrontal cortex. Furthermore, the research aims to address the means by which value signals are altered following a change in one’s overall goals, comparing a model in which features are modulated directly by a change in context, against an alternative in which the connectivity between feature neurons and value coding neurons are modulated by goal context, yet feature representations remain unchanged. This project promises to yield fundamental mechanistic insights into the neural computations underlying the production of value signals in the human brain, and the origin and neural basis of our individual preferences, which in turn serve a fundamental role in guiding human decision-making. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.