Every day we make countless decisions. Behavior is adaptive if we make choices that lead to positive outcomes (rewards) and avoid negative ones (punishments). Our lab studies brain circuits that enable humans to make adaptive decisions. We focus on brain regions involved in goal-directed behavior, and how activity changes with experience and internal states (hunger and satiety). For this, we use a variety of experimental techniques including pattern-based functional magnetic resonance imaging (fMRI), diffusion imaging, transcranial magnetic stimulation (TMS), and computational modeling.
We use the sense of smell as sensory model system for reward. Odors are extremely important for many decisions ranging from food search and intake to social interactions. Food odors allow us to manipulate reward identity independently of reward value, allowing us to study encoding of identity-specific outcomes. For this, the lab houses two custom-built, MR-compatible olfactometers.
Our research relates to clinical work in the Neurology Department by exploring diminished goal-directed behavior in neurological and psychiatric disorders such as addiction, Parkinson’s disease, and obesity. The ultimate goal of our work is to identify novel targets for biomarkers and treatment strategies for these conditions. The work is supported by grants from the NIH/NIDCD (R01DC015426) and the NIH/NIDA (R03DA040668).
Identity-specific coding of future rewards
We study the neural circuits that signal information about expected outcomes. The specific identity of expected outcomes is an important component for making goal-directed choices. A key region for identity-specific coding is the orbitofrontal cortex. Our experiments use food odors (e.g., dulce de leche vs. sautéed onions) and pattern-based functional imaging to study how specific outcomes are represented in the human orbitofrontal cortex, and how these representations are learned, and how they change with hunger. This research is fundamental for understanding brain disorders in which adaptive behavior is disrupted, such as addiction and eating disorders.
Howard JD, Gottfried JA, Tobler PN, Kahnt T. Identity-specific coding of future rewards in the human orbitofrontal cortex. Proc Natl Acad Sci USA 2015, 112(16):5195-200. PMID: 25848032
Howard JD, Kahnt T. Identity-Specific Reward Representations in Orbitofrontal Cortex Are Modulated by Selective Devaluation. J Neurosci. 2017 Mar 8;37(10):2627-2638. PMID: 28159906
Howard JD, Kahnt T. Identity prediction errors in the human midbrain update reward identity expectation in the orbitofrontal cortex. Nat Commun. 2018 Apr 23;9(1):1611. PMID: 29686225
Neurocomputational mechanisms of generalization
Generalization and inference allows us to apply knowledge that we have learned for specific stimuli to novel situations. An important trade-off exists between generalization and discrimination. While generalizing from previous experience can help us to behave more efficiently, discrimination prevents us from exhibiting stereotypical or maladaptive responses. In order to understand the computations contributing to generalization, we utilize mathematical models that allow us to formulate precise hypotheses and generate testable predictions for our neural data. A set of interconnected brain regions including the dopaminergic midbrain, the striatum and the hippocampus, is thought to support generalization. We study interactions between these brain regions and their specific contribution to generalization using a diverse set of experimental methods including pharmacology, non-invasive brain stimulation, and functional imaging. These studies provide insights into the mechanisms controlling the trade-off between generalization and discrimination and may provide a better understanding of several neuropsychiatric disorders in which generalization is disrupted, such as addiction, schizophrenia, anxiety disorders, and posttraumatic stress (PTSD).
Kahnt T, Park SQ, Burke CJ, Tobler PN. How glitter relates to gold: similarity-dependent reward prediction errors in the human striatum. Journal of Neuroscience 2012 Nov 14; 32(46):16521-9. PMID: 23152634
Kahnt T, Tobler PN. 2016. Dopamine regulates stimulus generalization in the human hippocampus. eLife;5:e12678
Connectivity of the human orbitofrontal cortex
We study the anatomical and functional connectivity of the brain regions involved in olfactory reward processing, including the orbitofrontal and piriform cortex, the amygdala, and the striatum. For this we use measures of anatomical (diffusion tensor and diffusion spectrum imaging), functional, and information-based connectivity (resting-state and task-based fMRI connectivity). The overall goal of this research is to characterize the functional roles of anatomical connections among olfactory brain regions. These results may provide insights into the nature of degeneration associated with age-related disorders such as Alzheimer’s disease and fronto-temporal dementia.
Kahnt T, Chang LJ, Park SQ, Heinzle J, Haynes JD. Connectivity-based parcellation of the human orbitofrontal cortex. Journal of Neuroscience 2012 May 2; 32(18):6240-50. PMID: 22553030
Kahnt T, Tobler PN. Dopamine modulates the functional organization of the orbitofrontal cortex. Journal of Neuroscience 2017 Feb 8;37(6):1493-1504; PMID: 28069917.
Our lab is equipped with two custom-built, MR-compatible olfactometers ("Benjamin" and "Rosie") to deliver appetitive food-odors directly to the nose of hungry human subjects. To measure breathing, a MR-compatible breathing belt and a spirometer is available to use in behavioral and fMRI studies. Neuroimaging is performed on the Siemens 3-Tesla PRISMA system at the Center for Translational Imaging (CTI), Department of Radiology, Northwestern University Feinberg School of Medicine.