Our lab studies brain circuits involved in learning and decision making. This includes the orbitofrontal cortex (OFC), the striatum, and the hippocampus. We use several experimental techniques suited for human research, such as pattern-based functional magnetic resonance imaging (fMRI), diffusion imaging, transcranial magnetic stimulation (TMS), and computational modeling.
An important sensory modalitiy for learning and decision making is the sense of smell. Odors play a critical role for many decisions ranging from food search to social interactions. Food odors allow us to manipulate reward identity (what it is) independently of reward value (how good it is), and thus allow us to study behavior that is directed toward specific outcomes. To deliver odor stimuli in behavioral and fMRI experiments, the lab houses three custom-built MR-compatible olfactometers (Benjamin, Rosie, and Tantor).
Our research relates to clinical work in the Neurology Department. Decision making is impaired in several neurological and psychiatric disorders such as addiction, dementia, and obesity. The ultimate goal of our work is to identify novel biomarkers and therapeutic targets for these conditions. Our work is currently supported by grants from NIDCD (R01 DC015426) and NIDDK (R21 DK118503).
Outcome-specific coding of future rewards
We study the neural circuits that signal information about expected outcomes. The identity of expected outcomes is an important component for making goal-directed decisions. A key region for outcome-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 to inform choices and how these representations are learned. In addition, we use non-invasive brain stimulation to test whether these representations are indeed necesssary for decison making. 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
Suarez JA, Howard JD, Schoenbaum G, Kahnt T. Sensory prediction errors in the human midbrain signal identity violations independent of perceptual distance. eLife. 2019 Apr 5; 8:e43962. PMID: 30950792
Stalnaker T, Howard JD, Takahashi YK, Gershman SJ, Kahnt T, Schoenbaum G. Dopamine neuron ensembles signal the content of sensory prediction errors. eLife. 2019 Nov 1; 8:e49315. PMID: 31674910
Howard JD, Reynolds R, Smith DE, Voss JL, Schoenbaum G, Kahnt T. Targeted Stimulation of Human Orbitofrontal Networks Disrupts Outcome-Guided Behavior. Curr Biol. 2020 Jan 16.
Mechanisms of generalization and model-based inference
Generalization and model-based inference allow us to apply knowledge that we have learned for specific problemns to novel situations. A set of interconnected brain regions including the dopaminergic midbrain, the orbitofrontal cortex and the hippocampus, is thought to support inference. We study interactions between these brain regions and their specific contribution to inference using a diverse set of experimental methods including computational modeling, pharmacology, TMS, and fMRI. These studies provide insights into the mechanisms underlying inference-based behavior and may provide a better understanding of several neuropsychiatric disorders in which generalization is disrupted, such as addiction, schizophrenia, 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. Dopamine regulates stimulus generalization in the human hippocampus. eLife. 2016 Feb 2; 5:e12678. PubMed PMID: 26830462
Wang F, Schoenbaum G, Kahnt T. Interactions between human orbitofrontal cortex and hippocampus support model-based inference. PLoS Biol. 2020 Jan 21;18(1):e3000578. PMID: 31961854.
Connectivity of the 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 weighted imaging, DWI) and functional connectivity measures. The overall goal of this research is to characterize the functional roles of anatomical connections of the orbitofrontal cortex and its connections to olfactory brain areas. These results may provide insights into the nature of degeneration associated with age-related disorders such as Alzheimer’s disease, Parkinson’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.
Zhou G, Lane G, Cooper SL, Kahnt T, Zelano C. Characterizing functional pathways of the human olfactory system. eLife. 2019 Jul 24; 8:e47177. PMID: 31339489.
Our Equipment and Facilities
Our lab is equipped with three custom-built, MR-compatible olfactometers ("Benjamin", "Rosie", and "Tantor") to deliver odors directly to the nose of human subjects. To measure respiratory behavior (sniffing), MR-compatible breathing belts and spirometers are 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.