Despite the clear relevance to clinical populations, very little is known about how the brain processes the learning mechanism (negative prediction error) that leads to the weakening of predictive relations, and what makes predictive relations so resistant to "breaking".
The aim of this proposal is to elucidate the neural mechanisms that process negative error in both appetitive (K99) and aversive (R00) settings. To do so, two extinction paradigms will be used, extinction by omission and extinction by overexpecation, in order to restrict the investigation to negative prediction error and eliminate other accounts of extinction that are not shared by both paradigms. In both types of extinction the predictive relation between a cue and an outcome is reduced by delivering a lower than expected outcome. In extinction by omission this learning occurs following the repeated presentation of the predictor in the absence of the outcome. In extinction by overexpecation, the concurrent presentation of two predictors of the same outcome are arranged to terminate in a single outcome. In order to determine how the healthy brain processes negative error, single cell recordings will be obtained from the central nucleus of the amygdala (CeA) and orbitofrontal cortex (OFC) during both extinction paradigms. Both CeA and the OFC have been implicated in extinction generally and in extinction by over-expectation specifically. By studying the role of these two regions, we will explore the mechanism of this involvement, testing the working hypothesis that the OFC provides predictive information regarding summed expectancies (overexpecation), which is used by the CeA to generate negative error signals at the time of reward. Since the weakening in associations seen during extinction is often transient, leading to renewal of the original behavioral response (also seen in relapse) over time or with changes in context, we will also examine the relationship between the strength of these signals during extinction and context-dependent renewal. Our working hypothesis is that renewal reflects an integrative process of summation between generalized outcome expectancy to a novel context and some residual outcome expectancy carried by the extinguished cue. If this is true, then OFC lesions should impair neural and behavioral renewal in our model. As noted earlier, this work will be done in both appetitive (K99) and aversive (R00) settings. Thus the proposed research will help determine the neural mechanisms involved in the weakening of associations, whether this mechanism is general or paradigm-specific, and whether appetitive and aversive extinction are processed by the same neural substrates. This will help understand what lies at the heart of association persistency and in turn take us a step closer to devising better treatments for disorders based on maladaptive associations. In addition to the research aims outlined above, the present proposal is designed to transition the primary investigator, Dr. Iordanova, from mentored researcher to independent scientist. This will be done by utilizing the mentored phase (K99) of the award to build Dr. Iordanova's research and professional skills. By carrying out the research proposed here Dr. Iordanova will 1. gain fundamental knowledge and skills in the field of appetitive learning;2. learn how to record from single cells in specific brin structures during behavioral paradigms, thus allowing her to obtain an online neural response during learning and behavior;3. extend her professional skills by communicating and disseminating the research outlined in this proposal nationally and internationally, thus widening her collaborative network. Dr. Iordanova's current expertise in the neurobiology of predictive fear learning (including the amygdala) will undoubtedly facilitate her acquisition of single cell recording skills in appetitive learning paradigms. This learning will also be facilitated by the exceptional facilities (electrophysiology rigs, behavioral apparatus, surgery and histology space and materials etc) and expertise provided not only by the Schoenbaum laboratory but by the whole Department of Anatomy and Neurobiology (Drs. Joseph Cheer, Patricio O'Donnell, Michael Shippley) at the University of Maryland. Dr Schoenbaum will also work to develop Dr. Iordanova's own mentoring and lab management skills. Overall, we believe this proposal provides Dr. Iordanova with an excellent opportunity to enhance her research and profession skills, so that she can secure a tenure track position at the end of the mentored phase and begin her career as a successful independent scientist.
Narrative At the heart of addiction, gambling and fear related (e.g., phobias) disorders are persistent maladaptive associations between one or more cues from the environment and a reinforcing event, and it is the apparent inability to break or reduce the strength of such associations that has rendered these disorders so resistant to treatment.
The aim of this project is to uncover how the healthy brain processes reductions in previously acquired associations between a cue and a biologically significant event (appetitive or aversive), and how the brain responds to the recovery of such associations. Uncovering these mechanisms in the healthy brain is essential for understanding the processes involved in the establishment of maladaptive associations and the development of new treatment for individuals who suffer from these disorders.