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      Empirical validation of a touchscreen probabilistic reward task in rats

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          Abstract

          Anhedonia, the loss of pleasure from previously rewarding activities, is implicated in several neuropsychiatric conditions, including major depressive disorder (MDD). In order to accelerate drug development for mood disorders, quantitative approaches are needed to objectively measure responsiveness to reward as a means to identify deficits. One such approach, the probabilistic reward task (PRT), uses visual discrimination methodology to quantify reward learning. In this computerized task, humans make visual discriminations, and probabilistic contingencies are arranged such that correct responses to one alternative are rewarded more often (rich) than correct responses to the other (lean). Healthy participants consistently develop a response bias in favor of the rich alternative. However, participants with MDD typically exhibit lower response biases, and this blunting correlates with current and future anhedonia. The present studies validated a touchscreen-based PRT in rodents with formal and functional similarity to the human task. First, rats were trained to discriminate between two lines that differed in length. Next, parametric manipulations of probabilistic contingencies, line-length stimuli, and drug treatment (amphetamine, 0.32–3.2 mg/kg; scopolamine, 0.1–1.0 mg/kg; oxycodone, 0.1–1.0 mg/kg) on response bias were evaluated. Results demonstrated orderly shifts in bias and discriminability that varied as a function of, respectively, the asymmetry of rich/lean probabilities and disparity in line lengths. Drugs that enhance reward responsiveness (amphetamine and scopolamine, but not oxycodone) increased bias, verifying pharmacological task sensitivity. Finally, performance outcomes under optimized conditions were replicated in female rats. Collectively, the touchscreen-based rodent PRT appears to have high preclinical value as a quantitative assay of reward learning.

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          Most cited references 43

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          Reconsidering anhedonia in depression: lessons from translational neuroscience.

          Anhedonia is a core symptom of major depressive disorder (MDD), the neurobiological mechanisms of which remain poorly understood. Despite decades of speculation regarding the role of dopamine (DA) in anhedonic symptoms, empirical evidence has remained elusive, with frequent reports of contradictory findings. In the present review, we argue that this has resulted from an underspecified definition of anhedonia, which has failed to dissociate between consummatory and motivational aspects of reward behavior. Given substantial preclinical evidence that DA is involved primarily in motivational aspects of reward, we suggest that a refined definition of anhedonia that distinguishes between deficits in pleasure and motivation is essential for the purposes of identifying its neurobiological substrates. Moreover, bridging the gap between preclinical and clinical models of anhedonia may require moving away from the conceptualization of anhedonia as a steady-state, mood-like phenomena. Consequently, we introduce the term "decisional anhedonia" to address the influence of anhedonia on reward decision-making. These proposed modifications to the theoretical definition of anhedonia have implications for research, assessment and treatment of MDD. Copyright © 2010 Elsevier Ltd. All rights reserved.
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            The validity of scopolamine as a pharmacological model for cognitive impairment: a review of animal behavioral studies.

            Scopolamine is used as a standard/reference drug for inducing cognitive deficits in healthy humans and animals. Effects are often interpreted in terms of a role of acetylcholine in mnemonic and/or attentional processes. In this paper an overview is given of the effects of scopolamine on animal behavior. Examination of the dose-response curve of systemically administered scopolamine indicates that sensory discrimination and attention are most sensitive to disruption. When higher doses (>0.03mg/kg) are used, deficits in other cognitive and non-cognitive functions (e.g., learning and memory, locomotor activity) are reported. Several behavioral processes (taste aversion, anxiety, short-term memory, attention) are found to be affected after intracerebral injections of scopolamine. It is concluded that effects on learning and memory performance which are observed after higher doses of scopolamine are mediated by (1) primary effects on attention and sensory/stimulus discrimination, (2) non-specific effects on behavior (e.g., locomotor activity, anxiety), and (3) peripheral side-effects (e.g., pupil dilation, salivation). Finally, the validity of scopolamine as a pharmacological model for cognitive impairment is discussed. The use of muscarinic M1 antagonists is suggested as a more selective and effective way of inducing cholinergic-induced cognitive deficits.
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              Toward an objective characterization of an anhedonic phenotype: a signal-detection approach.

              Difficulties in defining and characterizing phenotypes has hindered progress in psychiatric genetics and clinical neuroscience. Decreased approach-related behavior and anhedonia (lack of responsiveness to pleasure) are considered cardinal features of depression, but few studies have used laboratory-based measures to objectively characterize these constructs. To assess hedonic capacity in relation to depressive, particularly anhedonic, symptoms, 62 participants completed a signal-detection task based on a differential reinforcement schedule. Anhedonia was operationalized as decreased reward responsiveness. Unequal frequency of reward between two correct responses produced a response bias (i.e., a systematic preference to identify the stimulus paired with the more frequent reward). Subjects with elevated depressive symptoms (Beck Depression Inventory scores >/= 16) failed to show a response bias. Impaired reward responsiveness predicted higher anhedonic symptoms 1 month later, after controlling for general negative affectivity. Impaired tendency to modulate behavior as a function of prior reinforcement might underline diminished hedonic capacity in depression. When applied to a clinical population, objective assessments of participants' propensity to modulate behavior as a function of reward might provide a powerful tool for improving the phenotypic definition of depression and thus offer a reliable behavioral screening approach for neuroscience studies of depression.
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                Author and article information

                Contributors
                bkangas@mclean.harvard.edu
                Journal
                Transl Psychiatry
                Transl Psychiatry
                Translational Psychiatry
                Nature Publishing Group UK (London )
                2158-3188
                13 August 2020
                13 August 2020
                2020
                : 10
                Affiliations
                [1 ]GRID grid.240206.2, ISNI 0000 0000 8795 072X, McLean Hospital, ; Belmont, MA USA
                [2 ]GRID grid.38142.3c, ISNI 000000041936754X, Harvard Medical School, ; Boston, MA USA
                Article
                969
                10.1038/s41398-020-00969-1
                7426406
                32792526
                © The Author(s) 2020

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                Funding
                Funded by: FundRef https://doi.org/10.13039/100000026, U.S. Department of Health & Human Services | NIH | National Institute on Drug Abuse (NIDA);
                Award ID: K01-DA035974
                Award Recipient :
                Funded by: FundRef https://doi.org/10.13039/100000025, U.S. Department of Health & Human Services | NIH | National Institute of Mental Health (NIMH);
                Award ID: R37-MH068376
                Award ID: R01-MH101521
                Award ID: UH2-MH109334
                Award Recipient :
                Funded by: U.S. Department of Health & Human Services | NIH | National Institute of Mental Health (NIMH)
                Funded by: U.S. Department of Health & Human Services | NIH | National Institute of Mental Health (NIMH)
                Categories
                Article
                Custom metadata
                © The Author(s) 2020

                Clinical Psychology & Psychiatry

                clinical pharmacology, learning and memory

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