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Brain volume in chronic ketamine users - relationship to sub-threshold psychotic symptoms and relevance to schizophrenia. Psychopharmacology (Berl) 2022; 239:3421-3429. [PMID: 34228135 PMCID: PMC9584979 DOI: 10.1007/s00213-021-05873-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Accepted: 05/05/2021] [Indexed: 11/23/2022]
Abstract
RATIONALE Ketamine may model aspects of schizophrenia arising through NMDA receptor activity deficits. Although acute ketamine can induce effects resembling both positive and negative psychotic symptoms, chronic use may be a closer model of idiopathic psychosis. OBJECTIVES We tested the hypotheses that ketamine users had lower brain volumes, as measured using MRI, and greater sub-threshold psychotic symptoms relative to a poly-drug user control group. METHODS Ketamine users (n = 17) and poly-drug using controls (n = 19) were included in the study. All underwent volumetric MRI imaging and measurement of sub-threshold psychotic symptoms using the Comprehensive Assessment of At-Risk Mental State (CAARMS). Freesurfer was used to analyse differences in regional brain volume, cortical surface area and thickness between ketamine users and controls. The relationship between CAARMS ratings and brain volume was also investigated in ketamine users. RESULTS Ketamine users were found to have significantly lower grey matter volumes of the nucleus accumbens, caudate nucleus, cerebellum and total cortex (FDR p < 0.05; Cohen's d = 0.36-0.75). Within the cortex, ketamine users had significantly lower grey matter volumes within the frontal, temporal and parietal cortices (Cohen's d 0.7-1.31; FDR p < 0.05). They also had significantly higher sub-threshold psychotic symptoms (p < 0.05). Frequency of ketamine use showed an inverse correlation with cerebellar volume (p < 0.001), but there was no relationship between regional brain volumes and sub-threshold psychotic symptoms. CONCLUSIONS Chronic ketamine use may cause lower grey matter volumes as well as inducing sub-threshold psychotic symptoms, although these likely arise through distinct mechanisms.
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Cofresí RU, Piasecki TM, Bartholow BD, Schachtman TR. Enhanced conditioned "liking" of novel visual cues paired with alcohol or non-alcohol beverage container images among individuals at higher risk for alcohol use disorder. Psychopharmacology (Berl) 2022; 239:3567-3578. [PMID: 36094618 PMCID: PMC9464611 DOI: 10.1007/s00213-022-06231-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Accepted: 08/29/2022] [Indexed: 11/07/2022]
Abstract
RATIONALE/OBJECTIVE This study used an evaluative conditioning (EC) procedure to assess the affective properties of a CS for ingested drug reward in humans. Specifically, the study tested whether the evaluative response ("liking"/"disliking") to an arbitrary visual stimulus ("CS2," e.g., a purple hexagon) could be changed through pairings with an alcohol or non-alcohol beverage cue ("CS1," e.g., a full wine glass, a juice box), which is ostensibly a conditioned visual predictive stimulus for alcohol or non-alcohol liquid reward, respectively. METHODS Participants (N = 369, 18-23 years, 66% female, 79% white, 21% reporting no alcohol use ever or in the past year) received 24 CS1 pairings with each CS2. CS2 and CS1 evaluations were assessed pre- and post-conditioning. RESULTS Alcohol and non-alcohol CS2 "liking" correlated with alcohol use. "Liking" of the alcohol but not non-alcohol CS1 also correlated with alcohol use. Alcohol CS1 "liking" also correlated with alcohol and non-alcohol CS2 'liking," whereas non-alcohol CS1 'liking" correlated with non-alcohol but not alcohol CS2 "liking." CONCLUSIONS Taken together, findings support the idea that drug-related visual stimuli acquire appetitive (hedonic and/or incentive) properties as a function of individual differences in drug use, which entail individual differences in exposure to the conditioning effects of addictive substances like alcohol. Findings also suggest a link between drug use and the propensity to attribute affective/motivational significance to reward-predictive cues in general.
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Affiliation(s)
- Roberto U. Cofresí
- grid.134936.a0000 0001 2162 3504Department of Psychological Sciences, University of Missouri, Columbia, MO 65211 USA
| | - Thomas M. Piasecki
- grid.14003.360000 0001 2167 3675Center for Tobacco Research and Intervention and Department of Medicine, University of Wisconsin-Madison, Madison, USA
| | - Bruce D. Bartholow
- grid.134936.a0000 0001 2162 3504Department of Psychological Sciences, University of Missouri, Columbia, MO 65211 USA
| | - Todd R. Schachtman
- grid.134936.a0000 0001 2162 3504Department of Psychological Sciences, University of Missouri, Columbia, MO 65211 USA
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Agency rescues competition for credit assignment among predictive cues from adverse learning conditions. Sci Rep 2021; 11:16187. [PMID: 34376741 PMCID: PMC8355250 DOI: 10.1038/s41598-021-95541-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Accepted: 07/12/2021] [Indexed: 11/29/2022] Open
Abstract
A fundamental assumption of learning theories is that the credit assigned to predictive cues is not simply determined by their probability of reinforcement, but by their ability to compete with other cues present during learning. This assumption has guided behavioral and neural science research for decades, and tremendous empirical and theoretical advances have been made identifying the mechanisms of cue competition. However, when learning conditions are not optimal (e.g., when training is massed), cue competition is attenuated. This failure of the learning system exposes the individual’s vulnerability to form spurious associations in the real world. Here, we uncover that cue competition in rats can be rescued when conditions are suboptimal provided that the individual has agency over the learning experience. Our findings reveal a new effect of agency over learning on credit assignment among predictive cues, and open new avenues of investigation into the underlying mechanisms.
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Mollick JA, Kober H. Computational models of drug use and addiction: A review. JOURNAL OF ABNORMAL PSYCHOLOGY 2020; 129:544-555. [PMID: 32757599 PMCID: PMC7416739 DOI: 10.1037/abn0000503] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In this brief review, we describe current computational models of drug-use and addiction that fall into 2 broad categories: mathematically based models that rely on computational theories, and brain-based models that link computations to brain areas or circuits. Across categories, many are models of learning and decision-making, which may be compromised in addiction. Several mathematical models take predictive coding approaches, focusing on Bayesian prediction error. Other models focus on learning processes and (traditional) prediction error. Brain-based models have incorporated prefrontal cortex, basal ganglia, and the dopamine system, based on the effects of drugs on dopamine, motivation, and executive control circuits. Several models specifically describe how behavioral control may transition from habitual to goal-directed systems, consistent with computational accounts of compromised "model-based" control. Some brain-based models have linked this to the transition of behavioral control from ventral to dorsal striatum. Overall, we propose that while computational models capture some aspects of addiction and have advanced our thinking, most have focused on the effects of drug use rather than addiction per se, most have not been tested on and/or supported by human data, and few capture multiple stages and symptoms of addiction. We conclude by suggesting a path forward for computational models of addiction. (PsycInfo Database Record (c) 2020 APA, all rights reserved).
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Affiliation(s)
- Jessica A Mollick
- Clinical and Affective Neuroscience Lab, Department of Psychiatry, Yale University
| | - Hedy Kober
- Clinical and Affective Neuroscience Lab, Department of Psychiatry, Yale University
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Tang WK, Liang H, Lin Y, Zhang C, Tang A, Chan F, Freeman TP, Ungvari GS. Psychiatric Co-morbidity in Ketamine and Methamphetamine Dependence: a Retrospective Chart Review. Int J Ment Health Addict 2016. [DOI: 10.1007/s11469-016-9681-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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Laude JR, Fillmore MT. Alcohol cues impair learning inhibitory signals in beer drinkers. Alcohol Clin Exp Res 2016; 39:880-6. [PMID: 25872597 DOI: 10.1111/acer.12690] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Accepted: 01/23/2015] [Indexed: 12/01/2022]
Abstract
BACKGROUND Models of drug addiction emphasize the reciprocal influence of incentive-motivational properties of drug-related cues and poor impulse control resulting in drug use. Recent studies have shown that alcohol-related cues can impair response inhibition. What is unknown is whether these cues also disrupt learning of inhibitory associations. METHODS Participants performed a conditioned inhibition (CI) task and were required to learn that a neutral image was a conditioned inhibitor when presented in the context of either an alcohol image intended to draw their attention away from the to-be-trained inhibitor, or a control condition in which the alcohol image was absent. After training, subjects in each condition rated the likelihood that the neutral image would signal the outcome. Eye tracking was used to verify that attention to the neutral image was in fact reduced when the alcohol image was present. RESULTS Compared with controls those trained in the alcohol image condition reported a greater likelihood that the presence of the inhibitor would be followed by the outcome and thus were less able to acquire CI. Measures of eye tracking verified that attention to the alcohol cue was associated with this maladaptive behavior. CONCLUSIONS When alcohol cues are present, there is a reduced ability to learn that such information is irrelevant to an outcome, and this impairs ones' ability to inhibit perseveration of a response. This has implications for persistence of a drinking episode.
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Affiliation(s)
- Jennifer R Laude
- Department of Psychology, University of Kentucky, Lexington, Kentucky
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Schoevers RA, Chaves TV, Balukova SM, aan het Rot M, Kortekaas R. Oral ketamine for the treatment of pain and treatment-resistant depression†. Br J Psychiatry 2016; 208:108-13. [PMID: 26834167 DOI: 10.1192/bjp.bp.115.165498] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
BACKGROUND Recent studies with intravenous (i.v.) application of ketamine show remarkable but short-term success in patients with MDD. Studies in patients with chronic pain have used different ketamine applications for longer time periods. This experience may be relevant for psychiatric indications. AIMS To review the literature about the dosing regimen, duration, effects and side-effects of oral, intravenous, intranasal and subcutaneous routes of administration of ketamine for treatment-resistant depression and pain. METHOD Searches in PubMed with the terms 'oral ketamine', 'depression', 'chronic pain', 'neuropathic pain', 'intravenous ketamine', 'intranasal ketamine' and 'subcutaneous ketamine' yielded 88 articles. We reviewed all papers for information about dosing regimen, number of individuals who received ketamine, number of ketamine days per study, results and side-effects, as well as study quality. RESULTS Overall, the methodological strength of studies investigating the antidepressant effects of ketamine was considered low, regardless of the route of administration. The doses for depression were in the lower range compared with studies that investigated analgesic use. Studies on pain suggested that oral ketamine may be acceptable for treatment-resistant depression in terms of tolerability and side-effects. CONCLUSIONS Oral ketamine, given for longer time periods in the described doses, appears to be well tolerated, but few studies have systematically examined the longer-term negative consequences. The short- and longer-term depression outcomes as well as side-effects need to be studied with rigorous randomised controlled trials.
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Affiliation(s)
- Robert A Schoevers
- Robert A. Schoevers, MD PhD, Tharcila V. Chaves, MSc, Sonya M. Balukova, MSc, University of Groningen, University Medical Center Groningen, Department of Psychiatry, Research School of Behavioural and Cognitive Neurosciences (BCN), Interdisciplinary Center for Psychopathology and Emotion Regulation (ICPE), Groningen; Marije aan het Rot, PhD, Department of Psychology and Research School of Behavioral and Cognitive Neurosciences; Rudie Kortekaas, PhD, Department of Psychiatry, Interdisciplinary Center for Psychopathology and Emotion Regulation, Department of Neuroscience, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Tharcila V Chaves
- Robert A. Schoevers, MD PhD, Tharcila V. Chaves, MSc, Sonya M. Balukova, MSc, University of Groningen, University Medical Center Groningen, Department of Psychiatry, Research School of Behavioural and Cognitive Neurosciences (BCN), Interdisciplinary Center for Psychopathology and Emotion Regulation (ICPE), Groningen; Marije aan het Rot, PhD, Department of Psychology and Research School of Behavioral and Cognitive Neurosciences; Rudie Kortekaas, PhD, Department of Psychiatry, Interdisciplinary Center for Psychopathology and Emotion Regulation, Department of Neuroscience, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Sonya M Balukova
- Robert A. Schoevers, MD PhD, Tharcila V. Chaves, MSc, Sonya M. Balukova, MSc, University of Groningen, University Medical Center Groningen, Department of Psychiatry, Research School of Behavioural and Cognitive Neurosciences (BCN), Interdisciplinary Center for Psychopathology and Emotion Regulation (ICPE), Groningen; Marije aan het Rot, PhD, Department of Psychology and Research School of Behavioral and Cognitive Neurosciences; Rudie Kortekaas, PhD, Department of Psychiatry, Interdisciplinary Center for Psychopathology and Emotion Regulation, Department of Neuroscience, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Marije aan het Rot
- Robert A. Schoevers, MD PhD, Tharcila V. Chaves, MSc, Sonya M. Balukova, MSc, University of Groningen, University Medical Center Groningen, Department of Psychiatry, Research School of Behavioural and Cognitive Neurosciences (BCN), Interdisciplinary Center for Psychopathology and Emotion Regulation (ICPE), Groningen; Marije aan het Rot, PhD, Department of Psychology and Research School of Behavioral and Cognitive Neurosciences; Rudie Kortekaas, PhD, Department of Psychiatry, Interdisciplinary Center for Psychopathology and Emotion Regulation, Department of Neuroscience, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Rudie Kortekaas
- Robert A. Schoevers, MD PhD, Tharcila V. Chaves, MSc, Sonya M. Balukova, MSc, University of Groningen, University Medical Center Groningen, Department of Psychiatry, Research School of Behavioural and Cognitive Neurosciences (BCN), Interdisciplinary Center for Psychopathology and Emotion Regulation (ICPE), Groningen; Marije aan het Rot, PhD, Department of Psychology and Research School of Behavioral and Cognitive Neurosciences; Rudie Kortekaas, PhD, Department of Psychiatry, Interdisciplinary Center for Psychopathology and Emotion Regulation, Department of Neuroscience, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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Neuroscience of learning and memory for addiction medicine: from habit formation to memory reconsolidation. PROGRESS IN BRAIN RESEARCH 2015; 223:91-113. [PMID: 26806773 DOI: 10.1016/bs.pbr.2015.07.006] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Identifying effective pharmacological treatments for addictive disorders has remained an elusive goal. Many different classes of drugs have shown some efficacy in preclinical models, but the number of effective clinical therapeutics has remained stubbornly low. The persistence of drug use and the high frequency of relapse is at least partly attributable to the enduring ability of environmental stimuli associated with drug use to maintain behavioral patterns of drug use and induce craving during abstinence. We propose that stimuli associated with drug use exert such powerful control over behavior through the development of abnormally strong memories, and their ability to initiate subconscious sequences of motor actions (habits) that promote uncontrolled drug use. In this chapter, we will review the evidence suggesting that drugs of abuse strengthen associations with cues in the environment and facilitate habit formation. We will also discuss potential mechanisms for disrupting memories associated with drug use to help improve treatments for addiction.
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Coyle CM, Laws KR. The use of ketamine as an antidepressant: a systematic review and meta-analysis. Hum Psychopharmacol 2015; 30:152-63. [PMID: 25847818 DOI: 10.1002/hup.2475] [Citation(s) in RCA: 184] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/12/2014] [Revised: 02/01/2015] [Accepted: 02/12/2015] [Indexed: 12/28/2022]
Abstract
OBJECTIVE The current meta-analysis examines the effects of ketamine infusion on depressive symptoms over time in major depressive disorder (MDD) and bipolar disorder (BD). METHODS Following a systematic review of the literature, data were extracted from 21 studies (n = 437 receiving ketamine) and analysed at four post-infusion time points (4 h, 24 h, 7 days and 12-14 days). The moderating effects of several factors were assessed including: repeat/single infusion, diagnosis, open-label/participant-blind infusion, pre-post/placebo-controlled design and the sex of patients. RESULTS Effect sizes were significantly larger for repeat than single infusion at 4 h, 24 h and 7 days. For single infusion studies, effect sizes were large and significant at 4 h, 24 h and 7 days. The percentage of males was a predictor of antidepressant response at 7 days. Effect sizes for open-label and participant-blind infusions were not significantly different at any time point. CONCLUSIONS Single ketamine infusions elicit a significant antidepressant effect from 4 h to 7 days; the small number of studies at 12-14 days post infusion failed to reach significance. Results suggest a discrepancy in peak response time depending upon primary diagnosis - 24 h for MDD and 7 days for BD. The majority of published studies have used pre-post comparison; further placebo-controlled studies would help to clarify the effect of ketamine over time.
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Affiliation(s)
- Caoimhe M Coyle
- School of Life and Medical Sciences, University of Hertfordshire, Hatfield, UK
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10
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Freeman TP, Stone JM, Orgaz B, Noronha LA, Minchin SL, Curran HV. Tobacco smoking in schizophrenia: investigating the role of incentive salience. Psychol Med 2014; 44:2189-2197. [PMID: 24176189 DOI: 10.1017/s0033291713002705] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND Smoking is highly prevalent in people diagnosed with schizophrenia, but the reason for this co-morbidity is currently unclear. One possible explanation is that a common abnormality underpins the development of psychosis and independently enhances the incentive motivational properties of drugs and their associated cues. This study aimed to investigate whether incentive salience attribution towards smoking cues, as assessed by attentional bias, is heightened in schizophrenia and associated with delusions and hallucinations. METHOD Twenty-two smokers diagnosed with schizophrenia and 23 control smokers were assessed for smoking-related attentional bias using a modified Stroop task. Craving, nicotine dependence, smoking behaviour and positive and negative symptoms of schizophrenia were also recorded. RESULTS Both groups showed similar craving scores and smoking behaviour according to self-report and expired carbon monoxide (CO), although the patient group had higher nicotine dependence scores. Attentional bias, as evidenced by significant interference from smoking-related words on the modified Stroop task, was similar in both groups and correlated with CO levels. Attentional bias was positively related to severity of delusions but not hallucinations or other symptoms in the schizophrenia group. CONCLUSIONS This study supports the hypothesis that the development of delusions and the incentive motivational aspects of smoking may share a common biological substrate. These findings may offer some explanation for the elevated rates of smoking and other drug use in people with psychotic illness.
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Affiliation(s)
- T P Freeman
- Clinical Psychopharmacology Unit,University College London,UK
| | - J M Stone
- Department of Medicine, Division of Brain Sciences, Hammersmith Hospital,Imperial College London,UK
| | - B Orgaz
- Clinical Psychopharmacology Unit,University College London,UK
| | - L A Noronha
- Clinical Psychopharmacology Unit,University College London,UK
| | - S L Minchin
- Clinical Psychopharmacology Unit,University College London,UK
| | - H V Curran
- Clinical Psychopharmacology Unit,University College London,UK
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11
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Corlett PR, Cambridge V, Gardner JM, Piggot JS, Turner DC, Everitt JC, Arana FS, Morgan HL, Milton AL, Lee JL, Aitken MRF, Dickinson A, Everitt BJ, Absalom AR, Adapa R, Subramanian N, Taylor JR, Krystal JH, Fletcher PC. Ketamine effects on memory reconsolidation favor a learning model of delusions. PLoS One 2013; 8:e65088. [PMID: 23776445 PMCID: PMC3680467 DOI: 10.1371/journal.pone.0065088] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Accepted: 04/19/2013] [Indexed: 11/19/2022] Open
Abstract
Delusions are the persistent and often bizarre beliefs that characterise psychosis. Previous studies have suggested that their emergence may be explained by disturbances in prediction error-dependent learning. Here we set up complementary studies in order to examine whether such a disturbance also modulates memory reconsolidation and hence explains their remarkable persistence. First, we quantified individual brain responses to prediction error in a causal learning task in 18 human subjects (8 female). Next, a placebo-controlled within-subjects study of the impact of ketamine was set up on the same individuals. We determined the influence of this NMDA receptor antagonist (previously shown to induce aberrant prediction error signal and lead to transient alterations in perception and belief) on the evolution of a fear memory over a 72 hour period: they initially underwent Pavlovian fear conditioning; 24 hours later, during ketamine or placebo administration, the conditioned stimulus (CS) was presented once, without reinforcement; memory strength was then tested again 24 hours later. Re-presentation of the CS under ketamine led to a stronger subsequent memory than under placebo. Moreover, the degree of strengthening correlated with individual vulnerability to ketamine's psychotogenic effects and with prediction error brain signal. This finding was partially replicated in an independent sample with an appetitive learning procedure (in 8 human subjects, 4 female). These results suggest a link between altered prediction error, memory strength and psychosis. They point to a core disruption that may explain not only the emergence of delusional beliefs but also their persistence.
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Affiliation(s)
- Philip R Corlett
- Department of Psychiatry, Ribicoff Research Facility, Yale University, New Haven, Connecticut, United States of America.
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Adams RA, Stephan KE, Brown HR, Frith CD, Friston KJ. The computational anatomy of psychosis. Front Psychiatry 2013; 4:47. [PMID: 23750138 PMCID: PMC3667557 DOI: 10.3389/fpsyt.2013.00047] [Citation(s) in RCA: 443] [Impact Index Per Article: 40.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 05/16/2013] [Indexed: 11/13/2022] Open
Abstract
This paper considers psychotic symptoms in terms of false inferences or beliefs. It is based on the notion that the brain is an inference machine that actively constructs hypotheses to explain or predict its sensations. This perspective provides a normative (Bayes-optimal) account of action and perception that emphasizes probabilistic representations; in particular, the confidence or precision of beliefs about the world. We will consider hallucinosis, abnormal eye movements, sensory attenuation deficits, catatonia, and delusions as various expressions of the same core pathology: namely, an aberrant encoding of precision. From a cognitive perspective, this represents a pernicious failure of metacognition (beliefs about beliefs) that can confound perceptual inference. In the embodied setting of active (Bayesian) inference, it can lead to behaviors that are paradoxically more accurate than Bayes-optimal behavior. Crucially, this normative account is accompanied by a neuronally plausible process theory based upon hierarchical predictive coding. In predictive coding, precision is thought to be encoded by the post-synaptic gain of neurons reporting prediction error. This suggests that both pervasive trait abnormalities and florid failures of inference in the psychotic state can be linked to factors controlling post-synaptic gain - such as NMDA receptor function and (dopaminergic) neuromodulation. We illustrate these points using biologically plausible simulations of perceptual synthesis, smooth pursuit eye movements and attribution of agency - that all use the same predictive coding scheme and pathology: namely, a reduction in the precision of prior beliefs, relative to sensory evidence.
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Affiliation(s)
- Rick A Adams
- Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London , London , UK
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