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Castegnetti G, Zurita M, De Martino B. How usefulness shapes neural representations during goal-directed behavior. Sci Adv 2021; 7:7/15/eabd5363. [PMID: 33827810 PMCID: PMC8026134 DOI: 10.1126/sciadv.abd5363] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 02/18/2021] [Indexed: 05/13/2023]
Abstract
Value is often associated with reward, emphasizing its hedonic aspects. However, when circumstances change, value must also change (a compass outvalues gold, if you are lost). How are value representations in the brain reshaped under different behavioral goals? To answer this question, we devised a new task that decouples usefulness from its hedonic attributes, allowing us to study flexible goal-dependent mapping. Here, we show that, unlike sensory cortices, regions in the prefrontal cortex (PFC)-usually associated with value computation-remap their representation of perceptually identical items according to how useful the item has been to achieve a specific goal. Furthermore, we identify a coding scheme in the PFC that represents value regardless of the goal, thus supporting generalization across contexts. Our work questions the dominant view that equates value with reward, showing how a change in goals triggers a reorganization of the neural representation of value, enabling flexible behavior.
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Affiliation(s)
- G Castegnetti
- Institute of Cognitive Neuroscience, University College London, London, UK.
| | - M Zurita
- Institute of Cognitive Neuroscience, University College London, London, UK
| | - B De Martino
- Institute of Cognitive Neuroscience, University College London, London, UK.
- Wellcome Centre for Human Neuroimaging, University College London, London, UK
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2
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Castegnetti G, Bush D, Bach DR. Model of theta frequency perturbations and contextual fear memory. Hippocampus 2021; 31:448-457. [PMID: 33534196 PMCID: PMC8049035 DOI: 10.1002/hipo.23307] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Revised: 12/07/2020] [Accepted: 01/09/2021] [Indexed: 12/11/2022]
Abstract
Theta oscillations in the hippocampal local field potential (LFP) appear during translational movement and arousal, modulate the activity of principal cells, and are associated with spatial cognition and episodic memory function. All known anxiolytics slightly but consistently reduce hippocampal theta frequency. However, whether this electrophysiological effect is mechanistically related to the decreased behavioral expression of anxiety is currently unclear. Here, we propose that a reduction in theta frequency affects synaptic plasticity and mnemonic function and that this can explain the reduction in anxiety behavior. We test this hypothesis in a biophysical model of contextual fear conditioning. First, we confirm that our model reproduces previous empirical results regarding the dependence of synaptic plasticity on presynaptic firing rate. Next, we investigate how theta frequency during contextual conditioning impacts learning. These simulations demonstrate that learned associations between threat and context are attenuated when learning takes place under reduced theta frequency. Additionally, our simulations demonstrate that learned associations result in increased theta activity in the amygdala, consistent with empirical data. In summary, we propose a mechanism that can account for the behavioral effect of anxiolytics by impairing the integration of threat attributes of an environment into the cognitive map due to reduced synaptic potentiation.
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Affiliation(s)
- Giuseppe Castegnetti
- Computational Psychiatry Research, Department of Psychiatry, Psychotherapy, and PsychosomaticsUniversity of ZurichZurichSwitzerland
- Institute of Cognitive NeuroscienceUniversity College LondonLondonUK
| | - Daniel Bush
- Institute of Cognitive NeuroscienceUniversity College LondonLondonUK
- Queen Square Institute of NeurologyUniversity College LondonLondonUK
| | - Dominik R. Bach
- Computational Psychiatry Research, Department of Psychiatry, Psychotherapy, and PsychosomaticsUniversity of ZurichZurichSwitzerland
- Wellcome Centre for Human Neuroimaging and Max Planck/UCL Centre for Computational Psychiatry and Ageing ResearchUniversity College LondonLondonUK
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3
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Castegnetti G, Tzovara A, Khemka S, Melinščak F, Barnes GR, Dolan RJ, Bach DR. Representation of probabilistic outcomes during risky decision-making. Nat Commun 2020; 11:2419. [PMID: 32415145 PMCID: PMC7229012 DOI: 10.1038/s41467-020-16202-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 04/21/2020] [Indexed: 12/19/2022] Open
Abstract
Goal-directed behaviour requires prospectively retrieving and evaluating multiple possible action outcomes. While a plethora of studies suggested sequential retrieval for deterministic choice outcomes, it remains unclear whether this is also the case when integrating multiple probabilistic outcomes of the same action. We address this question by capitalising on magnetoencephalography (MEG) in humans who made choices in a risky foraging task. We train classifiers to distinguish MEG field patterns during presentation of two probabilistic outcomes (reward, loss), and then apply these to decode such patterns during deliberation. First, decoded outcome representations have a temporal structure, suggesting alternating retrieval of the outcomes. Moreover, the probability that one or the other outcome is being represented depends on loss magnitude, but not on loss probability, and it predicts the chosen action. In summary, we demonstrate decodable outcome representations during probabilistic decision-making, which are sequentially structured, depend on task features, and predict subsequent action.
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Affiliation(s)
- Giuseppe Castegnetti
- Computational Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.
- Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland.
- Institute of Cognitive Neuroscience, University College London, London, UK.
| | - Athina Tzovara
- Computational Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland
- Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
- Department of Computer Science & Faculty of Medicine, University of Bern, Bern, Switzerland
- Helen Wills Neuroscience Institute, University of California, Berkeley, USA
- Wellcome Centre for Human Neuroimaging, University College London, London, UK
| | - Saurabh Khemka
- Computational Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland
- Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Filip Melinščak
- Computational Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland
- Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Gareth R Barnes
- Wellcome Centre for Human Neuroimaging, University College London, London, UK
| | - Raymond J Dolan
- Wellcome Centre for Human Neuroimaging, University College London, London, UK
- Max Planck UCL Centre for Computational Psychiatry and Ageing, University College London, London, UK
| | - Dominik R Bach
- Computational Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland
- Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
- Wellcome Centre for Human Neuroimaging, University College London, London, UK
- Max Planck UCL Centre for Computational Psychiatry and Ageing, University College London, London, UK
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Bach DR, Castegnetti G, Korn CW, Gerster S, Melinscak F, Moser T. Psychophysiological modeling: Current state and future directions. Psychophysiology 2018; 55:e13214. [DOI: 10.1111/psyp.13209] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2018] [Revised: 05/08/2018] [Accepted: 05/16/2018] [Indexed: 12/14/2022]
Affiliation(s)
- Dominik R. Bach
- Clinical Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, Psychiatric HospitalUniversity of Zurich Zurich Switzerland
- Neuroscience Center ZurichUniversity of Zurich Zurich Switzerland
- Wellcome Trust Centre for Neuroimaging and Max Planck/UCL Centre for Computational Psychiatry and Ageing ResearchUniversity College London London United Kingdom
| | - Giuseppe Castegnetti
- Clinical Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, Psychiatric HospitalUniversity of Zurich Zurich Switzerland
- Neuroscience Center ZurichUniversity of Zurich Zurich Switzerland
| | - Christoph W. Korn
- Clinical Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, Psychiatric HospitalUniversity of Zurich Zurich Switzerland
- Neuroscience Center ZurichUniversity of Zurich Zurich Switzerland
- Institute for Systems NeuroscienceUniversity Medical Center Hamburg‐Eppendorf Hamburg Germany
| | - Samuel Gerster
- Clinical Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, Psychiatric HospitalUniversity of Zurich Zurich Switzerland
- Neuroscience Center ZurichUniversity of Zurich Zurich Switzerland
| | - Filip Melinscak
- Clinical Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, Psychiatric HospitalUniversity of Zurich Zurich Switzerland
- Neuroscience Center ZurichUniversity of Zurich Zurich Switzerland
| | - Tobias Moser
- Clinical Psychiatry Research, Department of Psychiatry, Psychotherapy, and Psychosomatics, Psychiatric HospitalUniversity of Zurich Zurich Switzerland
- Neuroscience Center ZurichUniversity of Zurich Zurich Switzerland
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Abstract
During fear conditioning, pupil size responses dissociate between conditioned stimuli that are contingently paired (CS+) with an aversive unconditioned stimulus, and those that are unpaired (CS-). Current approaches to assess fear learning from pupil responses rely on ad hoc specifications. Here, we sought to develop a psychophysiological model (PsPM) in which pupil responses are characterized by response functions within the framework of a linear time-invariant system. This PsPM can be written as a general linear model, which is inverted to yield amplitude estimates of the eliciting process in the central nervous system. We first characterized fear-conditioned pupil size responses based on an experiment with auditory CS. PsPM-based parameter estimates distinguished CS+/CS- better than, or on par with, two commonly used methods (peak scoring, area under the curve). We validated this PsPM in four independent experiments with auditory, visual, and somatosensory CS, as well as short (3.5 s) and medium (6 s) CS/US intervals. Overall, the new PsPM provided equal or decisively better differentiation of CS+/CS- than the two alternative methods and was never decisively worse. We further compared pupil responses with concurrently measured skin conductance and heart period responses. Finally, we used our previously developed luminance-related pupil responses to infer the timing of the likely neural input into the pupillary system. Overall, we establish a new PsPM to assess fear conditioning based on pupil responses. The model has a potential to provide higher statistical sensitivity, can be applied to other conditioning paradigms in humans, and may be easily extended to nonhuman mammals.
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Affiliation(s)
- Christoph W. Korn
- Department of Psychiatry, Psychotherapy, and PsychosomaticsUniversity of ZurichZurichSwitzerland
- Neuroscience Center ZurichUniversity of ZurichZurichSwitzerland
| | - Matthias Staib
- Department of Psychiatry, Psychotherapy, and PsychosomaticsUniversity of ZurichZurichSwitzerland
- Neuroscience Center ZurichUniversity of ZurichZurichSwitzerland
| | - Athina Tzovara
- Department of Psychiatry, Psychotherapy, and PsychosomaticsUniversity of ZurichZurichSwitzerland
- Neuroscience Center ZurichUniversity of ZurichZurichSwitzerland
- Wellcome Trust Centre for NeuroimagingUniversity College LondonLondonUK
| | - Giuseppe Castegnetti
- Department of Psychiatry, Psychotherapy, and PsychosomaticsUniversity of ZurichZurichSwitzerland
- Neuroscience Center ZurichUniversity of ZurichZurichSwitzerland
| | - Dominik R. Bach
- Department of Psychiatry, Psychotherapy, and PsychosomaticsUniversity of ZurichZurichSwitzerland
- Neuroscience Center ZurichUniversity of ZurichZurichSwitzerland
- Wellcome Trust Centre for NeuroimagingUniversity College LondonLondonUK
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Castegnetti G, Tzovara A, Staib M, Gerster S, Bach DR. Assessing fear learning via conditioned respiratory amplitude responses. Psychophysiology 2016; 54:215-223. [PMID: 27933608 PMCID: PMC6001548 DOI: 10.1111/psyp.12778] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Accepted: 09/26/2016] [Indexed: 11/27/2022]
Abstract
Respiratory physiology is influenced by cognitive processes. It has been suggested that some cognitive states may be inferred from respiration amplitude responses (RAR) after external events. Here, we investigate whether RAR allow assessment of fear memory in cued fear conditioning, an experimental model of aversive learning. To this end, we built on a previously developed psychophysiological model (PsPM) of RAR, which regards interpolated RAR time series as the output of a linear time invariant system. We first establish that average RAR after CS+ and CS− are different. We then develop the response function of fear‐conditioned RAR, to be used in our PsPM. This PsPM is inverted to yield estimates of cognitive input into the respiratory system. We analyze five validation experiments involving fear acquisition and retention, delay and trace conditioning, short and medium CS‐US intervals, and data acquired with bellows and MRI‐compatible pressure chest belts. In all experiments, CS+ and CS− are distinguished by their estimated cognitive inputs, and the sensitivity of this distinction is higher for model‐based estimates than for peak scoring of RAR. Comparing these data with skin conductance responses (SCR) and heart period responses (HPR), we find that, on average, RAR performs similar to SCR in distinguishing CS+ and CS−, but is less sensitive than HPR. Overall, our work provides a novel and robust tool to investigate fear memory in humans that may allow wide and straightforward application to diverse experimental contexts.
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Affiliation(s)
- Giuseppe Castegnetti
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Athina Tzovara
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland.,Wellcome Trust Centre for Neuroimaging, University College London, London, UK
| | - Matthias Staib
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Samuel Gerster
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Dominik R Bach
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland.,Wellcome Trust Centre for Neuroimaging, University College London, London, UK
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Bach DR, Gerster S, Tzovara A, Castegnetti G. A linear model for event-related respiration responses. J Neurosci Methods 2016; 270:147-155. [PMID: 27268156 PMCID: PMC4994768 DOI: 10.1016/j.jneumeth.2016.06.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Revised: 05/09/2016] [Accepted: 06/02/2016] [Indexed: 10/27/2022]
Abstract
BACKGROUND Cognitive processes influence respiratory physiology. This may allow inferring cognitive states from measured respiration. Here, we take a first step towards this goal and investigate whether event-related respiratory responses can be identified, and whether they are accessible to a model-based approach. NEW METHOD We regard respiratory responses as the output of a linear time invariant system that receives brief inputs after psychological events. We derive average responses to visual targets, aversive stimulation, and viewing of arousing pictures, in interpolated respiration period (RP), respiration amplitude (RA), and respiratory flow rate (RFR). We then base a Psychophysiological Model (PsPM) on these averaged event-related responses. The PsPM is inverted to yield estimates of cognitive input into the respiratory system. This method is validated in an independent data set. RESULTS All three measures show event-related responses, which are captured as non-zero response amplitudes in the PsPM. Amplitude estimates for RA and RFR distinguish between picture viewing and the other tasks. This pattern is replicated in the validation experiment. COMPARISON WITH EXISTING METHODS Existing respiratory measures are based on relatively short time-intervals after an event while the new method is based on the entire duration of respiratory responses. CONCLUSION Our findings suggest that interpolated respiratory measures show replicable event-related response patterns. PsPM inversion is a suitable approach to analysing these patterns, with a potential to infer cognitive processes from respiration.
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Affiliation(s)
- Dominik R Bach
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Switzerland; Neuroscience Center Zurich, University of Zurich, Switzerland; Wellcome Trust Centre for Neuroimaging, University College London, United Kingdom.
| | - Samuel Gerster
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Switzerland; Neuroscience Center Zurich, University of Zurich, Switzerland
| | - Athina Tzovara
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Switzerland; Neuroscience Center Zurich, University of Zurich, Switzerland
| | - Giuseppe Castegnetti
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Switzerland; Neuroscience Center Zurich, University of Zurich, Switzerland
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Castegnetti G, Tzovara A, Staib M, Paulus PC, Hofer N, Bach DR. Modeling fear-conditioned bradycardia in humans. Psychophysiology 2016; 53:930-9. [PMID: 26950648 PMCID: PMC4869680 DOI: 10.1111/psyp.12637] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 02/04/2016] [Indexed: 11/29/2022]
Abstract
Across species, cued fear conditioning is a common experimental paradigm to investigate aversive Pavlovian learning. While fear‐conditioned stimuli (CS+) elicit overt behavior in many mammals, this is not the case in humans. Typically, autonomic nervous system activity is used to quantify fear memory in humans, measured by skin conductance responses (SCR). Here, we investigate whether heart period responses (HPR) evoked by the CS, often observed in humans and small mammals, are suitable to complement SCR as an index of fear memory in humans. We analyze four datasets involving delay and trace conditioning, in which heart beats are identified via electrocardiogram or pulse oximetry, to show that fear‐conditioned heart rate deceleration (bradycardia) is elicited and robustly distinguishes CS+ from CS−. We then develop a psychophysiological model (PsPM) of fear‐conditioned HPR. This PsPM is inverted to yield estimates of autonomic input into the heart. We show that the sensitivity to distinguish CS+ and CS− (predictive validity) is higher for model‐based estimates than peak‐scoring analysis, and compare this with SCR. Our work provides a novel tool to investigate fear memory in humans that allows direct comparison between species.
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Affiliation(s)
- Giuseppe Castegnetti
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Athina Tzovara
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Matthias Staib
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Philipp C Paulus
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland.,Department of Psychology, Dresden University of Technology, Dresden, Germany
| | - Nicolas Hofer
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland
| | - Dominik R Bach
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Centre Zurich, University of Zurich, Zurich, Switzerland.,Wellcome Trust Centre for Neuroimaging, University College London, London, UK
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Abstract
Cardiac rhythm is generated locally in the sinoatrial node, but modulated by central neural input. This may provide a possibility to infer central processes from observed phasic heart period responses (HPR). Currently, operational methods are used for HPR analysis. These methods embody implicit assumptions on how central states influence heart period. Here, we build an explicit psychophysiological model (PsPM) for event‐related HPR. This phenomenological PsPM is based on three experiments involving white noise sounds, an auditory oddball task, and emotional picture viewing. The model is optimized with respect to predictive validity—the ability to separate experimental conditions from each other. To validate the PsPM, an independent sample of participants is presented with auditory stimuli of varying intensity and emotional pictures of negative and positive valence, at short intertrial intervals. Our model discriminates these experimental conditions from each other better than operational approaches. We conclude that our PsPM is more sensitive to distinguish experimental manipulations based on heart period data than operational methods, and furnishes a principled approach to analysis of HPR.
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Affiliation(s)
- Philipp C Paulus
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Center Zurich, University of Zurich, Zurich, Switzerland.,Department of Psychology, Technische Universität Dresden, Dresden, Germany
| | - Giuseppe Castegnetti
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Center Zurich, University of Zurich, Zurich, Switzerland
| | - Dominik R Bach
- Department of Psychiatry, Psychotherapy, and Psychosomatics, University of Zurich, Zurich, Switzerland.,Neuroscience Center Zurich, University of Zurich, Zurich, Switzerland.,Wellcome Trust Centre for Neuroimaging, University College London, London, UK
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Eriksson J, Castegnetti G, Conroy S, Ericsson G, Giacomelli L, Hellesen C. Deuterium density profile determination at JET using a neutron camera and a neutron spectrometer. Rev Sci Instrum 2014; 85:11E106. [PMID: 25430285 DOI: 10.1063/1.4889907] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
In this work we estimate the fuel ion density profile in deuterium plasmas at JET, using the JET neutron camera, the neutron time-of-flight spectrometer TOFOR, and fusion reactivities modeled by the transport code TRANSP. The framework has been tested using synthetic data, which showed that the density profile could be reconstructed with an average accuracy of the order of 10 %. The method has also been applied to neutron measurements from a neutral beam heated JET discharge, which gave nd/ne ≈ 0.6 ± 0.3 in the plasma core and nd/ne ≈ 0.4 ± 0.3 towards the edge. Correction factors for detector efficiencies, neutron attenuation, and back-scattering are not yet included in the analysis; future work will aim at refining the estimated density.
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Affiliation(s)
- J Eriksson
- EURATOM-VR, Department of Physics and Astronomy, Uppsala University, Sweden
| | - G Castegnetti
- EURATOM-VR, Department of Physics and Astronomy, Uppsala University, Sweden
| | - S Conroy
- EURATOM-VR, Department of Physics and Astronomy, Uppsala University, Sweden
| | - G Ericsson
- EURATOM-VR, Department of Physics and Astronomy, Uppsala University, Sweden
| | - L Giacomelli
- Department of Physics, Università degli Studi di Milano-Bicocca, Milano, Italy
| | - C Hellesen
- EURATOM-VR, Department of Physics and Astronomy, Uppsala University, Sweden
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