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      Repetition suppression: a means to index neural representations using BOLD?

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          Abstract

          Understanding how the human brain gives rise to complex cognitive processes remains one of the biggest challenges of contemporary neuroscience. While invasive recording in animal models can provide insight into neural processes that are conserved across species, our understanding of cognition more broadly relies upon investigation of the human brain itself. There is therefore an imperative to establish non-invasive tools that allow human brain activity to be measured at high spatial and temporal resolution. In recent years, various attempts have been made to refine the coarse signal available in functional magnetic resonance imaging (fMRI), providing a means to investigate neural activity at the meso-scale, i.e. at the level of neural populations. The most widely used techniques include repetition suppression and multivariate pattern analysis. Human neuroscience can now use these techniques to investigate how representations are encoded across neural populations and transformed by relevant computations. Here, we review the physiological basis, applications and limitations of fMRI repetition suppression with a brief comparison to multivariate techniques. By doing so, we show how fMRI repetition suppression holds promise as a tool to reveal complex neural mechanisms that underlie human cognitive function.

          This article is part of the themed issue ‘Interpreting BOLD: a dialogue between cognitive and cellular neuroscience’.

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          Most cited references116

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          Microstructure of a spatial map in the entorhinal cortex.

          The ability to find one's way depends on neural algorithms that integrate information about place, distance and direction, but the implementation of these operations in cortical microcircuits is poorly understood. Here we show that the dorsocaudal medial entorhinal cortex (dMEC) contains a directionally oriented, topographically organized neural map of the spatial environment. Its key unit is the 'grid cell', which is activated whenever the animal's position coincides with any vertex of a regular grid of equilateral triangles spanning the surface of the environment. Grids of neighbouring cells share a common orientation and spacing, but their vertex locations (their phases) differ. The spacing and size of individual fields increase from dorsal to ventral dMEC. The map is anchored to external landmarks, but persists in their absence, suggesting that grid cells may be part of a generalized, path-integration-based map of the spatial environment.
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            Repetition and the brain: neural models of stimulus-specific effects.

            One of the most robust experience-related cortical dynamics is reduced neural activity when stimuli are repeated. This reduction has been linked to performance improvements due to repetition and also used to probe functional characteristics of neural populations. However, the underlying neural mechanisms are as yet unknown. Here, we consider three models that have been proposed to account for repetition-related reductions in neural activity, and evaluate them in terms of their ability to account for the main properties of this phenomenon as measured with single-cell recordings and neuroimaging techniques. We also discuss future directions for distinguishing between these models, which will be important for understanding the neural consequences of repetition and for interpreting repetition-related effects in neuroimaging data.
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              A cortical representation of the local visual environment.

              Medial temporal brain regions such as the hippocampal formation and parahippocampal cortex have been generally implicated in navigation and visual memory. However, the specific function of each of these regions is not yet clear. Here we present evidence that a particular area within human parahippocampal cortex is involved in a critical component of navigation: perceiving the local visual environment. This region, which we name the 'parahippocampal place area' (PPA), responds selectively and automatically in functional magnetic resonance imaging (fMRI) to passively viewed scenes, but only weakly to single objects and not at all to faces. The critical factor for this activation appears to be the presence in the stimulus of information about the layout of local space. The response in the PPA to scenes with spatial layout but no discrete objects (empty rooms) is as strong as the response to complex meaningful scenes containing multiple objects (the same rooms furnished) and over twice as strong as the response to arrays of multiple objects without three-dimensional spatial context (the furniture from these rooms on a blank background). This response is reduced if the surfaces in the scene are rearranged so that they no longer define a coherent space. We propose that the PPA represents places by encoding the geometry of the local environment.
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                Author and article information

                Journal
                Philos Trans R Soc Lond B Biol Sci
                Philos. Trans. R. Soc. Lond., B, Biol. Sci
                RSTB
                royptb
                Philosophical Transactions of the Royal Society B: Biological Sciences
                The Royal Society
                0962-8436
                1471-2970
                5 October 2016
                5 October 2016
                : 371
                : 1705 , Theo Murphy meeting issue ‘Interpreting BOLD: a dialogue between cognitive and cellular neuroscience’ organized and edited by Anusha Mishra, Zebulun Kurth-Nelson, Catherine Hall and Clare Howarth
                : 20150355
                Affiliations
                [1 ]MRC Brain Network Dynamics Unit, Department of Pharmacology, University of Oxford , Mansfield Road, Oxford OX1 3TH, UK
                [2 ]Oxford Centre for Functional MRI of the Brain, Nuffield Department of Clinical Neurosciences, University of Oxford , John Radcliffe Hospital, Oxford OX3 9DU, UK
                [3 ]Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London , London WC1N 3BG, UK
                Author notes
                [†]

                These authors contributed equally to this study.

                One contribution of 15 to a Theo Murphy meeting issue ‘ Interpreting BOLD: a dialogue between cognitive and cellular neuroscience’.

                Author information
                http://orcid.org/0000-0002-4575-6472
                http://orcid.org/0000-0002-8678-5536
                Article
                rstb20150355
                10.1098/rstb.2015.0355
                5003856
                27574308
                f883d0de-746f-460d-9aaf-cf62346b5cb1
                © 2016 The Authors.

                Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

                History
                : 8 June 2016
                Funding
                Funded by: Wellcome Trust, http://dx.doi.org/10.13039/100004440;
                Award ID: 091593/Z/10/Z
                Award ID: 104765/Z/14/Z
                Funded by: James McDonnell Foundation;
                Award ID: JSMF220020372
                Categories
                1001
                133
                Articles
                Review Article
                Custom metadata
                October 5, 2016

                Philosophy of science
                repetition suppression,functional magnetic resonance imaging adaptation,neural representation,neural computation

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