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      Investigating the Subcortical Route to the Amygdala Across Species and in Disordered Fear Responses

      Journal of Experimental Neuroscience

      SAGE Publications

      Amygdala, pulvinar, superior colliculus, fear, connectivity

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          Abstract

          Over the past few decades, evidence has come to light that there is a rapid subcortical shortcut that transmits visual information to the amygdala, effectively bypassing the visual cortex. This pathway purportedly runs from the superior colliculus to the amygdala via the pulvinar, and thus presents a methodological challenge to study noninvasively in the human brain. Here, we present our recent work where we reliably reconstructed the white matter structure and directional flow of neural signal along this pathway in over 600 healthy young adults. Critically, we found structure-function relationships for the pulvinar-amygdala connection, where people with greater fibre density had stronger functional neural coupling and were also better at recognising fearful facial expressions. These results tie together recent anatomical evidence from other visual primates with very recent optogenetic research on rodents demonstrating a functional role of this pathway in producing fear responses. Here, we discuss how this pathway might operate alongside other thalamo-cortical circuits (such as pulvinar to middle temporal area) and how its structure and function may change according to the sensory input it receives. This newly established circuit might play a potentially important role in autism and/or anxiety disorders.

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          Most cited references 26

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          Dynamic causal modelling.

          In this paper we present an approach to the identification of nonlinear input-state-output systems. By using a bilinear approximation to the dynamics of interactions among states, the parameters of the implicit causal model reduce to three sets. These comprise (1) parameters that mediate the influence of extrinsic inputs on the states, (2) parameters that mediate intrinsic coupling among the states, and (3) [bilinear] parameters that allow the inputs to modulate that coupling. Identification proceeds in a Bayesian framework given known, deterministic inputs and the observed responses of the system. We developed this approach for the analysis of effective connectivity using experimentally designed inputs and fMRI responses. In this context, the coupling parameters correspond to effective connectivity and the bilinear parameters reflect the changes in connectivity induced by inputs. The ensuing framework allows one to characterise fMRI experiments, conceptually, as an experimental manipulation of integration among brain regions (by contextual or trial-free inputs, like time or attentional set) that is revealed using evoked responses (to perturbations or trial-bound inputs, like stimuli). As with previous analyses of effective connectivity, the focus is on experimentally induced changes in coupling (cf., psychophysiologic interactions). However, unlike previous approaches in neuroimaging, the causal model ascribes responses to designed deterministic inputs, as opposed to treating inputs as unknown and stochastic.
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            Neural bases of the non-conscious perception of emotional signals.

            Many emotional stimuli are processed without being consciously perceived. Recent evidence indicates that subcortical structures have a substantial role in this processing. These structures are part of a phylogenetically ancient pathway that has specific functional properties and that interacts with cortical processes. There is now increasing evidence that non-consciously perceived emotional stimuli induce distinct neurophysiological changes and influence behaviour towards the consciously perceived world. Understanding the neural bases of the non-conscious perception of emotional signals will clarify the phylogenetic continuity of emotion systems across species and the integration of cortical and subcortical activity in the human brain.
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              Visual capacity in the hemianopic field following a restricted occipital ablation.

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                Author and article information

                Journal
                J Exp Neurosci
                J Exp Neurosci
                EXN
                spexn
                Journal of Experimental Neuroscience
                SAGE Publications (Sage UK: London, England )
                1179-0695
                01 May 2019
                2019
                : 13
                Affiliations
                Queensland Brain Institute, University of Queensland, Brisbane, QLD, Australia
                Author notes
                Jessica McFadyen, Queensland Brain Institute, University of Queensland, Brisbane, QLD 4072 Australia. Email: j.mcfadyen@ 123456uq.edu.au
                Article
                10.1177_1179069519846445
                10.1177/1179069519846445
                6495431
                © The Author(s) 2019

                This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License ( http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages ( https://us.sagepub.com/en-us/nam/open-access-at-sage).

                Funding
                Funded by: Australian Research Council, FundRef https://doi.org/10.13039/501100000923;
                Award ID: CE140100007
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                January-December 2019

                connectivity, fear, superior colliculus, pulvinar, amygdala

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