Article

Evoked brain responses are generated by feedback loops

Wellcome Trust Centre for Neuroimaging, University College London, London WC1N 3BG, United Kingdom.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 01/2008; 104(52):20961-6. DOI: 10.1073/pnas.0706274105
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ABSTRACT Neuronal responses to stimuli, measured electrophysiologically, unfold over several hundred milliseconds. Typically, they show characteristic waveforms with early and late components. It is thought that early or exogenous components reflect a perturbation of neuronal dynamics by sensory input bottom-up processing. Conversely, later, endogenous components have been ascribed to recurrent dynamics among hierarchically disposed cortical processing levels, top-down effects. Here, we show that evoked brain responses are generated by recurrent dynamics in cortical networks, and late components of event-related responses are mediated by backward connections. This evidence is furnished by dynamic causal modeling of mismatch responses, elicited in an oddball paradigm. We used the evidence for models with and without backward connections to assess their likelihood as a function of peristimulus time and show that backward connections are necessary to explain late components. Furthermore, we were able to quantify the contribution of backward connections to evoked responses and to source activity, again as a function of peristimulus time. These results link a generic feature of brain responses to changes in the sensorium and a key architectural component of functional anatomy; namely, backward connections are necessary for recurrent interactions among levels of cortical hierarchies. This is the theoretical cornerstone of most modern theories of perceptual inference and learning.

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Available from: Marta I Garrido, Aug 22, 2015
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    • "Following the initial paper by Garrido et al. (2007a, 2007b), and confirmed by our identified localised sources (Youssofzadeh et al., 2013), we constructed a DCM network of five interconnected units (sources) consisting of right/left primary auditory cortex (r/lA1), right/left superior temporal gyrus (r/lSTG), and right inferior frontal gyrus (rIFG). Informed by the Montreal Neurological Institute (MNI) coordinates, the sources were set to be modelled using equivalent current dipoles (Kiebel et al., 2008a). "
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    • "where the term k ij = 1 for area-to-area feedforward connections of W ee and k ij = À1 for feedback connections. This was implemented due to evidence showing that feedback activity contributes to responses that have a polarity opposite to that of the N1m (Garrido et al., 2007). "
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