Structural and Effective Pathways to the Amygdala involved in Spatial Frequency and Emotion Processing

This poster was presented at the Organization for Human Brain Mapping (OHBM) 2016 conference in Geneva, Switzerland. Abstract is below:<div><br></div><div><b>Authors:</b></div><div>Jessica McFadyen^4,1, Martial Mermillod²^,3, Veronika Halász⁴, Jason Mattingley⁴^,5, Marta Garrido⁴^,1</div><div><br></div><div><b>Institutions:</b></div><div>¹Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia, ²University Grenoble Alpes, Grenoble, France, ³Institut Universitaire de France, Paris, France, ⁴Queensland Brain Institute, The University of Queensland, Brisbane, Australia, ⁵School of Psychology, The University of Queensland, Brisbane, Australia</div><div><b><br></b></div><div><b>Introduction:</b></div><div>The amygdala has been heavily implicated in significance processing of potentially rewarding or threatening stimuli. However, the neural pathways through which this occurs are only just beginning to be understood. In particular, a rapid colliculo-pulvinar 'subcortical' route to the amygdala that bypasses the visual cortex has been proposed to facilitate coarse but rapid visual processing and subsequent emotional responses (Tamietto & de Gelder, 2010). There is considerable debate in the literature over the existence and possible functions of this pathway, where alternative cortical visual processing streams are suggested as being more likely (Pessoa & Adolphs, 2010).</div><div><br></div><div><b>Methods:</b></div><div>This experiment employed dynamic causal modelling (DCM) to test two competing hypotheses for the neural networks recruited during face perception: 1) the 'dual hypothesis', where a path from the pulvinar to the amygdala is engaged alongside cortical visual pathways, or 2) the 'cortical hypothesis', where visual information only arrives at the amygdala cortically. To investigate whether the 'coarseness' of visual processing was different along the subcortical and cortical routes, the spatial frequency (SF) content of the face images was manipulated to be either broad (all frequencies), low (<6 cycles/image), or high (>24 cycles/image). Twenty-six participants performed a gender discrimination task on neutral or fearful faces presented in each of the three spatial frequency conditions, while neural activity was recorded using magnetoencephalography (MEG).</div><div><br></div><div><b>Results:</b></div><div>Mass univariate sensor space analyses revealed overall greater activity for high than low SF from 150ms onwards. There was, however, a distinct temporal advantage for low SF, which produced the earliest effect at 145ms and whose waveform was found to be shifted significantly earlier (~5-15 ms) earlier than high SF across multiple distributed sensors. Fearful faces elicited greater activity over left temporal sensors at early (150ms) and late (370ms) timepoints, neither of which interacted with SF processing. Bayesian model comparison of the hypothesised dynamic causal models showed that models including the subcortical route best explained the underlying neural architecture of the data compared with those without. Interestingly, comparison of a series of functional models found that all connections within the network were likely modulated by SF and emotion <i>except</i> the subcortical route. Furthermore, simulations on this winning model revealed a distinct temporal advantage of the subcortical route, which perturbed amygdala activity at 70ms (~ 40ms earlier than other cortical pathways). </div><div><b><br></b></div><div><b>Conclusions:</b></div><div>This suggests that the subcortical pathway is indeed engaged during face perception and that it likely influences amygdala activity significantly earlier than input from the visual cortex, whether it is driven by signals from the LGN or the pulvinar itself. Our modelling results suggest that activity along the subcortical route may not, however, be modulated by spatial frequency. This suggests that the subcortical route may play more of a general role in rapid visual processing.