Inter-areal causal interactions in the Gamma and Beta frequency bands define a functional hierarchy in the primate visual system J Vezoli1, A Bastos1, C Bosman2, J-M Schoffelen2, R Oostenveld2, P De Weerd2, H Kennedy3, P Fries4 |
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1Fries Lab, Ernst Strüngmann Institute, Germany |
| Cortico-cortical connectivity has been shown to be hierarchically organized such that bottom-up and top-down information are conveyed through the well-defined feedforward and feedback counter-streams, respectively. It remains however unclear what mechanisms the cortex might use to functionally segregate these different paths of information flow. In line with recent studies, showing that Gamma rhythms are predominantly found in the supragranular layers whereas Beta rhythms are strongest in the deep layers (Buffalo et al., 2011), we analyzed causal interactions in the Gamma and Beta frequency bands between seven visual areas of macaque monkeys performing a visuospatial attention task. LFP signals were recorded through electrocorticography and analyzed through spectrally resolved Granger causality. We show here that Gamma-band influences were predominant in the bottom-up direction, whereas Beta-band influences were predominant in the top-down direction. The functional asymmetry we identified was significantly correlated with anatomical data and was used to build a hierarchy model from functional data alone, which was highly similar to anatomical models of the primate visual system. These results open the possibility for the in vivo investigation of functional hierarchies in the healthy and diseased human brain. JV, AMB and CB contributed equally. JV was funded by the LOEWE-NeFF. |
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