Coherence influences the dimensionality of communication subspaces

The brain relies on communication between specialized cortical areas to accomplish complex cognitive tasks. To understand this ability of the brain, we need a deeper understanding of information transfer across cortical areas. There are two leading hypotheses for communication between cortical areas: 1) The communication through coherence (CTC) hypothesis posits that coherent oscillations between source and target populations of neurons are required for information propagation. 2) The information transmission via communication subspace (CS) hypothesis, recently introduced by Semedo et al., advances the idea that low-dimensional subspaces of population activity are responsible for communication across cortical areas. There is a clear divide between these two mechanisms and the CTC hypothesis, in particular, has been surrounded by considerable skepticism, with many authors reducing oscillations in the cortex to an epiphenomenon (viz., a by-product with no functional role).
Here, we reconcile these two mechanisms of communication through a spectral decomposition of communication subspaces. In our main result, we predict that coherence influences the dimensionality of the CS: Dimensionality is lowest, and the prediction performance is highest, at frequencies that exhibit a peak in coherence between a source and target population (e.g., V1 to V2). We arrive at these results by developing an analytical theory of communication for circuits described by stochastic dynamical systems exhibiting fixed-point solutions. We compute directly (i.e., by a simulation-free method) the predictive performance for the mean-subtracted activity of a target population from that of a source population, and show that our predictions are in agreement with the experimental results by Semedo et al. Then via a band-pass filtered version of the covariance matrix, we arrive at our main result. Hence, our theory makes experimentally-testable predictions of how oscillations influence interareal communication while advancing a new hypothesis for the functional role of oscillatory activity in the brain.