Neural Field Theory of the Alpha-Band Rhythms

This presentation offers a didactic account of a neural field theory (NFT) approach, developed progressively and systematically for more than 20 years, to studying whole-cortex activity patterns driven by the rhythmogenic circuitry of the corticothalamic (CT) system. It has been known since Berger that the ~10Hz alpha rhythm is the most prominent type of brain activity visible in human electroencephalography (EEG) and related recording modalities. Concentrated primarily over visual cortex, alpha sometimes displays a split peak; suppressed by visual inputs; and is often accompanied by a beta rhythm occurring at its harmonic. Later, the ~10 Hz mu and tau rhythms were found, respectively concentrated over motor and auditory cortex, and suppressed by corresponding sensory input. Early theories argued that separate groups of neurons fire at ~10 Hz at the relevant locations, but these lacked explanatory power. More recently, the alpha rhythm was argued to be a natural mode of activity in the cortex (Nunez) or corticothalamic system (Robinson), and analyzed using NFT. Our most recent work on this shows that just 4 corticothalamic activity eigenmodes are sufficient to explain the key features of alpha, mu, and tau rhythms - namely their frequency, structure, and topography. CT loops account for the basic 10 Hz frequency and alpha-beta correlations, with splitting arising from breaking of degeneracy due to cortical folding. We have observed split-beta and predict split-mu, split-tau, and harmonic tau rhythms to occur, plus split harmonic mu and tau. One of the key recent advances in this NFT variant is the idea that spatial peaks (e.g. the posterior concentration of alpha power) in the EEG appear due to constructive interference of modes in the relevant sensory region, which is which is suppressed (blocked) when CT gains are reduced by bottom-up sensory input and attention.