The alpha rhythm is the longest-studied brain oscillation and has been theorized to play a key role in cognition. Still, its physiology is poorly understood. In this study, we used microelectrodes and macroelectrodes in surgical epilepsy patients to measure the intracortical and thalamic generators of the alpha rhythm during quiet wakefulness. We first found that alpha in both visual and somatosensory cortex propagates from higher-order to lower-order areas. In posterior cortex, alpha propagates from higher-order anterosuperior areas toward the occipital pole, whereas alpha in somatosensory cortex propagates from associative regions toward primary cortex. Several analyses suggest that this cortical alpha leads pulvinar alpha, complicating prevailing theories of a thalamic pacemaker. Finally, alpha is dominated by currents and firing in supragranular cortical layers. Together, these results suggest that the alpha rhythm likely reflects short-range supragranular feedback, which propagates from higher- to lower-order cortex and cortex to thalamus. These physiological insights suggest how alpha could mediate feedback throughout the thalamocortical system.

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The alpha rhythm is the longest studied brain oscillation and has been theorized to 28 play a key role in cognition. Still, its physiology is poorly understood. In this study, we used 29 micro and macro electrodes in surgical epilepsy patients to measure the intracortical and 30 thalamic generators of the alpha rhythm during quiet wakefulness. We first found that alpha in 31 posterior cortex propagates from higher-order anterosuperior areas towards the occipital pole, 32 consistent with alpha effecting top-down processing. This cortical alpha leads pulvinar alpha, 33 complicating prevailing theories of a thalamic pacemaker. Finally, alpha is dominated by 34 currents and firing in supragranular cortical layers. Together, these results suggest that the alpha 35 2 rhythm likely reflects short-range supragranular feedback which propagates from higher to 36 lower-order cortex and cortex to thalamus. These physiological insights suggest how alpha could 37 mediate feedback throughout the thalamocortical system. 38Main Text: Alpha oscillations (7-13 Hz) 1 are the most salient EEG event during wakefulness 39 and may be fundamental for top-down cognitive processes 2,3 such as attention 4 , perception 5,6 , 40 functional inhibition 7 and working memory 8 . However, the underlying neural structure(s) and 41 circuits which generate alpha are intensely controversial. Studies have pointed to the thalamus as 42 the primary alpha pacemaker, with the classic posterior alpha rhythm driven by the pulvinar 43 and/or lateral geniculate nucleus (LGN) 4,[9][10][11] . Within the cortex, it's widely assumed that alpha 44 originates from infragranular layers driven by layer V pyramidal cells [12][13][14][15][16] . Despite the 45 prevalence of these hypotheses, the studies used to support them are not definitive; previous 46 electrophysiological literature have either used a distant reference susceptible to volume 47 conduction 4,12,14 , were performed in vitro 13 or relied on extracranial recordings 17 (see 48 Discussion). Crucially, none of these hypotheses have been directly tested via invasive 49 recordings in humans. We therefore analyzed focal micro and macro electrode recordings from 50 human neocortex and thalamus in surgical epilepsy patients to characterize alpha's generation 51 during quiet wakefulness.52 53 3We analyzed electrocorticography (ECoG) recordings of spontaneous alpha oscillations 54 (4.54±.87 minutes, mean ± standard deviation) in the occipital, posterior temporal, and parietal 55 cortices of 5 patients (3 of whom performed an eye closure task) ( Supplementary Fig. 1, 56 Supplementary Table 1) (ECoG Patients E1-5). Strikingly, alpha oscillations propagated as 57travelling waves from anterosuperior cortex towards posteroinferior areas ( Fig. 1-2, 58 Supplementary Fig. 4) 18 . To quantify this propagation, we used a two-pass third-order zero-59 phase shift Butterworth Filter between 7-13 Hz to extract alpha-band activity. The Hilbert 60Transform was then applied to find both the amplitude and phase of ongoing alpha...

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The problem of a polymer molecule whose two ends reside on opposite sides of a membrane or partition separating two solutions is solved exactly in the limit of no self-excluded volume. The monomers can go from one side of the membrane to the other only by threading serially through one hole in the membrane. The ends can be free, confined to run freely on the membrane surfaces, or be fixed to specific points on the membrane. It is found that the equilibrium thermodynamic phase transition is first order in all cases so that slight changes in pH, ionic strength, or temperature can move the polymer from being completely on one side of the membrane to being completely on the other side. Application to two biological problems are suggested: (1) the breaching of cell walls by the nuclear material of T2 bacteriophages, and (2) the transport of drugs that are affixed to these translocating polymers. The relation of this newly discovered transition to four other phase transitions that occur in isolated macromolecules (helix–random coil; equilibrium polymerization; polymer collapse; surface adsorption) is briefly discussed.