Origins of 1/f-like tissue oxygenation fluctuations in the murine cortex

Abstract

The concentration of oxygen in the brain spontaneously fluctuates, and the power distribution in these fluctuations has 1/f-like dynamics. Though these oscillations have been interpreted as being driven by neural activity, the origins of these 1/f-like oscillations is not well understood. Here, to gain insight of the origin of the 1/f-like oxygen fluctuations, we investigated the dynamics of tissue oxygenation and neural activity in awake behaving mice. We found that oxygen signal recorded from the cortex of mice had 1/f-like spectra. However, band-limited power in the local field potential, did not show corresponding 1/f-like fluctuations. When local neural activity was suppressed, the 1/f-like fluctuations in oxygen concentration persisted. Two-photon measurements of erythrocyte spacing fluctuations (‘stalls’) and mathematical modelling show that stochastic fluctuations in erythrocyte flow and stalling could underlie 1/f-like dynamics in oxygenation. These results show discrete nature of erythrocytes and their irregular flow, rather than neural activity, could drive 1/f-like fluctuations in tissue oxygenation.

High Throughput Detection of Capillary Stalling Events with Bessel Beam Two-Photon Microscopy

“…The increase in short stalls we found in our aged mice would be consistent with the increased spatial capillary speed heterogeneity found in older mice, where pockets of hypoxic tissue were also found more frequently 33 . On the other hand, while brief stalls are likely driving increases in flow heterogeneity and resultant pockets of hypoxic tissue, the diffusion of oxygen from the capillary tissue acts as a low pass filter of capillary oxygen dynamics 34 , and smooths out brief drops in oxygen, such that brief stalls would not likely induce critical levels of hypoxia in the adjacent tissue.…”