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

The concentration of oxygen in the brain spontaneously fluctuates, and the
distribution of power in these fluctuations has a 1/f-like spectra, where
the power present at low frequencies of the power spectrum is orders of
magnitude higher than at higher frequencies. 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 and
mathematical modelling show that stochastic fluctuations in erythrocyte
flow could underlie 1/f-like dynamics in oxygenation. These results
suggest that the discrete nature of erythrocytes and their irregular flow,
rather than fluctuations in neural activity, could drive 1/f-like
fluctuations in tissue oxygenation.