Neural correlates of blood flow measured by ultrasound

• Published in: Neuron (Cambridge, Mass.) Vol. 110; no. 10; pp. 1631 - 1640.e4
• Main Authors: Nunez-Elizalde, Anwar O., Krumin, Michael, Reddy, Charu Bai, Montaldo, Gabriel, Urban, Alan, Harris, Kenneth D., Carandini, Matteo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 18.05.2022
• Subjects: Animals; Cerebral Cortex; electrophysiology; hemodynamic coupling; Hemodynamics - physiology; Mice; Neurons - physiology; Neurovascular Coupling; Ultrasonography - methods; ultrasound measurements; hemodynamic coupling; electrophysiology; mice; ultrasound measurements
• ISSN: 0896-6273; 1097-4199
• DOI: 10.1016/j.neuron.2022.02.012

Functional ultrasound imaging (fUSI) is an appealing method for measuring blood flow and thus infer brain activity, but it relies on the physiology of neurovascular coupling and requires extensive signal processing. To establish to what degree fUSI trial-by-trial signals reflect neural activity, we performed simultaneous fUSI and neural recordings with Neuropixels probes in awake mice. fUSI signals strongly correlated with the slow (<0.3 Hz) fluctuations in the local firing rate and were closely predicted by the smoothed firing rate of local neurons, particularly putative inhibitory neurons. The optimal smoothing filter had a width of ∼3 s, matched the hemodynamic response function of awake mice, was invariant across mice and stimulus conditions, and was similar in the cortex and hippocampus. fUSI signals also matched neural firing spatially: firing rates were as highly correlated across hemispheres as fUSI signals. Thus, blood flow measured by ultrasound bears a simple and accurate relationship to neuronal firing. [Display omitted] •Neural activity was recorded during ultrasound imaging (fUSI) of blood flow in mice•fUSI signals matched the smoothed firing rate of local neurons, especially inhibitory•The ∼3 s smoothing filter is the stereotypical hemodynamic response of awake mice•Spatiotemporal correlations in firing rates largely explain correlations in blood flow Nunez-Elizalde et al. simultaneously measured neural activity with electrodes and blood flow with functional ultrasound imaging (fUSI) in awake mice. Their results establish that blood flow bears a simple and accurate relationship to local neuronal firing at frequencies <0.3 Hz and validate fUSI as a tool to infer neural activity.