Transcranial ultrasound stimulation modulates neuronal membrane potentials across broad timescales in the awake mammalian brain

Background

Transcranial ultrasound stimulation (TUS) offers noninvasive neuromodulation with high spatiotemporal precision, but its cellular-level effects in the awake brain remain poorly understood.

Objective

We investigated how low-intensity TUS modulates membrane voltage dynamics in individual cortical neurons in awake mice.

Methods

Using the genetically encoded voltage indicator SomArchon, we performed high-speed kilohertz voltage imaging in awake head-fixed mice. TUS was delivered with a 0.35 MHz transducer at 10 or 40 Hz pulse repetition frequency, at intensities below the estimated threshold for auditory brainstem activation. We analyzed changes in membrane potentials (Vm), spiking, and coordination across simultaneously recorded neurons.

Results

TUS evoked rapid (<10 ms) Vm depolarizations in 42.8 % of neurons, while only increasing spiking in 20.5 % of neurons, highlighting a direct effect of TUS on modulating synaptic inputs. Many neurons were entrained at both PRFs (20.8 % at 10 Hz; 12.7 % at 40 Hz) with Vm exhibiting significant phase-locking to individual TUS pulses. Vm entrainment was accompanied by increased temporal coordination across neurons and reset network synchrony. Furthermore, TUS-evoked cellular responses adapted over time, often transitioning from membrane depolarization to hyperpolarization upon repeated exposures, demonstrating prominent response depression.

Conclusion

By resolving single-neuron responses in the awake mammalian brain, our results demonstrate that TUS directly activates individual cortical neurons with latencies often shorter than 10 ms. TUS pulsed at physiologically relevant frequencies of 10 and 40 Hz robustly entrains neural dynamics, alters network coordination and evokes neuronal plasticity. These results highlight the therapeutic potential of designing TUS pulsing patterns to target desired neural dynamics and plasticity features.