Manipulating neuronal activity in the mouse brain with ultrasound: A comparison with optogenetic activation of the cerebral cortex.

Low-intensity focused ultrasound induces neuronal activation via mechanisms that remain to be elucidated. We recorded local field potential fluctuations in the motor cortex in response to ultrasound stimulation of the somatosensory barrel cortex, comparing them to those recorded in response to optogenetic stimulation of interneurons and pyramidal neurons of the somatosensory cortex in the same animals. Comparison of the waveform produced by ultrasound stimulation to those produced by optogenetic stimulation revealed similarities between ultrasound-induced responses and optogenetically-induced responses to pyramidal cell stimulation, but not interneuron stimulation, which may indicate that ultrasound stimulation is mediated by excitation of cerebral cortical pyramidal neurons. Comparison of post mortem evoked responses to responses in living tissue confirmed the necessity for excitable tissue in the evoked response. Collectively, these experiments demonstrate an excitation-dependent response to low-frequency transdural ultrasound stimulation of cerebral cortical neuronal activity.