Neuronal Electrical Activity in Neuronal Networks Induced by a Focused Femtosecond Laser

The spatial propagation of neuronal activity within neuronal circuits, which is associated with brain functions, such as memory and learning, is regulated by external stimuli. Conventional external stimuli, such as electrical inputs, pharmacological treatments, and optogenetic modifications, have been used to modify neuronal activity. However, these methods are tissue invasive, have insufficient spatial resolution, and cause irreversible gene modifications. To establish neuronal stimulation with less invasiveness and higher spatial resolution, we propose and demonstrate single-neuron stimulation using a focused femtosecond laser. Fluorescence Ca²⁺ imaging and microelectrode array recordings of extracellular potentials revealed Ca²⁺ influx into the target neuron and high-frequency electrical responses after laser irradiation. These results indicate that femtosecond laser-induced neuronal electrical activity has a greater number of electrical spikes, lasts longer after stimulation, and propagates to a region more distant from the target neuron compared with the properties evoked by electrical stimulation. Focused femtosecond laser-induced stimulation can be a promising tool for stimulating single neurons in neuronal networks.