Brain Stimulation by Network Resonance with Weak Electric Fields Probed by Optogenetics in Vitro (2014)

Undergraduates: Anna Foulser, Stephen L. Schmidt Flavio Frohlich

Faculty Advisor: Flavio Frohlich
Department: Psychology & Neuroscience

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Transcranial alternating current stimulation (tACS) is a method of noninvasive brain stimulation in which weak electric currents are applied to the brain. tACS has the potential to be used as a neuropsychiatric treatment. Because of the oscillating waveform of tACS, it may be possible to apply tACS at the same frequency as a patient¿s neural activity. It is not yet known which waveforms have the best effects for treatment. To simulate the effects of tACS on ongoing neural oscillations in vitro, we applied optogenetics and weak electric fields to cortical slices and recorded multiunit spiking activity using a multielectrode array. Slices were taken from mice whose Layer V pyramidal cells express channelrhodopsin. We used optogenetic stimulation to entrain the cortical network at 1Hz with pulses of light. Simultaneously, we applied weak electric fields at the same frequency (1Hz) and surrounding frequencies (0.8Hz, 1.2Hz, 2Hz) to mimic tACS. We hypothesized that the effect of tACS would be stronger when the internal and applied oscillations frequencies were matched. We successfully entrained cells in Layer V and surrounding frequencies at 1Hz. Cells did not entrain at surrounding frequencies. These results suggest that 1Hz is a preferred firing rate for Layer V pyramidal cells and that tACS may be used to enhance ongoing network activity. Our findings emphasize the importance of determining individual oscillation frequencies when using brain stimulation as a treatment.