James Dowsett: Enhancing steady state visually evoked potentials with tACS: precise frequency control with LCD glasses
Please post questions here.
interesting approach. Beyond the technical advantage for removing the tACS artifacts, do you anticipate any difference/advantage of using sawtooth waveforms over standard sinusoidal tACS for neural entrainment/behavioral modulation?
I do think that the waveform shape will have some effect on the neural activity. The best evidence of this that I've seen is in a 2010 paper by Flavio Fröhlich and David McCormick. In the supplementary material of that paper they showed that electric field ramps with higher slope are more successful at entraining network activity in vitro. These ramps of electric current reached the same peak voltage, the only difference was the gradient: steeper gradient resulted in more network activity. Therefore the steep gradient of the rising edge of the sawtooth wave should have greater effect on the relatively slow rise of a sine wave at the same frequency. Also some modelling work has shown that square waves might be more successful at entraining oscillations than sine waves.
I don't have any direct evidence of this yet but I hope to collect some data exploring different waveform shapes soon, now that this method is working.
Here is a link to the Frolich paper: https://www.sciencedirect.com/science/article/pii/S0896627310004630#app2
There is a link to the supplementary material at the bottom of that page