Figure 5. Application of HNN to test alternative hypotheses on the circuit level impact of tACS on the somatosensory tactile evoked response (adapted from Sliva et al., 2018).

(A) The early tactile evoked response from above somatosensory cortex before and after 10 min of 10 Hz alternating current stimulation over SI shows that the ~70 ms peak is more prominent in the post-tACS condition. Note that the timing of this peak in the sensor level signal is analogous to the 70 ms peak in the source localized signal in Figure 4B, since the tactile stimulation was the same in both studies and the early signal from SI is similar both at the source and sensor level. (B) HNN was applied to investigate the impact of several possible tACS induced changes in local synaptic efficacy and identify which could account for the observed evoked response data. The parameters in HNN were first adjusted to account for the pre-tACS response using the default HNN parameter set (solid blue line). The synaptic gains between the different cell types was then adjusted through the Set Parameters dialog box to predict that 2x gain in the local inhibitory synaptic weights best accounted for the post-tACS evoked response. (C) Simultaneous viewing of the cell spiking activity further predicted that there is less pyramidal neuron spiking at 70 ms post-tACS, despite the more prominent 70 ms current dipole peak.