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Monday, July 20 • 8:00pm - 9:00pm
P52: Connectivity modulation by dual-site transcranial alternating current stimulation based on spike-timing dependent plasticity

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Zoom Meeting Info:
Bettina Schwab is inviting you to a scheduled Zoom meeting.
Topic: CNS*2020 Poster Bettina Schwab
Time: Jul 20, 2020 08:00 PM Amsterdam, Berlin, Rome, Stockholm, Vienna

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Meeting ID: 995 5213 2300
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Bettina Schwab
, Peter König, Andreas K. Engel

Transcranial alternating current stimulation (tACS) noninvasively applies electric fields to the brain with the aim of entraining neural activity. As recordings of extracellular potentials are highly affected by the stimulation artifact, M/EEG recordings before and after tACS have become the standard to investigate neurophysiological effects of tACS in humans. In particular, we recently showed that dual-site tACS can modulate functional connectivity between the targeted regions outlasting the stimulation period, with in-phase stimulation (phase lag zero) increasing connectivity compared to anti-phase stimulation (phase lag π) [1]. Although the mechanism for such after-effects is not known, spike-timing dependent plasticity (STDP) has been proposed as a candidate [2,3]. We aim (1) to find a possible mechanism for our experimentally observed connectivity changes, and (2) to estimate if our dual- site tACS setting can successfully be extended to any stimulation frequency and target area.
We simulated two populations of each 1000 regularly spiking Izhikevich neurons [4] with realistic firing rate distributions. Excitatory connections from each neuron to 100 random neurons of the other population with synaptic delay were subject to an experimentally observed STDP rule [5]. tACS was applied as sinusoidal input currents to both populations with varying phase lags. To validate our model, we correlated experimentally found connectivity changes [1] between targeted sub-regions with the fiber length connecting those sub-regions.
Synaptic weight changes depended on tACS frequency, phase lag, and synaptic delay. For 10 Hz tACS, synaptic weight changes between in- and anti-phase tACS monotonically decreased within the range of physiological cortico-cortical conduction delays. Confirming this finding, our experimental data showed a negative correlation between functional connectivity modulation (in-phase vs anti-phase tACS) and fiber length. Extending the simulations to other tACS frequencies, we find that the expected direction of connectivity modulation can only be expected for low tACS frequencies and small delays or delays that are near multiples of the tACS cycle length.
In conclusion, our experimental findings [1] are in accordance with STDP of synapses between the stimulated regions. Nevertheless, the approach cannot be generalized to all tACS frequencies and delays. Most robust effects are expected for low tACS frequencies and small delays.

Acknowledgement: This work has been supported by DFG, SFB 936/project A3.

[1] Schwab, B. C., Misselhorn, J., & Engel, A. K., Modulation of large-scale cortical coupling by transcranial alternating current stimulation. Brain stimulation, 2019, 12(5), 1187-1196.
[2] Wischnewski, M., Engelhardt, M., Salehinejad, et al., NMDA receptor- mediated motor cortex plasticity after 20 Hz transcranial alternating current stimulation. 2019, Cerebral Cortex, 29(7), 2924-2931.
[3] Vossen, A., Gross, J., & Thut, G., Alpha power increase after transcranial alternating current stimulation at alpha frequency (α-tACS) reflects plastic changes rather than entrainment. 2015, Brain stimulation, 8(3), 499-508.
[4] Izhikevich, E. M., Simple model of spiking neurons. 2003, IEEE Transactions on neural networks, 14(6), 1569-1572.
[5] Froemke, R. C., & Dan, Y., Spike-timing-dependent synaptic modification induced by natural spike trains. 2002, Nature, 416(6879), 433-438.

avatar for Bettina Schwab

Bettina Schwab

PostDoc, Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf

Monday July 20, 2020 8:00pm - 9:00pm CEST
Slot 10