The aim of this study was to determine the effects of electrical stimulation on gamma oscillations and the more general mechanisms by which small currents can affect neuronal activity. In particular we studied the effects of both AC and DC fields (similar to the currents induced during transcranial electrical DC stimulation, tDCs).
We used hippocampal brain slices and uniform fields (<10 V/m, 0-50 Hz) to stimulate pharmacologically induced gamma oscillations.
- DC fields modulate the power of gamma activity
- Low frequency AC fields modulates gamma oscillations at the frequency of the stimulation
- Higher frequency stimulation generates sub-harmonics
The results of the Local Field Potential (LFP) recordings were then used to set the parameters of a computational model reproducing gamma activity and the effects of electrical stimulation. The network model was based onIzhikevich’s single neuron dynamics. The model gave explanations about the experiments in term of:
- Firing rate modulation with balanced excitation/inhibition
- Firing rate instantaneuous modulation
- Spiking timing
The model made predictions on the behaviour of single neurons that were tested with intracellular recordings. In particular the model predicted a peak of resonance of the spiking coherence with the field applied for very low intensity (0.2 V/m).
The combined experimental and modeling results showed that:
- The effects of fields are amplified non linearly by network dynamics
- It is possible to explain the amplitude and frequency-dependent effects of fields with a single model
- Fields induce rate and timing effects dependent on network dynamics
- Endogenous fields alone may affect network dynamics (theta-modulated gamma)
This work has just been published on the Journal of Neuroscience:
Reato D, Rahman A, Bikson M, Parra L. Low-intensity electrical stimulation affects network dynamics by modulating population rate and spike timing. Journal of Neuroscience. 2010; 30(45):15067-79 PDF
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