Thermal effects on neurons during stimulation of the brain

Abstract

All electric and magnetic stimulation of the brain deposits thermal energy in the brain. This occurs through either Joule heating of the conductors carrying current through electrodes and magnetic coils, or through dissipation of energy in the conductive brain. Objective. Although electrical interaction with brain tissue is inseparable from thermal effects when electrodes are used, magnetic induction enables us to separate Joule heating from induction effects by contrasting AC and DC driving of magnetic coils using the same energy deposition within the conductors. Since mammalian cortical neurons have no known sensitivity to static magnetic fi elds, and if there is no evidence of effect on spike timing to oscillating magnetic fields, we can presume that the induced electrical currents within the brain are below the molecular shot noise where any interaction with tissue is purely thermal. Approach. In this study, we examined a range of frequencies produced from micromagnetic coils operating below the molecular shot noise threshold for electrical interaction with single neurons. Main results. We found that small temperature increases and decreases of 1C caused consistent transient suppression and excitation of neurons during temperature change. Numerical modeling of the biophysics demonstrated that the Na-K pump, and to a lesser extent the Nernst potential, could account for these transient effects. Such effects are dependent upon compartmental ion fluxes and the rate of temperature change. Significance. A new bifurcation is described in the model dynamics that accounts for the transient suppression and excitation; in addition, we note the remarkable similarity of this bifurcation's rate dependency with other thermal rate-dependent tipping points in planetary warming dynamics. These experimental and theoretical findings demonstrate that stimulation of the brain must take into account small thermal effects that are ubiquitously present in electrical and magnetic stimulation. More sophisticated models of electrical current interaction with neurons combined with thermal effects will lead to more accurate modulation of neuronal activity.

Multifunctional Fiber‐Based Optoacoustic Emitter as a Bidirectional Brain Interface

“…shows that small temperature increases of 1 °C caused transient suppression of neurons. [ 60 ] This also proves that the temperature effect is not the main contributor to the neuronal response induced by mFOE. Taken together, we conclude that activation of neurons was due to the mFOE optoacoustic stimulation.…”

Spatial and Amplitude Dynamics of Neurostimulation: Insights from the Acute Intrahippocampal Kainate Seizure Mouse Model

“…Since KA is thought to act primarily on KA receptors with the highest density in the CA3 region 47 , the finding that CA3 stimulation of this region produces a favorable effect lasting several seconds supports that high-frequency stimulation probably can act locally in the stimulated region. This effect may be due to the direct inhibition of excitatory neurons in the target region 48 , activation of local inhibitory neurons 16 , thermal effects 15 , or extracellular effects like potassium accumulation 37 . Alternatively, CA3 and CA1 may be better targets than output regions like the subiculum since HFS may primarily modulate downstream rather than upstream areas.…”

“…Nevertheless, there is mounting evidence that neurostimulation acts by direct inhibition of neuronal activity 12 , activation of presynaptic inhibitory inputs 13 , and activation of efferent projections 14 . High-frequency stimulation (HFS, ~100-165 Hz) may also have thermal effects which can induce a transient suppression of neurons 15 . While HFS has been used more extensively 16 , low-frequency stimulation (LFS, ~1-10Hz) has significant promise for treating epilepsy 17,18 .…”

An Optrode Array for Spatiotemporally Precise Large-Scale Optogenetic Stimulation of Deep Cortical Layers in Non-human Primates

“…We also investigated whether our results could have been affected by local increase in brain temperature caused by the µLEDs heating up when activated. This concern arises with implantable devices 44 both in terms of temperature-induced tissue damage 45 and changes in spiking activity 24,46 . It is generally assumed that tissue damage is negligible for temperature increases < 1°C 29,47 .…”