Generation of action potentials or nerve impulses with infrared pulse laser, focused pulse microwaves (and/or maser pulse beam), focused pulse ultrasound

 

Excerpts from this study:

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« Action potentials or nerve impulses are not created only by electrical stimulation. It has been demonstrated that nerve stimulation by low-intensity pulsed infrared light is possible (2). In this case, action potentials are created by absorption of infrared energy. In other words, this absorption increases the temperature creating an action potential. It has been calculated that the temperature increase of 6°C (from baseline temperature) is the bio-physical mechanism responsible for stimulation of sciatic nerve of rats and frogs (2). This optical stimulation in vivo exhibits advantages over standard electrical means by providing high spatial selectivity, contact-free and artifact-free stimulation for peripheral nerves (3). »

 

« Another possible electromagnetic source for future noninvasive brain stimulation are microwaves. Currently, focused microwaves have been employed for thermal ablation of tumours (4). However, the brain absorption mechanism of microwave energy, counting for focused microwave brain stimulation is expected to be mediated by similar thermal effect present in infrared laser stimulation. In addition, future techniques concerning focusing microwave beam pulses, that is microwave amplification through stimulated emission of radiation (maser) pulses can play a major role in localized human deep brain stimulation, eliciting an action potential while increasing the baseline temperature. »

 

« A mechanical energy source such as high frequency sound is another possibility for noninvasive deep brain stimulation. Currently, focused ultrasound is combined with MRI to perform thermal ablation of tumours (5). However, it has been recently shown that focused pulse ultrasound excites mouse brain hippocampus area in vitro responses (6). »

 

Reference 2 | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1965456/

Excerpts :
« Temperature can affect action potential propagation in three ways: 1), the Nernst equilibrium potentials are inversely proportional to the absolute temperature; 2), the conductance of an open ion channel is dependent on a common temperature factor governing the rate for channel induction called a Q10; and 3), a change in temperature changes the amplitude and duration of the potential (41). One hypothesis for the physiological mechanism for optical stimulation involves sodium channel activation based on a local increase in the conductance as the channel transitions to the open state resulting from a temperature increase. »

 

« A second potential hypothesis is the activation of heat-sensitive channels, where the gating mechanism is markedly different from the other channel types: voltage-gated, ligand-gated, and mechanosensitive ion channels. »

 

 

 

Infrared light generates action potentials by thermally increasing the cell membrane capacitance

Optocapacitative generation of action potentials
From optogenetics to the optocapacitative technique
 
Shapiro et al (2012) (https://www.ncbi.nlm.nih.gov/pubmed/22415827) demonstrated that infrared radiation increases the cell membrane temperature and augments its electric capacitance. The current required to satisfy the equation Q = C x V depolarizes the membrane, reaching its excitation voltage threshold and eliciting an action potential.
 
The temperature change is small but rapid, a property which led Sapiro et al to hypothesize and show a capacitance change during infrared radiation.
 
It is noted that water in the vicinity of the membrane absorbs the radiation energy.
 
A recent study (https://www.ncbi.nlm.nih.gov/pubmed/29273263) used particles to serve as light-to-heat transducers to transfer infrared radiation energy directly to the membrane thereby minimizing absorption by water. (Above notes based on this study.)
 
 

Infrared nerve stimulation

 
 
"Action potentials locked in time with the laser pulses were observed at locations of neural projections several millimeters away from the site of stimulation."
 
 
“It has been shown that INS is feasible in the cochlea of acute and chronic deafened animals in which acoustic thresholds are significantly elevated. The evoked potentials from acutely deafened animals and optically stimulated chronic deafened animals were not significantly different from normal animals. This demonstrates the feasibility of optical stimulation of neural systems."