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. Author manuscript; available in PMC: 2015 May 1.
Published in final edited form as: Hear Res. 2014 Apr 4;0:72–88. doi: 10.1016/j.heares.2014.03.008

Table 3.

Comparison between INS, optogenetics, and optoacoustics

Features
Optogenetics INS Photoacoustics
thermal confinement stress confinement
Mechanism Expression of light sensitive ion channels in the plasma membrane. The ion channel/transporter expressed determines the sensitivity to the radiation wavelength and whether inhibition or excitation occurs. Confined heating of the plasma membrane. Heating is slow enough (>1 μs) that stress waves can travel from the heated volume but the heat delivered still remains confined in the target volume. Radiant energy and pulse length determine whether stimulation results in excitation or inhibition. Radiant energy is delivered faster than a stress relaxation wave can travel out of the heated volume (≪1 μs), which can results in the generation of considerable stress waves and pressure build-up
Wavelength 441, 450, 470, 485, 500, 535, 540, 545, 560, 566, 590 nm. Typically, but not limited to 1400–1600 nm and 1840–2100 nm Typically, but not limited to 532 nm and 420–2150 nm
Laser parameter Pulse length 1–10 ms, irradiance 1–10 W/cm2 Pulse length 5 μs to several ms, pulse repetition rate up to 1 kHz tested, threshold radiant exposure ~15 μJ/cm2 to 1500 μJ/cm2 Pulse length is typically 3–10 ns, radiant energy 0–6 μJ/pulse; pulse repetition rate < 10Hz.
Power for stimulation 1–10 W/cm2 As low as 40 mW;
Temporal properties Typically less than 50 Hz, novel ChR2 mutants respond up to 200 Hz. Sustained CAP responses shown up to 1 kHz; single fiber responses ~100–150 Hz. Onset response times ~2.5 ms
Challenges
“chromophore” Needs the targeted and selective expression of ion channels in a selected type of neurons Water is the main absorber and readily available at the cell; water between source results in unnecessary heating
pH changes Sustained stimulation changes cell pH with risk of damage Not documented
Heating of tissue Not documented Limits rate and maximum radiant exposure of stimulation Is likely and will limit rate and maximum radiant exposure of the stimulation
pressure wave formation not documented stress relaxation waves are generated an can result in photoacoustic stimulation used for stimulation