Laser Elicited Nerve Action Potentials

Photomed Laser Surg. 2012 Jul 10. [Epub ahead of print]

Electrophysiological Effects of Single Point Transcutaneous 650 and 808?nm Laser Irradiation of Rat Sciatic Nerve: A Study of Relevance for Low-Level Laser Therapy and Laser Acupuncture.

Chow R, Yan W, Armati P.


Nerve Research Foundation, Brain and Mind Research Institute, The University of Sydney , Camperdown NSW, Australia .


Abstract Objective: The purpose of this study was to evaluate effects of transcutaneous 650?nm and 808?nm laser irradiation (LI) to a single point overlying rat sciatic nerve; a comparison to four point LI and relevance to the clinical application of low-level laser therapy (LLLT) and laser acupuncture (LA).

Background data: Transcutaneous LI inhibits somatosensory and motor conduction when delivered to four points overlying sciatic nerve; however, effects of the same total energy delivered to a single point over the nerve, equating to laser acupuncture, are undefined.

Methods: Transcutaneous 808?nm, 450?mW, (13.5 or 54?J) continuous wave (cw) mode or 650?nm, 35?mW, (1.1 or 4.4?J), cw LI or sham LI, was applied for 30 or 120?sec to a single point overlying the midpoint of rat sciatic nerve. Somatosensory evoked potentials (SSEPs) and compound muscle action potentials (CMAPs) were then recorded after 10 and 20?min, and after 24 and 48?h.

Results: 120?sec of 808?nm LI increased SSEP amplitudes only at 10?min, with no effect of 30 or 120?sec at other time points on SSEPs or on CMAPs. LI 650?nm for 30 or 120?sec did not alter SSEPs or CMAPs at any time point.

Conclusions: Localized transcutaneous 808 LI to a single point overlying sciatic nerve increases SSEP amplitudes when compared with delivery of the same total energy to four points, which causes decreased SSEP amplitudes and conduction block. Therefore, the area and duration of delivery are important, independent variables with implications for clinical delivery of both LLLT and LA.

J Biomed Opt. 2009 Nov-Dec;14(6):060501.

Combined optical and electrical stimulation of neural tissue in vivo.

Duke AR, Cayce JM, Malphrus JD, Konrad P, Mahadevan-Jansen A, Jansen ED.

Low-intensity, pulsed infrared light provides a novel nerve stimulation modality that avoids the limitations of traditional electrical methods such as necessity of contact, presence of a stimulation artifact, and relatively poor spatial precision. Infrared neural stimulation (INS) is, however, limited by a 2:1 ratio of threshold radiant exposures for damage to that for stimulation. We have shown that this ratio is increased to nearly 6:1 by combining the infrared pulse with a subthreshold electrical stimulus. Our results indicate a nonlinear relationship between the subthreshold depolarizing electrical stimulus and additional optical energy required to reach stimulation threshold. The change in optical threshold decreases linearly as the delay between the electrical and optical pulses is increased. We have shown that the high spatial precision of INS is maintained for this combined stimulation modality. Results of this study will facilitate the development of applications for infrared neural stimulation, as well as target the efforts to uncover the mechanism by which infrared light activates neural tissue.

J Neurosci Methods. 2007 Jul 30;163(2):326-37. Epub 2007 Mar 31.

Pulsed laser versus electrical energy for peripheral nerve stimulation.

Wells J, Konrad P, Kao C, Jansen ED, Mahadevan-Jansen A.

Vanderbilt University, Department of Biomedical Engineering, 5824 Stevenson Center, Nashville, TN 37235, United States.

Transient optical neural stimulation has previously been shown to elicit highly controlled, artifact-free potentials within the nervous system in a non-contact fashion without resulting in damage to tissue. This paper presents the physiologic validity of elicited nerve and muscle potentials from pulsed laser induced stimulation of the peripheral nerve in a comparative study with the standard method of electrically evoked potentials. Herein, the fundamental physical properties underlying the two techniques are contrasted. Key laser parameters for efficient optical stimulation of the peripheral nerve are detailed. Strength response curves are shown to be linear for each stimulation modality, although fewer axons can be recruited with optically evoked potentials. Results compare the relative transient energy requirements for stimulation using each technique and demonstrate that optical methods result in highly selective functional nerve stimulation. Adjacent stimulation and recording of compound nerve potentials in their entirety from optical and electrical stimulation are presented, with optical responses shown to be free of any stimulation artifact. Thus, use of a pulsed laser exhibits distinct advantages when compared to standard electrical means for excitation of muscle potentials in the peripheral nerve in the research domain and possibly for clinical diagnostics in the future.

J Biomed Opt. 2005 Nov-Dec;10(6):064003.

Application of infrared light for in vivo neural stimulation.

Wells J, Kao C, Jansen ED, Konrad P, Mahadevan-Jansen A.

Vanderbilt University, Department of Biomedical Engineering, Box 351631, Station B, Nashville, Tennessee 37235, USA.

A novel method for damage-free, artifact-free stimulation of neural tissue using pulsed, low-energy infrared laser light is presented. Optical stimulation elicits compound nerve and muscle potentials similar to responses obtained with conventional electrical neural stimulation in a rat sciatic nerve model. Stimulation and damage thresholds were determined as a function of wavelength using a tunable free electron laser source (lambda = 2 to 10 microm) and a solid state holmium:YAG laser (lambda = 2.12 microm). Threshold radiant exposure required for stimulation varies with wavelength from 0.312 Jcm2 (lambda = 3 microm) to 1.22 Jcm2 (lambda = 2.1 microm). Histological analysis indicates no discernable thermal damage with suprathreshold stimulation. The largest damage/stimulation threshold ratios (>6) were at wavelengths corresponding to valleys in the IR spectrum of soft tissue absorption (4 and 2.1 microm). Furthermore, optical stimulation can be used to generate a spatially selective response in small fascicles of the sciatic nerve that has significant advantages (e.g., noncontact, spatial resolution, lack of stimulation artifact) over conventional electrical methods in diagnostic and therapeutic procedures in neuroscience, neurology, and neurosurgery.

Opt Lett. 2005 Mar 1;30(5):504-6.

Optical stimulation of neural tissue in vivo.

Wells J, Kao C, Mariappan K, Albea J, Jansen ED, Konrad P, Mahadevan-Jansen A.

Departments of Biomedical Engineering and Neurosurgery, Vanderbilt University, 2201 West End Avenue, Nashville, Tennessee 37235, USA.

For more than a century, the traditional method of stimulating neural activity has been based on electrical methods, and it remains the gold standard to date. We report a technological breakthrough in neural activation in which low-level, pulsed infrared laser light is used to elicit compound nerve and muscle potentials in mammalian peripheral nerve in vivo. Optically induced neural action potentials are spatially precise, artifact free, and damage free and are generated by use of energies well below tissue ablation threshold. Thus optical stimulation presents a simple yet novel approach to contact-free in vivo neural activation that has major implications for clinical neurosurgery, basic neurophysiology, and neuroscience.