Laser Stimulation of Auditory Neurons: Effect of Shorter Pulse Duration and Penetration Depth

Abstract

We have pioneered what we believe is a novel method of stimulating cochlear neurons, using pulsed infrared radiation, based on the hypothesis that optical radiation can provide more spatially selective stimulation of the cochlea than electric current. Very little of the available optical parameter space has been used for optical stimulation of neurons. Here, we use a pulsed diode laser (1.94 microm) to stimulate auditory neurons of the gerbil. Radiant exposures measured at CAP threshold are similar for pulse durations of 5, 10, 30, and 100 micros, but greater for 300-micros-long pulses. There is evidence that water absorption of optical radiation is a significant factor in optical stimulation. Heat-transfer-based analysis of the data indicates that potential structures involved in optical stimulation of cochlear neurons have a dimension on the order of approximately 10 microm. The implications of these data could direct further research and design of an optical cochlear implant.

Thermal Transients Excite Neurons through Universal Intramembrane Mechanoelectrical Effects

“…This study explored the effects of temperature changes on membrane capacitance and its associated currents in a joint attempt to clarify the experimental results of a key recent study [16] and to pave the way towards predictive modeling of INS [2][3][4][5][6][7][8][9][10][11][12][13][14][15] and other thermal neurostimulation techniques [18][19][20], which could potentially facilitate the development of more advanced and multimodal methods for neural circuit control. Another key motivation to pursue this problem came from our noting the very similar temperature-related capacitance rates of change observed in very different model systems [ Fig.…”

“…Both approaches also offer the long-term prospect of remotely affecting aberrant localized neural circuits that underlie many neurological diseases. A multitude of INS-related studies explored the ability of short-wave infrared (IR) pulses to stimulate neural structures including peripheral [3,4] and cranial nerves [5][6][7][8][9][10], retinal and cortical neurons [10][11][12], as well as cardiomyocytes [13,14]. It is stipulated that the INS phenomenon is mediated by temperature transients induced by IR absorption [15][16][17]; such transients can alternatively be induced using other forms of photoabsorption [18][19][20], or potentially by any other physical form of thermal neurostimulation that can be driven rapidly enough [21,22].…”

Optical stimulation enables paced electrophysiological studies in embryonic hearts

“…Infrared stimulation was first developed in nerves [24] and has been used to stimulate a variety of nerves and neurons [25][26][27][28][29][30], vestibular hair cells [31], and isolated myocytes [32] using multimode fibers. Additionally, we have recently demonstrated the use of infrared stimulation to optically pace whole intact embryonic [33] and adult hearts [34].…”

Attenuated infrared neuron stimulation response in cochlea of deaf animals may associate with the degeneration of spiral ganglion neurons

“…Compared to electrical stimulation, optical stimulation of the cochlea has attracted attention due to its high spatial precision, superior resolution, non-overlapping stimulation, with few stimulation artifacts or electrochemical interactions between the stimulation source and the tissue [2,3,20]. Previous studies on infrared laser auditory stimulation focused on cochlear functions by recording CAPs [3,8,11,14,21,22], and only a few studies measured oABRs evoked by optical stimulation in normal hearing animals [15,23]. The present study demonstrates that infrared laser pulses with wavelengths of 1850 nm could stimulate SGNs to evoke stable oABRs in both normal hearing and deafened guinea pigs.…”

“…Pulsed infrared lasers have been applied directly to evoke physiological responses in neuronal and other excitable cells both in vivo and in vitro without any prior genetic or chemical manipulation [4,5]. The targets of infrared lasers include peripheral and cranial motor nerves, vestibular hair cells, cochlear nerves, and the heart [6][7][8][9][10]. The advantage of direct infrared excitation makes it attractive for a variety of applications in basic and clinical research, ranging from hearing restoration to optical pacing [2].…”