Pulsed infrared light alters neural activity in rat somatosensory cortex in vivo

Abstract

Pulsed infrared light has shown promise as an alternative to electrical stimulation in applications where contact free or high spatial precision stimulation are desired. Infrared neural stimulation (INS) is well characterized in the peripheral nervous system; however, to date, research has been limited in the central nervous system. In this study, pulsed infrared light (λ=1.875 μm, pulse width=250 μs, radiant exposure=0.01–0.55 J/cm2, fiber size=400 μm, repetition rate=50–200 Hz) was used to stimulate the somatosensory cortex of anesthetized rats, and its efficacy was assessed using intrinsic optical imaging and electrophysiology techniques. INS was found to evoke an intrinsic response of similar magnitude to that evoked by tactile stimulation (0.3–0.4% change in intrinsic signal magnitude). A maximum deflection in the intrinsic signal was measured to range from 0.05% to 0.4% in response to INS, and the activated region of cortex measured approximately 2 mm in diameter. The intrinsic signal magnitude increased with faster laser repetition rates and increasing radiant exposures. Single unit recordings indicated a statistically significant decrease in neuronal firing that was observed at the onset of INS stimulation (0.5 s stimulus) and continued up to 1 s after stimulation onset. The pattern of neuronal firing differed from that observed during tactile stimulation, potentially due to a different spatial integration field of the pulsed infrared light compared to tactile stimulation. The results demonstrate that INS can be used safely and effectively to manipulate neuronal firing.

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].…”

Voltage-sensitive dye imaging reveals shifting spatiotemporal spread of whisker-induced activity in rat barrel cortex

“…Images were collected with a Redshirt Imaging System running CortiPlex software (Redshirt Imaging, Decatur, GA). Initially, intrinsic optical imaging (632-nm illumination) was performed by using previously published methods (Cayce et al 2011) to functionally locate barrel cortex. To localize the barrels, several rostral (condition 1) or caudal whiskers (condition 2) were stimulated and the activation maps were compared with a blank no-stimulus condition (condition 3).…”

In vitro neuronal depolarization and increased synaptic activity induced by infrared neural stimulation

“…One such study relied on calcium imaging to probe the visual cortex's response to INS and demonstrates a fast and slow component of the calcium signal [13], with another study showing that INS increased the spontaneous discharge rate of visual cortex neurons recorded in vivo in the Macaque through extracellular recordings of unit activity [14]. A similar study instead described the use of infrared light to cause neural inhibition [15]. The laser parameters, cell types and recording methods of these studies of the mechanism by which INS operates are detailed in Table 1.…”