Optical coherence tomography imaging of evoked neural activity in sciatic nerve of rat

Abstract

We investigate changes in optical coherence tomography (OCT) images in response to evoked neural activity in the sciatic nerve of rats in vitro. M-scans were obtained on peripheral nerves of rats using a swept source polarisation sensitive OCT system, while a nerve cuff acquired electrical neural recordings. From a total of 10 subjects: three had no stimulation (controls), three had paw stimulation, and four had nerve stimulation. Changes in the OCT signal intensity, phase retardation, phase, and frequency spectra were calculated for each subject and reference samples of a mirror and microspheres in solution. Observed changes in intensity in three paw stimulation and two nerve stimulation subjects and changes in frequency spectra amplitude in two paw stimulation subjects were above the reference noise level and were temporally consistent with osmotic swelling from ion currents during neural activity. Light scattering changes produced by osmotic swelling, which have previously been characterised in squid and crab nerves, are also thought to occur in myelinated fibres on a scale which is detectable using OCT. Imaging neural activity in myelinated tissue using OCT creates new possibilities for functional imaging in the peripheral and central nervous systems.

Optical birefringence changes in myelinated and unmyelinated nerves: A comparative study

“…While longer-duration pulses can excite unmyelinated fibers, the stimulation artifact pollutes neural recordings by obscuring CNAPs from myelinated axons. This is in agreement with OCT imaging of neural activity in rat sciatic nerves in which no retardance variations has been observed despite evidence of light scattering changes due to osmotic swelling from ion currents in the dynamic state [22].…”

“…However, these are not suitable for use in clinical applications. Alternatively, there are label‐free methods such as light scattering [18], birefringence [19], infrared spectroscopy [20], laser interferometric microscopy, [21] and optical coherence tomography (OCT) [22]. They are based on the detection of fast intrinsic optic signals (IOS) variations related with nerve activity.…”

Neurosurgical Intervention for Nerve and Muscle Biopsies

“…OCT uses low-coherence light to capture micrometer-resolution two-and three-dimensional images from within optical scattering media. Of note, this technique has been used in animal models to obtain high-resolution images of sciatic nerves, [128,129] to monitor microvasculature flow around peripheral nerves as they are electrically stimulated, [130,131] and to capture functional images of nerves [132]. The non-invasive nature of this technique makes biopsies of nerves possible without causing damage or impairing function, making studies such as those to visualize retinal nerve fibers in diabetic patients possible [133,134].…”

Neurosurgical Intervention for Nerve and Muscle Biopsies

“…OCT uses low-coherence light to capture micrometer-resolution two- and three-dimensional images from within optical scattering media. Of note, this technique has been used in animal models to obtain high-resolution images of sciatic nerves [ 126 , 127 ], to monitor microvasculature flow around peripheral nerves as they are electrically stimulated [ 128 , 129 ], and to capture functional images of nerves [ 130 ]. The non-invasive nature of this technique makes biopsies of nerves possible without causing damage or impairing function, making studies such as those to visualize retinal nerve fibers in diabetic patients possible [ 131 , 132 ].…”