  Significance: Imaging neural activity in myelinated tissue using optical
coherence tomography (OCT) creates new possibilities for functional imaging in
the peripheral and central nervous systems. Aim: To investigate changes in OCT
images in response to evoked neural activity in sciatic nerve of rat in vitro.
Approach: M-scans were obtained on peripheral nerves of rat using a swept
source polarisation sensitive OCT system, while a nerve cuff acquired
electrical neural recordings. From a total of 10 subjects: 3 had no stimulation
(controls), 3 had paw stimulation, and 4 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. Results: Observed changes in intensity in 3 paw stimulation and 2
nerve stimulation subjects and changes in frequency spectra amplitude in 2 paw
stimulation subjects were above the reference noise level and were temporally
consistent with osmotic swelling from ion currents during neural activity.
Conclusion: Light scattering changes produced by osmotic swelling, which have
previously been characterised in squid and crab nerve, are also thought to
occur in myelinated fibres on a scale which is detectable using OCT
