Real-Time Movies of Neuronal Activity by Imaging Intrinsic Changes in Optical Birefringence

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

“…Myelin is produced by oligodendrocyte and Schwann glial cells, which are ubiquitous in mammalian peripheral nerves and white matter of the brain and spinal cord and exhibits a strong birefringence [31]. In myelinated nerve, dynamic changes in the optical birefringence during neural activity have been characterised in a transmission polarisation study on sciatic nerve of mouse [32] revealing relative changes in the total acquired signal in the order of 0.1%, whereas dynamic changes in intensity have been modelled for a time domain OCT system [33] which estimated depth resolved changes in the acquired signal in the order of 1 × 10 −4 %. In the latter, visual inspection of predicted dynamic changes in an A scan also reveals possible changes in the phase and frequency spectra from Mie scattering.…”

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

“…As can be seen, there is no significant difference with the nerve orientation, except near the edge where the sample is thinner, confirming the strong light depolarization in the central part of the nerve. Moreover, contrary to experiments in very thin neural samples [26, 50–52], individual axons cannot be seen despite their strong birefringence because of a lack of contrast due to the averaging effect over many axons and to blurring from light scattering.…”

“…rat sciatic) nerves. Those high cut-off values were chosen according to the work of Badrenddine on lobster and mice sciatic nerves [12,26]. Because of the higher bandwidth that might be required for optical measurements in rat sciatic nerves, all experiments in these nerves were conducted with the low-noise S8745-01 PD.…”

“…Nerve fibers can basically be considered as long cylinders with cytoskeletal components such as microtubules and neurofilaments oriented along the longitudinal axis, with a membrane made of proteins and lipid molecules oriented radially [26]. Because of this structure, the optical properties are different for light polarized along the nerve longitudinal axis or in the transverse plane [39].…”

“…On the contrary, there are very few studies in mammals, while they would be valuable for translational research. Such methods have only been implemented in mouse brain dendrites [25] and, tentatively, in mice sciatic nerves [26]. Mammal peripheral nerves differ from crustacean ones in terms of myelination as well as number and diameter of axons [27][28][29][30].…”