Completed Project (2015-2019)

Research Team: Francesca Troiani (PhD thesis), Konstantin Nikolic, Timothy Constandinou
Funding: Engineering & Physical Sciences Research Council (EPSRC) DTA

Electric field reflection for inactive nerve

FDTD simulation of a portion of peripheral nerve reflecting a Gaussian light beam with central wavelength 850 nm.

In the last decades research has focused on developing new and improving old techniques to record neural activity. We have achieved astonishing results, however we are still limited due to invasiveness and resolution issues, since high resolution can only be achieved using invasive techniques. The need for a bridge between invasive and non-invasive techniques has now become compelling, and scientists are directing their efforts to study methods to detect neural activity using light. Light, as known, can travel through a material, and this property makes it possible to obtain measurements with high resolution but without touching the tissue. Optical measurements have become extremely popular, however nowadays neuroscientists focus mainly on measures related to the use of external markers that are injected inside the cell to create fluorescence when a change in calcium concentration or in voltage is detected.

The aim of this project is to detect neural activity optically without the use of any external marker, by measuring the changes in the refractive index of neurons during activity. Since these changes have been found to give an extremely small signal (one part per million in scattering measurements), interference techniques must be used to obtain significant results. In this project, Optical Coherence Tomography (OCT) will be used to observe the changes in the refractive index of a nerve. OCT is a low coherence interferometric technique, that relies on the echo time and amplitude of the light wave reflected by the sample in the same way ultrasonography does with sound waves. High spatial and temporal resolution are achieved through the use of low coherence interferometry. Through this new method we hope to be able to detect signal from specific fibres inside the nerve without injuring the nerve itself.


A finite difference time domain (FDTD) model for computation of A line scans in time domain optical coherence tomography (OCT) for a myelinated peripheral nerve. Source code available on Github at:


  • Troiani F, Nikolic K, Constandinou, TG, 2016, Optical Coherence Tomography for detection of compound action potential in Xenopus Laevis sciatic nerve, SPIE Photonics West (BIOS).
  • Troiani F, Nikolic K, and Constandinou T G, "Optical coherence tomography for compound action potential detection: a computational study," in Optical Coherence Imaging Techniques and Imaging in Scattering Media II, M. Wojtkowski, ed., Vol. 10416 of SPIE Proceedings (Optical Society of America, 2017), paper 104160A.
  • Troiani F, Nikolic K, Constandinou TG (2018) Simulating optical coherence tomography for observing nerve activity: A finite difference time domain bi-dimensional model. PLOS ONE 13(7): e0200392.