On 12 August, PhD student Mürsel Karadas will defend his PhD thesis "Highly Sensitive Magnetic Sensing of Neural Activity"
Time and place: Monday 12 August 2019 at 13:30.
Principal supervisor:
Associate Professor Axel Thielscher
Co supervisor: Associate Professor Lars G. Hanson
Examiners:
Associate Professor Sadasivan Puthusserypada, DTU Health Tech
Associate Professor Rune W. Berg, University of Copenhagen
Assistant Professor Romana Schirhagl, University of Groningen
Chairperson at defence:
TBA
Abstract:
Nitrogen-vacancy (NV) centers in diamond are novel tools in development to measure magnetic fields at very high sensitivity. They have advantages over other magnetometers by providing measurements at ambient conditions with exceptional spatial resolution. This can be achieved by embedding a layer of NV centers in a planar diamond substrate and placing it on a commercially available charge-coupled device (CCD) or complementary metal-oxide-semiconductors (CMOS) imaging sensor. In vitro electrophysiological recordings in brain slices is a proven method for the characterization of neural electrical activity and has strongly contributed to our understanding of the mechanisms that govern neural information processing. However, this traditional approach acquires signals from only a limited number of cellular positions, which severely limits its ability to characterize the dynamics of underlying neural networks. In this thesis, to address such challenges, we investigated the feasibility of wide-field imaging of neural network dynamics in brain slices that uses highly sensitive magnetometry based on NV centers in diamond.
Firstly, by employing comprehensive computational simulations accompanied by theoretical analyses, we determined the spatiotemporal characteristics of the neural fields caused by pyramidal cell activity in the rodent hippocampus. We used these characteristics to establish the required key performance parameters of an NV magnetometry-based imaging setup. Our results indicated that it will be feasible to image neural slice activity with the upcoming generation of NV magnetic field sensors. However, single-shot imaging of planar cell activity will remain challenging.
In the second part of this thesis, we presented a numerical model to determine the magnetic fields generated by action potentials traveling along the auditory pathway in the brainstem, and to estimate the feasibility of measuring these fields by NV magnetometry. In addition, the feasibility of optical stimulation as an alternative to electrical stimulation to trigger the action potentials was also assessed. Our main finding was that electrical stimulation is more effective than optical stimulation in terms of the achieved peak magnetic field strength. This suggests that the optical excitation does not provide substantial advantages over electric stimulation to record neural magnetic fields. In addition, our data supports the notion that neural magnetic field recording of the studied pathway is feasible with the current sensitivity levels of NV-based magnetometers, even though averaging of many trials will still be required.
This project provides comprehensive analysis tools to model electrical and optical stimulation of brain slices. We expect our approaches to be relevant for further studies of neural electric and magnetic fields arising from other brain regions.