Strength-frequency curve for micromagnetic neurostimulation through excitatory postsynaptic potentials (EPSPs) on rat hippocampal neurons and numerical modeling of magnetic microcoil (μcoil)

Objective: The objective of this study was to measure the effect of micromagnetic stimulation (μMS) on hippocampal neurons, by using single microcoil (μcoil) prototype, Magnetic Pen (MagPen). MagPen will be used to stimulate the CA3 magnetically and excitatory post synaptic potential (EPSP) measurements will be made from the CA1. The threshold for μMS as a function of stimulation frequency of the current driving the µcoil will be demonstrated. Finally, the optimal stimulation frequency of the current driving the μcoil to minimize power will be estimated. Approach: A biocompatible prototype, MagPen was built, and customized such that it is easy to adjust the orientation of the μcoil over the hippocampal tissue in an in vitro setting. Finite element modeling (FEM) of the μcoil was performed to estimate the spatial profiles of the magnetic flux density (in T) and the induced electric fields (in V/m). The induced electric field profiles generated at different values of current applied to the µcoil whether can elicit a neuron response was validated by numerical modeling. The modeling settings were replicated in experiments on rat hippocampal neurons. Main results: The preferred orientation of MagPen over the Schaffer Collateral fibers was demonstrated such that they elicit a neuron response. The recorded EPSPs from CA1 due to μMS at CA3 were validated by applying tetrodotoxin (TTX). Finally, it was interpreted through numerical analysis that increasing frequency of the current driving the μcoil, led to a decrease in the current amplitude threshold for μMS. Significance: This work reports that μMS can be used to evoke population EPSPs in the CA1 of hippocampus. It demonstrates the strength-frequency curve for µMS and its unique features related to orientation dependence of the µcoils, spatial selectivity and distance dependence. Finally, the challenges related to µMS experiments were studied including ways to overcome them.

Orientation dependence of optical activity in light scattering by nanoparticle clusters

The optical properties of nanoparticle clusters vary with the spatial arrangement of the constituent particles, but also the overall orientation of the cluster with respect to the incident light. This...

Curved, Expanded and Inclined Diffraction Patterns of Grating--Rotating Grating Around Three Axes (1)

The orientation-dependence of the interference/diffraction patterns of the 1D-double slit/1D-grating and 2D-cross-double slit/2D-cross-grating experiments have been studied experimentally and theoretically. However, the above experiments were limited to certain orientations, namely rotating around either one axis or two axes. In this article, the 3-axis-rotation apparatus is proposed/made, which can rotate the 1D-double slit/2D-cross-double slit and 1D-grating/2D-cross-grating, CW and CCW respectively, 00-3600 around three axes independently and sequentially. By this apparatus, the orientation-dependence of the patterns is systematically studied. Moreover, the experiments can be performed easily. Then we show that the photons, before landing on the detector/screen, behave as particles. The above observed phenomena provide the comprehensive information to theoretical study of the double slit/grating experiments. We suggest that the complete mathematical model should contain three rotation angles as parameters. Furthermore, the phenomena have potential applications.