Comparison of tactile, electrical, and magnetic neurostimulation methods on an earthworm model

Abstract

Micro-magnetic stimulation is a promising technique for the treatment of neurological conditions, allowing long-term implant stability and effective neuronal regulation. Despite this potential, further research is essential to fully understand its mechanisms. The earthworm, with its primitive nervous system comprising two linear giant fibers, the medial giant fiber (MGF) and the lateral giant fiber (LGF), is proposed as a suitable model for investigating magnetic stimulation. The goal of this thesis is to compare tactile, electrical, and magnetic stimulation in an earthworm model. Electrical stimulation triggered both giant fibers a single time and also a third longer spike of unknown origin. In contrast, tactile stimulation selectively triggered one type of fiber depending on stimulation site. The fiber was usually triggered multiple times and the third spike was absent. Several action potentials from the MGF were recorded after magnetic stimulation. The stimulus artifact blocked the first 10 ms of recording and therefore a direct relation between stimulus and stimulation could not be established. The stimulus was 1.4 μs long and reached 2.45 kV/m. The peak electric field required to achieve stimulation for a pulse of that length was estimated at 22.6 ± 10.5 kV/m. Magnetic stimulation did not reach this value and therefore it is unclear whether this action potentials were triggered by the magnetic pulse. In tactile stimulation, crosstalk is negligible and in electrical stimulation, it becomes a concern only when the distance is less than 2 cm. In contrast, magnetic stimulation presents significant crosstalk issues, which can be effectively mitigated by increasing the distance between the stimulation and recording sites. These findings suggest that the earthworm is an appropriate model for future research exploring the phenomenon of magnetic stimulation.