(K-433) Assessing the Acute Effects of TMS on Spatial Learning and Memory in Rats Performing the Barnes Maze Task

Brain disease currently affects 1-in-6 Americans¹, and with no cure currently existing for brain cell loss a therapeutic technique is needed to aid in neurorehabilitation. Although the acute effects of Transcranial magnetic stimulation (TMS) on learning and memory remain unclear, TMS has shown promise for enhancing cognitive functions³. The aim was to assess the acute effect of TMS on spatial learning and memory in rats. This could potentially provide insights applicable to the treatment of neurological or neuropsychiatric disorders.

A miniaturized TMS coil (5mm outer diameter) was used for experimentation² . It was made of a C-shape iron powder core with high saturated flux density (relative permeability: 75), insulated copper wires (30 turns), search coil (magnetic field measurement), and dipole probe (electric field measurement)². Two male Sprague-Dawley rats were tested, in a duration of 5 days each. The schedule was comprised of the following: baseline training (day 1), followed by alternating TMS or Sham treatments (days 2-5). During these trials the acquisition phase is first followed by a reversal learning phase and then the process is repeated. The design of the modified Barnes Maze was comprised of 16 holes with the escape hole alternating between hole 13 (acquisition) and hole 5 (reversal learning).

The miniaturized TMS Coil measured a maximum magnetic field of 174 mT in the air, and a maximum electric field of 5.2V/m at 3.5mm in saline.² The electric field was found to decay with distance along the Z axis.

The performance of the rats at both holes were measured in the following five categories: primary latency, complete latency, primary errors, complete errors, and hole deviation score. The results when the designated escape box was hole 13 (Fig 1-5) and hole 5 (Fig 6-10) both showed no significant differences between TMS or the control.

TMS seemed to have no significant improvement on the rats spatial learning and memory regardless of intended target hole. This may indicate that either TMS effects aren’t immediate since neuroplastic changes take time to occur, or changes don’t reflect in behavior immediately after TMS treatment. Future experimentation is needed to further understand the effects of TMS on spatial learning and memory.

This work was supported by Amazon and the Summer Undergraduate Research Experience (SURE) Program at the USC Viterbi School of Engineering.  All research was conducted under supervision of PhD mentor Wenxuan Jiang, and Principal Investigator Dr. Song in the USC Neural Modeling and Interface Lab.

¹ Brady, S. (2022). Knowing the signs and symptoms of brain disease. American Brain Foundation. https://www.americanbrainfoundation.org/signs-symptoms-of-brain-disease/

² Jiang, W., Isenhart, R., Sutherland, R. L., Lu, Z., Xu, H., Pace, J., Bonaguidi, M. A., Lee, D. J., Liu, C. Y., & Song, D. (2022). Subthreshold repetitive transcranial magnetic stimulation

suppresses ketamine-induced poly population spikes in rat sensorimotor cortex. Frontiers in Neuroscience, 16. https://doi.org/10.3389/fnins.2022.998704

³ Luber, B., & Lisanby, S. H. (2014). Enhancement of human cognitive performance using transcranial magnetic stimulation (TMS). NeuroImage, 85, 961–970. https://doi.org/10.1016/j.neuroimage.2013.06.007

⁴ QPS Neuropharmacology. (2022, August 25). Barnes Maze Test - QPS Neuropharmacology. https://qpsneuro.com/in-vivo-services/behavioral-tests/cognitive-tests/barnes-maze-test/