Assessment of the electric field induced by deep transcranial magnetic stimulation in the elderly using H-coil

The recent advancements in the design of TMS coils to reach specific cortical and subcortical regions have allowed the treatment of various neuropsychiatric disorders, whose prevalence increases with age. This could be also due to the anatomical and morphological changes with age of the brain tissues, such as the atrophy that characterizes the elderly cortex. This study provides a description of the electric field, the main engine of the stimulation, distribution induced in specific cerebral tissues. That was performed by comparing, making use of computational electromagnetic techniques, the E distributions in two human models of different ages (34 and 84 years-old males), the older one showing cortical atrophy in the prefrontal lobe. The analysis of the parameters describing the spread of the electric field distribution shows that the H1 coil is able to induce in the prefrontal cortex an E amplitude higher than the neural threshold and with a widespread distribution in both models, with a slight prevalence on the younger one. On the contrary, the maximum E penetration depth and the consequent capability to reach deeper targets in the brain, is slightly higher for the elderly model.