Transcranial magnetic stimulation (TMS) is a tool for neuromodulation that uses a time-varying magnetic field to stimulate the brain via an induced electric field (E-Field). Clinical data from Premier Psychiatric Research Institute on repetitive TMS (rTMS) for the treatment of depression shows that patients older than 55 years respond to deep rTMS with better efficacy than younger patients. Brain volume shrinks with age in adults older than 40 years, increasing the distance between their brain and scalp. In this paper, we have investigated how the induced E-Field from TMS is affected by brain-scalp distance (BSD). We have developed heterogeneous head models from MRI data of 50 subjects and created simplified head models using concentric spheres. Using finite-element analysis, we simulated TMS on these models to test the role of BSD in determining the strength and distribution of the E-Field.

To investigate inter-subject variability with respect to cerebrospinal fluid thickness and brain-scalp distance, and to investigate intra-subject variability with different coil orientations. Simulations of the induced electric field (E-Field) using a figure-8 coil over the vertex were conducted on 50 unique head models and varying orientations on 25 models. Metrics exploring stimulation intensity, spread, and localization were used to describe inter-subject variability and effects of non-brain anatomy. Both brain-scalp distance and CSF thickness were correlated with weaker stimulation intensity and greater spread. Coil rotations show that for the dorsal portion of the stimulated brain, E-Field intensities are highest when the anterior-posterior axis of the coil is perpendicular to the longitudinal fissure, but highest for the medial portion of the stimulated brain when the coil is oriented parallel to the longitudinal fissure. Normal anatomical variation in healthy individuals leads to significant differences in the site of TMS, the intensity, and the spread. These variables are generally neglected but could explain significant variability in basic and clinical studies. This is the first work to show how brain-scalp distance and cerebrospinal fluid thickness influence focality, and to show the disassociation between dorsal and medial TMS.

Transcranial Magnetic Stimulation (TMS) is a technique for neuromodulation that can be used as a non-invasive therapy for various neurological disorders. In TMS, a time varying magnetic field generated from an electromagnetic coil placed on the scalp is used to induce an electric field inside the brain. TMS coil geometry plays an important role in determining the focality and depth of penetration of the induced electric field responsible for stimulation. Clinicians and basic scientists are interested in stimulating a localized area of the brain, while minimizing the stimulation of surrounding neural networks. In this paper, a novel coil has been proposed, namely Quadruple Butterfly Coil (QBC) with an improved focality over the commercial Figure-8 coil. Finite element simulations were conducted with both the QBC and the conventional Figure-8 coil. The two coil’s stimulation profiles were assessed with 50 anatomically realistic MRI derived head models. The coils were positioned on the vertex and the scalp over the dorsolateral prefrontal cortex to stimulate the brain. Computer modeling of the coils has been done to determine the parameters of interest-volume of stimulation, maximum electric field, location of maximum electric field and area of stimulation across all 50 head models for both coils.

Emerging research on neuroplasticity processes in psychosis spectrum illnesses—from the synaptic to the macrocircuit levels—fill key gaps in our models of pathophysiology and open up important treatment considerations. In this selective narrative review, we focus on three themes, emphasizing alterations in spike-timing dependent and Hebbian plasticity that occur during adolescence, the critical period for prefrontal system development: (1) Experience-dependent dysplasticity in psychosis emerges from activity decorrelation within neuronal ensembles. (2) Plasticity processes operate bidirectionally: deleterious environmental and experiential inputs shape microcircuits. (3) Dysregulated plasticity processes interact across levels of scale and time and include compensatory mechanisms that have pathogenic importance. We present evidence that—given the centrality of progressive dysplastic changes, especially in prefrontal cortex—pharmacologic or neuromodulatory interventions will need to be supplemented by corrective learning experiences for the brain if we are to help people living with these illnesses to fully thrive.

Transcranial magnetic stimulation (TMS) is a non-invasive treatment for major depressive disorder. TMS coil design plays an important role in navigating the magnetic field to the required location in the brain. Development of deep brain TMS coils will help to stimulate sub-cortical structures, allowing for a significant expansion of the uses of TMS beyond superficial cortical targets. Stimulating deep brain regions may have beneficial effects on neurological disorders such as Parkinson's disease, Post-Traumatic Stress Disorder and mild traumatic brain injury. In this manuscript, design and testing of a multi-coil configuration, the Triple Halo Coil (THC) is proposed, which can stimulate deep brain structures such as the hippocampus and amygdala. A finite element tool is used to determine the induced electric field and magnetic field in these regions due to the THC alone and in combination with the Figure-of-8 coil. Analysis of the results are done with the help of an MRI-derived anatomically accurate heterogeneous head model of a 34-year-old man. Furthermore, the magnetic field of the THC is measured and compared with the simulated value.