Electroencephalography (EEG) in combination with Transcranial magnetic stimulation (TMS) to study useful biomarkers for neurological disorders.


Posted on: January 12, 2023

Recently a number of new TMS techniques and protocols have been developed as diagnostic tests to evaluate inhibited or overreactive connections in the cortex of the brain, also many new protocols using repetitive TMS to evoke plasticity in the cortex of the brain have shown efficacy to improve pathological conditions like depression, early Alzheimer’s dementia among other neurological conditions. Several studies have been used to demonstrate states of intracortical and subcortical motor control, utilizing physiological outputs of the motor cortex in the spinal cord D-waves or the skeletal muscle as motor evoked potentials. In order to monitor cortical states outside the motor cortex different output effects have been considered, in the case of major depressive disorder, for example, the effect of stimulating the dorsolateral prefrontal cortex (DLPFC) using TMS can be evaluated in the contralateral DLPFC. New applications combining well know techniques such as TMS–EEG, TMS–fMRI, and TMS–NIRS can be used to address the cortical effects of nonmotor cortical plasticity. The combination of TMS-EEG is of particular electrophysiological interest, changes in the normal configuration of the cortical electrical behavior can serve to find specific cortical adaptations to TMS, therefore being effective biomarkers to specific conditions.

Biomarkers are complex, ideally, there is a link between the biomarker and a chemical compound at the cellular level that strongly correlate with the signs and symptoms of the disease, also it would help to predict the progression of the disease. Consider glucose as a biomarker, measured in the bloodstream it reflects the incapacity of the pancreas to produce insulin or the cell membrane to transport the glucose into the intracellular level. Thus it can serve not only to diagnose a pathological condition such as Diabetes but as well serves to stratify the severity of the disease, showing a predictive value to prevent complications of the disease at advanced stages. A cortical biomarker for depression for example could assist in the early diagnosis as well as evaluating it progression and effect of potential treatments. 2 important features of a biomarker are high sensitivity and specificity.

Some good examples have been reported evaluating potential biomarkers as predictors of neurological diseases and potential therapies. Kimiskidis, 2015 reviewed protocols reporting the use of TMS and EEG in epilepsy, and changes evoked by TMS, he concluded: “TMS combined with EEG is a highly relevant technique for exploration of the pathophysiology of human epilepsies as well as a promising biomarker with diagnostic and prognostic potential”

Sun et, al. 2016 reported changes in TMS-EEG readings in patients with major depressive disorder resistant to treatment. TMS-evoked potentials (TEPs) recorded by EEG at the cortical level, were analyzed in the participants that received magnetic seizure therapy (MST), the authors identified changes in measures of cortical inhibition used, (N100 and long-interval cortical inhibition (LICI)). For the main results, the authors analyzed the outcomes of a scale for suicide ideation (SSI) and TPEs and reported: “The N100 and LICI in the frontal cortex-but not in the motor cortex-were indicators of remission of suicidal ideation with 89% accuracy, 90% sensitivity, and 89% specificity”

In an elegant report, Radhu et. al, 2017 showed the impact of LICI on Schizophrenia. Since previous reports have linked LICI to GABAergic inhibitory neurotransmission and deficits in GABAergic inhibitory neurotransmission are a reliable finding in patients with schizophrenia (SCZ), the authors collected LICI recordings from the DLPFC of first-degree relatives of patients with SCZ and their related “probands were investigated to assess frontal cortical inhibition.” The authors concluded that “impairments in frontal inhibition are specific to the pathophysiology of SCZ and may have the potential for use in diagnosis.” Another group reported the generation and modulation of gamma oscillatory activity (Tremblay, et. al, 2019) of the DLPFC could be utilized to develop stimulations protocols to target the DLPFC to delay, halt or even reverse pathophysiological processes and related functional impairments in individuals with schizophrenia

At Jali Medical, we offer innovative technology to further support your research. Also, noting the pp-TMS devices we have on our product line cover a wide range of options for clinicians and researchers. We are happy to share our insights, please let us know the convenient time to setup a conference call. Contact Us

About the author
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Francisco Benavides, MD
Neuroscientist

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