Direct Current Stimulation in Cell Culture Systems and Brain Slices-New Approaches for Mechanistic Evaluation of Neuronal Plasticity and Neuromodulation: State of the Art

Integration Analysis of miRNA Circulating Expression Following Cerebellar Transcranial Direct Current Stimulation in Patients with Ischemic Stroke

The aim of this study was to explore the molecular mechanisms underlying cerebellar transcranial direct current stimulation (ctDCS) as a rehabilitation intervention for patients with ischemic stroke, focusing on the role of microRNAs (miRNAs). Whole-transcriptome sequencing was employed to obtain circulating expression profiles of miRNAs, long non-coding RNAs (lncRNAs), circular RNAs (circRNAs), and mRNAs in patients with ischemic stroke before and after 3-week ctDCS. miRanda software was used to predict the target genes of miRNAs, while Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were conducted to identify biological functions and signaling pathways. Subsequently, competing endogenous RNA (ceRNA) regulatory networks comprising circRNA-miRNA-mRNA and lncRNA-miRNA-mRNA interactions were constructed. Key miRNAs in blood samples were validated through quantitative RT-PCR. In total, 43 miRNAs, 807 lncRNAs, 1,111 circRNAs, and 201 mRNAs were differentially expressed after ctDCS compared with before ctDCS. Bioinformatics analyses revealed significant enrichment of target genes regulated by differentially expressed miRNAs across multiple biological pathways. CeRNA regulatory networks implied that several miRNAs were closely related to the ctDCS. Among them, hsa-miR-181a-5p, hsa-miR-224-5p, and hsa-miR-340-3p showed significantly downregulated expression levels as confirmed by qRT-PCR. This study conducted the first-ever assessment of miRNA expression patterns in patients with ischemic stroke undergoing ctDCS. The findings revealed that ctDCS induces alterations in miRNA levels, suggesting their potential utility as therapeutic markers.

Non-Invasive Brain Sensing Technologies for Modulation of Neurological Disorders

The non-invasive brain sensing modulation technology field is experiencing rapid development, with new techniques constantly emerging. This study delves into the field of non-invasive brain neuromodulation, a safer and potentially effective approach for treating a spectrum of neurological and psychiatric disorders. Unlike traditional deep brain stimulation (DBS) surgery, non-invasive techniques employ ultrasound, electrical currents, and electromagnetic field stimulation to stimulate the brain from outside the skull, thereby eliminating surgery risks and enhancing patient comfort. This study explores the mechanisms of various modalities, including transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), highlighting their potential to address chronic pain, anxiety, Parkinson's disease, and depression. We also probe into the concept of closed-loop neuromodulation, which personalizes stimulation based on real-time brain activity. While we acknowledge the limitations of current technologies, our study concludes by proposing future research avenues to advance this rapidly evolving field with its immense potential to revolutionize neurological and psychiatric care and lay the foundation for the continuing advancement of innovative non-invasive brain sensing technologies.

Study on the Role of Physical Fields in TMAS to Modulate Synaptic Plasticity in Mice

OBJECTIVE

Transcranial magneto-acoustic stimulation (TMAS) is a composite technique combining static magnetic and coupled electric fields with transcranial ultrasound stimulation (TUS) and has shown advantages in neuromodulation. However, the role of these physical fields in neuromodulation is unclear. Synaptic plasticity is the cellular basis for learning and memory. In this paper, we varied the intensity of static magnetic, electric and ultrasonic fields respectively to investigate the modulation of synaptic plasticity by these physical fields.

METHODS

There are control, static magnetic field (0.1 T/0.2 T), TUS (0.15/0.3 MPa), and TMAS (0.15 MPa + 0.2 V/m, 0.3 MPa + 0.2 V/m, 0.3 MPa + 0.4 V/m) groups. Hippocampal areas were stimulated at 5 min daily for 7 days and in vivo electrophysiological experiments were performed.

RESULTS

TMAS induced greater LTP, LTD, and paired-pulse ratio (PPR) than TUS, reflecting that TMAS has a more significant modulation in both long- and short- term synaptic plasticity. In TMAS, a doubling of the electric field amplitude increases LTP, LTD and PPR to a greater extent than a doubling of the acoustic pressure. Increasing the static magnetic field intensity has no significant effect on the modulation of synaptic plasticity.

CONCLUSION

This paper argues that electric fields should be the main reason for the difference in modulation between TMAS and TUS and that changing the amplitude of the electric field affected the modulation of TMAS more than changing the acoustic pressure.

SIGNIFICANCE

This study elucidates the roles of the physical fields in TMAS and provides a parameterisation way to guide TMAS applications based on the dominant roles of the physical fields.

Brain stimulation-on-a-chip: a neuromodulation platform for brain slices

Electrical stimulation of ex vivo brain tissue slices has been a method used to understand mechanisms imparted by transcranial direct current stimulation (tDCS), but there are significant direct current electric field (dcEF) dosage and electrochemical by-product concerns in conventional experimental setups that may impact translational findings. Therefore, we developed an on-chip platform with fluidic, electrochemical, and magnetically-induced spatial control. Fluidically, the chamber geometrically confines precise dcEF delivery to the enclosed brain slice and allows for tissue recovery in order to monitor post-stimulation effects. Electrochemically, conducting hydrogel electrodes mitigate stimulation-induced faradaic reactions typical of commonly-used metal electrodes. Magnetically, we applied ferromagnetic substrates beneath the tissue and used an external permanent magnet to enable in situ rotational control in relation to the dcEF. By combining the microfluidic chamber with live-cell calcium imaging and electrophysiological recordings, we showcased the potential to study the acute and lasting effects of dcEFs with the potential of providing multi-session stimulation. This on-chip bioelectronic platform presents a modernized yet simple solution to electrically stimulate explanted tissue by offering more environmental control to users, which unlocks new opportunities to conduct thorough brain stimulation mechanistic investigations.

Individual electric field predicts functional connectivity changes after anodal transcranial direct-current stimulation in chronic stroke

The neuromodulation effect of anodal tDCS is not thoroughly studied, and the heterogeneous profile of stroke individuals with brain lesions would further complicate the stimulation outcomes. This study aimed to investigate the functional changes in sensorimotor areas induced by anodal tDCS and whether individual electric field could predict the functional outcomes. Twenty-five chronic stroke survivors were recruited and divided into tDCS group (n = 12) and sham group (n = 13). Increased functional connectivity (FC) within the surrounding areas of ipsilesional primary motor cortex (M1) was only observed after anodal tDCS. Averaged FC among the ipsilesional sensorimotor regions was observed to be increased after anodal tDCS (t(11) = 2.57, p = 0.026), but not after sham tDCS (t(12) = 0.69, p = 0.50). Partial least square analysis identified positive correlations between electric field (EF) strength normal to the ipsilesional M1 surface and individual FC changes in tDCS group (r = 0.84, p < 0.001) but not in sham group (r = 0.21, p = 0.5). Our results indicated anodal tDCS facilitates the FC within the ipsilesional sensorimotor network in chronic stroke subjects, and individual electric field predicts the functional outcomes.