The technique in question is high-frequency repetitive transcranial magnetic stimulation, or HF-rTMS, in which rapidly pulsed magnetic fields are applied over the primary motor cortex, the brain region that commands voluntary movement. Clinicians have long observed that this stimulation can improve motor recovery and dull neuropathic pain, but the two effects were almost always studied separately, and the cellular mechanism remained a black box. A team led by researchers at Xijing Hospital and the Fourth Military Medical University in Xi’an, China, set out to open that box, combining retrospective clinical data, a mouse model of spinal cord injury, single-nucleus RNA sequencing, electron microscopy, and viral gene therapy into one unusually complete causal chain.

The clinical evidence came first. The team reviewed records of 93 patients with spinal cord injury admitted between January 2018 and June 2025, of whom 40 received four consecutive weeks of HF-rTMS targeted at the left primary motor cortex at 10 Hz, 1,200 pulses per session. Compared with patients who did not receive stimulation, the treated group showed significantly greater gains on the modified Barthel index and manual muscle test, and, strikingly, only the stimulated group achieved a significant reduction in pain on the numerical rating scale. One therapy, two symptom domains, improved simultaneously in the same patients.

To understand why, the researchers turned to mice. They inflicted a standardized compression injury at the tenth thoracic vertebra, which produced lasting hind limb motor impairment measured by the Basso Mouse Scale, alongside mechanical allodynia and thermal hyperalgesia measured with von Frey filaments and a thermal testing apparatus. High-speed gait analysis on a glass floor added objective detail: injured mice walked more slowly, with worse coordination, and visibly shifted their weight away from painful hind paws. Five weeks of daily HF-rTMS, starting three days after injury, accelerated motor recovery, reversed both measures of pain hypersensitivity, and restored normal weight-bearing in the gait analysis. The mouse model faithfully reproduced the human motor-pain comorbidity, and the stimulation relieved both.

The mechanistic hunt then went molecular. The team sequenced roughly 90,000 individual nuclei from the primary motor cortex of uninjured, injured, and injured-and-stimulated mice, sorting them into nine major cell types. When they asked which biological processes were disrupted by injury and then reversed by stimulation, one theme dominated: mitochondrial energy metabolism, including oxidative phosphorylation, ATP synthesis coupled to electron transport, and aerobic respiration. And the reversal was strongest not in the excitatory neurons that send motor commands down the spinal cord, but in GABAergic inhibitory interneurons, the cells that keep cortical circuits balanced and prevent runaway excitation.

Mitochondria are the cell’s power plants, and their health depends on a constant cycle of fission and fusion. The master regulator of fission is a protein called dynamin-related protein 1, or Drp1, which pinches damaged mitochondria into smaller pieces so they can be repaired or cleared. Using transmission electron microscopy, the researchers identified GABAergic synapses in layer V of the motor cortex by their symmetric structure and pleomorphic vesicles, then measured the mitochondria inside those neurons. After injury, the mitochondria grew progressively larger and sparser, and their circularity, a marker linked to mitochondrial toxicity, climbed over five weeks. Western blots confirmed a rapid, sustained drop in Drp1 protein in the motor cortex, while the fusion proteins mitofusin 1 and 2 were untouched. The result was a bioenergetic crisis: ATP levels in the cortex fell sharply, and markers of damaged mitochondrial accumulation, VDAC-1 and Tom20, rose.

Here the story becomes remarkable in its specificity. Confocal imaging showed that the Drp1 loss occurred selectively within GAD67-positive GABAergic neurons, not in neighboring glutamatergic neurons, and that five weeks of HF-rTMS restored Drp1 expression only in that same inhibitory population. Electron microscopy confirmed that stimulation normalized mitochondrial size, density, and circularity in GABAergic neurons while leaving glutamatergic mitochondria largely unchanged. Cell-type-specific fluorescent staining for mitochondrial superoxide and the ATP synthase subunit ATP5A revealed elevated oxidative stress and diminished energy production confined to the inhibitory neurons, defects that both stimulation and Drp1 restoration reversed. Notably, the primary somatosensory cortex, a region deeply involved in pain perception, showed no such Drp1 response to stimulation, which may explain why clinical rTMS protocols aimed at the motor cortex tend to outperform those aimed at the sensory cortex for analgesia.

Correlation, however, is not causation, and this is where the study sets a new bar for neuromodulation research. Using adeno-associated viruses driven by the GAD67 promoter, the team overexpressed Drp1 exclusively in GABAergic neurons of the motor cortex. In injured mice, this single genetic intervention mimicked the entire therapeutic package: better motor scores from week two onward, reduced allodynia and hyperalgesia, improved gait, normalized mitochondrial ultrastructure, and ATP levels pushed back toward normal. Conversely, knocking Drp1 down in those same neurons worsened the injury phenotype and, most decisively, completely abolished every benefit of HF-rTMS. A pharmacological inhibitor of Drp1, Mdivi-1, likewise nullified the stimulation’s effects on motor function and pain. Drp1 in layer V GABAergic neurons of the motor cortex is thus both necessary and sufficient for the therapy to work, a bidirectional mediator of rTMS responsiveness.

Why would inhibitory interneurons be the vulnerable population? GABAergic neurons make up only about 15 to 20 percent of cortical cells but carry enormous metabolic demands, and spinal cord injury is known to reduce GABAergic inhibition in sensory and motor cortices, a disinhibition that contributes to both maladaptive motor plasticity and chronic pain. If Drp1 deficiency starves these neurons of ATP, their energy-intensive firing falters, cortical excitatory-inhibitory balance tips, and the motor-pain comorbidity follows. By restoring fission and bioenergetics in this microcircuit, HF-rTMS may re-arm the inhibitory system and, through the motor cortex’s descending connections to the periaqueductal gray and zona incerta, re-engage the brain’s endogenous pain-control machinery. The finding also carries a practical warning: common drugs that impair mitochondrial fission, including olanzapine, amitriptyline, escitalopram, and haloperidol, could theoretically blunt a patient’s response to rTMS, something clinicians may need to weigh when planning treatment.

The implications reach well beyond spinal cord injury. Mitochondria are not passive batteries but dynamic signaling hubs governing synaptic plasticity, calcium buffering, and cell survival, and this study provides the first cell-type-specific evidence linking a noninvasive brain stimulation therapy to the precise regulation of mitochondrial fission. The authors have launched a multicenter, double-blind, sham-controlled randomized clinical trial to convert the retrospective findings into guideline-grade evidence, and they caution that the molecular pathway connecting stimulation-induced neural activity to Drp1 transcription remains to be mapped. Still, the conceptual shift is profound: secondary neurodegeneration after central nervous system injury may be driven, at least in part, by a correctable bioenergetic failure in a defined set of cortical neurons, and the magnetic coil already sitting in rehabilitation clinics may be the tool that fixes it.

Subject of Research: Drp1-mediated mitochondrial dynamics in primary motor cortex GABAergic neurons as the mechanism of rTMS therapy after spinal cord injury

Article Title: Drp1 in M1 layer V GABAergic neurons orchestrates rTMS-mediated motor restoration and analgesia after spinal cord injury

Article References: Sun, X., Zhao, R., Zhang, K., Feng, X., Zhang, X., Yang, X., Li, Z., Tian, K., Kang, X., Lin, X., Gao, M., Hu, X., Lu, Y., Liang, Y., Luo, C., Wang, Y., & Yuan, H. (2026). Drp1 in M1 layer V GABAergic neurons orchestrates rTMS-mediated motor restoration and analgesia after spinal cord injury. Experimental & Molecular Medicine. https://doi.org/10.1038/s12276-026-01857-2

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01857-2

Keywords: spinal cord injury, transcranial magnetic stimulation, Drp1, mitochondrial dynamics, GABAergic neurons, primary motor cortex, neuropathic pain, motor recovery, bioenergetics, single-nucleus RNA sequencing, neuromodulation, Mdivi-1

The technical centerpiece of the study is a method the team calls STICR, a lentiviral barcoding system that stamps progenitor cells with unique heritable DNA sequences. When a barcoded progenitor divides, all of its descendants carry the same genetic tag, allowing researchers to reconstruct family trees long after development has moved on. By injecting the virus at a series of embryonic and postnatal timepoints—from embryonic day 11 through postnatal day 0—and collecting tissue at postnatal day 4, the team captured clones born during distinct developmental windows. Each labeled cell was then profiled with single-cell RNA sequencing, and its barcode was read out alongside its transcriptome, linking identity to ancestry in a single measurement.

Knowing what a cell is, however, is only half the story; knowing where it sits is equally important. To anchor their lineage data in anatomy, the researchers used MERFISH, a spatial transcriptomics method that maps thousands of genes across intact coronal sections of the forebrain. By registering the cellular profiles recovered from dissociated tissue onto these spatial maps, the team could ask not only which cell types share a common ancestor, but also how far those relatives traveled from one another. The result is a spatiotemporal clonal atlas: a record of lineage, identity and location woven together across the entire newborn forebrain rather than a single privileged region such as the cortex, which has dominated most prior lineage studies.

The scale of the dataset allowed the authors to run careful computational checks on their inferences. Because viral labeling captures only a fraction of cells, the team built simulation frameworks using ground-truth clones to model how partial sampling affects the recovery of lineage structure. These simulations, described in the paper’s extended data, quantified how many multicellular clones are needed to reliably detect the constituent cell types of a lineage and how often apparent fate biases could arise by chance. Such validation matters, because the study’s headline conclusions rest on statistical patterns of clone sharing between cell types rather than on direct observation of dividing cells.

Among the most consequential findings is a new view of the striatum, the brain’s major input hub for movement and reward. The atlas reveals previously unrecognized differences in how ventral and dorsal medium spiny neurons—the principal projection neurons of the striatum—are generated. It also uncovers lineage relationships that had gone unexplored: late-born medium spiny neurons share clonal ancestry with striatal astrocytes and with distinct subpopulations of olfactory bulb neurons. This connects the striatum’s developmental program to the continuous postnatal production of neurons that migrate into the olfactory bulb, a hallmark of the subventricular zone that has long fascinated neuroscientists studying adult neurogenesis.

The broader principle that emerges from the atlas is a tale of two lineages. Glutamatergic neurons—the forebrain’s excitatory workhorses—and astrocytes, the star-shaped glial cells that support synapses, are clonally related to one another and remain within their region of origin. A clone born in the cortex stays in the cortex; one born in the hippocampus stays in the hippocampus. GABAergic neurons, the inhibitory counterpart, follow a different rule. They are clonally linked to oligodendrocyte precursor cells, the myelin-forming lineage, and they disperse extensively, crossing regional and structural boundaries. The findings echo and extend earlier work showing that clonally related interneurons spread widely across the forebrain, but the new atlas places that dispersal within a whole-brain framework and ties it to glial fate.

That dispersal carries a provocative clinical hint. The researchers found that clones of GABAergic neurons with broad regional dispersion are enriched for genes implicated in neurodevelopmental disorders, including genes associated with autism. In other words, the cell lineages most likely to spread across the brain are also the ones whose genetic programs intersect most heavily with disease risk. This observation suggests that disruptions to widely dispersing inhibitory lineages could have consequences distributed across multiple brain regions, offering a potential developmental framework for understanding why genetic risk factors for neurodevelopmental conditions produce such varied and widespread effects.

The temporal dimension of the atlas adds further texture. By comparing clones labeled at different embryonic and postnatal stages, the team traced how lineage composition shifts over time: early-labeled clones are dominated by deep-layer cortical neurons, while later windows capture upper-layer neurons, glia and the postnatally generated populations destined for the olfactory bulb. In the olfactory bulb itself, the data distinguish embryonically or locally generated GABAergic neurons from postnatally born neurons still migrating through the rostral migratory stream at the time of collection. Cajal–Retzius cells, the pioneer neurons that guide cortical layering, also appear in the atlas with their own regionally specific lineage relationships to astrocytes and ependymal cells.

Methodologically, the study demonstrates how viral barcoding, single-cell transcriptomics and spatial transcriptomics can be fused into a single coherent picture of organ-scale development. The authors have made their resources broadly available: the single-cell and barcode datasets are deposited in the Gene Expression Omnibus under accession GSE341480, an interactive browser of the single-cell and MERFISH data is hosted through the UCSC cell browser, the image dataset is available through the Brain Image Library, and the custom analysis code is published on GitHub. For a field increasingly reliant on large-scale atlases, this openness means other laboratories can immediately interrogate the lineage relationships, test alternative hypotheses and integrate the data with their own developmental and disease-focused studies.

The implications reach well beyond the mouse. Human studies have suggested that individual cortical progenitors can produce both excitatory and inhibitory neurons, and the new mouse atlas provides a mechanistic reference against which human lineage data can be interpreted. By establishing that lineage fate—whether a progenitor’s descendants become neurons, astrocytes or oligodendrocyte precursor cells—is governed by regionally specific rules that differ fundamentally between excitatory and inhibitory lineages, the work offers a foundational framework for dissecting how the mammalian forebrain is assembled, and how that assembly goes awry in disease. As the authors note, the atlas is intended as a reference point for the field: a first whole-forebrain census of who is related to whom, where they ended up, and when they were born.

Subject of Research: Clonal lineage relationships and cell fate specification during mouse forebrain development

Article Title: Spatiotemporal clonal architecture of the newborn mouse forebrain

Article References: Yuan, G., Kunst, M., Steyert, M. R., Keefe, M. G., Mathieu, R., van Velthoven, C. T. J., McMillen, D., Waters, J., Fukushima, Y., Kazerounian, A., Alvarez-Buylla, A., Zeng, H., & Nowakowski, T. J. (2026). Spatiotemporal clonal architecture of the newborn mouse forebrain. Nature. https://doi.org/10.1038/s41586-026-11064-8

Image Credits: AI Generated

DOI: 10.1038/s41586-026-11064-8

Keywords: mouse forebrain, clonal lineage, lentiviral barcoding, spatial transcriptomics, MERFISH, single-cell RNA sequencing, GABAergic neurons, glutamatergic neurons, astrocytes, oligodendrocyte precursor cells, neurodevelopmental disorders, striatum