Biology subjects

Raffin, E.

Publications and source records attributed to Raffin, E..

6 recordsLinked to original sources

bioRxiv2026

Concurrent TMS and Spinal Cord fMRI Reveal Intensity-Dependent Modulation of Spinal Circuits

The spinal cord serves as a crucial relay for motor commands, yet the role of its local circuitry in sensorimotor integration remains poorly understood. Most non-invasive cortical stimulation studies, rely on electrophysiological readouts or inferred spinal function from corticospinal anatomy, leaving the downstream impact of cortical stimulation on spinal circuitry largely uncharted in vivo. Advances in spinal cord functional MRI (SC-fMRI) now enable spatially resolved imaging of segmental gray and white matter and their interactions with descending cortical inputs. Here, we introduce a multimodal framework that combines single-pulse transcranial magnetic stimulation (TMS) of the primary motor cortex with SC-fMRI to probe TMS-evoked spinal activity in humans. Using graded TMS intensities, we examined blood oxygenation level-dependent (BOLD) responses in the cervical spinal cord and asked how spinal activation depends on effective engagement of the descending motor system. Our findings reveal robust, intensity-dependent spinal BOLD responses aligned with descending pathways, with activation concentrated in expected territories such as the lateral corticospinal tract and ventral horn at segments innervating the stimulated hand muscle. By linking peripheral output to segment- and pathway-resolved spinal signals, these results demonstrate that concurrent TMS-SCfMRI can capture, in vivo, how cortical drive is expressed within human spinal circuitry and provide a new framework to measure spinal contributions to sensorimotor control with spatial specificity beyond traditional peripheral readouts. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=198 HEIGHT=200 SRC="FIGDIR/small/740278v1_ufig1.gif" ALT="Figure 1"> View larger version (59K): org.highwire.dtl.DTLVardef@119f96eorg.highwire.dtl.DTLVardef@46aa73org.highwire.dtl.DTLVardef@1609045org.highwire.dtl.DTLVardef@9fbf70_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2022

Pathway and directional specificity of Hebbian plasticity induction in the cortical visual motion processing network

Cortico-cortical paired associative stimulation (ccPAS), which repeatedly pairs single pulse TMS over two distant brain regions with a specific time interval, is thought to modulate synaptic plasticity. Applied to the motion cortical pathway, ccPAS has been shown to improve motion discrimination when specifically targeting backward projections, stimulating the medio-temporal area (MT) followed by the primary visual cortex (V1). However, there is no direct neuroimaging evidence of the spatial selectivity of the ccPAS effects (i.e., pathway or direction specificity) or detailing the exact nature of the ccPAS effects (i.e., the oscillatory signature, timing...). In this study, we applied ccPAS along the motion discrimination pathway, in the top-down direction (MT-to-V1: "Backward ccPAS") and in the bottom-up direction (V1-to-MT: "Forward ccPAS") in sixteen healthy volunteers and compared changes in visual network activity in response to single pulse TMS over V1 and MT using spectral granger causality (sGC). The sGC results showed common increases in direct V1-to-MT and V1-to-IPS bottom-up inputs in the high Beta/low Gamma band (25-40 Hz) for both ccPAS, probably reflecting task exposure. However, a clear distinction in information transfer occurred in the re-entrant MT-to-V1 signals, which were only modulated by Backward ccPAS. This difference was predictive of the behavioural improvements at the motion discrimination task. Our results support the view of the possibility to specifically enhance re-entrant Alpha oscillatory signals from MT-to-V1 to promote motion discrimination performance through Backward ccPAS. These findings contribute to better understanding visual processing in healthy subjects and how it can be modulated to pave the way to clinical translation in vision handicapped patients. The changes in re-entrant MT-to-V1 inputs could help to provide single-subject prediction scenarios in patients suffering from a visual system stroke, in whom visual recovery might partly rely on the top-down inputs to the spared V1 neurons.

neuroscience↗

bioRxiv2022

Concurrent TMS-fMRI to determine adaptive brain changes to virtual lesions interfering with visual processing

Understanding how focal perturbations lead to large-scale network (re)organization is essential for accurately predicting the behavioral consequences of brain lesions. In this study, we applied a virtual lesion approach by means of short bursts of 10 Hz transcranial magnetic stimulation (TMS) over either early visual areas (EVA) or the medio-temporal area (MT) in healthy participants, while acquiring concurrent functional MRI. TMS delivered during the early stages of motion processing selectively impaired direction discrimination at both sites, while global motion perception remained unaffected. These behavioral effects were accompanied by a common local increase in BOLD activity, but distinct patterns of network reorganization. Perturbation of EVA led to more robust and efficient functional adaptation, suggesting greater resilience to focal disruption. In contrast, behavioral impairments following MT stimulation were associated with a less organized, more random network structure. Together, these findings underscore the potential of TMS-fMRI coupling as a powerful approach for mapping causal disconnectomics--the dynamic relationships between localized neural disruption and widespread functional and behavioral outcomes providing a better understanding of lesion-induced brain changes in neurological disorders such as stroke. HighlightsO_LITMS-induced perturbation of the early visual areas (EVA) or the mediotemporal area (MT) area selectively impairs motion direction discrimination. C_LIO_LIThe TMS perturbation is associated with a context-dependent local up-scaling of BOLD activity in both areas. C_LIO_LIThe two visual areas display distinct topological networks adaptation in response to TMS, reflecting different levels of network resilience to a focal lesion. C_LIO_LITMS-fMRI coupling can be used to assess causal disconnectomics and to precisely map how a local perturbation propagates to large-scale behavioural deficits. C_LI

neuroscience↗

bioRxiv2020

Bifocal tACS Enhances Visual Motion Discrimination by Modulating Phase Amplitude Coupling Between V1 and V5 Regions

Visual motion discrimination involves reciprocal interactions in the alpha band between the primary visual cortex (V1) and the mediotemporal area (V5/MT). We investigated whether modulating alpha phase synchronization using individualized multisite transcranial alternating current stimulation (tACS) over V5 and V1 regions would improve motion discrimination. We tested 3 groups of healthy subjects: 1) an individualized In-Phase V1alpha-V5alpha tACS (0{degrees} lag) group, 2) an individualized Anti-Phase V1alpha-V5alpha tACS (180{degrees} lag) group and 3) a sham tACS group. Motion discrimination and EEG activity were compared before, during and after tACS. Performance significantly improved in the Anti-Phase group compared to that in the In-Phase group at 10 and 30 minutes after stimulation. This result could be explained by changes in bottom-up alpha-V1 gamma-V5 phase-amplitude coupling. Thus, Anti-Phase V1alpha-V5alpha tACS might impose an optimal phase lag between stimulation sites due to the inherent speed of wave propagation, hereby supporting optimized neuronal communication. IMPACT STATEMENTO_LIAlpha multisite (V1 and V5) tACS influences global motion discrimination and integration C_LIO_LIPhase-amplitude coupling is associated with visual performance C_LIO_LIMultisite Anti-Phase stimulation of strategic visual areas (V1 and V5) is associated with connectivity changes in the visual cortex and thus, associated with changes in direction acuity C_LI

neuroscience↗

bioRxiv2019

Electrocutaneous stimulation to the face inhibits motor evoked potentials in the hand: face-hand interactions revealed by afferent inhibition

Reorganization of the sensorimotor cortex following amputation and other interventions has revealed large-scale plastic changes between the hand and face representations. To investigate whether hand-face interactions are also present in the normal state of the system we measured sensorimotor interactions between these two areas using an afferent inhibition transcranial magnetic stimulation (TMS) protocol in which the TMS motor evoked potential (MEP) is inhibited when it is preceded by an afferent stimulus. We hypothesized that if hand-face interactions exist in the normal state of the system then stimulation of the face would inhibit hand MEPs. In two separate experiments we delivered an electrocutaneous stimulus to either the right upper lip (Experiment 1) or right cheek (Experiment 2) and recorded muscular activity from the right first dorsal interosseous (FDI). Both lip and cheek stimulation inhibited FDI MEPs. To investigate the specificity of this effect we conducted two additional experiments in which cutaneous stimulation was applied to either the right forearm (Experiment 3) or right arm (Experiment 4). Neither forearm nor arm stimulation inhibited FDI MEPs. These data provide the first evidence for face-to-hand afferent inhibition and we suggest that the mechanisms underlying these sensorimotor interactions could contribute to face/hand interactions observed following sensorimotor reorganisation.

neuroscience↗

bioRxiv2017

Use-dependent plasticity in human primary motor hand area:Synergistic interplay between training and immobilisation

Training and immobilization are powerful drivers of use-dependent plasticity in human primary motor hand area (M1HAND). Here we used transcranial magnetic stimulation to clarify how training and immobilisation of a single finger interact within M1HAND. Healthy volunteers trained to track a moving target with a finger for one week. The tracking skill acquired with the trained finger was transferred to a non-trained finger of the same hand. The cortical representations of the trained and non-trained finger muscle converged in proportion with skill transfer. Finger immobilisation alone attenuated the corticomotor representation and pre-existing tracking skill of the immobilized finger. The detrimental effects of finger immobilization were blocked by concurrent training of the non-immobilized finger. Conversely, immobilization of the non-trained fingers accelerated learning during the first two days of training. The results provide novel insight into use-dependent cortical plasticity, revealing synergistic rather than competitive interaction patterns within M1HAND.

neuroscience↗