A macroscopic link between interhemispheric tract myelination and cortico-cortical interactions during action reprogramming

Abstract

Myelination has been increasingly implicated in the function and dysfunction of the adult human brain. Although it is known that axon myelination shapes axon physiology in animal models, it is unclear whether a similar principle applies in the living human brain, and at the level of whole axon bundles in white matter tracts. Here, we hypothesised that in humans, cortico-cortical interactions between two brain areas may be shaped by the amount of myelin in the white matter tract connecting them. As a test bed for this hypothesis, we use a well-defined interhemispheric premotor-to-motor circuit. We combined TMS-derived physiological measures of cortico-cortical interactions during action reprogramming with multimodal myelin markers (MT, R1, R2* and FA), in a large cohort of healthy subjects. We found that physiological metrics of premotor-to-motor interaction are broadly associated with multiple myelin markers, suggesting interindividual differences in tract myelination may play a role in motor network physiology. Moreover, we also demonstrate that myelination metrics link indirectly to action switching by influencing local primary motor cortex dynamics. These findings suggest that myelination levels in white matter tracts may influence millisecond-level cortico-cortical interactions during tasks. They also unveil a link between the physiology of the motor network and the myelination of tracts connecting its components, and provide a putative mechanism mediating the relationship between brain myelination and human behaviour.

Strengthening connectivity between premotor and motor cortex increases inter-areal communication in the human brain

“…On the contrary, reductions in synaptic efficacy observed, for example, after medication in Parkinson’s disease, are mirrored in suppression of beta phase alignment within deeper structures of the motor control network (van Wijk et al, 2018). Our results are also consistent with previous investigations demonstrating, first, that inter-individual variation in myelination in PMv-related anatomical pathways is related to inter-individual variation in the impact that the induction of activity in PMv (with a TMS pulse) has on activity in M1 (Lazari et al, 2022b), and second that ccPAS induces measurable changes in the white matter track (Lazari et al, 2022a).…”

“…Depending on the inter-spike timing, ccPAS has been shown by several laboratories to result in either significant increases or decreases in functional coupling between PMv and M1 (Buch et al, 2011, Johnen et al, 2015, Casarotto et al, 2022 Relationship between changes in wPLI at rest and TFR changes during action control 2020, Turrini et al, 2022). Individual variation in functional connectivity between these regions has, in turn, been linked to individual variation in myelination of interconnecting pathways (Buch et al, 2011, Lazari et al, 2022b and ccPAS-induced changes in functional connectivity are also associated with matched changes in myelination (Lazari et al, 2022a). We demonstrate that increasing and decreasing short-term synaptic efficacy increases and decreases interregional brain communication in the PMv-M1 pathway.…”

Neurophysiological Markers of Premotor–Motor Network Plasticity Predict Motor Performance in Young and Older Adults

“…The application of the ccPAS protocol with M1 suprathreshold stimulation allowed us to track corticomotor excitability during the entire ccPAS intervention and derive an index of the plastic response of the targeted network; while we observed a linear increase of MEPs in young adults during ccPAS administration [46,48], no similar change was found in older adults in the present (Figure 1) and previous study [49]. We interpret this linear increase in motor excitability observed during PMv-M1 ccPAS as a result of the progressive increase of PMv-M1 interaction efficacy [46][47][48] and the expression and build-up of Hebbian plasticity due to the repeated and coherent activation of an excitatory PMv-to-M1 pathway [39,[41][42][43][44][45][46][47][48]. Interestingly, these changes can be of variable size in young and older individuals [46,49], possibly reflecting individual differences in the plastic potential of the PMv-M1 pathway.…”

“…A series of studies have successfully applied ccPAS in the motor system [34,35,[37][38][39][40][41][42], particularly over the PMv-M1 network, showing effective modulation of motor excitability [43][44][45][46][47][48] and hand motor functions [46,49]. However, to date, these results have been mainly observed in young adults.…”

Revealing influencing factors on global waste distribution via deep-learning based dumpsite detection from satellite imagery

“…Table 2 shows the name of 18 social attributes and their Spearman correlations with the number of dumpsites. Spearman correlation has been widely used in correlation analysis [44][45][46][47][48] . In detail, the analysis results of total dumpsites (ALL), domestic waste (DW), construction waste (CW) and agricultural waste (AW) are provided.…”