Publications

@article{bracklein_control_2022,

title = {The control and training of single motor units in isometric tasks are constrained by a common input signal},

author = { Mario Bräcklein and Deren Yusuf Barsakcioglu and Jaime Ibáñez and Jonathan Eden and Etienne Burdet and Carsten Mehring and Dario Farina},

editor = { J Andrew Pruszynski and Tirin Moore and Andrew Fuglevand},

url = {https://doi.org/10.7554/eLife.72871},

doi = {10.7554/eLife.72871},

issn = {2050-084X},

year  = {2022},

date = {2022-06-01},

urldate = {2023-09-08},

journal = {eLife},

volume = {11},

pages = {e72871},

abstract = {Recent developments in neural interfaces enable the real-time and non-invasive tracking of motor neuron spiking activity. Such novel interfaces could provide a promising basis for human motor augmentation by extracting potentially high-dimensional control signals directly from the human nervous system. However, it is unclear how flexibly humans can control the activity of individual motor neurons to effectively increase the number of degrees of freedom available to coordinate multiple effectors simultaneously. Here, we provided human subjects (N = 7) with real-time feedback on the discharge patterns of pairs of motor units (MUs) innervating a single muscle (tibialis anterior) and encouraged them to independently control the MUs by tracking targets in a 2D space. Subjects learned control strategies to achieve the target-tracking task for various combinations of MUs. These strategies rarely corresponded to a volitional control of independent input signals to individual MUs during the onset of neural activity. Conversely, MU activation was consistent with a common input to the MU pair, while individual activation of the MUs in the pair was predominantly achieved by alterations in de-recruitment order that could be explained by history-dependent changes in motor neuron excitability. These results suggest that flexible MU recruitment based on independent synaptic inputs to single MUs is unlikely, although de-recruitment might reflect varying inputs or modulations in the neuron’s intrinsic excitability.},

note = {Publisher: eLife Sciences Publications, Ltd},

keywords = {common synaptic input, motor control, motor unit, real-time decomposition},

pubstate = {published},

tppubtype = {article}

}

@article{bracklein_reading_2022,

title = {Reading and Modulating Cortical β Bursts from Motor Unit Spiking Activity},

author = { Mario Bräcklein and Deren Yusuf Barsakcioglu and Alessandro Del Vecchio and Jaime Ibáñez and Dario Farina},

url = {https://www.jneurosci.org/content/42/17/3611},

doi = {10.1523/JNEUROSCI.1885-21.2022},

issn = {0270-6474, 1529-2401},

year  = {2022},

date = {2022-04-01},

urldate = {2022-04-01},

journal = {Journal of Neuroscience},

volume = {42},

number = {17},

pages = {3611–3621},

abstract = {β Oscillations (13–30 Hz) are ubiquitous in the human motor nervous system. Yet, their origins and roles are unknown. Traditionally, β activity has been treated as a stationary signal. However, recent studies observed that cortical β occurs in “bursting events,” which are transmitted to muscles. This short-lived nature of β events makes it possible to study the main mechanism of β activity found in the muscles in relation to cortical β. Here, we assessed whether muscle β activity mainly results from cortical projections. We ran two experiments in healthy humans of both sexes (N = 15 and N = 13, respectively) to characterize β activity at the cortical and motor unit (MU) levels during isometric contractions of the tibialis anterior muscle. We found that β rhythms observed at the cortical and MU levels are indeed in bursts. These bursts appeared to be time-locked and had comparable average durations (40–80 ms) and rates (approximately three to four bursts per second). To further confirm that cortical and MU β have the same source, we used a novel operant conditioning framework to allow subjects to volitionally modulate MU β. We showed that volitional modulation of β activity at the MU level was possible with minimal subject learning and was paralleled by similar changes in cortical β activity. These results support the hypothesis that MU β mainly results from cortical projections. Moreover, they demonstrate the possibility to decode cortical β activity from MU recordings, with a potential translation to future neural interfaces that use peripheral information to identify and modulate activity in the central nervous system. 

SIGNIFICANCE STATEMENT We show for the first time that β activity in motor unit (MU) populations occurs in bursting events. These bursts observed in the output of the spinal cord appear to be time-locked and share similar characteristics of β activity at the cortical level, such as the duration and rate at which they occur. Moreover, when subjects were exposed to a novel operant conditioning paradigm and modulated MU β activity, cortical β activity changed in a similar way as peripheral β. These results provide evidence for a strong correspondence between cortical and peripheral β activity, demonstrating the cortical origin of peripheral β and opening the pathway for a new generation of neural interfaces.},

note = {Publisher: Society for Neuroscience 

Section: Research Articles},

keywords = {Motor Units, neural interfaces, neural oscillations, real-time decomposition, β oscillations},

pubstate = {published},

tppubtype = {article}

}