M1 dynamics share similar inputs for initiating and correcting movement

Motor cortex is integral to generating voluntary movement commands. However, as a dynamical system, it is unclear how motor cortical movement commands are informed by either new or sensory-driven corrective instructions. Here, we examine population activity in the primary motor cortex of macaques during a continuous, sequential arm movement task in which the movement instruction is updated several times over the course of a trial. We use Latent Factor Analysis via Dynamical Systems (LFADS) to decompose population activity into a portion explainable via dynamics, and a stream of inferred inputs required to instruct that dynamical system. The time series of inferred inputs had several surprising properties. First, input timing was more strongly locked to target appearance than to movement onset, suggesting that variable reaction times may be a function of how inputs interact with ongoing dynamics rather than variability in instruction timing. Second, inferred inputs were tuned nearly identically for both initial and corrective movements, suggesting a commonality in the structure of inputs across visually-instructed and corrective movements that was previously obscured by the complexity of the dynamical system that is M1.

Squat Jump Movement Onset Thresholds Influence on Kinetics and Kinematics

Background of Study: Differing movement onset thresholds have been used when analyzing the squat jump movement from force-time data obtained from a force platform. This makes comparisons difficult between investigations as this will impact the amount of the force-time curve that is analyzed. Objective: Thus, study examined the effect onset threshold had on kinetic and kinematic variables used in the assessment of the squat jump. Methods: Using a within-subject study design, fifteen recreational trained males performed three trials of squat jumps on a force platform. Each trial was analyzed using one of five different onset thresholds (2.5% SW, 5% SW, 10% SW, 20N, 5SD). Force, velocity, and power, as well as time to peak force, velocity, power and jump height were calculated using the vertical force data obtain from the force plate. Reliability was assessed using intraclass correlation coefficients and coefficients of variation. A one-way ANOVA was used to examine the impact of onset thresholds on all variables of interest. Results: The use of 10% SW and 5SD met minimum reliability criteria for all variables. Temporal related variables were impact to the greatest extent by differing thresholds with large (d > 1.20) significant differences. 10% SW showed the highest mean values of force, velocity, and power. Conclusions: The use of 5SD of the weighting phase is recommended as this showed high level of both absolute and relative reliability in addition to preserving a large portion of the force – time curve to be used in the analysis.

Cortical Motor Planning and Biomechanical Stability During Unplanned Jump-Landings in Males With ACL-Reconstruction

Context: Athletes with anterior cruciate ligament (ACL) reconstruction exhibit increased cortical motor planning during simple sensorimotor tasks compared to healthy controls. This may interfere with proper decision-making during time-constrained movements elevating the re-injury risk. Objective: To compare cortical motor planning and biomechanical stability during jump-landings between participants with ACL-reconstruction and healthy individuals. Design: Cross-sectional exploratory study. Setting: Laboratory patients or other participants: Ten males with ACL-reconstruction (28±4 yrs., 63±35 months post-surgery) and 17 healthy males (28±4 yrs.) completed pre-planned (landing leg shown before take-off; n=43±4) and unplanned (visual cue during flight; n=51±5) countermovement-jumps with single-leg-landings. Main outcome measures: Movement-related cortical potentials (MRCP) and frontal theta frequency power before the jump were analyzed using electroencephalography. MRCP were subdivided into three successive 0.5 sec epochs (readiness potential 1 and 2; RP and negative slope; NS) relative to movement onset (higher values indicative of more motor planning). Theta power was calculated for the last 0.5 sec prior to movement onset (higher values indicative of more focused attention). Biomechanical landing stability was measured via vertical peak ground reaction force, time to stabilization, and center of pressure. Results: Both conditions evoked MRCP at all epochs in both groups. During the unplanned condition, the ACL-reconstructed group exhibited slightly, but not significantly higher MRCP (RP-1:p=0.651, d=0.44, RP-2:p=0.451, d=0.48; NS:p=0.482, d=0.41). The ACL-reconstructed group also showed slightly higher theta power values during the pre-planned (p=0.175, d=0.5) and unplanned condition (p=0.422, d=0.3) reaching small to moderate effect sizes. In none of the biomechanical outcomes, both groups differed significantly (p>0.05). No significant condition and group interactions occurred (p>0.05). Conclusions: Our jump-landing task evoked MRCP. Although not significant between groups, the observed effect sizes provide first indication that males with ACL-reconstruction may persistently rely on more cortical motor planning associated with unplanned jump-landings. Confirmatory studies with larger sample sizes are warranted. Trial registry: clinicalTrials.gov (NCT03336060).

Superior colliculus saccade motor bursts do not dictate movement kinematics

The primate superior colliculus (SC) contains a topographic map of visual field locations, such that the anatomical location of any given active neuron defines a desired eye movement amplitude and direction. Complementing such a spatial code, SC neurons also exhibit saccade-related bursts that are tightly synchronized with movement onset. Current models suggest that such bursts, and their properties, constitute a temporal rate code that may dictate moment-to-moment movement evolution. However, a recent result demonstrated altered movement properties with minimal changes in SC motor burst strengths (Buonocore, Tian, Khademi, & Hafed, 2021). Here, I support such a dissociation between the SC temporal rate code and instantaneous movement evolution: SC burst strength varies depending on whether saccades are directed towards the upper or lower visual fields, but the movements themselves have similar kinematics. Thus, SC saccade-related motor bursts do not necessarily dictate movement kinematics, motivating investigating other possible functional roles for these bursts.

Changes in Corticospinal Circuits During Premovement Facilitation in Physiological Conditions

Changes in corticospinal excitability have been well documented in the preparatory period before movement, however, their mechanisms and physiological role have not been entirely elucidated. We aimed to investigate the functional changes of excitatory corticospinal circuits during a reaction time (RT) motor task (thumb abduction) in healthy subjects (HS). 26 HS received single pulse transcranial magnetic stimulation (TMS) over the primary motor cortex (M1). After a visual go signal, we calculated RT and delivered TMS at three intervals (50, 100, and 150 ms) within RT and before movement onset, recording motor evoked potentials (MEP) from the abductor pollicis brevis (APB) and the task-irrelevant abductor digiti minimi (ADM). We found that TMS increased MEPAPB amplitude when delivered at 150, 100, and 50 ms before movement onset, demonstrating the occurrence of premovement facilitation (PMF). MEP increase was greater at the shorter interval (MEP50) and restricted to APB (no significant effects were detected recording from ADM). We also reported time-dependent changes of the RT and a TMS side-dependent effect on MEP amplitude (greater on the dominant side). In conclusion, we here report changes of RT and side-dependent, selective and facilitatory effects on the MEPAPB amplitude when TMS is delivered before movement onset (PMF), supporting the role of excitatory corticospinal mechanisms at the basis of the selective PMF of the target muscle during the RT protocol.

Stopping vs Resting state during motor imagery paradigm

Current non-invasive Brain Machine interfaces commonly rely on the decoding of sustained motor imagery activity (MI). This approach enables a user to control brain-actuated devices by triggering predetermined motor actions. One major drawback of such strategy is that users are not trained to stop their actions. Indeed, the termination process involved in BMI is poorly understood with most of the studies assuming that the end of an MI action is similar to the resting state. Here we hypothesize that the process of stopping MI (MI termination) and resting state are two different processes that should be decoded independently due to the exhibition of different neural pattens. We compared the detection of both states transitions of an imagined movement, i.e. rest-to-movement (onset) and movement-to-rest (offset). Our results shows that both decoders show significant differences in term of performances and latency (N=17 Subjects) with the offset decoder able to detect faster and better MI termination. While studying this difference, we found that the offset decoder is primarily based on the use of features in Beta band which appears earlier. Based on this finding, we also proposed a Random Forrest based decoder which enable to distinguish three classes (MI, MI termination and REST).

Bereitschaftspotential in Multiple System Atrophy

Objective: Multiple system atrophy (MSA) is a neurodegenerative disorder manifesting as parkinsonism, cerebellar ataxia, and autonomic dysfunction. It is categorized into MSA with predominant parkinsonism (MSA-P) and into MSA with predominant cerebellar ataxia (MSA-C). The pathophysiology of motor control circuitry involvement in MSA subtype is unclear. Bereitschaftspotential (BP) is a feasible clinical tool to measure electroencephalographic activity prior to volitional motions. We recorded BP in patients with MSA-P and MSA-C to investigate their motor cortical preparation and activation for volitional movement.Methods: We included eight patients with MSA-P, eight patients with MSA-C, and eight age-matched healthy controls. BP was recorded during self-paced rapid wrist extension movements. The electroencephalographic epochs were time-locked to the electromyography onset of the voluntary wrist movements. The three groups were compared with respect to the mean amplitudes of early (1,500–500 ms before movement onset) and late (500–0 ms before movement onset) BP.Results: Mean early BP amplitude was non-significantly different between the three groups. Mean late BP amplitude in the two patient groups was significantly reduced in the parietal area contralateral to the movement side compared with that in the healthy control group. In addition, the late BP of the MSA-C group but not the MSA-P group was significantly reduced at the central parietal area compared with that of the healthy control group.Conclusions: Our findings suggest that patients with MSA exhibit motor cortical dysfunction in voluntary movement preparation and activation. The dysfunction can be practicably evaluated using late BP, which represents the cerebello-dentato-thalamo-cortical pathway.