Training-induced dynamics of accuracy and precision in human motor control

Hierarchical Organization and Adjustment of Force Coordination in Response to Self-Triggered and External-Triggered Cues in Simulated Archery Performance

The purpose of this study was to investigate the hierarchical organization of digit force production and its effect on stability and performance during the simulated archery task. The simulated archery shooting task required the production of a prescribed level of force in virtual space with the left hand and an equivalent force with all 4 fingers of right hand. A single trial had 2 phases, including static force production as aiming in archery and quick force release to shoot the virtual arrow. The timing of the force release was determined by the participant's choice or response to the external cue. The coordination indices, that is, the synergy index, of force stabilization were quantified in 2 hierarchies by decomposing the variance components. The accuracy and precision of the hit position of the virtual arrow were calculated as performance-related indices. The results confirmed that the precision, that is, reproducibility, of the performance was greater when the force release time was determined by the self-selected time, suggesting the beneficial effect of the anticipatory mechanism. There was a distinct synergistic organization of digit forces for the stabilization of net forces in both bimanual and multifinger levels, which was especially correlated with the precision of performance.

Neural Filtering of Physiological Tremor Oscillations to Spinal Motor Neurons Mediates Short-Term Acquisition of a Skill Learning Task

The acquisition of a motor skill involves adaptations of spinal and supraspinal pathways to alpha motoneurons. In this study, we estimated the shared synaptic contributions of these pathways to understand the neural mechanisms underlying the short-term acquisition of a new force-matching task. High-density surface electromyography (HDsEMG) was acquired from the first dorsal interosseous (FDI; 7 males and 6 females) and tibialis anterior (TA; 7 males and 4 females) during 15 trials of an isometric force-matching task. For two selected trials (pre- and post-skill acquisition), we decomposed the HDsEMG into motor unit spike trains, tracked motor units between trials, and calculated the mean discharge rate and the coefficient of variation of interspike interval (COVISI). We also quantified the post/pre ratio of motor units' coherence within delta, alpha, and beta bands. Force-matching improvements were accompanied by increased mean discharge rate and decreased COVISI for both muscles. Moreover, the area under the curve within alpha band decreased by ∼22% (TA) and ∼13% (FDI), with no delta or beta bands changes. These reductions correlated significantly with increased coupling between force/neural drive and target oscillations. These results suggest that short-term force-matching skill acquisition is mediated by attenuation of physiological tremor oscillations in the shared synaptic inputs. Supported by simulations, a plausible mechanism for alpha band reductions may involve spinal interneuron phase-cancelling descending oscillations. Therefore, during skill learning, the central nervous system acts as a matched filter, adjusting synaptic weights of shared inputs to suppress neural components unrelated to the specific task.

Dynamic motor practice improves movement accuracy, force control and leads to increased corticospinal excitability compared to isometric motor practice

The central nervous system has a remarkable ability to plan motor actions, to predict and monitor the sensory consequences during and following motor actions and integrate these into future actions. Numerous studies investigating human motor learning have employed tasks involving either force control during isometric contractions or position control during dynamic tasks. To our knowledge, it remains to be elucidated how motor practice with an emphasis on position control influences force control and vice versa. Furthermore, it remains unexplored whether these distinct types of motor practice are accompanied by differential effects on corticospinal excitability. In this study, we tested motor accuracy and effects of motor practice in a force or position control task allowing wrist flexions of the non-dominant hand in the absence of online visual feedback. For each trial, motor performance was quantified as errors (pixels) between the displayed target and the movement endpoint. In the main experiment, 46 young adults were randomized into three groups: position control motor practice (PC), force control motor practice (FC), and a resting control group (CON). Following assessment of baseline motor performance in the position and force control tasks, intervention groups performed motor practice with, augmented visual feedback on performance. Motor performance in both tasks was assessed following motor practice. In a supplementary experiment, measures of corticospinal excitability were obtained in twenty additional participants by application of transcranial magnetic stimulation to the primary motor cortex hot spot of the flexor carpi radialis muscle before and following either position or force control motor practice. Following motor practice, accuracy in the position task improved significantly more for PC compared to FC and CON. For the force control task, both the PC and FC group improved more compared to CON. The two types of motor practice thus led to distinct effects including positive between-task transfer accompanying dynamic motor practice The results of the supplementary study demonstrated an increase in corticospinal excitability following dynamic motor practice compared to isometric motor practice. In conclusion, dynamic motor practice improves movement accuracy, and force control and leads to increased corticospinal excitability compared to isometric motor practice.

Effect of standardized training in combination with masseter sensitization on corticomotor excitability in bruxer and control individuals: a proof of concept study

Recently, it has been proposed that bruxism could represent an overlearned behavior due to the absence of corticomotor plasticity following a relevant tooth-clenching task (TCT). This study assessed the modulatory effects of a nerve growth factor (NGF) injection on masseter muscle corticomotor excitability, jaw motor performance, pain, and limitation in bruxer and control participants following a TCT. Participants characterized as definitive bruxers or controls were randomly assigned to have injected into the right masseter muscle either NGF or isotonic saline (IS), resulting in a study with 4 arms: IS_Control (n = 7), IS_Bruxer (n = 7); NGF_Control (n = 6), and NGF_Bruxer (n = 8). The primary outcome was the masseter motor evoked potential (MEP) amplitude measured at baseline and after a TCT. After the interventions, significantly higher and lower MEP amplitude and corticomotor map area were observed, respectively, in the IS_Control and NGF_Control groups (P < 0.05). Precision and accuracy depended on the series and target force level with significant between-group differences (P < 0.01). NGF-induced masseter muscle sensitization, in combination with a training-induced effect, can significantly impact the corticomotor excitability of the masseter muscle in control participants indicating substantial changes in corticomotor excitability, which are not observed in bruxers. These preliminary findings may have therapeuthic implications for the potential to "detrain" and manage bruxism, but further studies with larger sample sizes will be needed to test this new concept.

Modality of Practice Modulates Resting State Connectivity During Motor Learning

When bookending skilled motor practice, changes in resting state functional magnetic resonance imaging (rs-fMRI; used to characterise synchronized patterns of activity when the brain is at rest) reflect functional reorganization that supports motor memory consolidation and learning. Despite its use in practice in numerous domains, the neural mechanisms underlying motor memory consolidation and learning that result from motor imagery practice (MIP) relative to physical practice are not well understood. The current study examined how rs-fMRI is modulated by skilled motor practice that results through either MIP or physical practice. Two groups of participants engaged in five days of MIP or physical practice of a dart throwing task. Performance and rs-fMRI were captured before and after training. Relative to physical practice, where focal changes in rs-fMRI within a cerebellar-cortical network were observed, MIP stimulated widespread changes in rs-fMRI within a frontoparietal network encompassing bilateral regions. Findings indicate that functional reorganization that supports motor memory consolidation and learning is not equivalent across practice modality. Ultimately, this work provides new information regarding the unique neural underpinnings MIP relies on to drive motor memory consolidation and learning.

Effect of Apical Microsurgery on Force Regulation of Incisor Teeth during Unpredictable Force Control Task

BACKGROUND

Apical microsurgery (AMS) involves removal of the root-end which can affect the force regulation of teeth.

OBJECTIVE

To investigate the force regulation of incisor teeth treated with AMS during the unpredictable force control task in comparison to their contralateral teeth with complete root apices, in humans.

METHODS

Fifteen eligible participants (8 women and 7 men; mean age 52.9 ± SD 4.4 years) performed a standardized unpredictable force control task which involved pulling and holding a force transducer with AMS-treated incisors and its contralateral control teeth (n =30 teeth). A series of four load masses: 100, 200, 50, and 300 gm were attached to the force transducer through a string in an unpredictable manner. The force profile obtained was divided into initial and later time-segments. The peak force and peak force rate during the initial time-segment, and the holding force and coefficient of variability during the later time-segments were calculated and compared by the repeated measures analysis of variance.

RESULTS

During the initial time-segment, the peak force and peak force rate were significantly lower in the AMS-treated teeth than in the controls (P = 0.001, P = 0.013, respectively). However, during the later time-segment, no significant differences in the holding force nor the coefficient of variability were observed between the AMS-treated teeth and their controls (P = 0.755, P = 0.213, respectively).

CONCLUSION

In contrast to incisors with complete normal root apices, AMS-treated incisors do not show robust changes in force regulation.

Assessment of masticatory function in older individuals with bimaxillary implant-supported fixed prostheses or with a natural dentition: A case-control study

STATEMENT OF PROBLEM

A clinical assessment of the masticatory performance of edentulous people treated with bimaxillary implant-supported fixed prostheses is lacking.

PURPOSE

The purpose of this case-control study was to compare the masticatory performance of edentulous people treated with bimaxillary implant-supported fixed prostheses to that of those with a natural dentition by using a simplified comminution test with hard viscoelastic test food and a mixing ability test.

MATERIAL AND METHODS

Thirty-six participants were recruited and divided into 2 equal groups (n=18) based on their dental status. The experimental group (7 women, mean ±standard deviation age=69.8 ±7.5 years) had bimaxillary implant-supported fixed prostheses, and the control group (9 women, mean ±standard deviation age=68.3 ±5.6 years) had a natural dentition. A hard viscoelastic food comminution test and a mixing ability test with 2-colored chewing gum were performed in both groups. The number and total area of the particles during the comminution test and the variance of hue during the mixing ability test were measured. The data were analyzed with the parametric (paired t test) and nonparametric (Mann-Whitney U) tests to assess differences between the groups (α=.05).

RESULTS

The experimental group exhibited significantly fewer pieces in the food comminution test than the control group (P=.001). The experimental group also showed significantly higher variance of hue values than the control group (P<.001).

CONCLUSIONS

Patients treated with bimaxillary implant-supported prostheses had reduced masticatory performance in comparison to those with a natural dentition, despite having been provided with satisfactory and well-functioning prostheses.

A conceptual model of oro-facial health with an emphasis on function

The individual inclination to lead an autonomous life until death is associated with requirements that may be of physiological, psychosocial and environmental nature. We aim to describe a conceptual oro‐facial health model with an emphasis on oro‐facial function, taking the domains of quality of life and patient‐centred values into account. In the context of oro‐facial function, the requirements of life are met when the oro‐facial system is in a fit state. ‘Fitness of the oro‐facial system, that is oro‐facial health, is a state that is characterised by an absence of, or positive coping with physical disease, mental disease, pain and negative environmental and social factors. It will allow natural oro‐facial functions such as sensing, tasting, touching, biting, chewing, swallowing, speaking, yawning, kissing and facial expression’. In the presented conceptual model of oro‐facial health, it is postulated that each individual has present and future potentials related to biological prerequisites and resources that are developed by an individual through the course of life. These potentials form the oro‐facial functional capacity. When the individual potentials together do not meet the requirements of life anymore, dysfunction and disease result. The oro‐facial system is subject to physiological ageing processes, which will inevitably lead to a decrease in the oro‐facial functional capacity. Furthermore, comorbid medical conditions might hamper oro‐facial function and, alongside with the ageing process, may lead to a state of oral hypofunction. Currently, there is a lack of widespread, validated, easy‐to‐use instruments that help to distinguish between states of oro‐facial fitness as opposed to oral hypofunction. Clearly, research is needed to establish adequate, validated instruments alongside with functional rehabilitation procedures.

Cognitive changes and neural correlates after oral rehabilitation procedures in older adults: a protocol for an interventional study

BACKGROUND

Epidemiological studies show an association between masticatory function and cognitive impairment. This has further strengthened the notion that tooth loss and impaired masticatory function may be risk factors for dementia and cognitive decline. Animal experiments have indicated a causal relationship and several possible mechanisms have been discussed. This evidence is, however, lacking in humans. Therefore, in the current interventional study, we aim to investigate the effect of rehabilitation of masticatory function on cognition in older adults.

METHODS

Eighty patients indicated for prosthodontic rehabilitation will be randomly assigned to an experimental or a control group. Participants will conduct neuropsychological assessments, masticatory performance tests, saliva tests, optional magnetic resonance imaging, and answer questionnaires on oral health impact profiles and hospital anxiety and depression scale before, 3 months, and 1 year after oral rehabilitation. The difference between the two groups is that the control group will be tested an additional time, (at an interval of about 3 months) before the onset of the oral rehabilitation procedure. The primary outcome is a change in measures of episodic memory performance.

DISCUSSION

Although tooth loss and masticatory function are widespread in older people, it is still an underexplored modifiable risk factor potentially contributing to the development of cognitive impairment. If rehabilitation of masticatory function shows positive effects on the neurocognitive function, this will have great implications on future health care for patients with impaired masticatory status. The present project may provide a new avenue for the prevention of cognitive decline in older individuals.

TRIAL REGISTRATION

The protocol for the study was retrospectively registered in ClinicalTrials.gov Identifier: NCT04458207, dated 02-07-2020.

Leveraging the effector independent nature of motor imagery when it is paired with physical practice

While considered analogous to physical practice, the nature of imagery-based skill acquisition—specifically whether or not both effector independent and dependent encoding occurs through motor imagery—is not well understood. Here, motor imagery-based training was applied prior to or after physical practice-based training to probe the nature of imagery-based skill acquisition. Three groups of participants (N = 38) engaged in 10 days of training of a dart throwing task: 5 days of motor imagery prior to physical practice (MIP-PP), motor imagery following physical practice (PP-MIP), or physical practice only (PP-PP). Performance-related outcomes were assessed throughout. Brain activity was measured at three time points using fMRI (pre/mid/post-training; MIP-PP and PP-MIP groups). In contrast with physical practice, motor imagery led to changes in global versus specific aspects of the movement. Following 10 days of training, performance was greater when motor imagery preceded physical practice, although remained inferior to performance resulting from physical practice alone. Greater activation of regions that support effector dependent encoding was observed mid-, but not post-training for the PP-MIP group. Findings indicate that changes driven by motor imagery reflect effector independent encoding, providing new information regarding how motor imagery may be leveraged for skill acquisition.

Semi-powered exoskeleton that regulates the muscular activity of jaw movement for oral functional rehabilitation/training

The sequential oral functions of mastication and swallowing are well tuned in humans. To prevent oral hypofunction as a risk factor for systemic frailty by oral motor training, semi-powered exoskeleton was developed and evaluated its loading/assist effects by monitoring electromyography signals and saliva secretion in healthy persons. The actuator of the driving unit combined mechanical and powered mechanics and was driven alternatively by an unpowered stainless-steel spring system for jaw-opening training by loading and a powered shape-memory alloy spring system to assist jaw closing. Sequential device movement was controlled by two electronic circuits with two magnetic switching systems to match human jaw movement. This exoskeleton realized a 25% increase of jaw-opening muscular activity for training, 15% saving of jaw-closing muscular activity for assistance, and 15% enhancement of saliva secretion, which could contribute to the prevention of oral frailty by maintenance and strengthening of oral function in the upcoming super-aging society.

Age-related changes in oral motor-control strategies during unpredictable load demands in humans

To investigate age-related changes in oral motor strategies in response to unpredictable load demands. Sixty-five healthy children (aged 3-17 yr) were divided into five age-groups based on their dental eruption stages and compared with a group of healthy adults (aged 18-35 yr). Each participant was asked to perform a standardized motor control task involving 'pulling' and 'holding' a force transducer with the anterior teeth. Different loads were attached to the force transducer in an unpredictable manner. The temporal force profile was divided into two time-segments (an initial segment and a later segment). The peak force and peak force rate during the initial time-segment, and the holding force and intra-trial variability (coefficient of variation) during the later time-segment, were measured. The results showed no differences in the peak force, peak force rate, holding force, and force variability in children compared with adults. However, the trends in the data evaluated using a segmented regression analysis showed that a breakpoint (abrupt change) consistently occurred in the late-mixed dentition group (age 9-11 yr) for most of the outcome variables. The results indicate that while the motor control strategies in children appear to be similar to those in adults, there is a shift in the oral motor developmental trend during the late-mixed dentition stage.

The Evolution of Neuroscience as a Research Field Relevant to Dentistry

The field of neuroscience did not exist as such when the Journal of Dental Research was founded 100 y ago. It has emerged as an important scientific field relevant to dentistry in view of the many neurally based functions manifested in the orofacial area (e.g., pain, taste, chewing, swallowing, salivation). This article reviews many of the novel insights that have been gained through neuroscience research into the neural basis of these functions and their clinical relevance to the diagnosis and management of pain and sensorimotor disorders. These include the neural pathways and brain circuitry underlying each of these functions and the role of nonneural as well as neural processes and their "plasticity" in modulating these functions and allowing for adaptation to tissue injury and pain and for learning or rehabilitation of orofacial functions.

Motor control strategies during unpredictable force control tasks in humans

BACKGROUND

There are fundamental similarities and differences between the jaw and hand motor systems. However, it is unclear how the two systems respond to unpredictable task demands.

OBJECTIVE

To investigate and compare the force control of the jaw motor system (OMS) and the hand motor system (HMS) during unpredictable load changes.

METHODS

Seventeen healthy adults (24.0 ± 4.3 years) performed two standardised force control tasks (OMS and HMS). During the OMS, the participants asked to bite and pull a force transducer with the front teeth. While during HMS they pinched and pulled the same force transducer with their index and thumb fingers. Series of loads were added to a string attached to the transducer in an unpredictable (sequential and non-sequential) manner. The entire force profile during the task was divided into "initial" and "latter" segments. The force control was analysed and compared between the OMS and HMS in terms of peak force during the initial segment and holding force and force variability during the latter segment.

RESULTS

The peak force, holding force and force variability were higher for the OMS than the HMS (P < .001). However, there were no differences in the peak force, holding force or force variability between the sequential and non-sequential load changes (P > .05).

CONCLUSIONS

The results showed that unpredictable load changes did not affect the force control during the motor control task. This study suggests that both the motor systems are optimised in performing simple motor control tasks and are rather resilient to motor unpredictability.

Neural and Behavioral Outcomes Differ Following Equivalent Bouts of Motor Imagery or Physical Practice

Despite its reported effectiveness for the acquisition of motor skills, we know little about how motor imagery (MI)-based brain activation and performance evolves when MI (the imagined performance of a motor task) is used to learn a complex motor skill compared to physical practice (PP). The current study examined changes in MI-related brain activity and performance driven by an equivalent bout of MI- or PP-based training. Participants engaged in 5 days of either MI or PP of a dart-throwing task. Brain activity (via fMRI) and performance-related outcomes were obtained using a pre/post/retention design. Relative to PP, MI-based training did not drive robust changes in brain activation and was inferior for realizing improvements in performance: Greater activation in regions critical to refining the motor program was observed in the PP versus MI group posttraining, and relative to those driven via PP, MI led only to marginal improvements in performance. Findings indicate that the modality of practice (i.e., MI vs. PP) used to learn a complex motor skill manifests as differences in both resultant patterns of brain activity and performance. Ultimately, by directly comparing brain activity and behavioral outcomes after equivalent training through MI versus PP, this work provides unique knowledge regarding the neural mechanisms underlying learning through MI.

Effects of Motor Training on Accuracy and Precision of Jaw and Finger Movements

Objective

To compare the effects of training of jaw and finger movements with and without visual feedback on precision and accuracy.

Method

Twenty healthy participants (10 men and 10 women; mean age 24.6 ± 0.8 years) performed two tasks: a jaw open-close movement and a finger lifting task with and without visual feedback before and after 3-day training. Individually determined target positions for the jaw corresponded to 50% of the maximal jaw opening position, and a fixed target position of 20 mm was set for the finger. Movements were repeated 10 times each. The variability in the amplitude of the movements was expressed as percentage in relation to the target position (D_accu—accuracy) and as coefficient of variation (CV_prec—precision).

Result

D_accu and CV_prec were significantly influenced by visual feedback (P = 0.001 and P < 0.001, respectively) and reduced after training jaw and finger movements (P < 0.001). D_accu (P = 0.004) and CV_prec (P = 0.019) were significantly different between jaw and finger movements. The relative changes in D_accu (P = 0.017) and CV_prec (P = 0.027) were different from pretraining to posttraining between jaw and finger movements.

Conclusion

The accuracy and precision of standardized jaw and finger movements are dependent on visual feedback and appears to improve more by training in the trigeminal system possibly reflecting significant neuroplasticity in motor control mechanisms.

Multimodal Sensory Stimulation of the Masseter Muscle Reduced Precision but Not Accuracy of Jaw-Opening Movements

A functional integration between the trigeminal and craniocervical sensorimotor systems has been demonstrated, with simultaneous jaw and head–neck movements during jaw opening–closing. We previously showed that pain induction in the masseter muscle increased the relative contribution of the neck component of integrated jaw–neck movements. Induced pain or manipulation of proprioception by vibration did not affect accuracy during a jaw-opening task in men. It is not known how multimodal sensory stimulation, with a combination of pain induction and vibration, affects jaw-opening accuracy and precision. The aim was to investigate how jaw–neck movements, and specifically accuracy and precision of jaw-opening, are affected during concomitant nociceptive and proprioceptive stimulation of the masseter muscle. Twenty-one healthy men performed jaw-opening to a target position, defined as 75% of individual maximum jaw opening, during control (Ctr), vibration of masseter muscles (Vib), pain induction in the masseter (Pain), and concomitant vibration and pain induction in the masseter muscle (VibPain). Simultaneous jaw and head movements were recorded with an optoelectronic system and amplitudes calculated for each jaw opening–closing cycle. Accuracy of jaw movements was defined as the achievement of the target position. Precision of jaw movements was defined as the cycle-to-cycle variability from the mean of cycles 2–10 (coefficient of variation, CV). Differences between the trials were analyzed with Friedman’s test, Dunn’s test, and Benjamini–Hochberg correction. There were no significant differences between the trials for jaw movement amplitudes. For head movements, amplitudes for cycles 2–10 were larger during Pain compared to Ctr and Vib (both p = 0.034), and larger during VibPain compared to Ctr (p = 0.034) and Vib (p = 0.035). There were no differences in accuracy of jaw movements between the trials. For precision of jaw movements, the cycle-to-cycle variability was larger during VibPain compared to Ctr (p = 0.027) and Vib (p = 0.018). For integrated jaw–neck motor strategy, there was a difference between pain and non-pain trials, but no differences between unimodal and multimodal stimulation trials. For achievement of jaw-opening to a target position, the results show no effect on accuracy, but a reduced precision of jaw movements during combined proprioceptive and nociceptive multimodal stimulation.

Changes in Muscle Activity in Response to Assistive Force during Isometric Elbow Flexion

This study investigated the muscle activity and force variability in response to perturbation of assistive force during isometric elbow flexion. Sixteen healthy right-handed young men (age: 22.0 ± 1.1 years; height: 171.9 ± 4.8 cm; weight 68.4 ± 11.2 kg) were recruited and the muscle activity of biceps brachii and triceps brachii were assessed using surface electromyography. Workload force and assistive force applied on isometric elbow flexion significantly affected the changes in both biceps and triceps muscle activities. A higher assistive force was shown to result in reduced biceps muscle activity compared to the unassisted period. In contrast, the efficiency of the assistive force acting on the biceps decreased as the assistive force increased. In general, the force variability of the biceps muscle remained approximately the same at lower workload force conditions than that at higher workload force conditions. In conclusion, higher assistive force may not yield a higher performance efficiency in human-assistive force interaction.

Behavioral learning and skill acquisition during a natural yet novel biting task

OBJECTIVE

To investigate the effect of short-term training on behavioral learning and skill acquisition during a natural yet novel biting task.

METHODS

Thirty (18 women) healthy volunteers in the age range of 18-32 years were divided into a naive (n = 17) and expert (n = 13) groups based on the self-reported familiarity to perform a complex behavioral biting task. The volunteers participated in a single experimental session divided into three sets with three series, each with ten trials of a standardized biting task. The task was to position, split and retrieve a sunflower seed from its shell without crushing the seed. The two consecutive sets were separated by fifteen minutes of short-term training. During the short-term training, the participants repeatedly performed the biting task for about fifteen minutes. A five-point grading system was devised to determine the performance and video registrations were made to determine the duration of the task.

RESULTS

There was a significant main effect of training on the task performance scores (P < .001). The performance scores of the naive group before training was significantly lower than all the sets of the expert group (P < .010). The performance scores of the naive group were also significantly better after training than before (P = .001). However, the expert group took significantly shorter time to complete the task than the naive group.

CONCLUSION

The results of the present study show a significant effect of training on the performance of a complex behavioral biting task. Training resulted in improved performance scores and a subtle decrease in the duration of the task.

Impact of sleep bruxism on training-induced cortical plasticity

PURPOSE

To investigate if sleep bruxism (SB) influences training-induced cortical plasticity and performance in terms of accuracy and precision of a tooth-clenching task (TCT).

METHODS

Thirty-eight participants were allocated into SB group (N=19) and control group (N=19) according to presence of SB based on a 2-week screening. The participants were instructed to perform a standardized TCT for 58min at three different force levels (10%, 20% and 40% of maximum voluntary contraction; MVC) in three series (first and third without visual-feedback and second with visual-feedback). Accuracy and precision of the TCT were calculated from actual bite force values. Transcranial magnetic stimulation was applied to elicit motor evoked potentials (MEPs) from the masseter and first dorsal interosseous muscle (FDI) before the TCT (pre-TCT-session) and 5-min after the TCT (post-TCT-session).

RESULTS

Accuracy was significantly dependent on the series and target force level (P<0.001), however, there was a significant decrease only in the control group at 10% MVC from first to third session (P<0.001). No significant differences between groups were observed for the precision of the TCT. Masseter MEPs in the SB group in the pre-TCT-session at 120% and 160% motor threshold were significantly lower than in the control group (P<0.05). Masseter MEPs of the control group in the post-TCT-session were significantly higher than the pre-TCT-session (P<0.05) but not SB. FDI MEPs were only dependent on stimulus intensity (P<0.001).

CONCLUSIONS

SB is associated with significant changes not only in excitability of corticomotor control but also motor learning of jaw movements and force control.

Alteration of occlusal vertical dimension induces signs of neuroplastic changes in corticomotor control of masseter muscles: Preliminary findings

PURPOSE

To investigate the effect of altering occlusal vertical dimension (OVD) in patients with severe attrition on corticomotor control of the masseter muscles as assessed by navigated transcranial magnetic stimulation (nTMS).

METHODS

Seven patients (58.6 ± 8.4 years) with decreased OVD due to severe attrition were given mandibular occlusal splints to alter the OVD with the instruction to wear during the whole awake time for a period of four weeks. Motor-evoked potentials (MEPs) and the motor cortex maps of the masseter muscles and first dorsal interosseous (FDI) muscles as control were recorded by nTMS at baseline and at least 4 weeks after the alteration of OVD. The stimulus-response curves of MEPs were analysed with two-way repeated-measures ANOVA, and the numerical rating scale scores, motor thresholds, onset latencies, motor cortex maps and centre of gravity (COG) were analysed with paired t tests.

RESULTS

There was a significant increase in the amplitude of the masseter muscle MEPs (P = 0.036), but no change in the motor cortex map areas (P = 0.111) four weeks after the alteration of OVD. Furthermore, there was no significant difference in either the amplitude of the FDI muscle MEPs (P = 0.466) or the motor cortex map areas (P = 0.230) before and after OVD alteration.

CONCLUSION

The results suggest that alteration of OVD in patients with severe attrition was associated with signs of neuroplastic changes in the corticomotor control of the masseter muscles. The results of the study may add to our understanding of the putative mechanisms related to cortical changes in response to OVD alterations.