The effects of a single dose of fluoxetine on practice-dependent plasticity

Objective

To determine whether a single dose of fluoxetine increases corticomotoneuronal excitability, motor performance and practice-dependent plasticity.

The effect of coordination mode on use-dependent plasticity.

OBJECTIVE: To evaluate the role of coordination mode on the generation of use-dependent plasticity (UDP) within the primary motor cortex (M1). METHODS: Ten healthy volunteers performed brisk repetitive thumb movements for 30 min in the opposite direction to those evoked by transcranial magnetic stimulation (TMS) prior to training. This practice was synchronized or syncopated with a 1 Hz auditory metronome in two separate sessions. Motor evoked potentials (MEPs) were recorded from 3 intrinsic thumb muscles, to assess changes in corticomotor excitability. RESULTS: Both synchronized and syncopated motor practice induced changes in the direction of TMS-evoked thumb movements, away from the baseline direction toward the trained direction. MEP amplitude increased following synchronized, but not syncopated, motor practice. Changes in movement direction and corticomotor excitability lasted for at least 30 minutes. CONCLUSIONS: UDP can be elicited in the presence or absence of changes in corticomotor excitability. SIGNIFICANCE: Motor practice that is synchronized with external pacing may promote UDP and facilitate corticomotor excitability in patient populations with reduced corticomotor output, such as stroke. Training that is syncopated with external pacing may promote UDP without increasing corticomotor excitability. This could be relevant for individuals with disorders characterized by maladaptive plasticity.     

Hand perceptions induced by single pulse transcranial magnetic stimulation over the primary motor cortex

Background

When single pulse transcranial magnetic stimulation (TMS) is applied over the primary motor cortex (M1) with sufficient intensity, it evokes muscular contractions (motor-evoked potentials, MEPs) and muscle twitches (TMS-evoked movements). Participants may also report various hand sensations related to TMS, but the perception elicited by TMS and its relationship to MEPs and evoked movements has not been systematically studied.

On-line flexibility of the cognitive tuning of corticospinal excitability: a TMS study in human gait

Human subjects have been found to be able to cognitively prepare themselves to resist to a TMS-induced central perturbation by selectively modulating the corticospinal excitability (CS). The aim of this study was to investigate the on-line adaptability of this cognitive tuning of CS excitability during human gait. Transcranial magnetic stimulation (TMS) was used both as a central perturbation evoking a movement and as a tool for quantifying the CS excitability before the movement was evoked. TMS was applied at mid-stance (evoking additional hip extension) or at the beginning of the swing (evoking hip flexion) with a random phase, thus evoking unpredictable flexion or extension movement. This was compared to a condition of fixed phase, in which the subjects knew in advance the direction of the evoked movement. In both conditions, we compared the amplitude of the TMS-evoked movement and the motor-evoked potentials (MEPs) of the muscles acting at the hip joint (RF/BF) according to two opposite instructions, either to cognitively prepare to "let go", or to cognitively prepare to "compensate" for the evoked movements. The results showed that the subjects were able to compensate for random TMS-evoked movements, but with a lower performance level in comparison to the fixed TMS-evoked movements. When they succeeded in the random-phase condition, the subjects used the same preparation strategy as in the fixed-phase condition; preparing to compensate resulted in a selective increase in the CS excitability to those muscles which would be involved in counteracting the possible central perturbation. This requires continuous change in the tuning of CS excitability within the stride and thus reveals the high flexibility of the cognitive tuning of CS excitability during gait.     

Promoting use-dependent plasticity with externally-paced training

Objective

To evaluate use-dependent plasticity (UDP) before and after training under metronome-paced and self-paced conditions.

Methods

Twelve healthy adults were recruited to this cross-over, pseudo-randomized, repeated measures study. Participants performed wrist extension training that was either self-paced, or externally-paced to an auditory metronome at their preferred movement frequency or at a more demanding frequency. Motor evoked potentials from transcranial magnetic stimulation of left primary motor cortex were recorded in right extensor carpi radialis (ECR) and flexor carpi radialis (FCR) to assess corticomotor excitability. The direction and velocity of TMS-evoked wrist movement (stimulus-evoked velocity, SEV) were measured before and after training to evaluate UDP.

Results

The most persistent UDP occurred when training was metronome-paced at the participant’s preferred movement frequency. This training protocol produced spatially selective modulation of resting ECR and FCR corticomotor excitability and directional tuning of TMS-evoked wrist movement toward the trained direction. Metronome-paced training at a more demanding frequency resulted in nonspecific facilitation of resting corticomotor excitability, and did not alter TMS-evoked wrist movement.

Conclusions

These novel findings indicate that externally-paced training at the individual’s preferred frequency facilitates UDP.

Significance

UDP underpins motor recovery after stroke. Externally-paced training may be a useful adjunct to movement rehabilitation therapy.     

Motor learning of hands with auditory cue in patients with Parkinson’s disease

Summary. In the present research, changes in motor cortex function were observed in relation to repetitive, voluntary thumb movement (training) in patients with Parkinson’s disease (PD) and normal control subjects. Changes in the direction of thumb movement due to motor evoked potential (MEP) by transcranial magnetic stimulation (TMS), after motor training with and without rhythmic sound, were measured using a strain gauge for 12 patients with PD and 9 normal control subjects. PD patients who experienced the freezing phenomena showed poor change in direction of TMS-induced movement after self-paced movement; however, marked change in direction of TMS-induced movement was observed after training with auditory cue. PD patients who had not experienced the freezing phenomena showed positive effects with the auditory cue, producing similar results as the normal control subjects. Two routes for voluntary movement are available in the nervous system. The decreased function of basal ganglia due to PD impaired the route from the basal ganglia to the supplementary motor cortex. These data suggest that the route from sensory input to cerebellum to premotor cortex could compensate for the decreased function of the route via the basal ganglia to the premotor cortex. Once change in the motor cortex occurred, such change persisted even after the interruption of training. These phenomena suggest that motor memory can be stored in the motor cortex.     

Modulation of use-dependent plasticity by d-amphetamine.

Use-dependent plasticity, thought to contribute to functional recovery after brain injury, is elicited by motor training. The purpose of this study was to determine if administration of d-amphetamine facilitates the effects of motor training on use-dependent plasticity. Healthy human volunteers underwent a training period of voluntary thumb movements under the effects of placebo or d-amphetamine in different sessions in a randomized double-blind, counterbalanced design. Previous work in a drug-naive condition showed that such training causes changes in the direction of thumb movements evoked by transcranial magnetic stimulation and in transcranial magnetic stimulation-evoked electromyographic responses. The endpoint measure of the study was the magnitude of training-induced changes in transcranial magnetic stimulation-evoked kinematic and electromyographic responses in the d-amphetamine and in the placebo conditions. Motor training resulted in increased magnitude, faster development and longer lasting duration of use-dependent plasticity under d-amphetamine compared to the placebo session. These results document a facilitatory effect of d-amphetamine on use-dependent plasticity, a possible mechanism mediating the beneficial effect of this drug on functional recovery after cortical lesions.     

Asymmetrical facilitation of motor-evoked potentials following motor practice

Use-dependent facilitation of motor-evoked potentials evoked by transcranial magnetic stimulation with repetition of simple movements has been well established. Motor-evoked potentials were recorded from two intrinsic hand muscles before and after blocks of motor practice in which study participants made repeated ballistic pinch responses with either their left or their right hand. Despite similar increases in behavioral performance by each hand (measured by the peak acceleration of the force generated by the index finger), practice-related increases in the amplitude of the motor-evoked potentials were greater in the left than in the right motor cortex of right-handed participants. This finding supports the hypothesis that the dominant motor cortex has a greater ability to reorganize with experience than the non-dominant motor cortex.     

Spontaneous movement tempo is influenced by observation of rhythmical actions

Observation of people performing movements facilitates motor planning, execution and memory formation. Tempo, a crucial aspect involved in the execution of rhythmic movements, is normally perceived and learned through auditory channels. In this work, we ascertained whether: first, the frequency of self-paced finger movements (SPMs), which in normal subjects is around 2 Hz, is modified by prior observation of movements performed at either 1 or 3 Hz; second, such changes are lasting; third, there is an effect of time interval between observation and performance. We finally determined the effect of providing explicit information about the upcoming motor task. Seventy-two normal subjects (12 groups) performed a simple finger sequence at different intervals after observation of videos of either landscapes or finger opposition movements. Both with and without information about the upcoming task, observation influenced the tempo of SPMs and led to memory formation. With knowledge of the upcoming task, such changes occurred at all observation–execution intervals, while without instructions, changes took place only when SPMs were performed immediately after observation. Compared to explicit instructions, the absence of instructions produced tempo's changes that more closely resembled the observed rhythms. We conclude that learning requires a prompt comparison between visual and sensorimotor representations of movements; moreover, learning with explicit instructions is more efficient, as activity in both the dorsal and ventral streams might be potentiated by the chatecholaminergic attentional systems that promote long-term potentiation. These results provide the bases for novel neurorehabilitation strategies in terms of temporal re-organization of movement.     

Motor learning affects visual movement perception

In the present study we investigated whether imitation of artificial movement trajectories of meaningless objects has an effect on how these trajectories are later perceptually processed within the human brain. During observation of a sequence of artificial object movements 10 participants (experimental group) actively imitated the trajectories during motor training and 10 participants (control group) solved a working memory task without motor training. The haemodynamic responses were recorded before and after the intervention while participants observed the movements and either had to detect colour changes of one of the objects (colour task, motor-irrelevant) or had to judge whether the movement pattern could be imitated with the hands (simulation judgement task, motor-relevant). The between-group comparison of the post-intervention haemodynamic responses revealed stronger activity for the motor training than for the control group during the simulation judgement task. This activity appeared in motor-related areas (supplementary motor area and inferior parietal lobe) and in the occipito-temporal area. During the colour task, the motor training group showed stronger activity in the occipital lobe. The control group did not reveal any stronger activity than the motor training group for either task. The results suggest that motor training has task-specific effects on neural processes that are involved in perception of movements. Furthermore, they indicate that motor-related areas are triggered by observed artificial object movements, but only if a motor-relevant task is pursued.