Role of primary sensorimotor cortex and supplementary motor area in volitional swallowing: a movement-related cortical potential study

We investigated the role of the cerebral cortex, particularly the face/tongue area of the primary sensorimotor (SMI) cortex (face/tongue) and supplementary motor area (SMA), in volitional swallowing by recording movement-related cortical potentials (MRCPs). MRCPs with swallowing and tongue protrusion were recorded from scalp electrodes in eight normal right-handed subjects and from implanted subdural electrodes in six epilepsy patients. The experiment by scalp EEG in normal subjects revealed that premovement Bereitschaftspotentials (BP) activity for swallowing was largest at the vertex and lateralized to either hemisphere in the central area. The experiment by epicortical EEG in patients confirmed that face/tongue SMI and SMA were commonly involved in swallowing and tongue protrusion with overlapping distribution and interindividual variability. BP amplitude showed no difference between swallowing and tongue movements, either at face/tongue SMI or at SMA, whereas postmovement potential (PMP) was significantly larger in tongue protrusion than in swallowing only at face/tongue SMI. BP occurred earlier in swallowing than in tongue protrusion. Comparison between face/tongue SMI and SMA did not show any difference with regard to BP and PMP amplitude or BP onset time in either task. The preparatory role of the cerebral cortex in swallowing was similar to that in tongue movement, except for earlier activation in swallowing. Postmovement processing of swallowing was lesser than that of tongue movement in face/tongue SMI; probably suggesting that the cerebral cortex does not play a significant role in postmovement processing of swallowing. SMA plays a supplementary role to face/tongue SMI both in swallowing and tongue movements.     

Voluntary finger movement in man: Cerebral potentials and theory

Three different brain potentials preceeding voluntary rapid finger flexion can be recorded from the skull surface by time reversed averaging. The early cortical activity preceding unilateral movement is bilateral and widespread (Bereitschaftspotential, BP). The same applies for the second potential (pre-motion positivity, PMP). Only the third potential (motor potential, MP) is unilateral and restricted to the contralateral motor cortex. In a total of 87 experiments with 39 subjects, the BP started on the average 750 ms (SD 360, SE 38.5) prior to rapid finger flexion. Its largest amplitude was found mid-parietally and averaged-5.3 V (SD 2.32, SE 0.4). Such amplitudes were found with averages of 800 and more movements per experiment. However, at the beginning of an experiment the BP is larger. Preceding finger movement, the BP was found bilaterally over the parietal and precentral cortex and over the midline. Over the frontal cortex, either no potential or positivity was recorded. In normal subjects, the BP always begins bilaterally and symmetrically. At parietal leads, it remains bilaterally-symmetrical. A slight contralateral preponderance begins about 400 ms prior to movement only over motor cortex, which becomes statistically significant at 150 ms. When comparing the parietal BP amplitude with the precentral amplitude on the ipsilateral side, where no superposition of the MP occurs, there is more negativity parietally than precentrally, although the parietal skull is about 11% thicker than the precentral. The BP is a negative shift of the cortical DC potential probably representing a preparatory process in the dendritic network of those cortical areas that are involved in the intended movement.The PMP is the next potential occurring 90–80 ms ( , SD 34.2, SE 2.95) prior to the first action potential in the contracting muscle (EMG). It was found in 85% of our subjects. The PMP has at its maximum, mid-parietally, a mean amplitude of +1.7 V (SD 1.6, SE 0.28). Like the BP, the PMP is bilateral and widespread in parietal and precentral leads of both sides and in the midline with a maximum at the anterior parietal region, despite the parietal skull being thicker than precentral. The short and the relatively constant onset time suggests that the PMP might reflect cortical activity (motor command) related to initiation of the tactually guided rapid finger movement under study.The MP starting 60–50 ms ( , SD 19.4, SE 3.1) prior to first activity in the agonist EMG is the last potential to occur and is the only unilateral potential: its localisation is limited to the hand area of the motor cortex contralateral to the moving finger. In bipolar recordings, contralateral versus ipsilateral precentral or contralateral precentral versus vertex, it appears as a sharp additional negativity. This additional negativity averaged-1.3 V (SD 0.64, SE 0.08). The MP reflects the motor cortical activity immediately preceding the movement.After movement onset, a complex potential is recorded, that is also seen with passive finger movement, largely representing a somatosensory (proprioceptive) evoked response. The possible meaning of the movement-related potentials is discussed in relation to a theory of central motor function.Supported by the Deutsche ForschungsgemeinschaftHabilitationsschrift of L.D. submitted to the Faculty of Clinical Medicine, University of Ulm (1974)     

Generator locations of movement-related potentials with tongue protrusions and vocalizations: subdural recording in human

Movement-related potentials (MRPs) associated with tongue protrusions and vocalizations were recorded from chronically implanted subdural electrodes over the lower perirolandic area in 7 patients being evaluated for epilepsy surgery. In 3 patients, tongue protrusions elicited a clearly defined, well localized slow negative Bereitschaftspotential (BP) at the motor tongue area, and a positive BP at the sensory tongue area. At the motor tongue area the negative BP was followed by a negative slope (NS′) and a motor potential (MP), and at the sensory tongue area the positive BP and a positive reafferent potential (RAP) were seen but no NS′ and MP could be identified. In the other 4 patients, tongue protrusions elicited positive BP, NS′ and MP at the motor and sensory tongue area, and positive RAP at the sensory area. It was concluded that BPs, NS′ and MPs are mainly generated in the motor cortex involving the crown as well as the anterior bank of the central fissure. The sensory cortex (areas 3a and 3b) also participated in the generation of BPs but to a lesser degree. Different degree of involvement of these multiple generators most likely explains the interindividual variability of polarity and distribution of the MRPs. RAPS most likely arise from primary sensory areas 1 and 2. Brain potentials were also recorded at the motor (2 patients) and sensory (2 patients) language areas, but no specific language-related potentials could be identified.Evoked potentials to lip stimulation were investigated in 4 patients. In 3 patients, the responses at the sensory tongue area (P16, N21 and P30) had the same latency but opposite polarity to those at the motor tongue area. In the other patient, the responses (P16, N21 and P30) at the motor and sensory tongue areas were of the same polarity. The MRPs to tongue protrusions in those 4 patients revealed the same polarity relationship between the pre- and postcentral potentials. However, the maximal amplitude of evoked potentials and MRPs was seen at almost the same electrodes, suggesting that the main generators for these MRPs and evoked potentials must be located at contiguous areas in the anterior and posterior bank, respectively, of the central fissure.     

Positive potentials of the human brain at different stages of preparation of a visually triggered saccade

The EEG of 10 right-handed subjects preceding saccades with mean values of latent periods were selected and averaged. Two standard paradigms of presentation of visual stimuli (central fixation stimulus-peripheral target succession): with a 200-ms inerstimulus interval (GAP) and successive single step (SS). During the period of central fixation, two kinds of positive potentials were observed: fast potentials of "inermediate" positivity (IP) developing 600-400 ms prior to saccade onset and fast potentials of "leading" positivity (LP), which immediately preceded the offset of the central fixation stimulus. Peak latency of the LP potentials was 300 ms prior to saccade onset in the SS paradigm and 400 ms in the GAP paradigm. These potentials were predominantly recorded in the frontal and frontosagittal cortical areas. Decrease in the latency by 30-50 ms in the GAP paradigm was associated with more pronounced positive potentials during the fixation period and absence of the initiation potential P-1' (or decrease in its amplitude). The obtained evidence suggest that the fast positive presaccadic potentials are of a complex nature related to attention, anticipation, motor preparation, decision making, saccadic initiation, and backward afferentation.     

Reduced Motor Cortex Activity during Movement Preparation following a Period of Motor Skill Practice

Experts in a skill produce movement-related cortical potentials (MRCPs) of smaller amplitude and later onset than novices. This may indicate that, following long-term training, experts require less effort to plan motor skill performance. However, no longitudinal evidence exists to support this claim. To address this, EEG was used to study the effect of motor skill training on cortical activity related to motor planning. Ten non-musicians took part in a 5-week training study learning to play guitar. At week 1, the MRCP was recorded from motor areas whilst participants played the G Major scale. Following a period of practice of the scale, the MRCP was recorded again at week 5. Results showed that the amplitude of the later pre-movement components were smaller at week 5 compared to week 1. This may indicate that, following training, less activity at motor cortex sites is involved in motor skill preparation. This supports claims for a more efficient motor preparation following motor skill training.     

Readiness potentials recorded from the scalp and depth leads.

Readiness potentials on voluntary hand movements were recorded from the scalp (C3, C4), premotor cortex, subcortical white matter and VL nucleus of the thalamus. Subjects were healthy right-handed men and patients with involuntary movement disorders. We obtained a slow negative shift of brain electrical potentials from the scalp and cortex preceding voluntary hand movements. The mean time interval between the onset of the readiness potential and the onset of motor activity (mean T) was 0.8 sec on right hand movements and 1.0 sec on left hand movements in healthy men. In cases with parkinsonism, the mean T value was 1.4 sec in patients with akinesia, 1.1 sec in those without akinesia. The amplitude of readiness potentials was higher in the scalp contralateral to the hand movement. The readiness potentials recorded from the VL nucleus and white matter were reversed in polarity from those of scalp and cortex. Simultaneous recordings from cortex and VL nucleus showed early onset of readiness potentials from the cortex by approximately 0.1 sec compared with the VL nucleus.     

Selective gating of lower limb cortical somatosensory evoked potentials (SEPs) during passive and active foot movements

We evaluated subcortical and cortical somatosensory evoked potentials (SEPs) in response to posterior tibial nerve stimulation in 4 experimental conditions of foot movement and compared them with the baseline condition of full relaxation. The experimental conditions were: (a) active flexion-extension of the stimulated foot; (b) active flexion-extension of the non-stimulated foot; (c) passive flexion-extension of the stimulated foot in complete relaxation; (d) tonic active flexion of the stimulated foot. We analyzed latencies and amplitudes of the subcortical P30 potential, of the contralateral pre-rolandic N37 and P50 responses and of the P37, N50 and P60 potentials recorded over the vertex. Latencies did not vary in any of the paradigms. The amplitude of subcortical P30 potential did not change during any of the paradigms. Among the cortical waves, P37, N50 and P60 amplitudes were significantly attenuated in all conditions except active movement of the non-stimulated foot (b). This attenuation was less during passive (c) than during active movements of the stimulated foot (a and d). The contralateral pre-rolandic waves N37 and P50 showed no significant decrease during any of the paradigms. These results suggest that gating occurs rostrally to the cervico-medullary junction, probably at cortical level. The different behavior of N37, P50 and P37, N50 cortical responses during movement of the stimulated foot provides evidence suggestive of a highly localized gating process occurring at cortical level. These potentials could reflect activation of separate, functionally distinct generators.     

Role of motor cortex in coordinating multi-joint movements: is it time for a new paradigm?

Reaching movements to spatial targets require motor patterns at the shoulder to be coordinated carefully with those at the elbow to smoothly move the hand through space. While the motor cortex is involved in this volitional task, considerable debate remains about how this cortical region participates in planning and controlling movement. This article reviews two opposing interpretations of motor cortical function during multi-joint movements. On the one hand, studies performed predominantly on single-joint movement generally support the notion that motor cortical activity is intimately involved in generating motor patterns at a given joint. In contrast, studies on reaching demonstrate correlations between motor cortical activity and features of movement related to the hand, suggesting that the motor cortex may be involved in more global features of the task. Although this latter paradigm involves a multi-joint motor task in which neural activity is correlated with features of movement related to the hand, this neural activity is also correlated to other movement variables. Therefore it is difficult to assess if and how the motor cortex contributes to the coordination of motor patterns at different joints. In particular, present paradigms cannot assess whether motor cortical activity contributes to the control of one joint or multiple joints during whole-arm tasks. The final point discussed in this article is the development of a new experimental device (KINARM) that can both monitor and manipulate the mechanics of the shoulder and elbow independently during multi-joint motor tasks. It is hoped that this new device will provide a new approach for examining how the motor cortex is involved in motor coordination.     

Towards a novel monitor of intraoperative awareness: selecting paradigm settings for a movement-based brain-computer interface

During 0.1-0.2% of operations with general anesthesia, patients become aware during surgery. Unfortunately, pharmacologically paralyzed patients cannot seek attention by moving. Their attempted movements may however induce detectable EEG changes over the motor cortex. Here, methods from the area of movement-based brain-computer interfacing are proposed as a novel direction in anesthesia monitoring. Optimal settings for development of such a paradigm are studied to allow for a clinically feasible system. A classifier was trained on recorded EEG data of ten healthy non-anesthetized participants executing 3-second movement tasks. Extensive analysis was performed on this data to obtain an optimal EEG channel set and optimal features for use in a movement detection paradigm. EEG during movement could be distinguished from EEG during non-movement with very high accuracy. After a short calibration session, an average classification rate of 92% was obtained using nine EEG channels over the motor cortex, combined movement and post-movement signals, a frequency resolution of 4 Hz and a frequency range of 8-24 Hz. Using Monte Carlo simulation and a simple decision making paradigm, this translated into a probability of 99% of true positive movement detection within the first two and a half minutes after movement onset. A very low mean false positive rate of <0.01% was obtained. The current results corroborate the feasibility of detecting movement-related EEG signals, bearing in mind the clinical demands for use during surgery. Based on these results further clinical testing can be initiated.     

Submovement Composition of Head Movement

Limb movement is smooth and corrections of movement trajectory and amplitude are barely noticeable midflight. This suggests that skeletomuscular motor commands are smooth in transition, such that the rate of change of acceleration (or jerk) is minimized. Here we applied the methodology of minimum-jerk submovement decomposition to a member of the skeletomuscular family, the head movement. We examined the submovement composition of three types of horizontal head movements generated by nonhuman primates: head-alone tracking, head-gaze pursuit, and eye-head combined gaze shifts. The first two types of head movements tracked a moving target, whereas the last type oriented the head with rapid gaze shifts toward a target fixed in space. During head tracking, the head movement was composed of a series of episodes, each consisting of a distinct, bell-shaped velocity profile (submovement) that rarely overlapped with each other. There was no specific magnitude order in the peak velocities of these submovements. In contrast, during eye-head combined gaze shifts, the head movement was often comprised of overlapping submovements, in which the peak velocity of the primary submovement was always higher than that of the subsequent submovement, consistent with the two-component strategy observed in goal-directed limb movements. These results extend the previous submovement composition studies from limb to head movements, suggesting that submovement composition provides a biologically plausible approach to characterizing the head motor recruitment that can vary depending on task demand.     

Characteristics of the motor potentials in disorders of the subcortical motor structures of the human brain

Properties of motor potentials (MPs) were studied in patients with disturbance of function of subcortical motor structures--disturbance causing parkinsonism manifestations. MPs components are singled out preceding movement--"readiness potential" (N1), "motor potential" (N2) and MP components which are electrophysiological correlates of realization processes (component P2) and movement completion (component N3). It is revealed that MPs in patients with parkinsonism are changed in comparison with the norm; the most significant differences are observed in components N1, P2, N3, what is expressed in prolongation and a certain amplitude decrease of these components. Amplitude-temporal parameters most similar to the norm belong to the component N2, which is considered as an electrophysiological correlate of movement triggering. A hypothesis is suggested on its cortical origin.     

Changes in the amplitude and direction of goal-directed hand movements in the lack of visual information

The goal of the present investigation was to determine the precision of goal-directed hand movements in the lack of visual information. The movement amplitude and direction was examined under different experimental conditions. Subjects were ten female and ten male university students. The motor test was drawing 10 cm long straight line and 24 cm long zigzag line in four different experimental conditions. 1) The drawing with open eyes was followed immediately with drawing with closed eyes. 2) The drawing was executed from memory in the lack of visual information. 3) Drawing with restricted amplitude or direction. 4) Drawing with verbal feedback. The errors of the target distance and the lateral deviations from the target were different under the different experimental conditions. The largest errors and underestimation of the target distance occurred in drawing horizontal straight line with closed eyes. No statistically significant gender differences were found. It is concluded that the practice, adjustment of single movement parameter to the target, and the verbal feedback assist better the accuracy of unseen goal-directed hand movement than the recent visual memory.     

Disruption of food-getting movements after removal of the motor or premotor zone of the cerebral cortex in cats]

Instrumental food-procuring movements were studied in cats before and after unilateral or bilateral ablation of the motor or premotor cortical area. It is shown that unilateral impairment of the motor area affects the strength and accuracy of movements of the contralateral fore-leg, whereas the ablation of the premotor area leads to a slowing down of movements and breaking of a goal-directed movement into separate components. Bilataral ablation of the motor area irreversibly abolished the instrumental reflex. The ablation of the premotor cortex destroyed the animal's reaction to the sound signal, but food-procuring movements of the fore-legs were disturbed only temporarily. The obtained data are discussed on the basis of the concept that in cats the above cortical areas play different roles in the organization of goal directed behaviour.     

Peripheral and central nervous responses evoked by small water movements in a cephalopod

Potentials were recorded from the epidermal head lines and from the CNS of young cuttlefish, Sepia officinalis, in response to weak water movements. 1. Within the test range 0.5-400 Hz a sinusoidal water movement elicits up to 4 components of response if the electrode is placed on a headline: (i) a positive phasic ON response; (ii) a tonic frequency-following microphonic response; (iii) a slow negative OFF response; and (iv) compound nerve impulses. 2. The amplitude of both the ON wave and the microphonic potential depends on stimulus frequency, stimulus amplitude and stimulus rise time. Frequencies around 100 Hz and short rise times are most effective in eliciting strong potentials. The minimal threshold was 0.06 microns peak-to-peak water displacement at 100 Hz (18.8 microns/s as velocity). 3. Change of direction of tangential sphere movement (parallel vs. across the head lines) has only a small effect on the microphonic and the summed nerve potentials. 4. Frequency and/or amplitude modulations of a carrier stimulus elicit responses at the onset and offset of the modulation and marked changes in the tonic microphonic response. 5. Evoked potentials can be recorded from the brain while stimulating the epidermal lines with weak water movements. The brain potentials differ in several aspects from the potentials of the head lines and show little or no onset or offset wave at the transitions of a frequency and amplitude modulation.     

Driving oscillatory activity in the human cortex enhances motor performance

Voluntary movement is accompanied by changes in the degree to which neurons in the brain synchronize their activity within discrete frequency ranges. Two patterns of movement-related oscillatory activity stand out in human cortical motor areas. Activity in the beta frequency (15-30 Hz) band is prominent during tonic contractions but is attenuated prior to and during voluntary movement. Without such attenuation, movement may be slowed, leading to the suggestion that beta activity promotes postural and tonic contraction, possibly at a cost to the generation of new movements. In contrast, activity in the gamma (60-90 Hz) band increases during movement. The direction of change suggests that gamma activity might facilitate motor processing. In correspondence with this, increased frontal gamma activity is related with reduced reaction times. Yet the possibility remains that these functional correlations reflect an epiphenomenal rather than causal relationship. Here we provide strong evidence that oscillatory activities at the cortical level are mechanistically involved in determining motor behavior and can even improve performance. By driving cortical oscillations using noninvasive electrical stimulation, we show opposing effects at beta and gamma frequencies and interactions with motor task that reveal the potential quantitative importance of oscillations in motor behavior.     

Comparing information about arm movement direction in single channels of local and epicortical field potentials from monkey and human motor cortex.

Cortical field potentials have been used for decades in neurophysiological studies to probe spatio-temporal activity patterns of local populations of neurons. Recently, however, interest in these signals was spurred as they were proposed as potential control signals for neuronal motor prostheses, i.e., for devices fit to record and decode brain activity to restore motor functions in paralyzed patients. Little is known, however, about the functional significance of these cortical field potentials. Here we compared information about arm movement direction in two types of movement related cortical field potentials, obtained during a four direction center-out arm reaching paradigm: local field potentials (LFPs) recorded with intracortical micro-electrodes from monkey motor cortex, and epicortical field potentials (EFPs) recorded with macro-electrode arrays subdurally implanted on the surface of the human cerebral cortex. While monkey LFPs showed a typical sequence of positive and negative potential peaks, an initial negative peak was the most salient feature of human EFPs. Individual contralateral LFPs from the monkey motor cortex carried approximately twice as much decoded information (DI) about arm movement direction (median 0.27 bit) as did individual EFPs from the contralateral hand/arm area of primary motor cortex in humans (median 0.12 bit). This relation was similar to the relation between median peak signal-to-noise ratios for directional modulation of movement related potentials (MRPs) of both types of signals. We discuss possible reasons for the observed differences, amongst them epi- vs. intracortical recording and the different electrode dimensions used to measure EFPs and LFPs.     

Occlusion of LTP-like plasticity in human primary motor cortex by action observation

Passive observation of motor actions induces cortical activity in the primary motor cortex (M1) of the onlooker, which could potentially contribute to motor learning. While recent studies report modulation of motor performance following action observation, the neurophysiological mechanism supporting these behavioral changes remains to be specifically defined. Here, we assessed whether the observation of a repetitive thumb movement--similarly to active motor practice--would inhibit subsequent long-term potentiation-like (LTP) plasticity induced by paired-associative stimulation (PAS). Before undergoing PAS, participants were asked to either 1) perform abductions of the right thumb as fast as possible; 2) passively observe someone else perform thumb abductions; or 3) passively observe a moving dot mimicking thumb movements. Motor evoked potentials (MEP) were used to assess cortical excitability before and after motor practice (or observation) and at two time points following PAS. Results show that, similarly to participants in the motor practice group, individuals observing repeated motor actions showed marked inhibition of PAS-induced LTP, while the "moving dot" group displayed the expected increase in MEP amplitude, despite differences in baseline excitability. Interestingly, LTP occlusion in the action-observation group was present even if no increase in cortical excitability or movement speed was observed following observation. These results suggest that mere observation of repeated hand actions is sufficient to induce LTP, despite the absence of motor learning.     

Relationship between esophageal muscle thickness and intraluminal pressure in patients with esophageal spasm

We previously showed, in normal subjects, a positive correlation between the esophageal contraction amplitude and peak muscle thickness. The goal of this study was to determine the relationship between esophageal muscle thickness and contraction amplitude in patients with high-amplitude peristaltic and simultaneous contractions. Eleven patients with high-amplitude peristaltic contractions, 8 with diffuse esophageal spasm (DES), 7 with nonspecific (NS) motor disorder of the esophagus, and 10 normal subjects were studied using simultaneous pressure and ultrasound imaging. Pressure was recorded by manometry and ultrasound imaging with a high-frequency ultrasound probe catheter. Recordings were performed in the lower esophageal sphincter (LES) and at 2, 4, 6, 8, and 10 cm above the LES during resting state and swallow-induced contractions. Baseline esophageal muscle was thicker in the distal, compared with the proximal esophagus both in normal subjects and patient groups. Patients with DES and nutcracker esophagus (NC) have a higher baseline muscle thickness compared with normal and NS patients. Correlation between the peak pressure and the peak muscle thickness was weaker in patients with NC and DES compared with normal subjects and patients with NS. Whereas normal subjects have good correlation between delta (difference between peak and baseline) muscle thickness and peak pressures, this relationship was absent in patients with NC and DES. Increase in contraction amplitude in patients with NC and DES was associated with an increase in baseline thickness of esophageal muscularis propria. Increase in baseline thickness was specific to patients with spastic motor disorders and was not seen in patients with NS.     

Control of the Elbow Extensor Muscles in Slow Targeted Extensions of the Arm in Humans

Relations between the kinematic parameters of slow (non-ballistic) targeted extension movements in the elbow joint of humans and characteristics of the movement-related EMG activity in the two heads of the m. triceps brachii were analyzed. Test movements were performed under conditions of application of non-inertional external loadings directed toward flexion. It was shown that the movement-related EMG activity of the elbow extensors, similarly to what was observed in the flexors at flexion movements with the same parameters, demonstrates a complex structure and includes dynamic and stationary phases. In the former phase, in turn, initial and main components can be differentiated. The rising edge and decay of the main component of the dynamic extensor EMG phase could be approximated by exponential functions; this component was never split into a few subcomponents. Dependences between the amplitudes of m. triceps brachii EMG phases and the amplitude of the movement (or external loading) were, as a rule, nonlinear but monotonic. An increase in the test movement velocity led to an increase in the rate of rise of the rising edge of the dynamic EMG phase, while an increment in the amplitude was less significant. Under the used test conditions, the activity of the elbow extensors was usually accompanied by some coactivation of the antagonists (m. biceps brachii). It is concluded that motor commands coming to the elbow extensors at performance of the extension test movements differ from motor commands to the flexors at analogous flexion test movements by a simpler structure and more tonic pattern. Biomechanical specificities of fixation of the mentioned muscle groups to the arm bones (stability of the moment for application of the extensor force under conditions of changing the joint angle vs variable moment of the flexor force) are considered one of the main reasons for such specificity of the patterns of the extensor and flexor motor commands.     

The Effects of Rhythmicity and Amplitude on Transfer of Motor Learning

We perform rhythmic and discrete arm movements on a daily basis, yet the motor control literature is not conclusive regarding the mechanisms controlling these movements; does a single mechanism generate both movement types, or are they controlled by separate mechanisms? A recent study reported partial asymmetric transfer of learning from discrete movements to rhythmic movements. Other studies have shown transfer of learning between large-amplitude to small-amplitude movements. The goal of this study is to explore which aspect is important for learning to be transferred from one type of movement to another: rhythmicity, amplitude or both. We propose two hypotheses: (1) Rhythmic and discrete movements are generated by different mechanisms; therefore we expect to see a partial or no transfer of learning between the two types of movements; (2) Within each movement type (rhythmic/discrete), there will be asymmetric transition of learning from larger movements to smaller ones. We used a learning-transfer paradigm, in which 70 participants performed flexion/extension movements with their forearm, and switched between types of movement, which differed in amplitude and/or rhythmicity. We found partial transfer of learning between discrete and rhythmic movements, and an asymmetric transfer of learning from larger movements to smaller movements (within the same type of movement). Our findings suggest that there are two different mechanisms underlying the generation of rhythmic and discrete arm movements, and that practicing on larger movements helps perform smaller movements; the latter finding might have implications for rehabilitation.