Hand Motor System Research Articles

Sensorimotor and interoceptive dimensions in concrete and abstract concepts.

Recent theories propose that abstract concepts, compared to concrete ones, might activate to a larger extent interoceptive, social and linguistic experiences. At the same time, recent research has underlined the importance of investigating how different sub-kinds of abstract concepts are represented. We report a pre-registered experiment, preceded by a pilot study, in which we asked participants to evaluate the difficulty of 3 kinds of concrete concepts (natural objects, tools, and food concepts) and abstract concepts (Philosophical and Spiritual concepts, PS, Physical Space Time and Quantity concepts, PSTQ, and Emotional, Mental State and Social concepts, EMSS). While rating the words, participants were assigned to different conditions designed to interfere with conceptual processing: they were required to squeeze a ball (hand motor system activation), to chew gum (mouth motor system activation), to self-estimate their heartbeats (interoception), and to perform a motor articulatory task (inner speech involvement). In a control condition they simply rated the difficulty of words. A possible interference should result in the increase of the difficulty ratings. Bayesian analyses reveal that, compared to concrete ones, abstract concepts are more grounded in interoceptive experience and concrete concepts less in linguistic experience (mouth motor system involvement), and that the experience on which different kinds of abstract and concrete concepts differs widely. For example, within abstract concepts interoception plays a major role for EMSS and PS concepts, while the ball squeezing condition interferes more for PSTQ concepts, confirming that PSTQ are the most concrete among abstract concepts, and tap into sensorimotor manual experience. Implications of the results for current theories of conceptual representation are discussed.

Motor control strategies during unpredictable force control tasks in humans.

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. To investigate and compare the force control of the jaw motor system (OMS) and the hand motor system (HMS) during unpredictable load changes. Seventeen healthy adults (24.0±4.3years) 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. 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). 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.

The importance of visuo-motor coordination in upper limb rehabilitation after ischemic stroke by robotic therapy

Abstract Stroke is an acute hypoperfusion of cerebral parenchyma that most often leads to outstanding motor deficits that can last for the rest of the patient’s life. The purpose of the neurorehabilitation process is to limit, as far is possible for the motor deficits and to bring the patient to an independent life. A modern method consists in robotic neurorehabilitation which is more and more used, associated with functional electrical stimulation (FES). At the lower limb, the use of robotic rehabilitation associated with FES is already considered a success due to relatively stereotypical movements of the lower limb. In opposition, the upper limb is more difficult to rehabilitate due to its more complex movements. Therefore, eye-hand coordination (EHC) constitutes an important factor that is conditioning the rehabilitation progress. The eye-hand coordination can be brutally disturbed by stroke with critical consequences on motor-executive component. The EHC development depends on the interaction between a feedback complex and the prediction of the upper limb motility in the space, and requires the association between visual system, oculomotor system and hand motor system. We analyzed the stroke impact on this sensorial-motor functional integration and looked for a possible solution for the interruption of coordination between eyes and the movements of the superior limb. We consider that our study can contribute to a better understanding and to a faster rehabilitation of the motor deficit in the upper limb after stroke. Key words: stroke, rehabilitation, eye-hand coordination, robotic neurorehabilitation,

Abstract #161: When stimulating the unaffected (healthy) hemisphere in stroke patients makes sense

Research investigating the use of noninvasive electrical stimulation (e.g., transcranial direct current stimulation (tDCS)) has provided compelling evidence that such stimulation can modulate sensorimotor function, behavior and cognition, and even facilitate recovery of function after a focal brain injury. Our understanding of the mechanisms that lead to such changes is limited, and the influence of variables such as current strength, electrode montage and which regions of the brain to target is the focus of ongoing investigations. The degree of structural and/or functional injury to relevant systems (e.g., hand-motor system, speech-motor system, and swallowing system) and their pathways has been shown to determine natural outcome after a stroke and the response to an experimental intervention. However, the degree of bihemispheric organization of these systems and how redundant a system is organized in the brain seems to contribute to how well a particular system recovers. The premorbid organizational structure might also affect neuroplasticity, since plastic changes such as changes in synapses, axonal sprouting, changes in myelination, could affect the lesional and peri-lesional region as well as homotop regions of the contralesional hemisphere. Plasticity-enhancing tools might have an additive effect, although there are potentially multiple targets depending on the systems organizational structure. tDCS has been shown to modulate motor cortical excitability, modify a stroke-induced abnormal imbalance in inter-hemispheric inhibition, and increase synaptic plasticity if combined with a peripheral rehabilitation therapy. In this talk I will present the responses of different systems in the brain, contrasting a system that is more unihemispherically organized and has less redundancy and with a system that is more bihemispherically organized and has more redundancy. A redundant system has more options for targeted stimulation and electrode montages than a non-redundant system.

Functional dissociation of temporal processing mechanisms during speech production and hand movement: An ERP study

Skilled motor actions are mediated by neural mechanisms that incorporate sensory feedback for driving or suppressing movement with remarkable temporal precision. The predictive coding model proposes that the brain performs this function by establishing an internal representation of timing to accelerate movement response time. However, it is unclear whether different neural mechanisms are involved in temporal processing of movement initiation and cessation. The present study examined how temporal information is encoded for initiation and cessation of speech and hand movement. Event-related potentials (ERPs) were recorded while young healthy subjects performed speech and hand movement initiation and cessation in response to temporally predictable and unpredictable visual stimuli. We found that predictable stimuli elicited faster movement in both speech and hand modalities, with shorter reaction times associated with movement cessation compared with initiation. Analysis of ERPs revealed that premotor neural activities were significantly attenuated before speech initiation and hand movement initiation and cessation for temporally predictable vs. unpredictable conditions, but an opposite pattern was observed for speech cessation. In addition, we observed that the premotor ERPs were significantly modulated during speech initiation vs. cessation, but no such effect was found during hand movement. Finally, we found that the premotor ERPs were strongly correlated with motor reaction time during movement initiation and cessation for speech and hand modalities only in response to temporally predictable stimuli. These findings indicate that premotor ERPs reflect a temporal predictive code for planning of movement initiation and cessation and highlight functional dissociation of temporal processing mechanisms in speech and hand motor systems.

Dynamic Changes in Upper-Limb Corticospinal Excitability during a 'Pro-/Anti-saccade' Double-Choice Task.

Under natural behavioral conditions, visually guided eye movements are linked to direction-specific modulations of cortico-spinal system (CSS) excitability in upper-limb muscles, even in absence of a manual response. These excitability changes have been shown to be compatible with a covert motor program encoding a manual movement toward the same target of the eyes. The aim of this study is to investigate whether this implicit oculo-manual coupling is enforced following every saccade execution or it depends on the behavioral context. Twenty-two healthy young adults participated in the study. Single-pulse transcranial magnetic stimulation was applied to the motor cortex at nine different time epochs during a double-choice eye task, in which the decision to execute a prosaccade or an antisaccade was made on the color of a peripheral visual cue. By analyzing the amplitude of the motor evoked potentials (MEP) in three distal muscles of the resting upper-limb, a facilitation peak of CSS excitability was found in two of them at 120 ms before the eyes begin to move. Furthermore, a long-lasting, generalized reduced corticomotor excitability develops following the eye response. Finally, a quite large modulation of MEP amplitude, depending on the direction of the saccade, is observed only in the first dorsal interosseous muscle, in a narrow time window at about 150 ms before the eye movement, irrespective of the type of the ocular response (pro-/anti-saccade). This change in CSS excitability is not tied up to the timing of the occurrence of the visual cue but, instead, appears to be tightly time-related to the saccade onset. Observed excitability changes differ in many respects from those previously reported with different behavioral paradigms. A main finding of our study is that the implicit coupling between eye and hand motor systems is contingent upon the particular motor set determined by the cognitive aspects of the performed oculomotor task. In particular, the direction-specific modulation in CSS excitability described in this study appears to be related to perceptual and decision-making processes rather than representing an implicit upper-limb motor program, coupled to the saccade execution.

Influence of Visual Prism Adaptation on Auditory Space Representation.

Prisms shifting the visual input sideways produce a mismatch between the visual versus felt position of one’s hand. Prism adaptation eliminates this mismatch, realigning hand proprioception with visual input. Whether this realignment concerns exclusively the visuo-(hand)motor system or it generalizes to acoustic inputs is controversial. We here show that there is indeed a slight influence of visual adaptation on the perceived direction of acoustic sources. However, this shift in perceived auditory direction can be fully explained by a subconscious head rotation during prism exposure and by changes in arm proprioception. Hence, prism adaptation does only indirectly generalize to auditory space perception.

Premotor neural correlates of predictive motor timing for speech production and hand movement: evidence for a temporal predictive code in the motor system.

The predictive coding model suggests that neural processing of sensory information is facilitated for temporally-predictable stimuli. This study investigated how temporal processing of visually-presented sensory cues modulates movement reaction time and neural activities in speech and hand motor systems. Event-related potentials (ERPs) were recorded in 13 subjects while they were visually-cued to prepare to produce a steady vocalization of a vowel sound or press a button in a randomized order, and to initiate the cued movement following the onset of a go signal on the screen. Experiment was conducted in two counterbalanced blocks in which the time interval between visual cue and go signal was temporally-predictable (fixed delay at 1000ms) or unpredictable (variable between 1000 and 2000ms). Results of the behavioral response analysis indicated that movement reaction time was significantly decreased for temporally-predictable stimuli in both speech and hand modalities. We identified premotor ERP activities with a left-lateralized parietal distribution for hand and a frontocentral distribution for speech that were significantly suppressed in response to temporally-predictable compared with unpredictable stimuli. The premotor ERPs were elicited approximately -100ms before movement and were significantly correlated with speech and hand motor reaction times only in response to temporally-predictable stimuli. These findings suggest that the motor system establishes a predictive code to facilitate movement in response to temporally-predictable sensory stimuli. Our data suggest that the premotor ERP activities are robust neurophysiological biomarkers of such predictive coding mechanisms. These findings provide novel insights into the temporal processing mechanisms of speech and hand motor systems.

Alternating Adaptation of Eye and Hand Movements to Opposite Directed Double Steps

ABSTRACTEye and hand movements can adapt to a variety of sensorimotor discordances. Studies on adaptation of movement directions suggest that the oculomotor and the hand motor system access the same adaptive mechanism related to the polarity of a discordance, because concurrent adaptations to opposite directed discordances strongly interfere. The authors scrutinized whether participants adapt their hand and eye movements to opposite directions (clockwise/counterclockwise) when both motor systems are alternatingly exposed to opposite directed double steps, and whether such adaptation is influenced by the allocation of effector to adaptation direction. The results showed that hand and eye movements adapted to opposite directions, but adaptation was biased to the counterclockwise direction. Aftereffects emerged nearly unbiased and independently for both motor systems. The authors conclude that the oculomotor and the hand motor system use independent mechanisms when they adapt to opposite polarities, although they interact during adaptation or concurrent performance.

Eye–hand coordination in on-line visuomotor adjustments

When we perform a visually guided reaching action, the brain coordinates our hand and eye movements. Eye-hand coordination has been examined widely, but it remains unclear whether the hand and eye motor systems are coordinated during on-line visuomotor adjustments induced by a target jump during a reaching movement. As such quick motor responses are required when we interact with dynamic environments, eye and hand movements could be coordinated even during on-line motor control. Here, we examine the relationship between online hand adjustment and saccadic eye movement. In contrast to the well-known temporal order of eye and hand initiations where the hand follows the eyes, we found that on-line hand adjustment was initiated before the saccade onset. Despite this order reversal, a correlation between hand and saccade latencies was observed, suggesting that the hand motor system is not independent of eye control even when the hand response was induced before the saccade. Moreover, the latency of the hand adjustment with saccadic eye movement was significantly shorter than that with eye fixation. This hand latency modulation cannot be ascribed to any changes of visual or oculomotor reafferent information as the saccade was not yet initiated when the hand adjustment started. Taken together, the hand motor system would receive preparation signals rather than reafference signals of saccadic eye movements to provide quick manual adjustments of the goal-directed eye-hand movements.

Early event-related potentials indicate context-specific target processing for eye and hand motor systems

Concurrent eye and hand movements toward a common visual target require different motor programs based on identical visual input. We used event-related brain potentials (ERP) to determine if and when the processing of the visual target differs for the two motor systems.The N2, an index for target evaluation, was more negative for the target of a hand than of an eye movement in two experiments. A possible interpretation for this finding is different visual target processing. Targets for hand movements require a different weighting of visual information, for example concerning features such as surface structure which are important for hand but not for eye movements.In experiment 2, the early C1-component, which had an average maximum at 67ms following target onset, was significantly more negative when subjects pointed at the stimuli. Traditionally, the C1 has been regarded as a sensory component, but recent studies have linked it to higher order processing, such as attention and expectations. Thus, the present data indicate that target processing for eye or hand movements is already context-specific during early visual information processing. We suggest that differences in a target's relevance for upcoming movements modify target processing as well as sensory expectations.

Global Processing Speed in Children With Low Reading Ability and in Children and Adults With Typical Reading Ability: Exploratory Factor Analytic Models

To investigate processing speed as a latent dimension in children with dyslexia and children and adults with typical reading skills. Exploratory factor analysis (FA) was based on a sample of multigenerational families, each ascertained through a child with dyslexia. Eleven measures--6 of them timed--represented verbal and nonverbal processes, alphabet writing, and motor sequencing in the hand and oral motor system. FA was conducted in 4 cohorts (all children, a subset of children with low reading scores, a subset of children with typical reading scores, and adults with typical reading scores; total N = 829). Processing speed formed the first factor in all cohorts. Both measures of motor sequencing speed loaded on the speed factor with the other timed variables. Children with poor reading scores showed lower speed factor scores than did typical peers. The speed factor was negatively correlated with age in the adults. The speed dimension was observed independently of participant cohort, gender, and reading ability. Results are consistent with a unified theory of processing speed as a quadratic function of age in typical development and with slowed processing in poor readers.

Covert word reading induces a late response in the hand motor system of the language dominant hemisphere

Recent work has demonstrated that overt reading influences the excitability of the language-dominant hand motor cortex. However, this effect was related to speech output, whereas results on silent reading have been inconsistent, and have not allowed for systematic investigation of the different stages of word recognition. To investigate a possible modulation of the cortical excitability mediating hand movements through different stages of covert reading, motor evoked potentials (MEP) from hand muscles in right-handed subjects were recorded. We showed a significant increase of the excitability of the hand motor cortex of the dominant hemisphere during late stages of covert word reading, whereas processing of abstract shapes had no effect and covert articulation induced a decrease in hand motor cortex excitability. There was no significant change of MEP amplitudes during earlier stages of covert reading in the dominant hemisphere or in the non-dominant hemisphere. Our results demonstrate a functional connection between cortical networks mediating linguistic processing and hand movements without concurrent activation of the motor cortex through overt articulation at late stages of word reading, which have been shown to involve converging activation of classic left frontal language regions. We speculate that the effect reported here is related to a cortical network mediating gestures which are a part of verbal communication. This supports recent theories on language evolution which postulate that language emerged through manual gestures.

Predictive eye and hand movements are differentially affected by schizophrenia

Schizophrenic patients are known to have problems suppressing reflexive eye movements. This is considered to indicate a dysfunction in prefrontal cortex. As the eye and hand motor systems are tightly coupled, we investigated whether predictive hand movements and eye-hand coordination are unimpaired in schizophrenic patients. Saccades and hand movements of 19 patients during an acute schizophrenic episode and 19 controls were measured in a task in which the predictability of target timing was varied. Schizophrenic patients generated more anticipatory and less visually triggered saccades than controls with both non-predictable and predictable target timing. Anticipatory saccades in the wrong direction were clearly directed towards previous target positions, indicating that they are indicators of erroneous prediction rather than of fixation instability. In contrast to saccades, the number of anticipatory and visually triggered hand movements was the same in patients as in controls. As a consequence, patients took longer to initiate a hand movement after a saccade than controls. Schizophrenic patients show increased predictive saccadic activity, but no qualitative changes in predictive saccades. Since prediction itself was not disturbed, the patients' deficit rather lies in the suppression or gating of anticipatory saccades than in their generation. This may be explained by a selective dysfunction of the basal ganglia oculomotor loop. As predictive hand movements were unimpaired, the problems in eye-hand coordination as expressed by a longer initiation time of hand movements relative to saccades are a direct consequence of impaired predictive saccadic behaviour.

Modulation of corticospinal activity by strong emotions evoked by pictures and classical music: a transcranial magnetic stimulation study

Using transcranial magnetic stimulation and skin conductance responses, we sought to clarify if, and to what extent, emotional experiences of different valences and intensity activate the hand-motor system and the associated corticospinal tract. For that purpose, we applied a newly developed method to evoke strong emotional experiences by the simultaneous presentation of musical and pictorial stimuli of congruent emotional valence. We uncovered enhanced motor-evoked potentials, irrespective of valence, during the simultaneous presentation of emotional music and picture stimuli (Combined conditions) compared with the single presentation of the two modalities (Picture/Music conditions). In contrast, vegetative arousal was enhanced during both the Combined and Music conditions, compared with the Picture conditions, again irrespective of emotional valence. These findings strongly indicate that arousal is a necessary, but not sufficient, prerequisite for triggering the motor system of the brain. We offer a potential explanation for this discrepant, but intriguing, finding in the paper.

Functional connectivity between cortical hand motor and language areas during recovery from aphasia

Previous data indicate that in healthy subjects, there is a connectivity between cortical areas for hand movement and language on the left hemisphere. This link is possibly mediated by the so-called mirror neuron system. The present study investigated the functional relationship between linguistic and hand movement processing in patients who were recovering from post-stroke aphasia. The excitability of the right- and left-hand motor cortex during language production in patients who were recovering from post-stroke aphasia and age-matched controls was investigated. As control, phonation was investigated. Hand motor cortex excitability was assessed with Motor Evoked Potentials which were elicited by Transcranial Magnetic Stimulation (TMS). In patients, reading aloud enhanced the excitability of the right hemispheric hand motor cortex, whereas phonation had no effect on hand motor cortex excitability. In the control group, an increased excitability of the left hemispheric hand motor system was found during reading aloud in accordance with previous data. The present data suggest a functional connectivity between regions mediating hand movements and reading. This may indicate that the right hemisphere participates in language processing as far as involved in single word reading in patients recovering from aphasia. The coactivation between cerebral representations of hand movements and language may be used therapeutically for aphasia rehabilitation.

The role of eye movements in visuo-manual adaptation

The present study evaluated the role of eye movements for manual adaptation to reversed vision. Subjects tracked a visual target using a mouse-driven cursor. In Experiment A, they were instructed to look at the target, look at the cursor, fixate straight ahead, or received no instructions regarding eye movements (Groups T, C, F, and N, respectively). Experiment B involved Groups T and C only. In accordance with literature, baseline manual tracking was more accurate when subjects were instructed to move their eyes rather than to fixate straight ahead. In contrast, no such benefit was observed for the adaptive improvement of tracking. We therefore concluded that transfer of information from the oculomotor to the hand motor system enhances the ongoing control of hand movements but not their adaptive modification; probably because the large computational demand of adaptation does not allow an additional processing of supplementary oculomotor signals. We further found adaptation to be worse in T than in any other group. In particular, adaptation was worse in T than in C although eye movements were the same: subjects in both groups moved their eyes in close relationship with the target rather than the cursor, Group C thus disobeying our instructions. The deficient performance of Group T is therefore not related to eye movements per se, but rather to our instructions. We conclude that an independently moving target strongly attracts eye movements independent of instruction (i.e. Groups T and C), but instructions may redirect spatially selective attention (i.e. Group T vs C), and thus influence adaptation.

Language perception activates the hand motor cortex: implications for motor theories of speech perception.

The precise mechanisms of how speech may have developed are still unknown to a large extent. Gestures have proven a powerful concept for explaining how planning and analysing of motor acts could have evolved into verbal communication. According to this concept, development of an action-perception network allowed for coding and decoding of communicative gestures. These were manual or manual/articulatory in the beginning and then became increasingly elaborate in the articulatory mode. The theory predicts that listening to the 'gestures' that compose spoken language should activate an extended articulatory and manual action-perception network. To examine this hypothesis, we assessed the effects of language on cortical excitability of the hand muscle representation by transcranial magnetic stimulation. We found the hand motor system to be activated by linguistic tasks, most notably pure linguistic perception, but not by auditory or visuospatial processing. The amount of motor system activation was comparable in both hemispheres. Our data support the theory that language may have evolved within a general and bilateral action-perception network.

Lateralisation may be a side issue for understanding language development

We add evidence in support of Corballis's gestural theory of language. Using transcranial magnetic stimulation, we found that productive and receptive linguistic tasks excite the motor cortices for both hands. This indicates that the language and the hand motor systems are still tightly linked in modern man. The bilaterality of the effect, however, implies that lateralisation is a secondary issue.

What is special about the brains of musicians?

What is special about the brains of musicians?