Temporal regularity of tapping by the left and right hands in timed and untimed finger tapping

Premotor cortical beta synchronization and the network neuromodulation of externally paced finger tapping in Parkinson's disease

Parkinson's disease (PD) is characterized by the disruption of repetitive, concurrent and sequential motor actions due to compromised timing-functions principally located in cortex-basal ganglia (BG) circuits. Increasing evidence suggests that motor impairments in untreated PD patients are linked to an excessive synchronization of cortex-BG activity at beta frequencies (13-30 Hz). Levodopa and subthalamic nucleus deep brain stimulation (STN-DBS) suppress pathological beta-band reverberation and improve the motor symptoms in PD. Yet a dynamic tuning of beta oscillations in BG-cortical loops is fundamental for movement-timing and synchronization, and the impact of PD therapies on sensorimotor functions relying on neural transmission in the beta frequency-range remains controversial. Here, we set out to determine the differential effects of network neuromodulation through dopaminergic medication (ON and OFF levodopa) and STN-DBS (ON-DBS, OFF-DBS) on tapping synchronization and accompanying cortical activities. To this end, we conducted a rhythmic finger-tapping study with high-density EEG-recordings in 12 PD patients before and after surgery for STN-DBS and in 12 healthy controls. STN-DBS significantly ameliorated tapping parameters as frequency, amplitude and synchrony to the given auditory rhythms. Aberrant neurophysiologic signatures of sensorimotor feedback in the beta-range were found in PD patients: their neural modulation was weaker, temporally sluggish and less distributed over the right cortex in comparison to controls. Levodopa and STN-DBS boosted the dynamics of beta-band modulation over the right hemisphere, hinting to an improved timing of movements relying on tactile feedback. The strength of the post-event beta rebound over the supplementary motor area correlated significantly with the tapping asynchrony in patients, thus indexing the sensorimotor match between the external auditory pacing signals and the performed taps. PD patients showed an excessive interhemispheric coherence in the beta-frequency range during the finger-tapping task, while under DBS-ON the cortico-cortical connectivity in the beta-band was normalized. Ultimately, therapeutic DBS significantly ameliorated the auditory-motor coupling of PD patients, enhancing the electrophysiological processing of sensorimotor feedback-information related to beta-band activity, and thus allowing a more precise cued-tapping performance.

Groups clapping in unison undergo size-dependent error-induced frequency increase

Humans clapping together in unison is a familiar and robust example of emergent synchrony. We find that in experiments, such groups (from two to a few hundred) always increase clapping frequency, and larger groups increase more quickly. Based on single-person experiments and modeling, an individual tendency to rush is ruled out as an explanation. Instead, an asymmetric sensitivity in aural interactions explains the frequency increase, whereby individuals correct more strongly to match neighbour claps that precede their own clap, than those that follow it. A simple conceptual coupled oscillator model based on this interaction recovers the main features observed in experiments, and shows that the collective frequency increase is driven by the small timing errors in individuals, and the resulting inter-individual interactions that occur to maintain unison.

Motor Timing and Covariation with Time Perception: Investigating the Role of Handedness

Time is a fundamental dimension of our behavior and enables us to guide our actions and to experience time such as predicting collisions or listening to music. In this study, we investigate the regulation and covariation of motor timing and time perception functions in left- and right-handers who are characterized by distinct brain processing mechanisms for cognitive-motor control. To this purpose, we use a combination of tasks that assess the timed responses during movements and the perception of time intervals. The results showed a positive association across left- and right-handers between movement-driven timing and perceived interval duration when adopting a preferred tempo, suggesting cross-domain coupling between both abilities when an intrinsic timescale is present. Handedness guided motor timing during externally-driven conditions that required cognitive intervention, which specifies the relevance of action expertise for the performance of timed-based motor activities. Overall, our results reveal that individual variation across domain-general and domain-specific levels of organization plays a steering role in how one predicts, perceives and experiences time, which accordingly impacts on cognition and behavior.

Manual asymmetry for temporal and spatial parameters in sensorimotor synchronization

Previous studies suggest a right hemisphere advantage for temporal processing and a left hemisphere advantage for planning of motor actions. In the present study, we studied sensorimotor synchronization of hand reaching movements with an auditory rhythm. Blindfolded right-handed participants were asked to synchronize left and right hand movements to an auditory rhythm (40 vs. 60 vs. 80 bpm) and simultaneously reproduce the amplitude of a previously shown movement. Constant and variable asynchronies and movement amplitude errors were measured. The results showed that (a) constant asynchrony was lesser with the left hand than the right hand and (b) constant and variable amplitude errors were lesser with the right hand than the left hand. We suggest that when hand reaching movements are synchronized with an auditory rhythm, the left hand/right hemisphere system appears relatively specialized in temporally adhering to the rhythm and the right hand/left hemisphere system in performing spatially accurate movements.

The 'Goldilocks Zone': getting the measure of manual asymmetries

Some studies have shown that manual asymmetries decrease in older age. These results have often been explained with reference to models of reduced hemispheric specialisation. An alternative explanation, however, is that hand differences are subtle, and capturing them requires tasks that yield optimal performance with both hands. Whereas the hemispheric specialisation account implies that reduced manual asymmetries should be reliably observed in older adults, the ‘measurement difficulty’ account suggests that manual asymmetries will be hard to detect unless a task has just the right level of difficulty—i.e. within the ‘Goldilocks Zone’, where it is not too easy or too hard, but just right. Experiment One tested this hypothesis and found that manual asymmetries were only detected when participants performed in this zone; specifically, performance on a tracing task was only superior in the preferred hand when task constraints were high (i.e. fast speed tracing). Experiment Two used three different tasks to examine age differences in manual asymmetries; one task produced no asymmetries, whilst two tasks revealed asymmetries in both younger and older groups (with poorer overall performance in the old group across all tasks). Experiment Three revealed task-dependent asymmetries in both age groups, but highlighted further detection difficulties linked with the metric of performance and compensatory strategies used by participants. Results are discussed with reference to structural learning theory, whereby we suggest that the processes of inter-manual transfer lead to relatively small performance differences between the hands (despite a strong phenomenological sense of performance disparities).

Developmental changes in lateralized inhibition of symmetric movements in children with and without Developmental Coordination Disorder

The present study investigates developmental changes in selective inhibition of symmetric movements with a lateralized switching task from bimanual to unimanual tapping in typically developing (TD) children and with Developmental Coordination Disorder (DCD) from 7 to 10 years old. Twelve right-handed TD children and twelve gender-matched children with DCD and probable DCD produce a motor switching task in which they have (1) to synchronize with the beat of an auditory metronome to produce bimanual symmetrical tapping and (2) to selectively inhibit their left finger's tapping while continuing their right finger's tapping and conversely. We assess (1) the development of the capacity to inhibit the stopping finger (number of supplementary taps after the stopping instruction) and (2) the development of the capacity to maintain the continuing finger (changes in the mean tempo and its variability for the continuing finger's tapping) and (3) the evolution of performance through trials. Results indicate that (1) TD children present an age-related increase in the capacity to inhibit and to maintain the left finger's tapping, (2) DCD exhibits persistent difficulties to inhibit the left finger's tapping, and (3) both groups improve their capacity to inhibit the left finger's movements through trials. In conclusion, the lateralized switching task provides a simple and fine tool to reveal differences in selective inhibition of symmetric movements in TD children and children with DCD. More theoretically, the specific improvement in selective inhibition of the left finger suggests a progressive development of inter-hemispheric communication during typical development that is absent or delayed in children with DCD.

Reduced motor asymmetry in older adults when manually tracing paths

Handedness, a preference towards using the right or left hand, is established in early childhood. Such specialisation allows a higher level of skill to be maintained in the preferred hand on specific tasks through continuous practice and performance. Hand asymmetries might be expected to increase with age because of the time spent practising with the preferred hand. However, neurophysiological work has suggested reduced hemispheric function lateralisation in the ageing brain, and behavioural studies have found reduced motor asymmetries in older adults (Przybyla et al., in Neurosci Lett 489:99-104, 2011). We therefore tested the predictions of behavioural change from reduced hemispheric function by measuring tracing performance (arguably one of the most lateralised of human behaviours) along paths of different thickness in a group of healthy young and older adults. Participants completed the task once with their preferred (right) hand and once with their non-preferred (left) hand. Movement time (MT) and shape accuracy (SA) were dependant variables. A composite measure of MT and SA, the speed accuracy cost function (SACF) provided an overall measure of motor performance. Older participants were slower and less accurate when task demands were high. Combined analyses of both hands revealed reduced asymmetries in MT and SACF in the older group. The young were significantly faster when tracing with their preferred hand, but older participants were equally slow with either hand. Our results are consistent with the growing literature reporting decreased hemispheric function lateralisation in the ageing brain.

Coupling between perception and action timing during sensorimotor synchronization

Time is an important parameter in behaviour, especially when synchronization with external events is required. To evaluate the nature of the association between perception and action timing, this study introduced pitch accented tones during performance of a sensorimotor tapping task. Furthermore, regularity of the pacing cues was modified by small (subliminal) or large (conscious) timing perturbations. A global analysis across the intervals showed that repeated accented tones increased the tap-tone asynchrony in the regular (control) and irregular (subliminal) trials but not in the irregular trials with awareness of the perturbations. Asynchrony variability demonstrated no effect of accentuation in the regular and subliminal irregular trials, whereas it increased in the conscious irregular trials. A local analysis of the intervals showed that pitch accentuation lengthened the duration of the tapping responses, but only in the irregular trials with large timing perturbations. These data underline that common timing processes are automatically engaged for perception and action, although this arrangement can be overturned by cognitive intervention. Overall, the findings highlight a flexible association between perception and action timing within a functional information processing framework.

Temporal evolution of the phase correction response in synchronization of taps with perturbed two-interval rhythms

Human sensorimotor synchronization is flexible but subject to temporal constraints. Previous research has shown that musicians tend to lose synchrony with target tones in an isochronous sequence when the sequence rate exceeds 8-10 Hz, presumably because phase correction ceases to function. The present study investigated directly the time required for an immediate phase correction response (PCR). Musicians tapped in synchrony with cyclic two-interval (short-long) rhythms, using the two hands in alternation. Perturbations were applied to the long interval, and the compensatory shift of the next tap (the PCR) was measured following the short interval, whose duration was varied from 100 to 300 ms. The PCR was found to increase gradually within this range, being nearly absent at 100 ms. Similar results were obtained when participants tapped only with the second tone in each rhythmic group, which confirms that the PCR is based on the preceding tone rather than on the preceding tap-tone asynchrony, and also when the second tone was omitted in the pacing sequence, which indicates that the PCR occurs automatically even when there is no synchronization target for the critical tap. These results extend earlier findings regarding rate limits of synchronization and also provide further support for an event-based phase resetting account of the PCR.

Timing and history-dependent processing during sensorimotor synchronization

Temporal processing is important during skilled actions and often underlies a successful performance. In the present study, functional connectivity profiles as determined by EEG coherence were evaluated in a switching paradigm that assessed the effect of movement rate history upon neural processing. To this end, right-handed subjects initiated tapping responses at a specific tempo, followed by a faster/slower tempo before switching back to the initial tempo. Left and right hand responses were performed and the alternative tempo was adopted by the same or opposite effector. The data showed an increased degree of contralateral intrahemispheric connectivity for slow tapping when preceded by fast tapping; an effect that was strongest for the left hand. When the opposite effector became involved in the switching process, intensification of interhemispheric and midline connectivity additionally occurred. No increase in functional coupling was observed for fast tapping when preceded by slow tapping. Overall, the observations illustrate that the dynamics of motor subroutines within a serial arrangement impose history-dependent operations in timing, which accordingly impacts on the effectiveness of neural processing.

Linear versus non-linear measures of temporal variability in finger tapping and their relation to performance on open- versus closed-loop motor tasks: comparing standard deviations to Lyapunov exponents

The nature of temporal variability during speeded finger tapping was examined using linear (standard deviation) and non-linear (Lyapunov exponent) measures. Experiment 1 found that right hand tapping was characterised by lower amounts of both linear and non-linear measures of variability than left hand tapping, and that linear and non-linear measures of variability were often negatively correlated with one another. Experiment 2 found that increased non-linear variability was associated with relatively enhanced performance on a closed-loop motor task (mirror tracing) and relatively impaired performance on an open-loop motor task (pointing in a dark room), especially for left hand performance. The potential uses and significance of measures of non-linear variability are discussed.

Categories of manual asymmetry and their variation with advancing age

Manual asymmetries were analyzed in 18- to 63-year-old right-handers in different motor tasks. This analysis aimed at describing the asymmetry profile for each task and assessing their stability across ages. For this purpose, performance of the right and left hands were analyzed in the following aspects: simple reaction time, rate of sequential finger movements, maximum grip force, accuracy in anticipatory timing, rate of repetitive tapping, and rate of drawing movements. In addition, stability of manual preference across ages was assessed through the Edinburgh inventory (Oldfield, 1971). The results indicated different profiles of manual asymmetry, with identification of three categories across tasks: symmetric performance (asymmetry indices close to zero), inconsistent asymmetry (asymmetry indices variable in magnitude and direction), and consistent asymmetry (asymmetry indices favoring a single hand). The different profiles observed in the young adults were stable across ages with two exceptions: decreased lateral asymmetry for maximum grip force and increased asymmetry for sequential drawing in older individuals. These results indicate that manual asymmetries are task specific. Such task specificity is interpreted to be the result of different sensorimotor requirements imposed by each motor task in association with motor experiences accumulated over the lifetime. Analysis of manual preference showed that strength of preference for the right hand was greater in older individuals.

Perceiving the numerosity of rapidly occurring auditory events in metrical and nonmetrical contexts

Experiment 1 determined the fastest tempo at which participants could tap in synchrony with every nth tone (n = 2 to 9) in an isochronous sequence. Tapping was difficult with every 5th or 7th tone but easy with every 2nd, 4th, or 8th tone, suggesting that evenly divisible groups of n tones are automatically subdivided into equal groups of 2 or 3-a form of auditory subitizing that generates metrical hierarchies commonly found in Western music. Experiments 2 and 3 sought evidence of subitizing and subdivision in timed explicit enumeration of short, rapidly presented tone sequences (n = 2 to 10). Enumeration accuracy decreased monotonically with n. Response time increased monotonically up to n = 5 or 6, but less between 2 and 3 than between 3 and 4. Thus, a single group of 2 or 3 tones perhaps can be subitized, but subdivision of larger groups into subgroups of 2 or 3 tones seems to be specific to a repetitive, metrical context.

Sensorimotor synchronization: A review of the tapping literature

Sensorimotor synchronization (SMS), the rhythmic coordination of perception and action, occurs in many contexts, but most conspicuously in music performance and dance. In the laboratory, it is most often studied in the form of finger tapping to a sequence of auditory stimuli. This review summarizes theories and empirical findings obtained with the tapping task. Its eight sections deal with the role of intention, rate limits, the negative mean asynchrony, variability, models of error correction, perturbation studies, neural correlates of SMS, and SMS in musical contexts. The central theoretical issue is considered to be how best to characterize the perceptual information and the internal processes that enable people to achieve and maintain SMS. Recent research suggests that SMS is controlled jointly by two error correction processes (phase correction and period correction) that differ in their degrees of cognitive control and may be associated with different brain circuits. They exemplify the general distinction between subconscious mechanisms of action regulation and conscious processes involved in perceptual judgment and action planning.

When two limbs are weaker than one: sensorimotor syncopation with alternating hands

This study addresses the demands of alternating bimanual syncopation, a coordination mode in which the two hands move in alternation while tapping in antiphase with a metronomic tone sequence. Musically trained participants were required to engage in alternating bimanual syncopation and five other coordination modes: unimanual syncopation where taps are made (with the left or right hand) after every tone; unimanual syncopation where taps are made after every other tone; bimanual synchronization with alternating hands; unimanual synchronized tapping with every tone; and unimanual tapping with every other tone. Variability in tap timing was greatest overall for alternating bimanual syncopation, indicating that it is the most difficult. This appears to be due to instability arising from the simultaneous presence of two levels of antiphase coordination (one between the pacing sequence and the hands, the other between the two hands) rather than factors relating to movement frequency or dexterity limits of the nonpreferred hand.

Lateral asymmetries in the development of the overarm throw

Lateral asymmetries of manual, pedal, and ocular preferences, and motor asymmetry in the performance of the forceful overarm throw were analyzed in 71 children aged 4 to 10 years old. Performance with each side of the body was assessed on the basis of qualitative analysis, as proposed by M. A. Roberton and L. Halverson (1984) for identification of developmental stages by components of the task. Lateral preference was indicated by the frequency the children used the right or the left side of their body to carry out different manual, pedal, and ocular tasks. The overarm throw movement pattern was developed with both sides of the body but at different levels. Development of the nondominant side lagged behind that of the dominant side at all ages; a significant asymmetry in performance detected in the 4-year-olds was stable up to the age of 10 years. Indices of asymmetry for lateral preference and performance were found to be specific because no consistent correlations were observed among them throughout the age periods studied. Those results show the multidimensional character of human laterality and imply a property of motor development that prevents asymmetry of performance from increasing because of unilateral practice.

The development of interlimb coordination during bimanual finger tapping

Normal subjects aged 7-25 years were asked to tap the index fingers of both hands: a) in four different patterns of interlimb coordination; b) at two different response frequencies; and c) both before and after the entraining metronome was turned off. The outcome variables of primary interest were the within-subject variability of interresponse intervals (IRI) as an index of timing precision; and deviations from prescribed response frequency, as an index of temporal tracking accuracy. Stability of timing precision and accuracy of temporal tracking increased significantly from 7 to 9 and from 9 to 11 years, with only minor advances thereafter. There were significant right-left performance asymmetries in all bimanual tasks; variability of IRI and deviations from prescribed rate were greater at the faster of the two response frequencies tested; and stability of IRI and accuracy of temporal tracking were greater with than without the metronome. Stability of IRI and accuracy of temporal tracking were strongly correlated in some bimanual tasks. The findings are discussed in terms of the two major theoretical perspectives on human brain-behavior relationships that have specifically addressed the issue of bimanual coordination.

Manual dexterity and keyboard use in spastic hemiparesis: a comparison between the impaired hand and the 'good' hand on a number of performance measures

OBJECTIVE

To assess the functional deficits in tapping performance of subjects with spastic hemiparesis.

DESIGN

In a pilot study, typing performance on a computer keyboard was examined on a number of performance measures.

SETTING

Department of Research and Development at the Werkenrode Institute.

SUBJECTS

Four subjects (mean age 16.4 years, standard deviation 1.8 years) with cerebral palsy and diagnosed as having spastic hemiparesis.

INTERVENTIONS

Subjects had to type a sequence of one or more keys as quickly as possible within an 8 second period with the fingers of both hands separately.

MAIN OUTCOME MEASURES

The average number of good and false responses were calculated. Within the false response category, four, mutually exclusive, types of errors were distinguished; wrong key, repetition, registrations under 75 ms and holding. Speed and regularity of the typing responses were also established.

RESULTS

The 'good' hand outperformed the impaired hand on all performance measures except on the amount of repetition errors made. The holding error was only present for the impaired hand, and there was an increase in holding errors from the index to the little finger in this hand. In addition, the impaired hand performed the task with a slower speed and in a more irregular fashion.

CONCLUSIONS

The results are discussed with reference to keyboard design. It is concluded that the standard 'QWERTY' keyboard hampers typing performance extensively, especially for subjects with left spastic hemiparesis. A learning method is presented in which the role of an external pacer (e.g. metronome) is discussed. This device can initially be used to decrease movement variability and, eventually, for increasing movement speed.

Neuromuscular-skeletal constraints upon the dynamics of perception-action coupling

Four right-handed subjects performed rhythmic flexion and extension movements of the index finger in time with an auditory metronome. On each block of trials the forearm of the response hand was placed in a prone, neutral or supine position. In the flex-on-the-beat condition, subjects were instructed to coordinate maximum excursion in the direction of finger flexion with each beat of the metronome. In the extend-on-the-beat condition, subjects were instructed to coordinate maximum excursion in the direction of finger extension with each beat of the metronome. The frequency of the metronome was increased from 1.75 Hz to 3.50 Hz in eight steps (8-s plateaus) of 0.25 Hz. During trials prepared in the extend-on-the-beat pattern or to phase wandering often occurred, particularly at higher pacing frequencies. In marked constrast, during trials prepared in the flex-on-the-beat pattern such transitions were never present. Both the frequency and the alacrity of these transitions were greater when the forearm was in a prone or neutral position than when the forearm was in a supine position. These results are discussed with reference to the constraints imposed on the coordination dynamics by the intrinsic properties of the neuromuscular-skeletal system.

The perceptual centre of a stimulus as the cue for synchronization to a metronome: evidence from asynchronies

In tasks where subjects are required to tap in synchrony to a sequence of evenly spaced uniform auditory stimuli (a metronome), tap onsets typically tend to anticipate the metronome's stimulus onsets. We investigated this phenomenon, called "negative asynchrony", as a function of (1) the duration of the stimuli (1 or 2, 50, 100, and 300 msec), (2) the rise time of the stimuli (0%, 40%, and 80% of stimulus duration), and (3) the interstimulus onset interval duration (500, 700, and 900 msec). The results from three experiments with 28 different subjects showed a significant reduction of the negative asynchrony with longer stimulus durations, and the reduction was not significantly affected by the tempo of the stimulus sequence. Also, a prolongation of the rise time of the stimuli caused an analogous reduction of the negative asynchrony. Findings were taken to suggest that subjects use the perceptual centre rather than physical onset of stimulus as the cue with which to synchronize their responses to metronome stimuli. It is concluded that perceptual processes play an important role in synchronization.

Synchronizing actions with events: the role of sensory information

Tasks requiring the subject to tap in synchrony to a regular sequence of stimulus events (e.g., clicks) usually elicit a response pattern in which the tap precedes the click by about 30-50 msec. This "negative asynchrony" was examined, first, by instructing subjects to use different effectors for tapping (hand vs. foot; Experiments 1 and 2), and second, by administering extrinsic auditory feedback in addition to the intrinsic tactile/kinesthetic feedback (Experiment 2). Experiment 3 controlled whether the results observed in Experiment 2 were due to purely sensory factors within the auditory modality. Results suggest that taps are synchronized with clicks at the central level by superimposing two sensory codes in time: the tactile/kinesthetic code that represents the tap (the afferent movement code) and the auditory code that represents the click (the afferent code that results from the guiding signal). Because the processing times involved in code generation are different for these two central codes, the tap has to lead over the click.

Modulation of somatosensory evoked potentials during isometric contraction in relation to hand use

The aim of the study was to assess the effect of the hand used on the modulation of somatosensory evoked potentials (SEPs) during isometric contraction. SEPs to median nerve stimulation were assessed during dynamic (increase and decrease of force) and hold phases of isometric contractions. The experiments were carried out with the right or left hand. The changes in the SEP amplitude were found to vary with the hand used. When isometric contractions were performed by the right hand the amplitudes of the later components diminished during the dynamic phases, except for the component N140-P190 which increased. The amplitude of N55-P100 diminished during both the dynamic and hold phases. When isometric contractions were performed by the left hand the amplitudes of the early components diminished during the dynamic phases. These results show that the changes in SEP during isometric contraction depend on the hand used.