Reversal of bimanual feedback responses with changes in task goal

We show that fast bimanual coordinative feedback responses can be reversed with changes in task goals. Participants moved a flexible virtual object across a finish line with an upward movement of both hands. In one condition, the middle of the object had to be aligned with a spatial goal at the end of the movement. In the second condition, the object had to be kept at a specific length. During the movement, a velocity-dependent force field was applied randomly to one of the hands to the left or to the right. Depending on the task condition, the unperturbed hand showed fast feedback corrections, either in or against the direction of the force field on the other hand. In the object-length condition we found evidence for a mixture of task goals: early in the movement the correction of the unperturbed hand was aimed at stabilizing object length; later in the movement, the correction reversed direction to reach a symmetric body posture in the end of the movement. The observed differences in feedback responses between task conditions also influenced the covariance structure of unperturbed movements and the adaptation when a specific force field was applied repeatedly to one of the hands. The results are congruent with the notion that coordination is established flexibly through a representation of the task-relevant controlled variables, rather than through a direct interaction between motor commands.     

The effects of movements on caudate sensory responses

The aim of this experiment was to assess the effects of movement on somatosensory processing in the caudate nucleus. Units were recorded extracellularly in the caudate of awake partially restrained cats. Unit responses were evoked by either natural stimuli (brushing and skin indentation) or transcutaneous electrical stimulation. Response patterns evoked by stimuli presented when the cat was at rest were compared to responses evoked by similar stimuli presented when the cat was either making buccolingual movements or turning its head. In the majority of cases, movement suppressed caudate somatosensory responses. However, impressive augmentation of responses was seen in some cells with either type of movement.     

Effects of voluntary movements on early auditory brain responses

It has not been clear whether or not early information processing in the human auditory cortex is altered by voluntary movements. We report a movementrelated, complex event-related potential consisting of relatively long-lasting amplitude and phase perturbations induced in an ongoing auditory steady-state response (SSR) by brief self-paced finger movements. Our results suggest that processing in the auditory cortex during the first 50–100 ms after stimulus delivery is affected before, during, and after voluntary movements, beginning with a 1- to 2-ms delay in the SSR wave form starting 1–2 s before the movement.This research was supported in part by the Department of the Navy, Naval Medical Research and Development Command, Bethesda, Maryland under work unit ONR.WR.30020(6429). The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the U.S. Government. Approved for release, distribution unlimited.     

Tactile feedback contributes to consistency of finger movements during typing

Touch typing movements are typically too brief to use on-line feedback. Yet, previous studies have shown that blocking tactile feedback of the fingertip of typists leads to an increase in typing errors. To determine the contribution of tactile information to rapid fine motor skills, we analyzed kinematics of the right index finger during typing with and without tactile feedback. Twelve expert touch typists copy-typed sentences on a computer keyboard without vision of their hands or the computer screen. Following control trials, their right index fingertip was anesthetized, and sentences were typed again. The movements of the finger were recorded with an instrumented glove and electromagnetic position sensor. During anesthesia, typing errors of that finger increased sevenfold. While the inter-keypress timing and average kinematics were unaffected, there was an increase in variability of all measures. Regression analysis showed that endpoint variability was largely accounted for by start location variability. The results suggest that tactile cues provide information about the start location of the finger, which is necessary to perform typing movements accurately.     

Timing of bimanual movements and deafferentation: implications for the role of sensory movement effects

In a repetitive tapping task, the within-hand variability of intertap intervals is reduced when participants tap with both hands instead of single-handedly. This bimanual advantage has been attributed to timer as opposed to motor variance (according to the Wing-Kristofferson model; Helmuth and Ivry 1996) and related to the additional sensory consequences of the movement of the extra hand in the bimanual case (Drewing et al. 2002). In the present study the effect of sensory feedback of the movement on this advantage was investigated by comparing the results of a person (IW) deafferented below the neck with those of age-matched controls. IW showed an even more pronounced bimanual advantage than controls, suggesting that the bimanual advantage is not due to actual sensory feedback. These results support another hypothesis, namely that bimanual timing profits from the averaging of different central control signals that relate to each effectors movements.     

Somatosensory and brainstem auditory evoked responses in sleep-related periodic leg movements

The pathophysiological mechanisms of sleep-related periodic leg movements (sPLM) and restless legs syndrome are unknown. Evoked potentials have been demonstrated to be abnormal in a variety of episodic movement disorders. In the present study, mixed nerve somatosensory and brainstem auditory evoked responses were examined in patients with polysomnographically documented sPLM who also had restless legs. Normal lower extremity (posterior tibial nerve stimulation) and upper extremity (median nerve stimulation) somatosensory evoked responses were recorded in a group of 10 patients with documented sPLM. Brainstem auditory evoked responses also were normal. These findings do not provide any evidence for a primary afferent sensory disturbance and indirectly support a recently forwarded hypothesis that sPLM is a reflection of suppression of descending inhibitory influences on pyramidal tract function.     

Neural correlates of auditory feedback control in human

Auditory feedback plays an important role in natural speech production. We conducted a functional magnetic resonance imaging (fMRI) experiment using a transformed auditory feedback (TAF) method to delineate the neural mechanism for auditory feedback control of pitch. Twelve right-handed subjects were required to vocalize /a/ for 5 s, while hearing their own voice through headphones. In the TAF condition, the pitch of the feedback voice was randomly shifted either up or down from the original pitch two or three times in each trial. The subjects were required to hold the pitch of the feedback voice constant by changing the pitch of original voice. In non-TAF condition, the pitch of the feedback voice was not modulated and the subjects just vocalized /a/ continuously. The contrast between TAF and non-TAF conditions revealed significant activations; the supramarginal gyrus, the prefrontal area, the anterior insula, the superior temporal area and the intraparietal sulcus in the right hemisphere, but only the premotor area in the left hemisphere. This result suggests that auditory feedback control of pitch is mainly supported by the right hemispheric network.     

Developmental changes in unimanual and bimanual aiming movements

The aim of this study was twofold: (a) analyze the development of reaction time (RT) and movement time (MT) for bimanual and unimanual movements and (b) investigate the interaction of age and sex on the changes in RT and MT. Participants (5-, 8-, and 11-year-olds) were asked to aim at target buttons under three conditions of movement: unimanual, bimanual symmetrical, and bimanual nonsymmetrical. As expected, RTs for bimanual symmetrical movements were shorter than RTs for unimanual and bimanual nonsymmetrical movements in the 5-year-olds. By the age of 8, bimanual nonsymmetrical movements still yielded longer RTs than unimanual and bimanual symmetrical movements, which no longer differed from each other. Regarding MT, in the 2 younger groups there was an advantage of unimanual over bimanual symmetrical movements. The latter were executed faster than nonsymmetrical movements at all ages. These results suggest that the evolution of RT and MT with age reflects development of interhemispheric transfer of information. It appears that the functional improvement of such transfer, which depends on the corpus callosum, progressively enables contralateral motor inhibition and the coordination of complex bilateral movements. The exchange of movement feedback information could mature more slowly than that of feed-forward information, explaining the extended time course of MT evolution.     

Effect of transcranial magnetic stimulation on bimanual movements

Transcranial magnetic stimulation (TMS) of the motor cortex can interrupt voluntary contralateral rhythmic limb movements. Using the method of "resetting index" (RI), our study investigated the TMS effect on different types of bimanual movements. Six normal subjects participated. For unimanual movement, each subject tapped either the right or left index finger at a comfortable rate. For bimanual movement, index fingers of both hands tapped in the same (in-phase) direction or in the opposite (antiphase) direction. TMS was applied to each hemisphere separately at various intensities from 0.5 to 1.5 times motor threshold (MT). TMS interruption of rhythm was quantified by RI. For the unimanual movements, TMS disrupted both contralateral and ipsilateral rhythmic hand movements, although the effect was much less in the ipsilateral hand. For the bimanual in-phase task, TMS could simultaneously reset the rhythmic movements of both hands, but the effect on the contralateral hand was less and the effect on the ipsilateral hand was more compared with the unimanual tasks. Similar effects were seen from right and left hemisphere stimulation. TMS had little effect on the bimanual antiphase task. The equal effect of right and left hemisphere stimulation indicates that neither motor cortex is dominant for simple bimanual in-phase movement. The smaller influence of contralateral stimulation and the greater effect of ipsilateral stimulation during bimanual in-phase movement compared with unimanual movement suggest hemispheric coupling. The antiphase movements were resistant to TMS disruption, and this suggests that control of rhythm differs in the 2 tasks. TMS produced a transient asynchrony of movements on the 2 sides, indicating that both motor cortices might be downstream of the clocking command or that the clocking is a consequence of the 2 hemispheres communicating equally with each other.     

Spatial and cross-modal attention alter responses to unattended sensory information in early visual and auditory human cortex

Attending to a visual or auditory stimulus often requires irrelevant information to be filtered out, both within the modality attended and in other modalities. For example, attentively listening to a phone conversation can diminish our ability to detect visual events. We used functional magnetic resonance imaging (fMRI) to examine brain responses to visual and auditory stimuli while subjects attended visual or auditory information. Although early cortical areas are traditionally considered unimodal, we found that brain responses to the same ignored information depended on the modality attended. In early visual area V1, responses to ignored visual stimuli were weaker when attending to another visual stimulus, compared with attending to an auditory stimulus. The opposite was true in more central visual area MT+, where responses to ignored visual stimuli were weaker when attending to an auditory stimulus. Furthermore, fMRI responses to the same ignored visual information depended on the location of the auditory stimulus, with stronger responses when the attended auditory stimulus shared the same side of space as the ignored visual stimulus. In early auditory cortex, responses to ignored auditory stimuli were weaker when attending a visual stimulus. A simple parameterization of our data can describe the effects of redirecting attention across space within the same modality (spatial attention) or across modalities (cross-modal attention), and the influence of spatial attention across modalities (cross-modal spatial attention). Our results suggest that the representation of unattended information depends on whether attention is directed to another stimulus in the same modality or the same region of space.     

Effect of cigarette smoking on reactive hyperaemia in the human finger

The effect elicited by cigarette smoking on the reactive hyperaemia that develops following release of arterial occlusion in human skin was investigated, and compared to the corresponding effects elicited by oral administration of indomethacin (an inhibitor of the prostaglandin-forming enzyme cyclo-oxygenase) or nicotine, or by smoking of nicotine-free cigarettes. Finger blood flow was determined in human volunteers, using venous occlusion plethysmography, in the basal state and after 5 min of arterial occlusion. All subjects were studied before and after they had smoked two tobacco cigarettes, two herbal (nicotine-free) cigarettes, or chewed a nicotine chewing gum. The determinations before and after tobacco smoking were repeated after administration of indomethacin. In separate series, the effects of smoking on heart rate and systemic blood pressure were recorded. The basal finger blood flow was significantly (P less than 0.05) diminished following cigarette smoking, by about 35%, and so was the reactive hyperaemia (P less than 0.05), by about 55%. The reactive hyperaemia after administration of indomethacin in combination with cigarette smoking did not differ from that obtained after cigarette smoking alone. The reactive hyperaemia was not affected by oral administration of nicotine, or by smoking of two herbal cigarettes. Cigarette smoking elicited increases in heart rate and systemic blood pressure that were of similar magnitude before and after indomethacin. From these data, we conclude that cigarette smoking elicits an inhibitory effect on the reactive hyperaemia in the human finger. This effect is probably not caused by nicotine, and seems to act via blockade of the vascular relaxation normally medicated by locally formed cyclo-oxygenase products.     

Muscle activation patterns and kinetics of human index finger movements

1. The present study was conducted to determine whether dynamic interaction torques are significant for control of digit movements and to investigate whether such torques are compensated by specific muscle activation patterns. 2. Angular positions of the metacarpophalangeal (MP) and proximal interphalangeal (PIP) joints of the index finger in the flexion/extension plane were recorded with the use of planar electrogoniometers. Muscle activation patterns were monitored with the use of fine wire and surface electromyography of intrinsic and extrinsic finger muscles. 3. Dynamic interaction torques associated with index finger movements were large in relation to joint torques produced by muscles, especially in faster movements. The significance of dynamic interaction torques was demonstrated in model simulations of two-joint finger motion in response to joint torque inputs. Removal of interaction torques from the model inputs produced movements that differed greatly from digit motions produced by human subjects. 4. Electromyogram (EMG) and torque patterns associated with finger movements of different speeds indicated that muscle activity is necessary not only for producing motion at the joints but also to counteract segmental interaction torques. This was especially evident during movements that required voluntary maintenance of a constant MP joint angle during motion of the distal segment about the PIP joint. Under these conditions, muscle moments acting at the MP acted directly to counteract torques at the MP arising from motion at the PIP. 5. Neural mechanisms underlying control of index finger movement are discussed with reference to the implications of dynamic interaction torques. Potential control strategies include accurate programming of muscle activation patterns, appropriate use of motion-dependent peripheral afferent information, and control of the finger as a viscoelastic system through coactivation of flexor and extensor musculature. It is concluded that additional research incorporating study of motion in three dimensions and the use of mechanical models of the finger and related musculature is required to determine how interaction torques are compensated during finger motion.     

Comparing movement preparation of unimanual,bimanual symmetric,and bimanual asymmetric movements

The goal of this study was to determine the process or processes most likely to be involved in reaction-time costs for spatially cued bimanual reaching. We used reaction time to measure the cost of bimanual symmetric movements compared to unimanual movements (a bimanual symmetric cost) and the cost for bimanual asymmetric movements compared to symmetric movements (a bimanual asymmetric cost). The results showed that reaction times were comparable for all types of movements in simple reaction time; that is, there was neither a bimanual symmetric cost nor an asymmetric cost. Therefore, unimanual, bimanual symmetric, and bimanual asymmetric movements have comparable complexity during response initiation. In choice conditions, there was no bimanual symmetric cost but there was a bimanual asymmetric cost, indicating that the preparation of asymmetric movements is more complex than symmetric movements. This asymmetric cost is likely the result of interference during response programming.     

Memory and coordination in bimanual isometric finger force production

Isometric force output of the dominant hand has previously been shown to decline when feedback of that output is withdrawn. This effect is more pronounced for higher levels of force output, and appears to rely upon visuomotor memory processes. In the present study these existing findings are extended to a task where subjects produced force output with both the dominant and non-dominant hand, and with both hands together. The results suggested that force change following the withdrawal of feedback follows the same pattern in bimanual conditions as it does in unimanual conditions. In addition it was found that the proportion of the total force contributed by each hand in the bimanual condition varied through a trial, which was achieved without a corresponding drop in force output when feedback was available. Taken together, the results support the idea of a central representation for target force level, which, when available, makes use of visual information to control a mutually redundant pair of effectors.     

Selective priming of maternal responses by auditory and olfactory cues from mouse pups

Previous data have shown that maternal behavior can be primed in mice by exposure to sound and smell from pups. This experiment shows that both types of cues act selectively on different maternal responses. Three groups of 20 naïve females were given an initial exposure respectively to both auditory and olfactory cues from pups, to auditory cues alone, or to olfactory cues alone. Their results during a subsequent standard test for maternal behaviour were then compared with those of 20 naïve control females, not previously exposed to cues from pups. The results favor the assumption of a selective priming process, olfactory cues exerting a positive effect on cleaning of pups, auditory cues exerting a positive effect on nest-building.     

Interaction between different sensory cues in the control of human gait

This experiment investigates the interaction of different sensory cues in the control of propulsive forces in human gait which in turn allow the body's forward progression to be regulated. The aim of this work was to determine how optic flow and leg-somatosensory feedback interact in this control. We therefore determined whether the responses to sinusoidal perturbations of optic flow were accentuated when leg-somatosensory feedback was modified by varying the support resistance. Subjects walked on a treadmill which was driven by their own locomotor activity (1) with a sinusoidal variation of optic flow velocity, (2) with a sinusoidal variation of support resistance which modified leg-somatosensory information and (3) with both visual and leg-somatosensory modification at different frequencies. The response of the subject was measured as changes in speed and propulsive power. The response to sinusoidal perturbations of optic flow was found to be increased and time delayed when visual perturbations are coupled with support perturbations in comparison with the response observed with visual perturbations only. This result shows the influence of leg-somatosensory feedback on the weighting of optic flow. Inversely, it was also found that the motor response to support perturbation was different when the flow was congruent (i.e., corresponding to the subject's virtual speed) and when it was not. This latter result shows the influence of optic flow on the weighting of leg-somatosensory feedback. The interaction between optic flow and leg-somatosensory feedback argues in favor of a multimodal sensory control of propulsive forces. This multimodal sensory control would be based on all the sensory feedback and all their mutual sensorial interaction. Therefore, the modification of one sensory input modifies not only this input but also the integration of the other inputs.     

The control of bimanual reach-to-grasp movements in hemiparkinsonian patients

The basal ganglia are thought to participate in the control and programming of a variety of motor behaviours. However, the precise nature of this participation still remains to be clarified. This paper examines the proposal that the basal ganglia may serve to scale the amplitude of limb movements, with basal-ganglia dysfunction leading to the inappropriate scaling of intended motor activity. Several authors have suggested that examining the loss of function in Parkinson's-disease (PD) patients offers perhaps the best way of learning about the role played by the basal ganglia in human motor function. While it has previously been reported that PD patients underscale the transport phase of their reach-to grasp movements, it has generally been assumed that the grasp component is normal. In this paper we demonstrate, using a group of hemiparkinson patients, that the scaling of the grasp component is also underscaled in PD patients.     

Age-related changes in the bimanual advantage and in brain oscillatory activity during tapping movements suggest a decline in processing sensory reafference

Deficits in the processing of sensory reafferences have been suggested as accounting for age-related decline in motor coordination. Whether sensory reafferences are accurately processed can be assessed based on the bimanual advantage in tapping: because of tapping with an additional hand increases kinesthetic reafferences, bimanual tapping is characterized by a reduced inter-tap interval variability than unimanual tapping. A suppression of the bimanual advantage would thus indicate a deficit in sensory reafference. We tested whether elderly indeed show a reduced bimanual advantage by measuring unimanual (UM) and bimanual (BM) self-paced tapping performance in groups of young (n = 29) and old (n = 27) healthy adults. Electroencephalogram was recorded to assess the underlying patterns of oscillatory activity, a neurophysiological mechanism advanced to support the integration of sensory reafferences. Behaviorally, there was a significant interaction between the factors tapping condition and age group at the level of the inter-tap interval variability, driven by a lower variability in BM than UM tapping in the young, but not in the elderly group. This result indicates that in self-paced tapping, the bimanual advantage is absent in elderly. Electrophysiological results revealed an interaction between tapping condition and age group on low beta band (14–20 Hz) activity. Beta activity varied depending on the tapping condition in the elderly but not in the young group. Source estimations localized this effect within left superior parietal and left occipital areas. We interpret our results in terms of engagement of different mechanisms in the elderly depending on the tapping mode: a ‘kinesthetic’ mechanism for UM and a ‘visual imagery’ mechanism for BM tapping movement.     

Intracerebral sources of human auditory steady-state responses

The objective of this study was to localize the intracerebral generators for auditory steady-state responses. The stimulus was a continuous 1000-Hz tone presented to the right or left ear at 70 dB SPL. The tone was sinusoidally amplitude-modulated to a depth of 100% at 12, 39, or 88 Hz. Responses recorded from 47 electrodes on the head were transformed into the frequency domain. Brain electrical source analysis treated the real and imaginary components of the response in the frequency domain as independent samples. The latency of the source activity was estimated from the phase of the source waveform. The main source model contained a midline brainstem generator with two components (one vertical and lateral) and cortical sources in the left and right supratemporal plane, each containing tangential and radial components. At 88 Hz, the largest activity occurred in the brainstem and subsequent cortical activity was minor. At 39 Hz, the initial brainstem component remained and significant activity also occurred in the cortical sources, with the tangential activity being larger than the radial. The 12-Hz responses were small, but suggested combined activation of both brainstem and cortical sources. Estimated latencies decreased for all source waveforms as modulation frequency increased and were shorter for the brainstem compared to cortical sources. These results suggest that the whole auditory nervous system is activated by modulated tones, with the cortex being more sensitive to slower modulation frequencies.