Extrinsic muscles of the hand signal fingertip location more precisely than they signal the angles of individual finger joints

 Studies have demonstrated that muscle spindle organs provide the majority of the proprioceptive information available to the nervous system about limb position. Other studies suggest that a sense of position may be lacking in the fingers, as subjects were unaware of rather large excursions of finger joints if the excursions were made slowly enough. We sought to investigate the basis for this unexpected finding with a biomechanical model of the human long finger and the forearm muscles which actuate it, in order to study potential contributions of spindle organs in the extrinsic muscles of the hand to a sense of position of the finger. The model, based on cadaver data, allowed us to determine how precisely estimates of the lengths of the extrinsic finger muscles can be transformed into estimates of: (1) the flexion/extension angles of the individual finger joints, and (2) the location of the fingertip in the flexion/extension plane. We found that, for some finger positions, length information from all three extrinsic muscles was not sufficient to precisely estimate the flexion angles of all finger joints. Precision of joint angle estimates could be as poor as ±18% of joint range of motion. However, length information from just two of the extrinsic muscles taken together could always provide information sufficient to estimate the location of the fingertip relative to the metacarpophalangeal joint within a reasonably small tolerance (±one-half thickness of the fingertip). Furthermore, it was possible to make this estimate without determining any of the finger joint angles. These results suggest that spindles in the extrinsic muscles alone can signal fingertip location, even though they may not provide sufficient information to estimate the individual joint angles that set the position of the fingertip. Thus, an absence of position sense for individual joints (the sense many studies have tried to measure) may say little about a sense of location of the tip of the finger. Received: 3 March 1998 / Accepted: 2 September 1998     

The inhibitory effect of acupuncture on the tonic vibration reflex (TVR) in man

The effect of acupuncture on the tonic vibration reflex (TVR) has been examined in healthy men. Vibrations (100 Hz) were applied over the muscle bellies of either finger flexion muscles or extension muscles, while finger flexions and extensions were measured by a strain attached to the middle finger. A stainless steel acupuncture needle was inserted for 10 min into an acupuncture point named "Chu-Chih (LI-II)". After the application of acupuncture, TVRs in both flexion and extension muscles were significantly less than those observed before the application of acupuncture. The inhibitory effect of acupuncture almost disappeared 10 min after removing the needle. Acupuncture transiently inhibits TVR in extension and flexion muscles in man.     

Anticipatory postural adjustments stabilise the whole upper-limb prior to a gentle index finger tap

Little is known about anticipatory postural adjustments (APAs) developing when body segments of tiny mass are moved. Thus, APAs in the human upper-limb were investigated during a gentle and small index finger tap (35 mm stroke in 50 ms). This task was fulfilled by ten subjects either with prone or supine hand. EMG was recorded from Flexor Digitorum Superficialis (FDS), the prime mover, and from several upper-limb muscles under slight tonic contraction. Regardless of hand posture, EMG was inhibited in Flexor Carpi Radialis and facilitated in Extensor Carpi Radialis well before the FDS burst. With the prone hand, the prime mover activity was preceded by Biceps inhibition and Triceps facilitation; this effect reverted in sign with the supine hand. A postural reversal was also observed in Anterior Deltoid and Trapezius which were both inhibited with the prone hand. The effect in Trapezius was present only with the unsupported forearm. It is thus demonstrated that a gentle small finger tap produces well-defined anticipatory natural synergies behaving as the most “classical” APAs: (1) they are distributed to several upper-limb muscles creating a postural chain aiming to prevent the effects of the interaction torques generated by the voluntary movement; (2) they change in amplitude according to the level of postural stability and (3) they revert in sign when movement direction is reverted. These results are also corroborated by data obtained from a simple mechanical model simulating finger tapping in a fictive upper-limb. A possible role of APAs in controlling movements’ accuracy is also discussed.     

Activities of single precentral neurons of the monkey during different tasks of forelimb movements

The neuronal activity in the motor cortex of the rhesus monkey was investigated in three different tasks performed with finger, wrist, and arm movements. A total of 125 neuronal activities were analysed. They were classified into five groups in terms of muscular contractions provoked by intracortical stimulation; neurons related to contractions of finger, wrist, elbow, shoulder, or trunk muscles. The neuronal activities in three tasks performed with finger, wrist, or arm movements were investigated for each group. Most of the neurons related to the contractions of elbow, shoulder, or trunk muscles were associated solely with arm movement. Smaller numbers of neuronal activities changed their firing frequencies in association with two or three tasks. Neurons related to the contractions of finger and wrist muscles showed various firing patterns in the three tasks; some responded to a single task with wrist or arm movement, while others changed their activities in association with more than one task. The presence of multi-task related neurons is discussed with respect to the multisegmental termination of corticospinal axons in the spinal cord.     

Toward direct biocontrol using surface EMG signals: control of finger and wrist joint models

Increased interest in virtual reality (VR) and telemanipulation has created a growing need for the development of new interfacing devices for measuring controlling actions of the human hand. The objective of the present study was to determine if surface electromyography signals (SEMG) from the flexor digitorum superficialis (FDS), and flexor carpi ulnaris (FCU) generated during flexion-extension of the human index finger and wrist can be used for controlling the flexion-extension of the finger and wrist of a simple geometric computer model. A simple geometric computer model of finger and wrist joints was developed. Eighteen subjects controlled the computer model using the SEMG signals from their FDS and FCU. The results indicate that the SEMG signals from the FDS and FCU muscles can be used as a direct biocontrol technique for controlling the finger and wrist models. This study establishes the proof of concept for direct biological control of the dynamic motion of the finger and wrist models for use in virtual reality environments and telemanipulation.     

Joint sense, muscle sense, and their combination as position sense, measured at the distal interphalangeal joint of the middle finger.

1. An anatomical peculiarity allows the hand to be positioned so that the terminal phalanx of the middle finger cannot be moved by voluntary effort. When positioned in this way only joint and cutaneous mechanisms subserve position sense. By altering the position of the hand the muscles are again engaged and able to move the finger. Moving the joint then also excites muscular afferents. 2. The position sense of twelve subjects was assessed with and without engagement of the muscles at the joint. Three tests were used in which either angular displacement, angular velocity or duration of displacement were held constant. 3. When muscular attachment was restored, performance in all tests was greatly enhanced. As engagement of the muscles caused little change in the 'stiffness' of the joint, it is unlikely that the improved performance resulted from increased discharges from the joint receptors. Cutaneous mechanisms are unlikely to mediate this improvement as they are likely to have been unaffected by engagement of muscles. It is concluded that intramuscular receptors are partly responsible for normal position sense. 4. In seven of the twelve subjects the test finger was anaesthetized to isolate the contribution of intramuscular receptors. This muscle sense was variable. In some subjects it provided accurate kinaesthetic information but in others the information was crude. If with the test finger anaesthetized subjects exerted voluntary tension with the muscles that move the joint the muscle sense was improved.     

Influence of tactile afferents on the coordination of muscles during a simulated precision grip

The mechanisms by which the nervous system coordinates multiple muscles for the control of finger movements are not well understood. One possibility is that groups of muscles may be enlisted into synergies by last-order inputs that project across multiple motor nuclei. In this study we investigated the role that tactile input might play in coupling together the activities of motor units in two muscles involved in generating the precision grip. Cross-correlation analysis was used to assess the degree of synchrony in the discharge times of pairs of motor units recorded from index-finger and thumb flexor muscles while human subjects performed an isometric task that mimicked a precision grip. The magnitude of synchrony is thought to reflect the extent to which divergent last order inputs provide common synaptic input across motor neurons. Synchrony was evaluated under two simulated-gripping conditions: gripping with normal tactile input and gripping when tactile input from the digit pads was eliminated by applying flexion forces to fittings glued to the finger nails. Synchrony between motor units of index finger flexor and thumb flexor muscles, while substantial, was not significantly different across the two tactile-input conditions. These findings suggest that tactile input is not required to activate the divergent last-order inputs that couple together the activities of the index finger and thumb flexor muscles during the precision grip.     

A variant of the Cannieu-Riche communication: case report

A variant of Cannieu-Riche communication was encountered during the dissection studies. The communication was between the digital branch to the index finger and branch to the adductor pollicis muscle. Terminal communications between motor nerves may provide muscles with double motor innervation, and are important for the motor innervation of the hand, in particular the thenar muscles. This variant should be kept in mind during surgical operations, electrophysiological examinations of the hand.     

A Model of the Upper Extremity for Simulating Musculoskeletal Surgery and Analyzing Neuromuscular Control

Biomechanical models of the musculoskeletal system are frequently used to study neuromuscular control and simulate surgical procedures. To be broadly applicable, a model must be accessible to users, provide accurate representations of muscles and joints, and capture important interactions between joints. We have developed a model of the upper extremity that includes 15 degrees of freedom representing the shoulder, elbow, forearm, wrist, thumb, and index finger, and 50 muscle compartments crossing these joints. The kinematics of each joint and the force-generating parameters for each muscle were derived from experimental data. The model estimates the muscle–tendon lengths and moment arms for each of the muscles over a wide range of postures. Given a pattern of muscle activations, the model also estimates muscle forces and joint moments. The moment arms and maximum moment-generating capacity of each muscle group (e.g., elbow flexors) were compared to experimental data to assess the accuracy of the model. These comparisons showed that moment arms and joint moments estimated using the model captured important features of upper extremity geometry and mechanics. The model also revealed coupling between joints, such as increased passive finger flexion moment with wrist extension. The computer model is available to researchers at .     

Selectivity of voluntary finger flexion during ischemic nerve block of the hand

During ischemic nerve block of an extremity the cortical representations of muscles proximal to the block are known to expand, increasing the overlap of different muscle representations. Such reorganization mimics that seen in actual amputees. We investigated whether such changes degrade voluntary control of muscles proximal to the block. Nine subjects produced brief, isometric flexion force selectively with each fingertip before, during, and after ischemic block at the wrist. We recorded the isometric force exerted at the distal phalanx of each digit, along with electromyographic (EMG) activity from intrinsic and extrinsic finger muscles. Despite paralysis of the intrinsic hand muscles, and associated decrements in the flexion forces exerted by the thumb, index, and little fingers, the selectivity of voluntary finger flexion forces and of EMG activity in the extrinsic finger muscles that generated these forces remained unchanged. Our observations indicate that during ischemic nerve block reorganization does not eliminate or degrade motor representations of the temporarily deafferented and paralyzed fingers.     

Hypotheses for ongoing evolution of muscles of the upper extremity

There are organs and muscles in the human body that may be considered rudimentary in that they have insignificant or undetermined function. Several such muscles are found in the upper extremity. In this review, four muscles that appear to be undergoing evolutionary changes are discussed: flexor digitorum superficialis to the fifth finger, anconeus, palmaris longus, and anconeus epitrochlearis. The present study synthesizes, advances and extends previously described work about these muscles and extends the hypotheses and concludes that: (a) the flexor digitorum superficialis to the fifth finger is currently under adaptive evolution, (b) the anconeus has currently stabilized its evolution and is serving as a transient stability augmenter during a short portion of the human lifespan, and (c) the entire distal upper extremity is currently in the process of undergoing evolutionary change. Understanding of these muscles and their evolutionary context is important for understanding of impact on function, dysfunction, treatment and future research.     

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.     

Sequential activation of neurons in primate motor cortex during unrestrained forelimb movement

We trained monkeys to perform an unrestrained, reaching movement of the arm. Electromyogram (EMG) recordings of forelimb muscles revealed sequential activation, proximal to distal, of muscle groups involved in the task. The delay in onset of EMG activity between proximal (shoulder and elbow) and distal (wrist and finger) muscles was approximately 60 ms. We identified the neurons in the forelimb area of the contralateral motor cortex as controlling particular joints by previously defined criteria involving responses to somatosensory stimulation and effects of intracortical microstimulation. Many cells discharged prior to the onset of EMG activity acting on the appropriate joint, whereas others began firing at a later phase of the movement. The population of all proximal cells altered discharge patterns approximately 60 ms earlier than the population of distal cells. A small percentage of cells showed an initial inhibitory change in discharge frequency, and this inhibition typically occurred prior to the excitatory changes seen in the majority of cells. The results are discussed in terms of the "nested-zone" model of the forelimb motor cortex. The data support one of the predictions of this model, namely that discharges of identified cells within the cortical zones are causally related to voluntary movement at appropriate forelimb joints.     

Climbing-specific finger flexor performance and forearm muscle oxygenation in elite male and female sport climbers

Climbing performance relies to a great extent on the performance of the finger flexor muscles. Only a few studies investigated this performance in top class climbers and only one study compared gender-specific differences. This study investigated the climbing-specific finger flexor strength and endurance and related muscular oxygenation in 12 elite female and male climbers and 12 non-climbers. After the assessment of maximum voluntary finger flexor contraction (MVC), two isometric finger flexor endurance tests were performed at 40% MVC until exhaustion. A continuous isometric test was followed by an intermittent isometric test (10?s contraction, 3?s rest). Changes in oxygenation of finger flexor muscles were recorded using near infrared spectroscopy. MVC and strength-to-weight ratio were greater in climbers than non-climbers (P?=?0.003; P?相似文献   

Evaluation of spectral characteristics of physiological tremor of finger based on mechanical model.

A mathematical model for a physiological tremor of a finger, hereafter referred to as tremor, has been developed in order to evaluate the variation of amplitudes and frequencies at two peaks obtained in the power spectrum of the tremor under two conditions: (a) four loads of weight, 50, 100, 150, and 200 g, are added to the finger (state of load of weight), and (b) the finger is held in a horizontal position with a weight of 200 g for ten minutes (state of fatigue). The mathematical model for the tremor consists of a mechanical system of the finger and a reflex feedback system via the spinal and the supraspinal pathways. In the condition of the load of the weight, the two peaks shown in the tremor spectrum at about 10 Hz and 25 Hz under the condition of no load are generated by the existence of the spinal and the supraspinal pathways. The variation of the frequencies at the two peaks due to the load of the weight, which is not obtained by the previous model (Sakamoto et al., 1998), is possible to evaluate by use of the reflex feedback system which includes the terms up to the second order derivative. The amplitudes at the two peaks of the tremor spectrum increase with the additional weight on the finger because of the increase of the activity level of the active element of muscles controlling the finger. This element is one of the sub-systems constituting the tremor model. Because the activity level of the active element corresponds to the contraction force produced by the muscles, the increase of the amplitudes at the two peaks results from the progress of the recruitment of the motor unit activity by the addition of the weight. The term presenting the activity level is here introduced in the tremor model, so that the phenomenon is found. In the condition of the state of fatigue, the amplitudes at the two peaks increase with the progress of the fatigue because the active element is presented as a function of the time course, so that the activity level of the active element increases with the time course. The increase of the activity level implies the progresses of the recruitment and synchronization of the motor unit activity due to the fatigue. These results obtained from the analysis of the tremor model verify the hypothesis that the amplitude of the tremor oscillation is attributable to the changes of the activity of the spinal and the supraspinal systems.     

Reduced muscle selectivity during individuated finger movements in humans after damage to the motor cortex or corticospinal tract

We investigated how damage to the motor cortex or corticospinal tract affects the selective activation of finger muscles in humans. We hypothesized that damage relatively restricted to the motor cortex or corticospinal tract would result in unselective muscle activations during an individuated finger movement task. People with pure motor hemiparesis attributed to ischemic cerebrovascular accident were tested. Pure motor hemiparetic and control subjects were studied making flexion/extension and then abduction/adduction finger movements. During the abduction/adduction movements, we recorded muscle activity from 3 intrinsic finger muscles: the abductor pollicis brevis, the first dorsal interosseus, and the abductor digit quinti. Each of these muscles acts as an agonist for only one of the abduction/adduction movements and might therefore be expected to be active in a highly selective manner. Motor cortex or corticospinal tract damage in people with pure motor hemiparesis reduced the selectivity of finger muscle activation during individuated abduction/adduction finger movements, resulting in reduced independence of these movements. Abduction/adduction movements showed a nonsignificant trend toward being less independent than flexion/extension movements in the affected hands of hemiparetic subjects. These changes in the selectivity of muscle activation and the consequent decrease in individuation of movement were correlated with decreased hand function. Our findings imply that, in humans, spared cerebral motor areas and descending pathways that remain might activate finger muscles, but cannot fully compensate for the highly selective control provided by the primary motor cortex and the crossed corticospinal system.     

Further insight into the task-dependent excitability of motor evoked potentials in first dorsal interosseous muscle in humans

We have reexamined the contradictory evidence in which task-dependent excitation of motor evoked potentials (MEPs) in the first dorsal interosseous (FDI) muscle was stronger with increasingly more complex finger tasks than with individual finger movement tasks. In the first step of the experiment, based on previous findings, we investigated remarkable functional differences between intrinsic and extrinsic hand muscles during complex finger tasks (precision and power grip). During the performance of the tasks, the optimal stimulus intensity of the transcranial magnetic stimulation (TMS) was applied to the contralateral motor cortex. MEPs of the FDI, extensor carpi radialis (ECR), and flexor carpi radialis (FCR) muscles were recorded simultaneously with increased background EMG activity step by step in both tasks. The intensity threshold of TMS was lower in the precision grip. Furthermore, the MEP amplitudes of FDI muscle dependent on the background EMG activity were different between these two tasks, i.e., MEP amplitudes and regression coefficients in a precision grip were larger than those in a power grip. Although our results for MEP amplitude and threshold in the FDI muscle were similar to previous reported evidence, the different contributions of a synergistic muscle (in particular, the ECR muscle) during performance in these tasks was new evidence. Since there were no differences in cutaneous afferent effects on both tasks, corticomotoneuronal (CM) cells connected to FDI motoneurons seemed generally to be more active during precision than power gripping, and there were different contributions from synergistic muscles during the performance of these tasks. In the second part of the experiment, the results obtained from the complex tasks were compared with those from a simple task (isolated index finger flexion). MEP amplitudes, dependent on the background EMG activity during isolated index finger flexion, varied among subjects, i.e., the relationship between the MEP amplitude and the background EMG of the FDI muscle showed individual, strategy-dependent modulation. There were several kinds of individual motor strategies for performing the isolated finger movement. The present results may explain the previous contradictory evidence related to the contribution of the CM system during coordinated finger movement.     

Activation of intrinsic and extrinsic finger muscles in relation to the fingertip force vector

Surface EMG was recorded from two intrinsic and two extrinsic muscles of the index finger during a two-dimensional isometric force task in the plane of flexion and extension. Subjects applied force isometrically at the fingertip in eight equally spaced directions, encompassing 360 degrees. Target forces spanned the range from 20% to 50% of maximum for each direction. The effect of varying the metacarpophalangeal (MCP) and interphalangeal (IP) joint angles was investigated. We found that when applying isometric force with the fingertip, the intrinsic muscles of the index finger behaved as a single unit whose region of activation overlapped that of the extrinsic flexor and extensor muscles. The activation region of the intrinsic muscles also spanned a range of force directions for which the extrinsic muscles were virtually inactive. The activation of all muscles, with the exception of the extrinsic extensor, was modified by changing the MCP and IP joint angles. Both IP flexion and MCP extension produced rotation of the resultant activity vector in the direction of MCP flexion. However, the relative rotation was much greater with IP flexion than MCP extension. The effect of IP flexion is linked to rotation of the force direction where joint torque switches from extension to flexion, while the effect of MCP extension is more likely related to changes in muscle length and MCP moment arm. Our results suggest that the primary role of intrinsic finger muscles is to precisely control the direction of fingertip force, while extrinsic muscles provide stability of the joints.     

The effects of muscimol inactivation of small regions of motor and somatosensory cortex on independent finger movements and force control in the precision grip

This study investigated the effects of inactivating small regions of the primary somatosensory (SI) and motor (MI) cortex on the control of finger forces in a precision grip. A monkey was trained to grasp and lift a computer-controlled object between the thumb and index finger and to hold it stationary within a narrow position window for 2 s. The grip force applied perpendicular to the object surface, the lifting or load force applied tangentially in the vertical direction, and the vertical displacement were sampled at 100 Hz. Also, the ability of the monkey to extract small pieces of food from narrow wells of a Klüver board was analyzed from video-tape. Preliminary single-unit recordings and microstimulation studies were used to map the extent of the thumb and index-finger representation within SI and MI. Two local injections of 1 μl each (5 μg/μl) of the GABA_A-agonist muscimol were used to inactivate the thumb and index region of either the pre- or post-central gyrus. The precision grip was differently affected by muscimol injection into either SI or MI. MI injections produced a deficit in the monkey’s ability to perform independent finger movements and a general weakness in the finger muscles. Whole-hand grasping movements were inappropriately performed in an attempt to grasp either the instrumented object or morsels of food. Although the effect seemed strongest on intrinsic hand muscles, a clear deficit in digit extension was also noted. As a result, the monkey was unable to lift and maintain the object within the position window for the required 2 s, and, over time, the grip force decreased progressively until the animal stopped working. Following SI injections, the most obvious effect was a loss of finger coordination. In grasping, the placement of the fingers on the object was often abnormal and the monkey seemed unable to control the application of prehensile and lifting forces. However, the detailed analysis of forces revealed that a substantial increase in the grip force occurred well before any deficit in the coordination of finger movements was noted. This observation suggests that cutaneous feedback to SI is essential for the fine control of grip forces. Received: 05 October 1998 / Accepted: 30 March 1999     

Perceptual constancy and the perceived magnitude of muscle forces

The present study used a force-matching task to measure how accurately subjects could match a force using different muscle groups. Forces ranging in magnitude from 2 to 10 N were produced and matched by three muscle groups: the elbow flexors, the forearm and hand muscles involved in the palmar prehensile grasp, and the index finger flexors. The ability to match forces was considered in terms of precision, that is, how closely the matching forces approximated the reference force produced on the contralateral side, and accuracy, which is the reproducibility of the matching force estimates. The results indicated that the perceived magnitude of forces varied as a function of the muscle group generating the force. Forces produced by the index finger flexors were consistently overestimated in magnitude when matched by elbow flexion forces, and elbow forces were underestimated when matched by flexing the index finger. When evaluated in terms of constant and absolute errors, the index finger flexors were the most precise matching muscle group and the elbow flexors the least precise. These results suggest that forces are perceived relatively, and are scaled with reference to the operating range of the muscles. They also indicate that there is little perceptual constancy in the perceived magnitude of forces generated by different muscle groups.