Neuronal activity in somatosensory cortex of monkeys using a precision grip. III. Responses to altered friction perturbations.
The purpose of this investigation was to examine the activity changes in single units of the somatosensory cortex in response to lubricating and adhesive coatings applied to a hand-held object. Three monkeys were trained to grasp an object between the thumb and index fingers and to lift and hold it stationary within a narrow position window for 1 s before release. Grip forces normal to the skin surface, load forces tangential to the skin surface, and the displacement of the object were measured on each trial. Adhesive (rosin) and lubricant (petroleum jelly) coatings were applied to the smooth metal surface of the object to alter the friction against the skin. In addition, neuronal activity evoked by force pulse-perturbations generating shear forces and slip on the skin were compared with the patterns of activity elicited by grasping and lifting the coated surfaces. Following changes in surface coatings, both monkeys modulated the rate at which grip forces normal to the skin surface and load forces tangential to the skin surface were applied during the lifting phase of the task. As a result, the ratio of the rates of change of the two forces was proportionately scaled to the surface coating properties with the more slippery surfaces, having higher ratios. This precise control of normal and tangential forces enabled the monkeys to generate adequate grip forces and prevent slip of the object. From a total of 386 single neurons recorded in the hand area of the somatosensory cortex, 92 were tested with at least 1 coating. Cell discharge changed significantly with changes in surface coating in 62 (67%) of these cells. Of these coating-related cells, 51 were tested with both an adhesive and lubricating coating, and 45 showed significant differences in activity between the untreated metal surface and either the lubricant or the adhesive coating. These cells were divided into three main groups on the basis of their response patterns. In the first group (group A), the peak discharge increased significantly when the grasped surface was covered with lubricant. These cells appeared to be selectively sensitive to slip of the object on the skin. The second group (group B) was less activated by the adhesive surface compared with either the untreated metal or the lubricated surface, and they responded mainly to variations in the force normal to the skin surface. These cells provide useful feedback for the control of grip force. The third group (group C) responded to both slips and to changes in forces tangential to the skin. Most of these cells responded with a biphasic pattern reflecting the bidirectional changes in load force as the object was first accelerated and then decelerated. One hundred sixty-eight of the 386 isolated neurons were tested with brief perturbations during the task. Of these, 147 (88%) responded to the perturbation with a significant change in activity. In most of the cells, the response to the perturbation was shorter than 100 ms with a mean latency of 44.1 +/- 16.3 (SD) ms. For each of the cell groups, the activity patterns triggered by the perturbations were consistent with the activity patterns generated during the grasping and lifting of the coated object. (+info)
Control of fingertip forces in multidigit manipulation.
Previous studies of control of fingertip forces in skilled manipulation have focused on tasks involving two digits, typically the thumb and index finger. Here we examine control of fingertip actions in a multidigit task in which subjects lifted an object using unimanual and bimanual grasps engaging the tips of the thumb and two fingers. The grasps resembled those used when lifting a cylindrical object from above; the two fingers were some 4.25 cm apart and the thumb was approximately 5.54 cm from either finger. The three-dimensional forces and torques applied by each digit and the digit contact positions were measured along with the position and orientation of the object. The vertical forces applied tangential to the grasp surfaces to lift the object were synchronized across the digits, and the contribution by each digit to the total vertical force reflected intrinsic object properties (geometric relationship between the object's center of mass and the grasped surfaces). Subjects often applied small torques tangential to the grasped surfaces even though the object could have been lifted without such torques. The normal forces generated by each digit increased in parallel with the local tangential load (force and torque), providing an adequate safety margin against slips at each digit. In the present task, the orientations of the force vectors applied by the separate digits were not fully constrained and therefore the motor controller had to choose from a number of possible solutions. Our findings suggest that subjects attempt to minimize (or at least reduce) fingertip forces while at the same time ensure that grasp stability is preserved. Subjects also avoid horizontal tangential forces, even at a small cost in total force. Moreover, there were subtle actions exerted by the digits that included changes in the distribution of vertical forces across digits and slight object tilt. It is not clear to what extent the brain explicitly controlled these actions, but they could serve, for instance, to keep tangential torques small and to compensate for variations in digit contact positions. In conclusion, we have shown that when lifting an object with a three-digit grip, the coordination of fingertip forces, in many respects, matches what has been documented previously for two-digit grasping. At the same time, our study reveals novel aspects of force control that emerge only in multidigit manipulative tasks. (+info)
Trapeziectomy for basal thumb joint osteoarthritis: 3- to 19-year follow-up.
A consecutive series of 40 trapeziectomies in 30 patients with basal thumb joint osteoarthritis was reviewed. Sixteen thumbs had pan-trapezial and 24 thumbs trapeziometacarpal osteoarthritis. Simple excision without soft tissue interposition was performed by the same surgeon using an identical surgical technique. Twenty-eight patients were female (mean age 57 years) with a mean follow-up of 11 (3-19) years. Twenty-eight patients were satisfied with their operation, with 26 thumbs being pain free. Thumb pinch strength was improved by 40% compared to preoperative values, but still remained 22% weaker than the non-operated side. (+info)
Holt-Oram syndrome revisited. Two patients in the same family.
Holt-Oram syndrome was first described in 1960 as an association of familial heart disease and musculoskeletal abnormalities. The most important findings include atrial septal defects, atrioventricular conduction abnormalities, vascular hypoplasia, and upper limb musculoskeletal deformities. We report two patients with this syndrome in the same family and discuss the variability of the musculoskeletal abnormalities and their association with the cardiac morphologic defects. Both patients in this study had associated eosinophilia, which has not been reported in the literature. (+info)
Activity-dependent conduction block in multifocal motor neuropathy.
Patients with multifocal motor neuropathy may complain of muscle fatigue, even though the degree of conduction block assessed at rest has improved with treatment. To explore the mechanism involved, we examined changes in muscle force during maximum voluntary contraction (MVC) and monitored conduction block before and after MVC in five patients with multifocal motor neuropathy. The results were compared with those for the contralateral unaffected homonymous muscles. For one patient, who had bilateral involvement, a normal subject of a similar age and stature served as the control. Results of conduction studies were also compared with those from six patients with amyotrophic lateral sclerosis (ALS) with similar compound muscle action potential (CMAP) amplitudes after proximal stimulation. During MVC for 60 s, the affected muscles developed prominent fatigue; the force at the end of contraction compared with the initial force was significantly lower for the affected muscles [42 +/- 19% (mean +/- standard deviation) of the initial force] than for the control muscles (94 +/- 9%; P = 0.01). After MVC, the amplitude ratio of CMAPs after proximal versus distal nerve stimulation transiently decreased to 19 +/- 14% of that before MVC in the affected muscles, but not in the control muscles (94 +/- 3.8% of that before MVC) and in patients with ALS (95 +/- 6.7%). In one patient with a focal lesion in the forearm, nerve excitability was monitored at the lesion site before and after MVC for 120 s. There were significant increases in axonal threshold (approximately 48%) and supernormality (approximately 135%) immediately after MVC, suggesting that the axonal membrane had undergone hyperpolarization and, by extrapolation, that this had precipitated the conduction block. This study is the first to show that activity-dependent conduction block plays a role in human disease by causing muscle fatigue. (+info)
Randomized controlled trial of nettle sting for treatment of base-of-thumb pain.
There are numerous published references to use of nettle sting for arthritis pain but no randomized controlled trials have been reported. We conducted a randomized controlled double-blind crossover study in 27 patients with osteoarthritic pain at the base of the thumb or index finger. Patients applied stinging nettle leaf (Urtica dioica) daily for one week to the painful area. The effect of this treatment was compared with that of placebo, white deadnettle leaf (Lamium album), for one week after a five-week washout period. Observations of pain and disability were recorded for the twelve weeks of the study. After one week's treatment with nettle sting, score reductions on both visual analogue scale (pain) and health assessment questionnaire (disability) were significantly greater than with placebo (P = 0.026 and P = 0.0027). (+info)
Effects of repetitive transcranial magnetic stimulation on movement-related cortical activity in humans.
Several lines of evidence suggest that low-rate repetitive transcranial magnetic stimulation (rTMS) of the motor cortex at 1 Hz reduces the excitability of the motor cortex and produces metabolic changes under and at a distance from the stimulated side. Therefore, it has been suggested that rTMS may have beneficial effects on motor performance in patients with movement disorders. However, it is still unknown in what way these effects can be produced. The aim of the present study is to investigate whether rTMS of the motor cortex (15 min at 1 Hz) is able to modify the voluntary movement related cortical activity, as reflected in the Beretischaftspotential (BP), and if these changes are functionally relevant for the final motor performance. The cortical movement-related activity in a typical BP paradigm of five healthy volunteers has been recorded using 61 scalp electrodes, while subjects performed self-paced right thumb oppositions every 8-20 s. After a basal recording, the BP was recorded in three different conditions, counterbalanced across subjects: after rTMS stimulation of the left primary motor area (M1) (15 min, 1 Hz, 10% above motor threshold), after 15 min of sham rTMS stimulation and following 15 min of voluntary movements performed with spatio-temporal characteristics similar to those induced by TMS. The tapping test was used to assess motor performance before and after each condition. Only movement-related trials with similar electromyographic (onset from muscular 'silence') and accelerometric patterns (same initial direction and similar amplitudes) were selected for computing BP waveforms. TMS- evoked and self-paced thumb movements had the same directional accelerometric pattern but different amplitudes. In all subjects, the real rTMS, but neither sham stimulation nor prolonged voluntary movements, produced a significant amplitude decrement of the negative slope of the BP; there was also a shortening of the BP onset time in four subjects. The effect was topographically restricted to cortical areas which were active in the basal condition, irrespective of the basal degree of activation at every single electrode. No changes in the tapping test occurred. These findings suggest that rTMS of the motor cortex at 1 Hz may interfere with the movement related brain activity, probably through influence on cortical inhibitory networks. (+info)
Volar plate arthroplasty of the thumb interphalangeal joint.
The fibrocartilaginous volar plate of the thumb interphalangeal joint is anatomically quite similar to the volar plate of the digital proximal interphalangeal joint. Due to this similarity, Eaton's technique of volar plate arthroplasty may also be utilized in fracture-dislocations of the thumb interphalangeal joint. (+info)