Never too little: Grip and lift forces following probabilistic weight cues in patients with writer's cramp.

OBJECTIVE: Planning of voluntary object-related movements requires the estimation of the most probable object properties. We investigated how 14 writer's cramp (WC) patients compared to 14 controls use probabilistic weight cues in a serial grip-lift task. METHODS: In every grip-lift trial, an object of either light, medium or heavy weight had to be grasped and lifted after a visual cue gave a probabilistic prediction of the object weights (e.g. 32.5% light, 67.5% medium, 0 % heavy). We determined peak (1) grip force GF, (2) load force LF, (3) grip force rate GFR, (4) load force rate LFR, while we registered brain activity with functional magnetic resonance imaging. RESULTS: In both groups, GFR, LFR and GF increased when a higher probability of heavy weights was announced. When a higher probability of light weights was indicated, controls reduced GFR, LFR and GF, while WC patients did not downscale their forces. There were no inter-group differences in blood oxygenation level dependent activation. CONCLUSIONS: WC patients could not utilize the decision range in motor planning and adjust their force in a probabilistic cued fine motor task. SIGNIFICANCE: The results support the pathophysiological model of a hyperfunctional dopamine dependent direct basal ganglia pathway in WC.

The origin of the heartbeat and theories of muscle contraction. Physiological concepts and conflicts in the 19th century.

The origin of the incessant rhythmical heartbeat and the mechanism of muscle contraction have fascinated scientists over centuries. This short review outlines physiological explanations that were discussed in the 19th century starting with Albrecht von Haller (1708-1777), an 18th century physiologist who proposed that the heart has an intrinsic irritability. He argued that under normal conditions the inflow of blood stimulates the heart muscle to contract by mechanical touch and distension. Johannes Müller (1800-1858, physiologist in Bonn and Berlin) contended that the influence of the sympathetic nerve, specifically the activity of intracardiac ganglia, is the foremost cause of the heartbeat. Walter H. Gaskell and Theodor Engelmann (physiologists in Cambridge and Utrecht, respectively) independently criticized this neurogenic theory. They reported experimental evidence that supported the myogenic theory of the origin of the heartbeat, which has been accepted since about 1900. The concept of cardiac mechano-sensitivity, which can be traced back to A. von Haller, is currently resurging. Concerning mechanisms of contraction, Edward A. Schäfer (1850-1935), histologist and physiologist in Edinburgh, described differences between cardiac and skeletal muscle and coined the term sarcomere. Based on microscopic studies of cross-striated muscle, Schäfer outlined a detailed and plausible mechanism of muscle contraction in 1892. He put forward that during muscle shortening the "clear part of the muscle substance" (actin) might pass into longitudinal canals, which exist between the "sarcous elements" (myosin). His model foresaw fundamental elements of the sliding filament model, which was discovered by the Huxleys about 60 years later.

Cold and heavy: grasping the temperature-weight illusion.

The apparent heaviness of weights placed on the skin depends on their temperature. We studied the effects of such a temperature-weight illusion (TWI) on perception and action in 21 healthy volunteers. Cold (18 °C), thermal-neutral (32 °C, skin temperature) and warm (41 °C) test objects were placed onto the palm of the non-dominant hand. Their veridical mass was 350 g (light) or 700 g (heavy). Perception of heaviness was assessed with two psychophysical experiments (magnitude estimation, cross modal matching). Cold heavy objects felt about 20% heavier than thermal-neutral objects of the same mass, shape and material. In a subsequent grip-lift experiment, the test objects were grasped with a precision grip of the dominant hand and lifted off the palm of the non-dominant hand. The grip and lift forces exerted by the fingertips were recorded. The temperature of the objects had significant effects (ANOVA, p < 0.05) on the peak grip and lift forces and on the peak grip force rate (i.e., the initial force incline). The peak grip force was about 10% higher when cold heavy objects were grasped and lifted, compared to lifts of otherwise identical thermal-neutral objects. The TWI was less pronounced when light objects or warm objects were handled. In conclusion, cooling of an object increases its apparent heaviness (perception) and influences scaling of the fingertip forces during grasping and lifting (action).

Parkinsonian patients do not utilize probabilistic advance information in a grip-lift task.

INTRODUCTION: Patients with Parkinson's disease (PD) are known to have decision-making impairments in tasks involving probabilistic information. How PD patients utilize task-relevant probabilistic advance information to plan and initiate common motor tasks like grasping has not yet been studied. METHODS: PD patients (n = 15, OFF medication) and control participants repeatedly grasped and lifted an object, the weight of which could be light, medium, or heavy. Visual cues provided explicit probabilistic information about the upcoming weight at the start of each grip-lift trial. This information allows the force of the grasping fingers to be scaled predictively so that it matches the likely weight, with a suitable rate of initial force increase. Deterministic cues announced the upcoming weight with certainty in other grip-lift trials. In a weight adjustment experiment, participants associated each probabilistic cue with a specific heaviness. RESULTS: The weight adjustment experiments showed that the probabilistic cues were understood correctly. However, PD patients utilized the probabilistic information significantly less than controls during the grip-lift task. Specifically, patients did not initiate their grasp more forcefully when probabilistic cues announced a high likelihood (66.7% probability) of a heavy weight, in contrast to controls. Thus, probabilistic cues that encouraged a more vigorous action had no effect in PD. Nevertheless, patients and controls scaled their forces appropriately when deterministic cues announced the forthcoming weights unambiguously. CONCLUSIONS: PD patients do not invest a high movement effort to initiate a grip-lift unless the necessity of such a vigorous action initiation is decidedly clear.

Rediscovery of Otto Frank's contribution to science.

In the late 19th century, German physiologist Otto Frank (1865-1944) embarked on a near life-long research program of laying down the mathematical, methodological, and theoretical foundations in order to understand and define the performance of the heart and circulatory system in all their complexity. The existence of the "Frank-Starling law" testifies to this. Two of his seminal publications have been translated into English previously, introducing Frank's research on the dynamics of the heart and the arterial pulse to a wider audience. It is likely that there are a host of other comparable achievements and publications of Frank that are still unknown to the international scientific (cardiological and physiological) community. However, their influence can still be felt and seen in modern cardiology and cardio-physiology, such as in the development of modern interactive simulating and teaching programs. We have translated and commented on ten of these papers, which can be read in parallel with the German originals. These publications show a wealth of theoretical assumptions and projections regarding the importance of the sarcomere, the development of models of contraction, thermo-dynamical considerations for muscular activity, differences between cardiac and skeletal muscles, problems related to methodology and measurement, and the first pressure-volume diagram (published 120 years ago). These topics were envisioned by Frank long before they became a focus of subsequent modern research. Nowadays, frequent measurements of pressure-volume relationships are made in research using the pressure-volume conductance catheter technique. In commenting Frank's scientific topics, we try to show how interconnected his thinking was, and thus how it enabled him to cover such a wide range of subjects.

Trunk muscle activation pattern in parkinsonian camptocormia as revealed with surface electromyography.

INTRODUCTION: Camptocormia is frequently seen in Parkinson's disease (PD) and multiple system atrophy. It is characterized by a pathological forward bending of the trunk during standing, often combined with a lateral trunk deviation. The etiology of camptocormia in PD is still unknown. Muscle MRI studies show abnormalities mainly of the erector spinae confirmed by muscle biopsies. Quantitative electromyographic examination of trunk muscle activity is missing. METHODS: Ventral (rectus and obliquus externus abdominis) and dorsal (iliocostalis lumborum, longissimus, multifidus) trunk muscles and the rectus femoris were recorded bilaterally with surface electromyography in standing PD patients with camptocormia (n = 10) and matched healthy controls (n = 10) who mimicked the patients' posture. EMG amplitudes were compared quantitatively. In controls, the relation between varying degrees of trunk flexion and EMG was established systematically. RESULTS: Increasing forward trunk flexion was associated with increasing back muscle activity in controls, while abdominal muscle activity was negligible. During anterolateral trunk flexion, back muscle activity increased particularly on the contralateral side. The patients showed a similar pattern. However, normalized EMG activity of their trunk extensors was significantly higher than in controls, often reaching half-maximal amplitudes. Their rectus femoris and oblique abdominal muscles were overactive, but to a lesser extent. CONCLUSIONS: PD patients with camptocormia must use the functional reserve of their lumbar trunk muscles to counteract gravity. We interpret this as a weakness of the paravertebral muscles. Compared to the other examined muscles the paravertebral muscles are most affected. The increased EMG activity of the rectus femoris warrants further research.

Mechanosensitivity: From Aristotle's sense of touch to cardiac mechano-electric coupling.

Scientific interest in mechanosensation likely commenced with Aristotle's description of the sense of touch in his treatise de Anima [On the Soul]. Considering touch as a vital sense distributed over the whole body, the philosopher outlined a "physiological concept" at the macro-level already 2400 years ago. From this starting point, we outline the onset of modern sensory physiology during the early 19th century. Physiologists distinguished between outer and inner senses at that time, without, however, referring to specific receptors or nerves. We then outline how research on four topics concerning cardiac mechano-electric coupling developed up until the 1960's (cardio-respiratory coupling, Bainbridge reflex, Bezold-Jarisch reflex, stretch-induced arrhythmias). Following the discovery of macroscopic phenomena (e.g. change of heart rate, induced by atrial distension) during that period, researchers sought to identify the pertinent receptors and reflex loops, while nowadays the underlying subcellular mechanisms such as stretch-activated ion channels are under investigation.

Probabilistic information on object weight shapes force dynamics in a grip-lift task.

Advance information, such as object weight, size and texture, modifies predictive scaling of grip forces in a grip-lift task. Here, we examined the influence of probabilistic advance information about object weight. Fifteen healthy volunteers repeatedly grasped and lifted an object equipped with a force transducer between their thumb and index finger. Three clearly distinguishable object weights were used. Prior to each lift, the probabilities for the three object weights were given by a visual cue. We examined the effect of probabilistic pre-cues on grip and lift force dynamics. We expected predictive scaling of grip force parameters to follow predicted values calculated according to probabilistic contingencies of the cues. We observed that probabilistic cues systematically influenced peak grip and load force rates, as an index of predictive motor scaling. However, the effects of probabilistic cues on force rates were nonlinear, and anticipatory adaptations of the motor output generally seemed to overestimate high probabilities and underestimate low probabilities. These findings support the suggestion that anticipatory adaptations and force scaling of the motor system can integrate probabilistic information. However, probabilistic information seems to influence motor programs in a nonlinear fashion.

Activity of upper limb muscles during human walking.

The EMG activity of upper limb muscles during human gait has rarely been studied previously. It was examined in 20 normal volunteers in four conditions: walking on a treadmill (1) with unrestrained natural arm swing (Normal), (2) while volitionally holding the arms still (Held), (3) with the arms immobilized (Bound), and (4) with the arms swinging in phase with the ipsilateral legs, i.e. opposite-to-normal phasing (Anti-Normal). Normal arm swing involved weak rhythmical lengthening and shortening contractions of arm and shoulder muscles. Phasic muscle activity was needed to keep the unrestricted arms still during walking (Held), indicating a passive component of arm swing. An active component, possibly programmed centrally, existed as well, because some EMG signals persisted when the arms were immobilized during walking (Bound). Anti-Normal gait involved stronger EMG activity than Normal walking and was uneconomical. The present results indicate that normal arm swing has both passive and active components.

Thermoreception and nociception of the skin: a classic paper of Bessou and Perl and analyses of thermal sensitivity during a student laboratory exercise.

About four decades ago, Perl and collaborators were the first ones who unambiguously identified specifically nociceptive neurons in the periphery. In their classic work, they recorded action potentials from single C-fibers of a cutaneous nerve in cats while applying carefully graded stimuli to the skin (Bessou P, Perl ER. Response of cutaneous sensory units with unmyelinated fibers to noxious stimuli. J Neurophysiol 32: 1025-1043, 1969). They discovered polymodal nociceptors, which responded to mechanical, thermal, and chemical stimuli in the noxious range, and differentiated them from low-threshold thermoreceptors. Their classic findings form the basis of the present method that undergraduate medical students experience during laboratory exercises of sensory physiology, namely, quantitative testing of the thermal detection and pain thresholds. This diagnostic method examines the function of thin afferent nerve fibers. We collected data from nearly 300 students that showed that 1) women are more sensitive to thermal detection and thermal pain at the thenar than men, 2) habituation shifts thermal pain thresholds during repetititve testing, 3) the cold pain threshold is rather variable and lower when tested after heat pain than in the reverse case (order effect), and 4) ratings of pain intensity on a visual analog scale are correlated with the threshold temperature for heat pain but not for cold pain. Median group results could be reproduced in a retest. Quantitative sensory testing of thermal thresholds is feasible and instructive in the setting of a laboratory exercise and is appreciated by the students as a relevant and interesting technique.

Functional impact of the rhabdosphincter branch of the pelvic nerve on the membranous urethra in comparison to that of the pudendal nerve in male rabbits.

INTRODUCTION: The innervation of the membranous urethra (MU) is still under debate. We analysed the functional effects of electrostimulation of the rhabdosphincter branch of the pelvic nerve (RBP) on the MU in a standardized male rabbit model, paying attention both to the efferent and the possible afferent effects of stimulation. MATERIAL AND METHODS: Six male rabbits (chinchilla bastards) were included in this study. Pudendal nerve branches as well as pelvic nerve branches were exposed bilaterally in all animals. Randomized electrostimulation trials of both the pudendal nerve fibres and the RBP were carried out using a biphasic signal (0.3 mA, 200 mus). The stimulation frequency ranged from 10 to 40 Hz in a randomized pattern. Changes in MU pressure were measured urodynamically. The pressure changes occurring as a result of stimulation were compared in both nerve structures. At the end of the stimulation trial, the RBP and the pudendal nerve were dissected at different positions before repeating the stimulation and the MU pressure recording. RESULTS: The mean MU baseline pressure without stimulation was 24 cm H(2)O (range 21-27) in all animals. During unilateral pudendal stimulation, the mean pressure response rose by highly significant values (p < 0.005) compared to baseline. The pressure response was frequency dependent. Stimulation of the RBP resulted in a small but significant change of the MU pressure in the lower frequency range (10 and 20 Hz) (p > 0.05). On performing stimulation at higher frequencies, there was no significant difference from baseline. The pressure response of the MU during stimulation of the intact RBP did not differ significantly from the response after dissection of the RBP. However, after dissecting the pudendal nerve, the MU pressure response to RBP stimulation was diminished. CONCLUSION: Our results confirm the primacy of the pudendal nerve in the innervation of the MU. Stimulation of the RBP, however, may produce an afferent signal which is transmitted to the pudendal nerve, thus resulting in a pressure increase of the MU and contributing towards continence. We showed the importance of the RBP to maintain full urinary continence in rabbits. Our results suggest that substantially higher continence rates can be achieved through a nerve-sparing procedure in radical prostatectomy. Nerve-sparing radical prostatectomy incidentally also protects the RBP from injury.

Grasping with the left and right hand: a kinematic study.

The goal of the present study was to compare prehension movements of the dominant and the non-dominant hand. Twenty right-handed volunteers (age 20-30 years) reached forward to grasp a cylindrical object, which was lifted and then placed into a target position in a retraction-insertion movement. The movements were performed at three different velocities (normal, deliberately fast, or slowly) both, under visual control, and in a no-vision condition. Analysis of the kinematic data revealed that the speed of hand transport influenced pre-shaping of both hands in a similar way. In the visual condition, the grip aperture increased about linearly with peak transport velocity, while it increased non-linearly with shorter movement duration. Comparison of the regression parameters showed that these relationships were nearly identical for both hands. The dominant hand was faster in inserting the object into the target position. Otherwise, no significant inter-manual differences were found. During prehension without visual control, the fingers opened more and movement duration was prolonged. Except for a larger grip aperture of the dominant hand at the end of the acceleration phase, the kinematic data of both hands were again comparable. This invariance was in contrast to performance in fine motor skills such as a pegboard test and drawing movements, where there was a clear advantage of the dominant hand. The similar pre-shaping of both hands during prehension is discussed with regard to a common motor representation of grasping.

Cortical representation of the urge to void: a functional magnetic resonance imaging study.

PURPOSE: The urge to void generally increases with bladder distention but the relationship between the 2 factors is complex. When the bladder is moderately filled, the desire to void can be called forth deliberately but it can also be suppressed. To elucidate human brain mechanisms that are active during such intentional modulations of the desire to void we performed functional magnetic resonance imaging in healthy volunteers. MATERIALS AND METHODS: Brain activity was studied in 22 young women. At moderate bladder filling (about 350 ml) they periodically suppressed or enhanced the urge to void without allowing urine to pass. A manual task with a dynamometer, in which the current urge to void was expressed as grip force, demonstrated that the intensity of sensations could be influenced voluntarily. We also examined brain activity during repetitive (1 Hz) contractions of pelvic floor muscles after the bladder was emptied. RESULTS: Significant brain activity associated with an increased urge to void was found in the insular cortex, frontal opercula, supplementary motor area (SMA), cingulate motor area (CMA), right posterior parietal cortex, left prefrontal cortex and cerebellum. Trends toward activation were detected in the thalamus, peri-aquaeductal gray matter and ventral pons. Suppression of the urge to void significantly activated the left superior frontal lobe. The SMA and CMA were active during voluntary rhythmical contractions of pelvic floor muscles. CONCLUSIONS: Sensation intensity of the desire to void can be influenced intentionally. Frontoparietal cortical areas and the SMA/CMA seem to be involved in this process.

Living a normal life with the nondominant hemisphere: magnetic resonance imaging findings and clinical outcome for a patient with left-hemispheric hydranencephaly.

In hemihydranencephaly, the human brain lacks 1 complete hemisphere. An occlusion of the carotid artery, affecting all supplied territories, is thought to be the underlying mechanism. This extremely rare disorder, of which only 7 cases have been reported to date, is thought to occur before the last trimester of gestation (20th to 27th week), after neural migration but before synaptogenesis. We report on a 36-year-old man born at term, with no complications, from nonconsanguineous healthy parents. Cranial computed tomography had been performed because of left-sided headaches. Because of the imaging findings, the patient presented at our institution for additional MRI and clinical testing (including the Motor Activity Log, Wolf motor function test, 2-point discrimination test, Purdue pegboard test, gross motor function test, Physician Rating Scale, and Aachener aphasia test, including patterns for spontaneous speech, repetition, naming, comprehension, written language, and the token test). The patient's disabilities were related to deficits in fine motor control and reduced precision. Therefore, the patient was unable to perform the Purdue pegboard test with his affected hand. According to the Aachener aphasia test, no aphasia could be demonstrated for this strongly left-handed patient. Strong mirror movements were found. Cortical reorganization is possible if damage occurs in very early childhood. Motor function and speech were controlled by the remaining, nonaffected hemisphere, with a remarkable outcome. Because the damage is thought to occur before synaptogenesis, existing or prepared cortical areas and pathways have the potential to execute the lacking functions of the destroyed hemisphere.

Recovery of the precision grip in children after traumatic brain injury.

OBJECTIVE: To identify quantitative parameters that are sensitive enough to detect impairments and improvements of grasping in children after traumatic brain injury (TBI) by analyzing the isometric fingertip forces of a precision grip-lift task. DESIGN: Follow-up and case-control study. SETTING: Tertiary pediatric trauma rehabilitation center in Germany. PARTICIPANTS: Thirteen children (age range, 5-14 y) with moderate or severe TBI. Trauma severity was assessed with the Glasgow Coma Scale (score range, 3-9) and the Injury Severity Score (range, 16-66 points). Control data were obtained from 13 age- and gender-matched healthy children. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Children were examined 3 times (t0, t1, t2). The first date of examination (t0) was defined by the Barthel Index (part B, >20 points). Reexaminations followed after 1 (t1) and 5 (t2) months of inpatient rehabilitation. Quantitative measures included 3 grip-force parameters, 2 load force parameters, 1 parameter of the coordination between grip force and load force, and 3 timing parameters in a precision grip-lift task. Clinical improvements and recovery of activities of daily living were described with the Barthel Index (qualitative measure). RESULTS: Peak grip force, maximum negative load force, grip force in the static phase and its standard deviation, and grip-force/load-force ratio at maximum grip force showed significant improvements during the observation period (5 mo). Also, the preparation phase and preload duration, but not the load duration, changed significantly. CONCLUSIONS: Impairments and the recovery of grasping in children after TBI can be objectified with quantitative analyses of the precision grip. Several grip-force and timing parameters were sensitive for the description of restitution processes.

Sensorimotor recovery in children after traumatic brain injury: analyses of gait, gross motor, and fine motor skills.

The recovery of gait, gross motor proficiency, and hand function was examined in 23 children (13 males, 10 females; age 4 years 7 months to 15 years 10 months) with traumatic brain injury (TBI) over five months of in patient rehabilitation. We used gait analysis, the Gross Motor Function Measure, the Developmental Hand Function Test, and the Purdue Pegboard test. Brain injury had been severe (initial Glasgow Coma Scale GCS <8) in 17 children and moderate (GCS 8-10) in six children. Compared with healthy control children of the same age and sex, repeated gait analyses in ambulatory children with brain injury showed significant reductions of velocity, stride length and cadence, and impaired balance. Spatiotemporal gait variables were correlated with Gross Motor Function Measure scores. Hand function tests revealed deficits in fine motor skills, speed, and coordination. Degree of impairment increased with trauma severity. Despite significant improvements, differences in gait velocity, stride length, and hand function of children with brain injuries and controls were still present about 8 months after TBI. Hand motor skills improved less than gait. Young age at injury was not associated with better recovery.

Analyses of gait, reaching, and grasping in children after traumatic brain injury.

OBJECTIVE: To evaluate motor behavior in children after traumatic brain injury (TBI) with quantitative instrumented measures of gait and of functional hand movements (reaching, grasping) and with clinical assessments. DESIGN: Case-control study. SETTING: Tertiary pediatric trauma rehabilitation center in Germany. PARTICIPANTS: Twenty children (age range, 6-13 y) with moderate or severe TBI were examined 1+/-1.2 years (mean +/- standard deviation) postinjury. Fifteen were reexamined 2 months later. Control data were obtained from 20 healthy children and matched for age, gender, and school grade. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Quantitative measures included 10 spatiotemporal gait parameters and 6 variables describing reaching and grasping. Qualitative scores of gait and upper-limb movements were also obtained. RESULTS: Gait velocity and step and stride lengths were significantly smaller in children after TBI than in control subjects (Mann-Whitney U test, P<.05). Reach-to-grasp movements of the TBI children were characterized by a significantly longer reaction time (Mann-Whitney U test, P<.05) and movement duration, reduced velocity, and coordination deficits. The instrumented measures did not change significantly in 2 months. Several significant correlations between clinical and instrumented measures were obtained. CONCLUSION: Functional motor behavior is affected in children after moderate or severe TBI. To supplement clinical assessments with objective data, impairments of gait, reaching, and grasping movements can be recorded with instrumented measures.

Brain regions controlling nonsynergistic versus synergistic movement of the digits: a functional magnetic resonance imaging study.

Human hand dexterity depends on the ability to move digits independently and to combine these movements in various coordinative patterns. It is well established that the primary motor cortex (M1) is important for skillful digit actions but less is known about the role played by the nonprimary motor centers. Here we use functional magnetic resonance imaging to examine the hypothesis that nonprimary motor areas and the posterior parietal cortex are strongly activated when healthy humans move the right digits in a skillful coordination pattern involving relatively independent digit movements. A task in which flexion of the thumb is accompanied by extension of the fingers and vice versa, i.e., a learned "nonsynergistic" coordination pattern, is contrasted with a task in which all digits flex and extend simultaneously in an innate synergistic coordination pattern (opening and closing the fist). The motor output is the same in the two conditions. Thus, the difference when contrasting the nonsynergistic and synergistic tasks represents the requirement to fractionate the movements of the thumb and fingers and to combine these movements in a learned coordinative pattern. The supplementary (and cingulate) motor area, the bilateral dorsal premotor area, the bilateral lateral cerebellum, the bilateral cortices of the postcentral sulcus, and the left intraparietal cortex showed stronger activity when the subjects made the nonsynergistic flexion-extension movements of the digits than when the synergistic movements were made. These results suggest that the human neural substrate for skillful digit movement includes a sensorimotor network of nonprimary frontoparietal areas and the cerebellum that, in conjunction with M1, control the movements of the digits.