D.I. McCloskey

Differences between the senses of movement and position shown by the effects of loading and vibration of muscles in man

Abstract Recent experiments have shown that if a muscle is vibrated at 100 Hz with a physiotherapy vibrator, then the joint about which that muscle operates is perceived to be moving as if the vibrated muscle were lengthening. Also, the position of the joint at any moment is perceived to be as if the vibrated muscle were stretched. Here, these distortions of sensation were investigated further at the elbow joint. The velocity of the illusory movement induced by vibration is slowed in proportion to the load borne by tensing the vibrated muscle, and at any load the velocity is slower if the muscle is fatigued. The error of position is increased by loading the vibrated muscle. Vibration of lower frequency but greater amplitude can induce errors of position without inducing illusions of movement. It is argued that separate lines of information can arise in muscle to signal positions and movements.

The role of joint receptors in human kinaesthesia when intramuscular receptors cannot contribute.

1. Kinaesthetic acuity was tested at the distal interphalangeal joint of the middle finger when the hand was postured so that the joint was effectively disengaged from its muscular attachments. Subjects were required to detect the direction of 5 deg movements applied at different angular velocities from a mid‐position under control conditions, after intra‐articular injection of a plasma expander and after intra‐articular injection of a local anaesthetic. 2. Kinaesthetic performance was enhanced after the injection of a plasma expander and deteriorated after injection of local anaesthetic. This deterioration could not be explained by spread of the local anaesthesic from the injection site on the dorsum of the joint. 3. The results suggest that the discharge of joint receptors can produce perceived signals of joint movement. Under normal conditions these receptors may duplicate the kinaesthetic input from muscle spindle endings.

Changes in motor commands, as shown by changes in perceived heaviness, during partial curarization and peripheral anaesthesia in man

1. The centrally generated ‘effort’ or direct voluntary command to motoneurones required to lift a weight was studied using a simple weight‐matching task when the muscles lifting a reference weight were weakened. This centrally generated input to motoneurones was increased when the lifting muscles were partially paralysed with curare or decamethonium as judged by the increased perceived heaviness of a reference weight lifted by the weakened muscles.

Effects of related sensory inputs on motor performances in man studied through changes in perceived heaviness

1. The perception of the heaviness of lifted objects was studied using a weight‐matching task when sensory inputs from parts related to the lifting task were altered.

Proprioceptive sensation at the terminal joint of the middle finger.

This paper extends previous work (Gandevia & McCloskey, 1976) on proprioception in the terminal joint of the middle finger. By positioning the finger in appropriate ways proprioceptive acuity at the joint can be assessed when no muscular afferents could contribute, or when afferents in the flexor but not the extensor could contribute, or when afferents from both muscles could contribute. Digital nerve block anaesthetizes joint and cutaneous receptors and so was used to study the contributions from muscle afferents in isolation. Displacements (10 degrees) at various angular velocities were better detected when muscle afferents from both flexor and extensor muscles could contribute. This was so whether joint and cutaneous receptors were also available, or after digital anaesthesia. Performance when only muscle afferents are available is, however, inferior to that when all sensory mechanisms are intact. It is concluded that muscle afferents contribute to kinaesthesia, and that a full complement of such receptors from agonist and antagonist muscles gives superior acuity to that achieved when only the receptors of one of the muscle groups is available. The angular displacements necessary for 70% correct detection were determined at angular velocities between 0.25 degrees and 160 degrees/s. Proprioceptive performance was optimal with all proprioceptive mechanisms intact over the range of angular velocities 10 degrees ‐80 degrees/s: 70% correct detection of displacements of 0.8 degrees‐1.2 degrees occurred in this range. Performance deteriorated slightly at higher velocities of displacement. Performance was significantly poorer when only joint and cutaneous receptors could contribute (in the absence of intramuscular receptors), and when only intramuscular receptors could contribute (in the absence of joint and cutaneous receptors). Full proprioceptive acuity depends upon the availability of receptors in muscles and in skin and/or joints.

Pre- and postjunctional actions of neuropeptide Y and related peptides.

The effects of neuropeptide Y (NPY) and related peptide fragments on blood pressure and vagal action at the heart were compared in the anaesthetized rat. A change in vagal action was taken as a measure of presynaptic activity and a change in blood pressure was taken as a measure of postsynaptic activity. NPY, NPY-(13-36), PYY-(13-36), des-Ser22-NPY-(13-36) and a stabilized 13-36 analogue of NPY (ANA NPY) all exerted pressor actions and attenuated vagal action at the heart. The maximum vagal inhibitory or presynaptic action in order of potency was NPY, ANA-NPY, PYY-(13-36) significantly greater than NPY-(13-36), des-Ser22-NPY-(13-36). The order of potency for the half time of this effect was NPY, ANA-NPY significantly longer than PYY-(13-36) and NPY-(13-36), which were significantly longer than des Ser22-NPY-(13-36). For the pressor or postsynaptic effects, NPY increased blood pressure significantly more and for a longer duration than all the 13-36 fragments, which were not demonstrably different in this respect. These results are consistent with the proposal that there are two populations of NPY receptors. The C-terminal flanking peptide of NPY (CPON) and desamido-NPY had no effect on either vagal action at the heart or on blood pressure.

Effects of externally imposed elastic loads on the ability to estimate position and force.

Normal adult subjects attempted, with vision excluded, to match the position of the left index finger by pointing to it with the right one, using only flexion-extension movements at the right elbow. An elastic load applied at the right wrist was altered from trial to trial. When instructed to align the fingers, subjects were found to select the position of the right forearm by taking into account both a position signal and some measure of the force exerted by the elbow flexors. When instructed to match a target force, instead of position, the subjects were able to give greater weighting to signals of force than in the position matching task.

Task-dependent changes in gain of the reflex response to imperceptible perturbations of joint position in man.

1. It has been demonstrated recently that, when suitably instructed, subjects could alter the stiffness at the elbow in response to a slowly and imperceptibly changing elastic load. Although evidence was provided in favour of this occurring via changes in gain of the reflex response to stretch, changes in the degree of co‐contraction could not be entirely ruled out. The major objective of the present experiments was to determine if subjects could alter stiffness at the wrist in a similar task, and then to determine whether they retained this ability when co‐contraction was made impossible by anaesthetizing the nerve to the wrist extensors. A second objective was to determine if changes in stiffness could be controlled independently at the wrist and elbow. 2. Subjects, with eyes closed, initially held position constant against a constant force that loaded the flexors. For the wrist, they were instructed: (i) to keep the hand as still as possible (keep position constant) or (ii) to let the hand be moved by the perturbation (keep force constant). The perturbation was an initially imperceptible elastic load whose direction (loading or unloading) could not be predicted. Subjects were also asked to indicate when the perturbation was first perceived. 3. When asked to hold position constant or force constant at the wrist, subjects demonstrated task‐dependent changes in stiffness prior to perception of the perturbation. These changes in stiffness were still achieved when the nerve to the wrist extensors was anesthetized and thus co‐contraction was prevented. 4. Five subjects demonstrated the ability to control stiffness independently at the wrist and the elbow although most subjects had difficulty with the task we employed to demonstrate this. 5. The results demonstrate: (i) that for the wrist, set‐dependent changes in stiffness that occur prior to perception of a slowly developing perturbation can be mediated by changes in gain of reflex responses to those perturbations, and (ii) that stiffness can be controlled independently at the wrist and elbow, presumably in part by changes in gain of stretch reflexes.

Prolonged inhibition of cardiac vagal action following sympathetic stimulation and galanin in anaesthetized cats

1. Stimulation of the right cardiac sympathetic nerve for 3 min at 16 Hz in the presence of effective beta‐adrenoceptor blockade evoked prolonged attention of cardiac vagal action in the cat: 40.8 +/‐ 5.4% maximum inhibition of cardiac vagal action on prolonging pulse interval, with half‐time to recovery of 8.3 +/‐ 1.4 min. 2. Intravenous injection of galanin (1.6‐3.1 nmol/kg) evoked prolonged attenuation of cardiac vagal action: 40.9 +/‐ 8.2% maximum inhibition with a half‐time to recovery of 13.6 +/‐ 2.6 min. This effect of galanin was not significantly different from the action of sympathetic nerve stimulation. A slight depressor response (‐14.4 +/‐ 1.9 mmHg) was seen in nine of sixteen cats. 3. Intravenous injection of neuropeptide Y (NPY) (2.8‐6.3 nmol/kg) evoked slight attenuation of cardiac vagal action: 11.9 +/‐ 4.5% maximum inhibition of cardiac vagal action on pulse interval, with a half‐time to recovery of 4.1 +/‐ 1.7 min. Blood pressure increased by 68.6 +/‐ 5.7 mmHg. 4. Following administration of guanethidine (1 mg/kg I.V.) the inhibitory effect of sympathetic nerve stimulation on cardiac vagal action was significantly reduced (P less than 0.001). The responses to exogenous NPY and galanin on vagal action were unchanged after guanethidine. 5. The prolonged attenuation of cardiac vagal action can be mimicked by exogenous galanin in the cat but not by exogenous NPY.

Respiratory modulation of baroreceptor and chemoreceptor reflexes affecting heart rate through the sympathetic nervous system

1. Brief stimuli were delivered to the carotid body chemoreceptors or the carotid sinus baroreceptors at different phases of the respiratory cycle in anaesthetized dogs. Chemoreceptor stimulation was achieved by injecting small volumes (0·2‐0·5 ml.) of warmed saline equilibrated with CO2 near to the carotid bodies on both sides. Baroreceptor stimulation was achieved by injecting larger volumes (2‐5 ml.) of saline equilibrated with air into the region of the carotid bifurcation on both sides, after first clamping the common carotid arteries.