Task-dependent control of human masseter muscles from ipsilateral and contralateral motor cortex

Corticotrigeminal projections to human masseter motoneuron pools were investigated with focal transcranial magnetic stimulation (TMS). Responses in left and right masseter muscles were quantified from the surface electromyogram (EMG) during different biting tasks. During bilateral biting, TMS elicited motor evoked potentials (MEPs) in both masseter muscles. On average, the MEP area in the masseter contralateral to the stimulus was 39% larger than in the ipsilateral muscle, despite comparable pre-stimulus EMG in both muscles. MEPs elicited while subjects attempted unilateral activation of one masseter muscle were compared with those obtained in the same muscle during a bilateral bite at an equivalent EMG level. MEPs in the masseter contralateral to the stimulated hemisphere were significantly smaller during unilateral compared with bilateral biting. There was no significant difference in the size of ipsilateral MEPs during ipsilateral and bilateral biting. We conclude that the corticotrigeminal projections to masseter are bilateral, with a stronger contralateral projection. The command for unilateral biting is associated with a reduced excitability of corticotrigeminal neurons in the contralateral, but not the ipsilateral motor cortex. We suggest that this may be accomplished by reduced activity of a population of corticotrigeminal neurons which branch to innervate both masseter motoneuron pools.     

Reflex control of cat extrinsic and intrinsic tongue muscles exerted by intraoral receptors

The effects of mechanical and noxious stimulation of the palatal and lingual surfaces on the activity of the extrinsic and intrinsic tongue muscles have been studied in cats. Stimulation of the hard palate produced mainly activation of extrinsic tongue muscles while inhibition was elicited by stimulating the soft palate. Longlasting pressure on the hard palate caused rhythmic tongue flapping by intermittent genioglossal activity. The intrinsic tongue muscles, m. transversus and m. verticalis, were activated by noxious stimuli applied to the hard palate, the effects apparently being mediated by high-threshold afferents. Mechanical and noxious stimulation applied to the dorsal and ventral lingual surfaces of the tongue either activated or inhibited the extrinsic tongue muscles depending on the reflex area stimulated. The intrinsic tongue muscles were activated by noxious stimuli applied to the tongue surfaces. The anastomoses running between the hypoglossal and lingual nerves were found to mediate mainly nociceptive afferent impulses travelling from the hypoglossal to the lingual nerve. The intrinsic muscles were found to be controlled by anastomosal nociceptive afferents.     

Reactive grip force control in persons with cerebellar stroke: effects on ipsilateral and contralateral hand

This study investigates the cerebellar contribution to reactive grip control by examining differences between (22–48 years) subjects with focal cerebellar lesion due to ischaemic stroke (CL) and healthy subjects (HS). The subjects used a pinch grip to grasp and restrain an instrumented handle from moving when it was subject to unpredictable load forces of different rates (2, 4, 8, 32 N/s) or amplitudes (1, 2, 4 N). The hand ipsilateral to the lesion of the cerebellar subjects showed delayed and more variable response latencies, e.g., 278 ± 162 ms for loads delivered at 2 N/s, compared to HS 180 ± 53 ms (P = 0.005). The CL also used a higher pre-load grip force with the ipsilateral hand, 1.6 ± 0.8 N, than the HS, 1.3 ± 0.6 N (P = 0.017). In addition, the contralateral hand in subjects with unilateral cerebellar stroke showed a delayed onset of the grip response compared to HS. Cerebellar lesions thus impair the reactive grip control both in the ipsilateral and contralateral hand.     

Reflex tone in the tongue muscles

Summary The tonus of the tongue muscles was studied in animals. Experiments were performed on anesthetized cats. The tongue was stretched with weights ranging from 20 to 30 g. Reaction of the tongue to stretching was registered by a cathode ray oscillograph. It was established that the more the tongue is stretched, the greater its electric activity i. e. the more pronounced the proprioceptive reflex of stretching. Section of hypoglossal nerves destroys the tonus of the tongue muscles at rest, as well as proprioceptives reflexes to stretching.Presented by Active Member of the Academy of Medical Sciences, USSR, A. F. Tur     

Finger force perception during ipsilateral and contralateral force matching tasks

The aims of the present study were to compare matching performance between ipsilateral and contralateral finger force matching tasks and to examine the effect of handedness on finger force perception. Eleven subjects were instructed to produce reference forces by an instructed finger (index—I or little—L finger) and to reproduce the same amount force by the same or a different finger within the hand (i.e., ipsilateral matching task), or by a finger of the other hand (i.e., contralateral matching task). The results of the ipsilateral and contralateral tasks in the present study commonly showed that (1) the reference and matching forces were matched closely when the two forces were produced by the same or homologous finger(s) such as I/I task; (2) the weaker little finger underestimated the magnitude of reference force of the index finger (I/L task), even with the higher level of effort (relative force), but the two forces were matched when considering total finger forces; (3) the stronger index finger closely matched the reference force of the little finger with the lower level of relative force (i.e., L/I task); (4) when considering the constant errors, I/L tasks showed an underestimation and L/I tasks showed an overestimation compared to I/I tasks. There was no handedness effect during ipsilateral tasks. During the contralateral task, the dominant hand overestimated the force of the non-dominant hand, while the non-dominant hand attempted to match the absolute force of the dominant hand. The overall results support the notion that the absolute, rather than relative, finger force is perceived and reproduced during ipsilateral and contralateral finger force matching tasks, indicating the uniqueness of finger force perception.     

Median frequency estimates of paraspinal muscles: reliability analysis

The technique of monitoring the frequency shift of the electromyographic signal through a single parameter, the median frequency (MF), was investigated with regard to its reliability characteristics as tested on two back muscle groups: the multifidus and iliocostalis lumborum. The proportion of variance in the MF parameters accounted for by the test/retest reliability as well as by the left versus right side analysis is satisfactory for the multifidus, it is, however, consistently lower for the iliocostalis. For the purpose of measuring muscular function, the MF recording technique appears to be well suited for clinical research, its application in the assessment of muscular dysfunction of back muscles is nevertheless far from simple.     

Posture‐related stiffness mapping of paraspinal muscles

The paraspinal compartment acts as a bone–muscle composite beam of the spine. The elastic properties of the paraspinal muscles play a critical role in spine stabilization. These properties depend on the subjects’ posture, and they may be drastically altered by low back pain. Supersonic shear wave elastography can be used to provide quantitative stiffness maps (elastograms), which characterize the elastic properties of the probed tissue. The aim of this study was to challenge shear wave elastography sensitivity to postural stiffness changes in healthy paraspinal muscles. The stiffness of the main paraspinal muscles (longissimus, iliocostalis, multifidus) was measured by shear wave elastography at the lumbosacral level (L3 and S1) for six static postures performed by volunteers. Passive postures (rest, passive flexion, passive extension) were performed in a first shear wave elastography session, and active postures (upright, bending forward, bending backward) with rest posture for reference were performed in a second session. Measurements were repeated three times for each posture. Sixteen healthy young adults were enrolled in the study. Non‐parametric paired tests, multiple analyses of covariance, and intra‐class correlations were implemented for analysis. Shear wave elastography showed good to excellent reliability, except in the multifidus at S1, during bending forward, and in the multifidus at L3, during bending backward. Yet, during bending forward, only poor quality was recorded for nine volunteers in the longissimus. Significant intra‐ and inter‐muscular changes were observed with posture. Stiffness significantly increased for the upright position and bending forward with respect to the reference values recorded in passive postures. In conclusion, shear wave elastography allows reliable assessment of the stiffness of the paraspinal muscles except in the multifidus at S1 and longissimus, during bending forward, and in the multifidus at L3, during bending backward. It reveals a different biomechanical behaviour for the multifidus, the longissimus, and the iliocostalis.     

Guitarfish possess ipsilateral as well as contralateral retinofugal projections

Autoradiographic analysis of the primary retinal projections in the thornback guitarfish reveals both contralateral and ipsilateral projections to diencephalic, pretectal, and tegmental nuclei and the optic tectum. A total of 12 retino-recipient cell groups receive ipsilateral as well as contralateral inputs.     

Synaptic connexions of alpha extensor motoneurones with ipsilateral and contralateral cutaneous nerves

1. Synaptic responses of alpha extensor motoneurones to stimulation of cutaneous nerves of the hind limb were recorded from the lumbosacral region in decerebrate and decerebrate-spinal unanaesthetized cats. Responses to ipsi- and contralateral stimulation are compared.2. Usually a single volley in an ipsilateral cutaneous nerve led to an inhibitory post-synaptic potential while one in a contralateral cutaneous nerve led to an excitatory post-synaptic potential or to discharge of the cell, thus demonstrating the classical reciprocal innervation pattern. In some cells either ipsilateral or crossed spinal action was of opposite sign to normal.3. Tests using graded stimulation showed the range of myelinated afferents associated with crossed spinal actions to be narrower than that for ipsilateral actions; for the sural nerve the ranges are 1-6 mu and 1-9 mu respectively. A substantial proportion of the coarser myelinated afferents do not make connexion with alpha motoneurones on either side of the cord; in the sural nerve this proportion includes the range 10-17 mu.4. Central transmission times for ipsilateral and crossed-spinal actions were estimated after making systematic allowance for conduction time to the cord in the associated cutaneous afferents. Mean values for inhibitory pathways from ipsilateral cutaneous nerves were about 2 msec, while those for crossed spinal facilitatory pathways were notably greater, 3-5 msec.5. Crossed spinal actions were more profoundly depressed by anaesthesia than were corresponding ipsilateral actions.6. Interpretation of the results was aided by a separate study of the input to the spinal cord; stimulus strength is related to the diameters of the cutaneous fibres excited and to peripheral conduction time in those fibres.     

Reaching to ipsilateral or contralateral targets: within-hemisphere visuomotor processing cannot explain hemispatial differences in motor control

Aiming movements made to visual targets on the same side of the body as the reaching hand typically show advantages as compared to aiming movements made to targets on the opposite side of the body midline in the contralateral visual field. These advantages for ipsilateral reaches include shorter reaction time, higher peak velocity, shorter duration and greater endpoint accuracy. It is commonly hypothesized that such advantages are related to the efficiency of intrahemispheric processing, since, for example, a left-sided target would be initially processed in the visual cortex of the right hemisphere and that same hemisphere controls the motor output to the left hand. We tested this hypothesis by examining the kinematics of aiming movements made by 26 right-handed subjects to visual targets briefly presented in either the left or the right visual field. In one block of trials, the subjects aimed their finger directly towards the target; in the other block, subjects were required to aim their movement to the mirror symmetrical position on the opposite side of the fixation light from the target. For the three kinematic measures in which hemispatial differences were obtained (peak velocity, duration and percentage of movement time spent in deceleration), the advantages were related to the side to which the motor response was directed and not to the side where the target was presented. In addition, these effects tended to be larger in the right hand than in the left, particularly for the percentage of the movement time spent in deceleration. The results are interpreted in terms of models of biomechanical constraints on contralateral movements, which are independent of the hemispace of target presentation.     

Reflex response and control of the human soleus and gastrocnemius muscles during walking and running at increasing velocity

We measured the soleus and the gastrocnemius H-reflex modulation in seven subjects during walking at 4.5 km/h and during running at 8, 12 and 15 km/h. The recordings in the medial gastrocnemius were corrected for cross-talk from the soleus muscle. The gastrocnemius H-reflex was in general lower than the soleus H-reflex. In both muscles the H-reflex increased significantly from walking to running but also with increasing running speed. The peak of EMG activity increased in both muscles with increasing speed. The V-wave of both muscles was absent or rather low during walking, but it increased significantly from walking to running with increasing running speed in the soleus but not in the medial gastrocnemius. In both muscles the V-wave was highest just prior to heel strike. It is suggested that this was due to a high firing frequency of the motoneurones in this phase of the movement. It is concluded that a shift towards the faster gastrocnemius at higher running speeds on behalf of the soleus muscle did not occur. The fact that the physiological cross-sectional area of the soleus is much larger than that of the lumped gastrocnemii is most probably the reason why the soleus is important also at higher running velocities.     

Unilateral induced neocortical malformation and the formation of ipsilateral and contralateral barrel fields

Freezing lesions to the developing cortical plate of rodents results in a focal malformation resembling human 4-layered microgyria, and this malformation has been shown to result in local and widespread disruptions of neuronal architecture, connectivity, and physiology. Because we had previously demonstrated that microgyria caused disruptions in callosal connections, we hypothesized that freeze lesions to the postero-medial barrel sub-field (PMBSF) in one hemisphere would affect the organization of this barrel field contralaterally. We placed freeze lesions in the presumptive PMBSF of neonatal rats and, in adulthood, assessed the architecture of the ipsilateral and contralateral barrel fields. Malformations in the PMBSF resulted in a substantial decrease in the number of barrels as identified by cytochrome oxidase activity. More importantly, we found an increase in the total area of the contralateral PMBSF, although there was no difference in individual barrel cross-sectional areas, indicating an increase in the area of inter-barrel septae.This increase in the septal area of the contralateral PMBSF is consistent with changes in callosal and/or thalamic connectivity in the contralateral hemisphere. These results are another example of both local and widespread disruption of connectional architecture following induction of focal microgyria.     

Magnetic stimulation of the human brain: facilitation of motor responses by voluntary contraction of ipsilateral and contralateral muscles with additional observations on an amputee

An intense rapidly changing magnetic field generated in a coil over the scalp can excite motor pathways to hand muscles. With a suprathreshold stimulus, the amplitude of the muscle action potential of the abductor digiti minimi is increased: by weak contraction of the muscle itself, by weak contraction of the ipsilateral first dorsal interosseus, by stronger contraction of the contralateral abductor digiti minimi, but not by contraction of the contralateral first dorsal interosseus, nor by the ipsilateral quadriceps muscle. This facilitation of response to brain stimulation may occur by two mechanisms, one related to the focussing of attention onto a particular hand, the second involving a rise in excitability of homologous motor pathways.     

Reflex control of cerebral circulation

Summary The change of the volume velocity of the blood circulation was studied in the brain meninges during stimulation of intestinal interoceptors, which caused hypertension and increased the blood circulation of the brain. The thermoelectric method was employed. In stimulation of interoceptors with occluded carotid arteries there was a decrease in volume velocity of the blood circulation of the brain, instead of increase. When cuffs were placed on the area of carotid bifurcation the increase of the volume velocity was less marked than in the original reaction (before the application of the cuffs). It was concluded that the impulses from the baroreceptors of the sinocarotid zone during the pressor interoceptive reaction cause decrease of the tonus of the brain vessels and provide increased blood supply to the brain.Presented by Active Member of the Academy of Medical Sciences, USSR, V.N. Chernigovsky