1,721,130 research outputs found
Human Walking along a Curved Path. II. Gait Features and EMG Patterns.
No full textWe recorded basic gait features and associated patterns of leg muscle activity, occurring during continuous body progression when humans walked along a curved trajectory, in order to gain insight into the nervous mechanisms underlying the control of the asymmetric movements of the two legs. The same rhythm was propagated to both legs, in spite of inner and outer strides diverging in length (P < 0.001). There was a phase lag in limb displacement between the inner and outer leg of 7% of the total cycle duration (P = 0.0001). Swing velocity was greater for outer than inner foot (P < 0.001). The duration of the stance phase diminished and increased in the outer and inner leg (P < 0.01), respectively, and was associated with trunk leaning toward the inside of the path. Muscle activity was not dramatically altered during curved walking. The amplitude of soleus burst during stance increased in the outer (P < 0.05) and decreased in the inner leg (P < 0.05), without changes in timing. Tibialis anterior activity increased in both legs during the swing phase (P < 0.05); it was advanced on the outer and delayed on the inner side (P < 0.01; 2% of the cycle). The peroneus longus burst decreased in both legs, but more in the inner than the outer leg, and lasted longer in the inner leg at the onset of swing. Closing the eyes did not affect the gait pattern and muscle activity during turning. The command to walk along a curved path may exploit the basic mechanisms of the spinal locomotor generator, thereby limiting the computational cost of turning
Tuning of a basic coordination pattern constructs straight-ahead and curved walking in humans.
No full textWe tested the hypothesis that common principles govern the production of the locomotor patterns for both straight-ahead and curved walking. Whole body movement recordings showed that continuous curved walking implies substantial, limb-specific changes in numerous gait descriptors. Principal component analysis (PCA) was used to uncover the spatiotemporal structure of coordination among lower limb segments. PCA revealed that the same kinematic law accounted for the coordination among lower limb segments during both straight-ahead and curved walking, in both the frontal and sagittal planes: turn-related changes in the complex behavior of the inner and outer limbs were captured in limb-specific adaptive tuning of coordination patterns. PCA was also performed on a data set including all elevation angles of limb segments and trunk, thus encompassing 13 degrees of freedom. The results showed that both straight-ahead and curved walking were low dimensional, given that 3 principal components accounted for more than 90% of data variance. Furthermore, the time course of the principal components was unchanged by curved walking, thereby indicating invariant coordination patterns among all body segments during straight-ahead and curved walking. Nevertheless, limb- and turn-dependent tuning of the coordination patterns encoded the adaptations of the limb kinematics to the actual direction of the walking body. Absence of vision had no significant effect on the intersegmental coordination during either straight-ahead or curved walking. Our findings indicate that kinematic laws, probably emerging from the interaction of spinal neural networks and mechanical oscillators, subserve the production of both straight-ahead and curved walking. During locomotion, the descending command tunes basic spinal networks so as to produce the changes in amplitude and phase relationships of the spinal output, sufficient to achieve the body turn
Effects of stimulus intensity, cervical cord tractotomies and cerebellectomy on somatosensory evoked potentials from skin and muscle afferents of cat hindlimb.
No full textThe somatosensory evoked potentials (SEPs) recorded from the sensory cortex were investigated by using graded stimulation of skin and muscle nerves from contralateral hind limb in the cat. Sections were made of the middle cervical cord to assess the pathways involved in mediating SEPs evoked by large and small diameter fibers. Dorsal column (DC) section caused a decrease of SEPs from skin group I afferents, and a small increase in those from group I muscle afferents. A subsequent section of dorso-lateral fasciculus (DLF) further decreased SEPs from skin and eliminated SEPs from muscle, evoked at low stimulus intensity. When the stimulus recruited group III fibres, SEPs were still present after DC and DLF section, both from skin and muscle nerves. Section of ALT in addition to DC confirmed a major role played by DLF (mainly spino-cervical tract of Morin) in transmitting impulses from muscle afferents; the role of DLF in mediating potentials evoked from skin is less remarkable than that of DC. Cerebellectomy did not change any SEP, however evoked. Previous results in the literature are discussed, taking into account the methodologies employed by various authors, and the possible interactions among pathways mediating SEPs
Influences of locus coeruleus, raphe dorsalis, and periaqueductal gray matter on somatosensory recipient thalamic nuclei.
No full textSpontaneous and evoked discharge of neurons in the nucleus ventralis posterolateralis (VPL) and spontaneous discharge of neurons in the posterior group and nucleus lateralis posterior (LP) were conditioned by brief trains of stimuli to the locus ceruleus (LC), raphe dorsalis (RD), and periaqueductal gray matter (PAG) in cats anesthetized with pentobarbital or ketamine. Stimulation of LC and RD was without effect on VPL neurons, but induced a long-latency, long-lasting inhibition of LP neurons. Stimulation of the PAG induced marked inhibition of the firing of neurons in all three thalamic nuclei. No differences were found between cats anesthetized with ketamine or pentobarbital
Task-dependent effects from foot muscle afferents onto leg muscles in humans. Electroenceph. clin. Neurophysiol. 101: 339-348.
No full textQuiet stance control is affected by prior treadmill but not overground locomotion
No full textTreadmill locomotion is different with respect
to overground walking and may require an adapted control
mode. The relevant neural computational eVort may produce
lasting eVects encroaching upon the performance of a
subsequent postural task. The hypothesis of the present
study was that, contrary to overground walking, treadmill
walking has eVects on quiet stance variables, in the assumption
that the imposed locomotor activity is more critical to
stance control than natural walking. Nine young subjects
performed three diVerent walking sessions: treadmill with
eyes closed, treadmill with eyes open, overground walking
with eyes open. Body sway area and sway path and the
position of the centre of foot pressure during stance were
recorded by a dynamometric platform under control, postwalking
and post-recovery conditions, alternatively with
eyes closed and eyes open. At variance with overground
walking, treadmill locomotion produced an eVect on body
orientation in space during the subsequent stance trials.
This consisted in a forward inclination of the body, not
accompanied by increased body sway, lasting for a few
minutes. Presence or absence of vision during treadmill
locomotion did not induce diVerences in the amplitude or
time-course of the post-eVect. We argue that body inclination
would be the consequence of a change in the postural
reference produced by a message arising from treadmill
locomotion itself, possibly connected to particularities in
the control mode of this type of walking
Spinal pathways mediating SEPs from cutaneous and muscle nerves in the cat.
No full texthe Authors give evidence on the function of a pathway mediating somatosensory evoked potentials (SEPs) from muscle nerves, other than the dorsal columns: physiological and anatomical data prove its location to be in the spinothalamic tract. Previous contrasting results on the topic are discussed
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