Biomedical subjects

C M Bastiaanse

Publications and source records attributed to C M Bastiaanse.

6 recordsLinked to original sources

PubMed2006

Suppression of cutaneous reflexes by a conditioning pulse during human walking.

There are two ways in which responses to successive unexpected stimuli are attenuated, namely through habituation and conditioning. For the latter, it suffices that the unexpected stimulus is preceded by another just perceivable stimulus. In spinal cord reflexes this is termed conditioning, while in brainstem reflexes this is usually referred to as prepulse inhibition. Cutaneous reflexes in Tibialis Anterior (TA) are particularly strong during gait and they are thought to involve a transcortical loop. Can these reflexes be suppressed by giving a brief pulse prior to a reflex-evoking pulse given to the same nerve? To examine this question, electromyographic signals were recorded in healthy humans during walking. Sural nerve stimulation (train of five pulses (1 ms duration)) at 200 Hz were applied at two times perception threshold during different phases of the step cycle. The preceding pulse (single pulse of 1 ms at same intensity) was applied to the same nerve 150 ms before the reflex-evoking pulse train. Conditioning stimulation with a single pulse lowered significantly the following reflex response in the ipsilateral TA but much less in other muscles such as biceps femoris. The preceding pulse did not disturb the phase-dependent modulation or the typical reflex reversal. The finding that TA is selectively involved indicates that the suppressing mechanism may involve the motor cortex, which is known to be involved in the control of TA. The conditioning pulse did not cause a reduction in background activity. Therefore, the suppression of the reflex responses points to a premotoneuronal source such as presynaptic inhibition.

Adult↗

PubMed2005

Cutaneous reflexes evoked during human walking are reduced when self-induced.

Reflex responses are often less pronounced when they are self-induced, but this question has barely been investigated quantitatively. The issue is particularly relevant for locomotion since it has been shown that reflexes elicited during normal gait are important for the regulation of locomotion. The cortex is thought to be involved in the control of reflexes during gait, but it is unclear whether it plays a role in the modulation of these reflexes during the step cycle. During gait, weak electrical stimulation of the sural nerve elicits reflexes in various leg muscles. Are these reflexes different when subjects themselves trigger the stimuli instead of being randomly released by the computer? Cutaneous reflexes were elicited by sural nerve stimulation in 16 phases of the gait cycle in healthy subjects. The stimuli were triggered either by computer or by the subjects themselves. In 6 out of 7 subjects it was observed that the facilitatory responses in leg muscles were smaller and the suppressive responses were more suppressive following self-generated stimuli. In some muscles such as tibialis anterior (TA) both effects were seen (reduced facilitation at end stance and exaggerated suppression at end swing). In all subjects the modulation of anticipatory influences was muscle specific. In the main group of six subjects, the mean reduction in reflex responses was strongest in the TA (max. 30.7%; mean over 16 phases was 12.5%) and weakest in peroneus longus (PL, max. 10.1%; mean over 16 phases was 2.6%). The observation that facilitation is reduced and suppression enhanced in several muscles is taken as evidence that anticipation of self-induced reflex responses reduces the excitatory drive to motoneurones, for example through presynaptic inhibition of facilitatory reflex pathways.

Adult↗

PubMed2001

Reflex adaptations during treadmill walking with increased body load.

Load dependent reflex adaptations were studied in healthy subjects walking on a split-belt treadmill. Compensatory reflex responses were elicited in the right leg extensor muscles during mid-stance by a short acceleration of the right treadmill belt. Electromyographic activity (EMG) was recorded from the right medial gastrocnemius (GMR), soleus (SO) and tibialis anterior (TA) muscles of the right leg as well as from the gastrocnemius of the left unperturbed leg (GML). To study the adaptational reflex behavior, multiple measurements were taken during walking with normal (control) and increased body load and after removing the load. In most experiments the compensatory EMG response in the GMR consisted of a short inhibitory and a subsequent excitatory component. Both reflex components were larger when the body was loaded. During the course of continuous loading, divergent reflex adaptations of different degrees and directions were observed in the subjects. In one group of subjects the reflex response increased to a higher level of EMG activity. In a second group EMG activity first increased and afterwards decreased to baseline level. A subsequent removal of body loading resulted in a slow adaptation to the control reflex values in both groups. Neither the EMG activity in the GM nor the reflex responses in the GMR after increasing the load changed differently in the two groups. Our results suggest that load information is not simply used in a fixed input/output relationship of the actual biomechanical conditions of a subject. Load information is rather used to slowly modify the reflex response, to achieve the desired posture during walking.

Adaptation, Physiological↗

PubMed2001

Neuronal coordination of arm and leg movements during human locomotion.

We aimed to study the neuronal coordination of lower and upper limb muscles. We therefore evaluated the effect of small leg displacements during gait on leg and arm muscle electromyographic (EMG) activity in walking humans. During walking on a split-belt treadmill (velocity 3.5 km/h), short accelerations or decelerations were randomly applied to the right belt during the mid or end stance phase. Alternatively, trains of electrical stimuli were delivered to the right distal tibial nerve. The EMG activity of the tibialis anterior (TA), gastrocnemius medialis (GM), deltoideus (Delt), triceps (Tric) and biceps brachii (Bic) of both sides was analysed. For comparison, impulses were also applied during standing and sitting. The displacements were followed by specific patterns of right leg and bilateral arm muscle EMG responses. Most arm muscle responses appeared with a short latency (65-80 ms) and were larger in Delt and Tric than in Bic. They were strongest when deceleration impulses were released during mid stance, associated with a right compensatory TA response. A similar response pattern in arm muscles was obtained following tibial nerve stimulation. The arm muscle responses were small or absent when stimuli were applied during standing or sitting. The arm muscle responses correlated more closely with the compensatory TA than with the compensatory GM responses. The amplitude of the responses in most arm muscles correlated closely with the background EMG activity of the respective arm muscle. The observations suggest the existence of a task-dependent, flexible neuronal coupling between lower and upper limb muscles. The stronger impact of leg flexors in this interlimb coordination indicates that the neuronal control of leg flexor and extensor muscles is differentially interconnected during locomotion. The results are compatible with the assumption that the proximal arm muscle responses are associated with the swinging of the arms during gait, as a residual function of quadrupedal locomotion.

Adult↗

PubMed2000

Modulation of cutaneous reflexes by load receptor input during human walking.

To investigate the influence of load on the modulation of cutaneous reflexes, evoked by sural nerve stimulation, electromyographic activity in different leg muscles (tibialis anterior, gastrocnemius medialis (GM), biceps femoris, and soleus muscles (SO)) was recorded in healthy humans during treadmill walking with different body loads. Sural nerve stimulation was applied at two times perception threshold during different phases of the step cycle. Reflex amplitudes increased with body unloading and decreased with body loading. The reflex responses were not a simple function of the level of background activity. For example, in GM and SO, the largest reflex responses occurred during walking with body unloading, when background activity was decreased. Hence, stable ground conditions (body loading) yielded smaller reflexes. It is proposed that load receptors are involved in the regulation of cutaneous reflex responses in order to adapt the locomotor pattern to the environmental conditions.

Adult↗

PubMedDate not supplied

Gait acts as a gate for reflexes from the foot.

During human gait, electrical stimulation of the foot elicits facilitatory P2 (medium latency) responses in TA (tibialis anterior) at the onset of the swing phase, while the same stimuli cause suppressive responses at the end of swing phase, along with facilitatory responses in antagonists. This phenomenon is called phase-dependent reflex reversal. The suppressive responses can be evoked from a variety of skin sites in the leg and from stimulation of some muscles such as rectus femoris (RF). This paper reviews the data on reflex reversal and adds new data on this topic, using a split-belt paradigm. So far, the reflex reversal in TA could only be studied for the onset and end phases of the step cycle, simply because suppression can only be demonstrated when there is background activity. Normally there are only 2 TA bursts in the step cycle, whereas TA is normally silent during most of the stance phase. To know what happens in the stance phase, one needs to have a means to evoke some background activity during the stance phase. For this purpose, new experiments were carried out in which subjects were asked to walk on a treadmill with a split-belt. When the subject was walking with unequal leg speeds, the walking pattern was adapted to a gait pattern resembling limping. The TA then remained active throughout most of the stance phase of the slow-moving leg, which was used as the primary support. This activity was a result of coactivation of agonistic and antagonistic leg muscles in the supporting leg, and represented one of the ways to stabilize the body. Electrical stimulation was given to a cutaneous nerve (sural) at the ankle at twice the perception threshold. Nine of the 12 subjects showed increased TA activity during stance phase while walking on split-belts, and 5 of them showed pronounced suppressions during the first part of stance when stimuli were given on the slow side. It was concluded that a TA suppressive pathway remains open throughout most of the stance phase in the majority of subjects. The suggestion was made that the TA suppression increases loading of the ankle plantar flexors during the loading phase of stance.

Electric Stimulation↗