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Anticipatory postural adjustments during walking
$5 die la sensitivity to movements (with the properties of passive la afferents serving as a standard of reference). When passive sensitivity to small stretches is low (as at short muscle length or during large concomitant movements) static action may paradoxically augment it, and when it is high (as at long mean muscle length) dynamic action may paradoxic ally reduce i t . These paradoxes largely arise from the extremely non-linear behaviour of passive spindles (i.e. spindles deprived of fusimotor drive), and fusimotor efferents in fact act to partly linearize spindle properties so as to maintain stretch sensitivity at relatively high (YD) or relatively low (Ys) levels. Since direct recordings from fusimotor "y-efferents during natural movement have not so far been achieved, their function remains a matter of controversy. Studies on different paradigms in different preparations have led to widely ranging views (see Hulliger, Reviews Physiol. Biochem. Pharmacol., 101, 1 110, 1984). These encompass the notion of a relatively strict a-y linkage (microneurography in man) as well as the concept of largely independent central control of skeletomotor and fusimotor neurones (cat locomotion), and they further include intermediate patterns of efferent control, such as ~-Ts coupling with scope for independent "fD adjustment, or c~-Tt) coupling with independent control of 7s activity. Experimental evidence to support the notion of 'fusimotor set' (entailing a task-specific and highly flexible) control of ~,s-and ";,D-activity will be discussed. This concept may provide the basis for a more general theory of fusimotor function and unify, by degrees, the widely diverging views prevailing at present.
S 3.03 SPINAL C O R D CIRCUITS IN MAN. R. Tanaka (Tokyo, Japan) Studies on the animal spinal cord have accumulated detailed information about spinal reflex circuitries, including their functional connection with various supraspinal centers, and have provided many interesting hypotheses on their roles in motor control. Experiments can be performed on the h u m a n spinal cord which can test the validity of these hypotheses in a more physiological condition; that is, usage of the intact, unanaesthetized CNS and natural purposeful movements such as occur in daily life. However, there are some disadvantages for the analysis of spinal circuits in man. No such radical procedures as surgical access to the spinal cord and nerves, intracellular recording techniques, etc, are possible. So far the most profitable technique for the present aim has be en the monosynaptic reflex testing established by Lloyd. This technique had been utilized successfully for analysis of central connections of spinal reflexes in animals until the intoduction of intracellular recording techniques. This method is realized in h u m a n experiments by usage of the H-reflex.
It is easy for h u m a n subjects to consistently repeat various motor task s of the extremities. The excitability of related motoneurons, and possibly interneurons, in the spinal reflex pathways, can be tested in the performance of such motor tasks. The present talk will particularly address 'reciprocal inhibition' in motor control, a most important concept in neurology, and discuss the neural mechanisms underlying this phenomenon.
S 3.04 ANTICIPATORY D U R I N G WALKING.
POSTURAL
ADJUSTMENTS
H. For~sberg (Stockholm, Sweden) The movement of a body segment to a new position during stance would displace the center of gravity unless it was associated with compensatory movements of other parts of the body. In addition to static changes of equilibrium, a moving body segment exerts dynamic forces against the body. There seems to be a general principle that all movements are preceded by postural contractions, i.e. respiration, reflexes and voluntarily induced movements. An arm pull that would induce a forward sway is counteracted by postural contractions on the dorsal aspect of the leg, which is organized in a fixed pattern starting in the ankle muscles and radiating proximally. An arm push is preceded by a wave of contractions on the ventral aspect of the leg. Similar patterns of postural contractio ns are elicited by external disturbances of the body, and it has been suggested that the same neural circuits are involved (Cordo and Nashner, J. Neurophysiol. 47:287 302, 1982). In a recent study the postural adjustments during treadmill walking have been investigated by letting subjects pull or push on a handle. A p u l l / p u s h on the handle during walking was preceded by anticipatory postural contractions superimposed on the ordinary locomotor contractions. In the support leg a wave of contract ions radiated proximally oil the ventral or dorsal side of the leg dependent on the direction of the arm movement. A quite different pattern of postural contractions was initiated in the swing leg. The activation of anticipatory postural adjustments prior to voluntary movements is thus maintained during walking. The postural adjustments in the support leg have the same pattern as the postural synergies elicited during fixed stance by external perturbations or voluntary movements. The postural synergies are organized in parallel with the locomotion generating circuits since the postural activity is added to the locomotor activity. They are, however, also phasically controlled by the locomotor circuits releasing different synergies in different phases of the step cycle.
S 3.03 SPINAL C O R D CIRCUITS IN MAN. R. Tanaka (Tokyo, Japan) Studies on the animal spinal cord have accumulated detailed information about spinal reflex circuitries, including their functional connection with various supraspinal centers, and have provided many interesting hypotheses on their roles in motor control. Experiments can be performed on the h u m a n spinal cord which can test the validity of these hypotheses in a more physiological condition; that is, usage of the intact, unanaesthetized CNS and natural purposeful movements such as occur in daily life. However, there are some disadvantages for the analysis of spinal circuits in man. No such radical procedures as surgical access to the spinal cord and nerves, intracellular recording techniques, etc, are possible. So far the most profitable technique for the present aim has be en the monosynaptic reflex testing established by Lloyd. This technique had been utilized successfully for analysis of central connections of spinal reflexes in animals until the intoduction of intracellular recording techniques. This method is realized in h u m a n experiments by usage of the H-reflex.
It is easy for h u m a n subjects to consistently repeat various motor task s of the extremities. The excitability of related motoneurons, and possibly interneurons, in the spinal reflex pathways, can be tested in the performance of such motor tasks. The present talk will particularly address 'reciprocal inhibition' in motor control, a most important concept in neurology, and discuss the neural mechanisms underlying this phenomenon.
S 3.04 ANTICIPATORY D U R I N G WALKING.
POSTURAL
ADJUSTMENTS
H. For~sberg (Stockholm, Sweden) The movement of a body segment to a new position during stance would displace the center of gravity unless it was associated with compensatory movements of other parts of the body. In addition to static changes of equilibrium, a moving body segment exerts dynamic forces against the body. There seems to be a general principle that all movements are preceded by postural contractions, i.e. respiration, reflexes and voluntarily induced movements. An arm pull that would induce a forward sway is counteracted by postural contractions on the dorsal aspect of the leg, which is organized in a fixed pattern starting in the ankle muscles and radiating proximally. An arm push is preceded by a wave of contractions on the ventral aspect of the leg. Similar patterns of postural contractio ns are elicited by external disturbances of the body, and it has been suggested that the same neural circuits are involved (Cordo and Nashner, J. Neurophysiol. 47:287 302, 1982). In a recent study the postural adjustments during treadmill walking have been investigated by letting subjects pull or push on a handle. A p u l l / p u s h on the handle during walking was preceded by anticipatory postural contractions superimposed on the ordinary locomotor contractions. In the support leg a wave of contract ions radiated proximally oil the ventral or dorsal side of the leg dependent on the direction of the arm movement. A quite different pattern of postural contractions was initiated in the swing leg. The activation of anticipatory postural adjustments prior to voluntary movements is thus maintained during walking. The postural adjustments in the support leg have the same pattern as the postural synergies elicited during fixed stance by external perturbations or voluntary movements. The postural synergies are organized in parallel with the locomotion generating circuits since the postural activity is added to the locomotor activity. They are, however, also phasically controlled by the locomotor circuits releasing different synergies in different phases of the step cycle.