E. Pierrotdeseilligny, ASSESSING CHANGES IN PRESYNAPTIC INHIBITION OF IA AFFERENTS DURING MOVEMENT IN HUMANS, Journal of neuroscience methods, 74(2), 1997, pp. 189-199
Different methods, based on different principles, have been proposed t
o estimate changes in presynaptic inhibition of Ia terminals (accompan
ied by primary afferent depolarization, (PAD)) during voluntary contra
ction in humans. (i) A discrepancy between the H-reflex amplitude, at
an equal level of EMG activity, in two situations (e.g., walking and s
tanding) may be taken as suggesting a different control of PAD interne
urones in the two cases. (ii) A conditioning stimulation (vibration or
electrical stimulation) is used to activate PAD interneurones and to
evoke presynaptic inhibition of the afferent volley of the test reflex
. The resulting long-lasting depression of the reflex depends on the e
xcitability of PAD interneurones, but can be contaminated by long-last
ing post-synaptic effects. (iii) The amount of reflex facilitation evo
ked by a purely monosynaptic Ia volley varies inversely with the on-go
ing presynaptic inhibition of Ia afferents mediating the conditioning
volley, and can be used to assess this on-going presynaptic inhibition
. None of these methods can provide by itself unequivocal evidence for
a change in presynaptic inhibition of la terminals, but reasonably re
liable interpretations may be proposed when congruent results are obta
ined with different methods. Thus it has been shown that, during selec
tive voluntary contraction, presynaptic inhibition is decreased on Ia
afferents projecting on motoneurones of the contracting muscle and inc
reased on Ia afferents projecting on motor nuclei not involved in the
contraction. (C) 1997 Elsevier Science B.V.