G. Schalow et Ga. Zach, EXTERNAL LOOPS OF HUMAN PREMOTOR SPINAL OSCILLATORS IDENTIFIED BY SIMULTANEOUS MEASUREMENTS OF INTERSPIKE INTERVALS AND PHASE-RELATIONS, General physiology and biophysics, 15, 1996, pp. 95-119
Single nerve-fibre action potentials (APs) were recorded extracellular
ly from alpha and gamma-motoneurons and secondary muscle spindle affer
ents from a ventral S4 nerve root (some afferents are contained in low
er sacral motor roots) in an individual with traumatic spinal cord les
ion sub TH1. Simultaneous interspike intervals (IIs) of, and phases be
tween, the APs of 5 nerve fibres were measured, and distributions were
constructed. The II distributions were of a broad peak type. Phase di
stributions showed 1 to 3 peaks interpreted as phase relations between
the firings of the nerve fibres. Under certain phase relations, the r
hythmic firing of alpha and gamma-motoneurons is further interpreted a
s an interaction of oscillatory firing neuronal subnetworks driving al
pha and gamma-motoneurons. Following repetitive touch and pin-prick st
imulation in- and outside the anal reflex area, the II distributions o
f alpha and gamma-motoneurons and of secondary spindle afferents assim
ilated partly or fully, while preserving their phase relations. This c
oordinated firing is interpreted as the oscillatory firing of alpha ne
uronal networks building up an external loop to the periphery via the
gamma-loop. Upon touch, pin-prick, and anal reflex stimulation, and an
al and bladder catheter pulling, the values and the number of the phas
e relations changed. Mostly two phase relations per oscillation cycle
were observed. Two phase relations probably represent the physiologic
case for the somatic nervous system. Only one phase relation was found
when full synchronization of all units occurred. Three phase relation
s were found when the parasympathetic nervous system division interact
ed with the somatic one. Based on data obtained from brain-dead indivi
duals it is discussed that the increased synchronization and instabili
ty in the number and the values of phase relations suggested pathologi
c functioning of the caudal functionally disconnected spinal cord in p
atients with spinal cord lesions: Oscillatory firing neuronal networks
, which lost their specific properties, interacted more easily and uns
pecifically with other oscillatory firing networks. Further, it is dis
cussed that physiologic tremor is caused by chance synchronization of
oscillatory firing neuronal networks and therefore originates in the c
entral nervous system (CNS). Since spinal oscillators build up externa
l loops to the periphery, it is suggested that in patients with incomp
lete spinal cord lesions it should be possible to re-preformate oscill
atory firing neuronal networks by a rhythm training, to reduce spastic
ity and to re-train useful movements, especially locomotion.