Evans, Pamela; (2001) Crossed reflexes of the human lower limbs: A study using the Hoffman Reflex. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

Knowledge of the mechanisms involved in the modulation of activity in spinal pathways has increased considerably in recent years. The way in which spinal afferent activity interacts with pattern generator networks and descending control is of particular interest. During locomotion the activity of the two lower limbs is coordinated and it would be anticipated that proprioceptive afferents from one limb might contribute to coordination of the two limbs. The purpose of the present study was to examine possible communication between the limbs. Connections between afferents in the peripheral nerves of one lower limb and the motoneurones of muscles in the opposing limb were investigated. Conditioning electrical stimuli were applied to peripheral nerves in humans at rest and changes in the H- reflexes of muscles in the contralateral limb were monitored. Four pathways have been examined, including pathways between afferents of the tibial nerve and the femoral nerve and the contralateral motoneurone pools of soleus and quadriceps. Crossed inhibitory connections have been identified in three of the four pathways and in two of these the earliest component of the inhibition has been shown to be mediated by group I afferents. A late crossed facilitation has been demonstrated, which could be explained by activity in group II afferents. In relation to the use of the H-reflex as a tool for inferring synaptic inputs to motoneurones, a study was made of the variability of the soleus H-reflex. A decrease in variability with increasing size was identified. The underlying mechanisms which may contribute to the variability changes were examined. A further comparative study was made of the behaviour of the H-reflex of gastrocnemius.

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