Testing for pre-synaptic and post-synaptic changes in the soleus H reflex pathway following selective muscle vibration in humans.

Muscle vibration does not affect post-synaptic excitability of the corresponding motoneuronal pool, the concurrent depression of the monosynaptic reflex resulting from a pre-motoneuronal block of Ia spindle afferents. Indeed (1) both homonymous and heteronymous soleus responses (to electrical stimulation of the posterior tibial nerve (TN) and femoral nerve (FN), respectively) are clearly depressed during selective vibration of the homologous muscle (namely soleus (S) or quadriceps (Q)), but remain completely unchanged during vibration of the heterologous muscle (i.e. Q or S); (2) the effectiveness of facilitatory conditioning of FN and TN Ia afferents, respectively on the S motoneuronal pool is definitely reduced during vibration of the homologous muscle (namely Q and S).

[Study of click-induced vestibule-sternocleidomastoid reflex recorded with surface electromyography]. / Studio del riflesso vestibolo-sternocleidomastoideo indotto da clicks e registrato tramite elettromiografia di superficie.

The otolithic organs serve to control posture and maintain the visual objective during linear accelerations. Recent experimental research in man and animals has suggested that it may be possible to explore the function of these organs by studying the vestibule-sternocleidomastoid reflex induced by high intensity clicks. The aim of the present work was to identify the parameters which are most reproducible in normal subjects and, therefore, best suited to this purpose. The instrument normally used to study evoked auditory potentials (ERA) was used to perform an electromyographic recording at the surface of the sternocleidomastoid muscle (SCM) and then average the electromyographic response to short clicks (0.1 ms) introduced through the headphones. In normal subjects clicks at an intensity of 85-100 dB HL evoked a reproducible electromyographic response in the venter of the SCM muscle with an average latency of 8.75 ms. The latency parameter proved to present the most suitable characteristics for possible clinical use. The possibility of using this method to study human vestibular lesions is certainly enticing although further research is needed to better characterize the precise site of origin for the vestibule-sternocleidomastoid reflex.

Ocular myasthenia mimicking a one-and-a-half syndrome.

A 52-year-old patient developed an eye movement disorder first resembling a left internuclear ophthalmoplegia and subsequently a "one-and-a-half syndrome" as the presenting symptoms of ocular myasthenia gravis. No accompanying myasthenic features were present except for the fluctuation in the amplitude of dissociated nystagmus. This patient shows that an oculomotor disorder considered a typical pontine lesion may instead be caused by myasthenia gravis, even in the absence of other clinical and electrophysiologic features of neuromuscular deficit.