Acoustic Clicks Activate both the Canal and Otolith Vestibulo-Ocular Reflex Pathways in Behaving Monkeys

Acoustic activation of the vestibular system has been well documented in humans and animal models. In the past decade, sound-evoked myogenic potentials in the sternocleidomastoid muscle (cVEMP) and the extraocular muscles (oVEMP) have been extensively studied, and their potentials as new tests for vestibular function have been widely recognized. However, the extent to which sound activates the otolith and canal pathways remains controversial. In the present study, we examined this issue in a recently developed nonhuman primate model of acoustic activation of the vestibular system, i.e., sound-evoked vestibulo-ocular reflexes (VOR) in behaving monkeys. To determine whether the canal and otolith VOR pathways are activated by sound, we analyzed abducens neurons' responses to clicks that were delivered into either ear. The main finding was that clicks evoked short-latency excitatory responses in abducens neurons on both sides. The latencies of the two responses, however, were different. The mean latency of the contralateral and ipsilateral abducens neurons was 2.44 ± 0.4 and 1.65 ± 0.28 ms, respectively. A further analysis of the excitatory latencies, in combination with the known canal and otolith VOR pathways, suggests that the excitatory responses of the contralateral abducens neurons were mediated by the contralateral disynaptic VOR pathways that connect the lateral canal to the contralateral abducens neurons, and the excitatory responses of the ipsilateral abducens neurons were mediated by the ipsilateral monosynaptic VOR pathways that connect the utricle to the ipsilateral abducens neurons. These results provide new insights into the understanding of the neural basis for sound-evoked vestibular responses, which is essential for developing new tests for both canal and otolith functions in humans

Malformação de Chiari tipo I: relato de dois casos com apresentações clínicas pouco usuais Type I Chiari malformation: report of two cases with unusual clinical presentation

Relatamos dois casos de malformação de Chiari do tipo 1, com apresentações clínicas pouco usuais. O primeiro caso refere-se a uma paciente de 17 anos, com quadro agudo de insuficiência respiratória e o segundo caso a uma paciente com síndrome vestibular associada a síndrome cerebelar leve e cefaléia. Em ambos os casos o exame neurológico demonstrou a presença de nistagmo do tipo "downbeating". Enfatizamos a valorização da semiologia neurológica, determinando a investigação complementar adequada e o tratamento efetivo.<br>We describe two patients with Chiari type I malformation with unusual clinical presentation. The first one with clinical picture of acute respiratory insuficiency and the second one with vestibular and mild cerebellar syndrome and headache. In both cases the neurological examination demonstrated the presence of "downbeating nystagmus". We emphasize the value of neurological semiology, determining a correct complementary evaluation and effective treatment