Reflex responses of masseter muscles to sound

Acoustic stimuli can evoke reflex EMG responses (acoustic jaw reflex) in the masseter muscle. Although these were previously ascribed to activation of cochlear receptors, high intensity sound can also activate vestibular receptors. Since anatomical and physiological studies, both in animals and humans, have shown that masseter muscles are a target for vestibular inputs we have recently reassessed the vestibular contribution to masseter reflexes. We found that high intensity sound evokes two bilateral and symmetrical short-latency responses in active unrectified masseter EMG of healthy subjects: a high threshold, early p11/n15 wave and a lower threshold, later p16/n21 wave. Both of these reflexes are inhibitory but differ in their threshold, latency and appearance in the rectified EMG average. Experiments in healthy subjects and in patients with selective lesions showed that vestibular receptors were responsible for the p11/n15 wave (vestibulo-masseteric reflex) whereas cochlear receptors were responsible for the p16/n21 wave (acoustic masseteric reflex). The possible functional significance of the double vestibular control over masseter muscles is discussed

Melatonin inhibits rat medial vestibular nucleus neuron activity <i>in vitro</i>

The present study evaluated the effects of melatonin on the discharge rate of tonically active medial vestibular nucleus (MVN) neurons in an in vitro slice preparation of the rat dorsal brainstem. The results demonstrated that, when melatonin was applied to the slice for a period of 7–10 min, a decrease in MVN neuron firing rate was observed in 21/58 (36%) of the cells sampled. The inhibitory effects of melatonin were present in synaptic uncoupling condition and were mimicked by 2-iodomelatonin, a non-selective agonist with high affinity for melatonin membrane receptor subtypes (MT1, MT2, MT3). The MT2 receptor antagonists luzindole and 4-phenyl-2-propionamidotetraline and the MT3 receptor antagonist prazosin did not, however, antagonise the inhibitory effects of melatonin, indicating that melatonin may act on MVN neurons through an MT1 receptor-mediated mechanism

Il Sistema integrato di educazione e di istruzione 0-6 anni: una indagine sulle percezioni degli educatori e dei genitori

Obiettivo del presente studio è quello di proporre una riflessione teorica su quelli che il recente DL ha individuato come i principali attori la cui attività sinergica andrà a determinare il nuovo sistema educativo (famiglie, educatori, insegnanti e istituzioni); e di indagare le opinioni di famiglie, educatori, e insegnanti sull’esperienza del sistema educativo 0-6, attraverso l’analisi dei risultati di un questionario che è stato somministrato a un campione composto da rappresentanti di tutte queste categorie

Intracortical inhibitory and excitatory circuits of the human masseteric motor cortex

Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated in the masseter muscles of 12 subjects and the cortical silent period (SP) as well as long interval intracortical inhibition (LICI) in 9 subjects

Short interval paired pulse TMS during voluntary contraction: evidence of the balance between two antagonistic systems and importance of a low intensity conditioning stimulus

Muscle activation is usually reported to reduce the excitability of the inhibitory and facilitatory intracortical circuits tested in the SICI/ICF paradigm. The present work was to study these effects in more detail by examining how different levels of volitional contraction affect short interval intracortical inhibition (SICI) and short interval intracortical facilitation (SICF) evaluated with a range of stimulus intensities

Analisis del grado de motivacion de los alumnos de la Universidad de Talca

210 p.El problema continuo que enfrentan los profesores, es el por que alumnos se desempeñan mejor que otros. ¿Que es lo que motiva para que su desempeño sea mas eficiente?. Lo primordial de esta investigación ha sido analizar el grado de motivación en los alumnos de la Universidad de Talca. Esta investigación ha entregado ciertas diferencias con respecto al grado de motivación de los alumnos en las carreras de la Universidad de Talca. En la carrera de Ingeniería Comercial/Inf, obtuvo el menor grado de motivación con un 62,81% y el mayor grado de motivación lo obtuvo Ingeniería en Ejecución Mecánica con un 90,24%. En la evaluación general; el grado de motivación es del 79,8%, lo que indica que hay un alto grado de motivación hacia el estudio, sin embargo , esto se trata de un promedio, en donde se ha expuesto a evaluación ocho factores y cada uno de estos con sus respectivas variables. El análisis arroja factores que obtienen un bajo nivel de motivación; como es el factor satisfacción de necesidades de protección y seguridad, con excepción de la variable permanecer en la Universidad, y el factor satisfacción de necesidades de reconocimiento. En contraparte, el factor Profesor, en general obtiene un alto grado de motivación. Lo mismo sucede con el factor Infraestructura de la Universidad, con excepción de las variables espacios amplios, horarios de clases adecuados, salas con calefacción y disponibilidad de computadores. Con lo anteriormente expuesto se ha dejado en evidencia los puntos que deben ser revisados para obtener un mayor grado de motivación en los alumnos hacia el estudio, obteniéndose así mejores resultados en un futuro próximo

Patterns of Damage in Chronic Angle-Closure Glaucoma Compared to Primary Open-Angle Glaucoma

PURPOSE: To compare patterns of damage in chronic angle-closure glaucoma (CACG) to a control group of patients with primary open-angle glaucoma (POAG). DESIGN: Retrospective cross-sectional study. METHODS: SETTING: Academic tertiary-care glaucoma clinic. STUDY POPULATION: Thirty-two eyes of 32 patients with CACG and good-quality Heidelberg Retina Tomograph (HRT) images (pixel standard deviation =-15.0 dB) were enrolled. Control eyes with POAG meeting similar criteria and matched for severity of field loss ( 1 dB) and race were selected. OUTCOME MEASURES: Presence of focal rim loss (<= 1 clock hour), HRT stereometric parameters, and extent and location of field loss. RESULTS: The average mean deviation was -5.1 dB in both groups. Patients with CACG were more hyperopic (0.6 +/- 0.4 vs -1.4 +/- 0.5 D; P < .001) and had higher TOP at the time of imaging (15.8 +/- 0.8 vs 13.9 +/- 0.9 mm Hg; P = .015). Focal disc damage was not less frequent in PACG eyes (19% vs 24%; P = .545). Eyes with PACG had smaller cup area, cup volume, and mean cup depth and larger rim/disc area ratio (P < .05 for all), which persisted after adjusting for disc size, age, refractive error, and TOP. The average (+/- SD) number of abnormal test locations was similar in the 2 groups (P = .709), although CACG eyes were less likely to have paracentral points involved (47% vs 72%; P = .04). CONCLUSIONS: Patterns of glaucomatous damage seem to be different in CACG compared with POAG. This difference in patterns of damage may adversely affect detection of early disease or its progression in CACG. (Am J Ophthalmol 2011;152:74-80. (C) 2011 by Elsevier Inc. All rights reserved.

Measurement of Optic Disc Size and Rim Area with Spectral-Domain OCT and Scanning Laser Ophthalmoscopy

PURPOSE. To compare optic disc and neuroretinal rim area measurements from spectral-domain optical coherence tomography (SD-OCT) to those from confocal scanning laser ophthalmoscopy. METHODS. Seventy-one eyes from 43 normal subjects or suspected/definite glaucoma patients were prospectively enrolled. All subjects had biometry with the IOLMaster and disc/retinal nerve fiber layer imaging with Cirrus SD-OCT (Optic Disc Cube 200x200) and Heidelberg Retina Tomograph (HRT). Uncorrected disc and rim areas and measurements corrected for eye magnification with Bennett's formula (AL-corrected measurements), along with 308 sectoral rim areas, vertical cup-to-disc ratio (VCDR), and cup volume, were compared between the two devices. RESULTS. The median (range) axial length (AL) was 24.2 mm (22.4-27.7 mm). Mean keratometry-corrected HRT disc area measurements were larger than AL-corrected HRT and SD-OCT measurements (P 0.481). HRT rim area was larger than Cirrus measurements (P < 0.001) and the difference decreased with decreasing rim area. HRT VCDR and cup volume were significantly smaller than Cirrus measurements (P < 0.001). The correlations for sectoral rim areas between the two devices were moderate at best (intraclass correlation coefficients = 0.12-0.65). CONCLUSIONS. HRT overestimated optic disc area as compared to SD-OCT. A portion of the difference in HRT and SD-OCT disc measurements is due to HRT's magnification correction algorithm. Rim area measurements from HRT were larger than from SD-OCT, likely a result of different definitions for the reference plane and differences in disc area measurements. Disc parameters from the two devices are not interchangeable. (Invest Ophthalmol Vis Sci. 2012;53:4519-4530) DOI:10.1167/iovs.11-836

Modulation of masseter exteroceptive suppression by non-nociceptive upper limb afferent activation in humans

The effects induced by non-noxious electrical stimulation of upper limb nerves on exteroceptive suppression (ES) of masseter muscle EMG activity were studied in 15 healthy subjects. EMG activity of masseter muscles was recorded bilaterally and great care was taken to minimise the activation of afferents other than the stimulated ones. Masseter ES was elicited by applying a non-noxious electrical stimulus to the skin above the mental nerve (Mt) of one side, during a voluntary contraction of masseter muscles at a prescribed steady clenching level. Onset and offset latencies and duration of early and late components of masseter ES (ES1 and ES2, respectively) were evaluated in control conditions and compared to those obtained when a non-noxious electrical stimulation was delivered separately to Med or Rad or simultaneously to both nerves (Med-Rad) of one side. Upper limb nerve stimulation could be simultaneous or it could precede or follow Mt stimulation by various time intervals. In control conditions, ES1 latency onset and duration values (mean ± SD) were 11.3±2.9 ms and 16.9±2.1 ms, respectively, and ES2 latency onset and duration values were 44.5±6.0 ms and 28.6±11.1 ms, respectively. No significant differences were observed which were related to the side being recorded. Two types of effects, opposite in nature, were shown on masseter ES, depending on the time intervals between Mt and upper limb nerve stimulation. The first effect, which was facilitatory, consisted of a significant increase in ES1 and ES2 duration. A maximal increase in ES1 duration (134–155% compared to control value) occurred when upper limb nerve stimulation preceded that of Mt by 18–30 ms. Maximal ES2 lengthening (115–145%) was observed when upper limb nerve stimulation followed that of the Mt by 10 ms. The second effect was inhibitory and affected only ES2, which appeared completely eliminated when Med stimulation preceded that of Mt by 40–80 ms. By contrast, ES1 was never suppressed at any interstimulus interval. These data might reflect the different action of the central outflow, following the upper limb-induced effects, on the different neuronal circuits mediating ES1 and ES2

Intracortical modulation of cortical-bulbar responses for the masseter muscle

Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated in the masseter muscles of 12 subjects and the cortical silent period (SP) in nine subjects. Motor evoked potentials (MEPs) were recorded from contralateral (cMM) and ipsilateral (iMM) masseters, activated at 10% of maximal voluntary contraction (MVC). Interstimulus intervals (ISIs) were 2 and 3 ms for SICI, 10 and 15 ms for ICF. TMS of the left masseteric cortex induced MEPs that were larger in the cMM than the iMM; stimulation of right masseteric cortex produced a similar asymmetry in response amplitude. SICI was only observed using a CS intensity of 70% AMT and was equal in both cMM and iMM. SICI was stronger at higher TS intensities, was abolished by muscle activation greater than 10% MVC, and was unaffected by coil orientation changes. Control experiments confirmed that SICI was not contaminated by any inhibitory peripheral reflexes. However, ICF could not be obtained because it was masked by bilateral reflex depression of masseter EMG caused by auditory input from the coil discharge. The SP was bilateral and symmetric; its duration ranged from 35 to 70 ms depending on TS intensity and coil orientation. We conclude that SICI is present in the cortical representation of masseter muscles. The similarity of SICI in cMM and iMM suggests either that a single pool of inhibitory interneurons controls ipsi- and contralateral corticotrigeminal projections or that inhibition is directed to bilaterally projecting corticotrigeminal fibres. Finally, the corticotrigeminal projection seems to be weakly influenced by inhibitory interneurons mediating the cortical SP