Effects of the stimulus phase on the air-conducted ocular vestibular evoked myogenic potential in healthy subjects.

OBJECTIVE: The study aimed to examine the effect of the stimulus phase of air-conducted sound on ocular vestibular evoked myogenic potentials (oVEMPs). METHODS: oVEMPs were recorded after air-conducted sounds (500Hz, 4ms duration), presented with initial condensation (positive), rarefaction (negative), and alternant polarities from 12 healthy subjects. RESULTS: Most responses showed a bifid n10 peak separated by ∼1.9ms. The most prominent sub-peak after condensation was shorter than the most prominent sub-peak after rarefaction; however, the first sub-peak was shorter after the rarefaction stimuli. When a third sub-peak appeared, it occurred before the most prominent sub-peak after condensation and after the most prominent sub-peak after rarefaction. The latency difference between this third sub-peak and the closest sub-peak was shorter than the difference among the others sub-peaks, in both cases; the oVEMPs after alternating stimuli was an amalgam of the responses to the different stimuli. CONCLUSIONS: The findings suggest that the negative to positive change of the stimulus was the main event responsible for the stimulation, and that when a third sub-peak appeared it was related to the initiation or the end of the stimulus. SIGNIFICANCE: These findings suggested that the oVEMP response, obtained by air conducted sound, was secondary to stimulation of the same type of afferent vestibular unit, independent of the stimulus polarity.

Expression of praxis induction on cortical excitability in juvenile myoclonic epilepsy.

OBJECTIVE: This study aimed to evaluate the effects of praxis induction on sensorimotor cortical and transcallosal excitability in juvenile myoclonic epilepsy (JME). METHODS: A total of 36 subjects (18-62years) were included. The JME group was screened by video-electroencephalography neuropsychological protocol and divided into JME without praxis induction [JME-WI (n=12)], JME with praxis-induced seizures or epileptiform discharges [JME-PI (n=10)], and healthy controls (n=14). Motor and somatosensory cortical excitability and transcallosal pathways were evaluated through single-pulse transcranial magnetic stimulation (sTMS) and somatosensory evoked potentials (SEPs). RESULTS: Motor and transcallosal excitabilities tested with sTMS were not different in the motor-dominant or non-dominant hemisphere among groups. Significant differences were found in cortical SEP amplitudes in the P27 component of the non-dominant hemisphere (p=0.03, Cohen's d=0.98), N35 in the dominant hemisphere (p=0.04, Cohen's d=0.96), and P27-35 interpeak amplitude in both somatosensory cortices of the JME-PI group (p=0.03, Cohen's d=0.96; p=0.02, Cohen's d=1.05) when compared with healthy controls. Giant SEPs were observed in two (16.7%) and five (50%) patients of the JME-WI and JME-PI groups, respectively. Cortical latencies did not reveal differences. CONCLUSIONS: Praxis induction was associated with enhanced excitability in the somatosensory cortex of JME patients. SIGNIFICANCE: These findings may help clarifying the less favorable therapeutic response in the JME-PI group and indicate identifying praxis induction as an important determinant in differentiating between JME patients.

Electrophysiological evaluation of the pudendal nerve and urethral innervation in female stress urinary incontinence.

INTRODUCTION AND HYPOTHESIS: Although still a matter of debate, stress urinary incontinence (SUI) may be accompanied by damage to urethral and pelvic floor innervations, thus promoting dysfunctions of the urethral support and sphincteric closure mechanisms. The aim of this study was to analyze the pelvic floor and urethral innervations through pelvic electrophysiological tests to identify whether neurological alterations interfere with urinary continence and urethral functional activity. METHODS: This prospective study included 52 women, 33 with clinically and urodynamically proven SUI and 19 continent volunteers matched for age, height, parity, and number of vaginal deliveries by the propensity score method. The patients were divided according to the severity of urinary loss evaluated by measuring abdominal leak point pressure (ALPP). Pudendal nerve terminal motor latency (PNTML), pudendal somatosensory evoked potential (SSEP) latencies, urethral and clitoral sensory thresholds, and urethroanal reflex latency were tested. RESULTS: SUI and control subjects did not differ in PNTML, SSEP latency, and clitoral sensory thresholds. However, reduced responsiveness to urethral electrosensitivity and prolonged urethroanal reflex latency were detected in most incontinent patients. In addition, urethral electrosensitivity was altered in suspected intrinsic sphincteric dysfunction. CONCLUSIONS: Urethral afferent pathways can be altered in women with SUI and may play an important role in evoking intrinsic sphincteric dysfunction.

Agrupamento de sensações somatossensoriais com estimulação de corrente senoidal / Clustering of somatosensory sensations during sinusoidal current stimulation

Fibras finas (FF) aferentes primárias mediam a percepção de sensações relacionadas à dor e à temperatura, e as fibras grossas (FG) ao tato. O objetivo deste trabalho é avaliar percepções relacionadas às FF (picada, pontada, agulhada, queimação) e às FG (aperto, pressão, vibração e movimento)evocadas por estimulação elétrica senoidal com 5 Hz e 2 kHz, respectivamente. O dedo indicador da mão esquerda de 150 voluntários, sem doença neurológica conhecida e medicação, foram estimulados nessas frequências com intensidades decorrente igual ao limiar de sensibilidade (LS) e 1,5 vezes LS.O voluntário escolheu das 8 palavras, 3 que mais se aproximavam à sua percepção do estímulo. Outro grupo de 60 voluntários foi utilizado como controle, sendo que as 3 palavras foram escolhidas sem nenhuma estimulação. O valor de “1” foi atribuído à palavra escolhida, e “0” à não selecionada. As sensações foram agrupadas utilizando-se o vizinho mais próximo (single linkage) e a correlação entre variáveis binárias(tetrachloric correlation). Os resultados indicam uma tendência a sensações de fibras grossas sem estimulação, sendo que 5 Hz evoca principalmente as sensações de fibras finas e 2 kHz as de fibras grossas. A exceção foi a sensação de FF queimação, a qual se mostrou inconsistente em ambos os grupos.

Thin fibers mediate the perception related to temperature and painful sensations, and thick fibers the perception related to touch. This work tries to evaluate the perceptions related to thin (prick, pang, twinge and burning) and thick fibers (squeeze, pressure, movement and vibration) evoked by sinusoidal stimulation with 5 Hz and2 kHz, respectively. The left index fingers of 150 volunteers, without known neurological problems or under medication, were stimulatedat these frequencies and at current intensities equal to the sensory threshold and 1.5 times the sensory threshold. The volunteers chose three words out of eight that better represented the sensation felt during the stimulus. Another group of 60 volunteers was used as control, for which the three words were chosen with no stimulation. The value “1” was attributed to each sensation chosen and “0” forthe others. The sensations were clustered using the single linkage nearest neighbor method and the tetrachloric correlation between binary variables. The results showed a tendency to thick fiber sensations with 2 kHz or no stimulation, while 5 Hz evoked thin fiber sensations. The exception was the FF sensation of burning, which did not fit into any group.

Perceptions and electric senoidal current stimulation.

OBJECTIVE: To analyze the relationship between perceptions and electrical senoidal current stimulation (ESCS). METHOD: The study population comprise 100 healthy volunteers. ESCS of 5 Hz and 2 kHz were applied to the left index finger at one and 1.5 sensory threshold. Following each stimulus train a list of eight words (four related to thin fiber sensations and four related to thick fiber sensations) was presented to the subjects who were asked to choose the three words closer to the experienced sensation. Each chosen word was given a score 1; final results were obtained by the sum of the scores for the words related to thin and thick fiber systems for each situation. RESULTS: For 5 Hz ESCS at one and 1.5 sensory threshold thin fibers had significantly higher scores than thick fibers; for 2 kHz ESCS, thick fibers had significantly higher scores. CONCLUSION: These results show that there is a relation between different sensations and ESCS of different frequencies.

Perceptions and electric senoidal current stimulation

OBJETIVO: Estudar a relação entre as sensações evocadas por estimulação elétrica por corrente senoidal (ESCS). MÉTODO: 100 voluntários normais foram estudados. ESCS a 5 Hz e 2 kHz foram aplicadas no dedo indicador esquerdo com uma e 1,5 vezes o limiar sensorial. Listas de oito palavras (4 relacionadas a fibras grossas, 4 a fibras finas) foram apresentadas após cada estimulação e foi solicitado que o sujeito escolhesse as 3 palavras que mais se aproximassem das sensações experimentadas. Às palavras escolhidas foi dado o escore 1. Os resultados finais para análise foram obtidos da soma dos escores para as palavras relacionadas aos diferentes sistemas de fibras. RESULTADOS: Para ESCS a 5 Hz sensações relacionadas a fibras finas foram significantemente mais escolhidas, já para estimulações a 2 kHz sensações relacionadas a fibras grossas foram significantemente mais escolhidas. CONCLUSÃO: Estes resultados mostram um relação entre diferentes percepções e diferentes freqüências de correntes elétricas senoidais.