INTRODUCTION: Areas of the brain that are associated with the vestibular system can be activated using galvanic vestibular stimulation. These areas can be studied through a combination of galvanic vestibular stimulation with functional magnetic resonance imaging (fMRI). In order to provide an appropriate sequence of galvanic stimulation synchronous with the MRI pulse sequence, a specific electronic device that was built and assessed is presented. METHODS: The electronic project of the GVS is divided in analog and digital circuits. The analog circuits are mounted in an aluminum case, supplied by sealed batteries, and goes inside the MRI room near to the feet of the subject. The digital circuits are placed in the MRI control room. Those circuits communicate through each other by an optical fiber. Tests to verify the GVS-MRI compatibility were conducted. Silicone (in-house) and Ag/AgCl (commercial) electrodes were evaluated for maximum balance and minimal pain sensations. fMRI experiments were conducted in eight human volunteers. RESULTS: GVS-MRI compatibility experiments demonstrate that the GVS did not interfere with the MRI scanner functionality and vice versa. The circular silicone electrode was considered the most suitable to apply the galvanic vestibular stimulation. The 1 Hz stimulation sinusoid frequency produced the biggest balance and the less pain sensations when compared to 2 Hz. The GVS was capable of eliciting activation in the precentral and postcentral gyri, in the central sulcus, in the supplementary motor area, in the middle and inferior frontal gyri, in the inferior parietal lobule, in the insula, in the superior temporal gyrus, in the middle cingulate cortex, and in the cerebellum. CONCLUSION: This study shows the development and description of a neurovestibular stimulator that can be safely used inside the MRI scanner room without interfering on its operation and vice versa. The developed GVS could successfully activate the major areas involved with multimodal functions of the vestibular system, demonstrating its validity as a stimulator for neurovestibular research. To the best of our knowledge, this is the first work that shows the development and the construction of a galvanic vestibular stimulator that could be safely used inside the MRI room.

The Kullback-Leibler distance (or relative entropy) is applied in the analysis of functional magnetic resonance (fMRI) data series. Our study is designed for event-related (ER) experiments, where a brief stimulus is presented and a long period of rest is followed. In particular, this relative entropy is used as a measure of the "distance" between the probability distributions p1 and p2 of the signal levels related to stimulus and non-stimulus. In order to avoid undesirable divergences of the Kullback-Leibler distance, a small positive parameter delta is introduced in the definition of the probability functions in such a way that it does not bias the comparison between both distributions. Numerical simulations are performed so as to determine the probability densities of the mean Kullback-Leibler distance $\overline{D}$ (throughout the N epochs of the whole experiment). For small values of N (N < 30), such probability densities $f(\overline{D})$ are found to be fitted very well by Gamma distributions (chi2 < 0.0009). The sensitivity and specificity of the method are evaluated by construction of the receiver operating characteristic (ROC) curves for some values of signal-to-noise ratio (SNR). The functional maps corresponding to real data series from an asymptomatic volunteer submitted to an ER motor stimulus is obtained by using the proposed technique. The maps present activation in primary and secondary motor brain areas. Both simulated and real data analyses indicate that the relative entropy can be useful for fMRI analysis in the information measure scenario.

A ressonância magnética funcional permite uma localização acurada da área da linguagem para fins de cirurgia de epilepsia, mas requer a colaboração do paciente na execução da tarefa proposta, o que pode limitar a sua utilização em pacientes com retardo mental. Nós apresentamos o caso de uma mulher com 34 anos de idade, com retardo mental, que foi submetida a duas tarefas distintas de geração silenciosa de palavras, por categoria e letras. Encontramos forte ativação da área de Broca na tarefa mais complexa. Sugerimos que um estudo com múltiplas tarefas pode ser útil em pacientes com retardo mental.

Functional MRI produces a more accurate localization of the language areas for epilepsy surgery purpose, but requires the patient cooperation. We report a 34 years-old woman with mental retardation who underwent two different verbal fluency tasks, category and word naming. We found a strong activation of the Broca’s area in the most difficult task. We suggest that a multi-task fMRI study could be successful in patients with cognitive delay.

A síndrome de Pusher caracteriza-se por uma alteração do equilíbrio na qual pacientes com lesões encefálicas empurram-se em direção ao lado parético utilizando o membro não-afetado. O papel do sistema vestibular na alteração postural da síndrome de Pusher ainda não foi devidamente elucidado. OBJETIVO: Neste estudo objetivamos avaliar o papel dos canais semicirculares horizontais na expressão clínica da síndrome de Pusher, através da aplicação das provas calórica e rotatória. FORMA DE ESTUDO: Observacional, clínico e prospectivo. MATERIAL E MÉTODO: Avaliamos 9 pacientes com AVC e síndrome de Pusher internados na Enfermaria de Neurologia do HCFMRP-USP. Os pacientes foram submetidos à avaliação neurológica clínica e neuropsicológica, NIHSS, Scale for Contraversive Pushing - SCP, teste calórico e teste rotatório. RESULTADOS: Foram estudados 9 pacientes (5 homens) com idade média de 71,8 ± 5,9 anos e com NIHSS médio de 18.33. Três pacientes apresentaram preponderância direcional contralateral à lesão encefálica na prova calórica. Na prova rotatória, foram observados quatro pacientes com preponderância direcional na análise de velocidade da componente lenta. CONCLUSÃO: Os resultados do presente estudo indicam que a disfunção dos canais semicirculares não parece ser fundamental para a expressão da síndrome de Pusher.

Pusher syndrome is an interesting disorder of balance in patients with encephalic lesions characterized by the peculiar behavior of actively pushing away from the non-hemiparetic side and resisting against passive correction, with a tendency to fall toward the paralyzed side. The role of vestibular system on the pushing behavior is not clear. AIM: To evaluate horizontal semicircular canal function in patients with Pusher syndrome, using caloric and rotation tests. STUDY DESIGN: Observational prospective. MATERIAL AND METHOD: We evaluated 9 inpatients with stroke and Pusher syndrome at the neurological unit of HCFMRP-USP. We applied neurological and neuropsychological exams, NIHSS, Scale for contraversive pushing (SCP), caloric and rotation tests. RESULTS: We evaluated 9 patients (5 men) with mean age of 71.8 ± 5.9 and mean NIHSS of 18.33. Three patients presented contralateral directional preponderance on caloric test and we found four patients with directional preponderance on analysis of the slow phase velocity of rotation test response. CONCLUSION: Our findings indicate that a dysfunction of semicircular canals does not seem to be relevant for the clinical manifestations of the Pusher syndrome.