Effect of TMS coil orientation on the spatial distribution of motor evoked potentials in an intrinsic hand muscle

Souza VH, Vieira TM, Peres ASC, Garcia MAC, Vargas CD, Baffa O

Previous reports on the relationship between coil orientation and amplitude of motor evoked potential (MEP) in transcranial magnetic stimulation (TMS) did not consider the effect of electrode arrangement. Here we explore this open issue by investigating whether TMS coil orientation affects the amplitude distribution of MEPs recorded from the abductor pollicis brevis (APB) muscle with a bi-dimensional grid of 61 electrodes. Moreover, we test whether conventional mono- and bipolar montages provide representative MEPs compared to those from the grid of electrodes. Our results show that MEPs with the greatest amplitudes were elicited for 45° and 90° coil orientations, i.e. perpendicular to the central sulcus, for all electrode montages. Stimulation with the coil oriented at 135° and 315°, i.e. parallel to the central sulcus, elicited the smallest MEP amplitudes. Additionally, changes in coil orientation did not affect the spatial distribution of MEPs over the muscle extent. It has been shown that conventional electrodes with detection volume encompassing the APB belly may detect representative MEPs for optimal coil orientations. In turn, non-optimal orientations were identified only with the grid of electrodes. High-density electromyography may therefore provide new insights into the effect of coil orientation on MEPs from the APB muscle.

Dream Reporting May Help Diagnose Schizophrenia

This week "Agência FAPESP" website featured a text on a research about how dream reporting may help diagnose schizophrenia. The research is conducted by Professor Sidarta Ribeiro, a neuroscientist and director of the Brain Institute of the Federal University of Rio Grande do Norte (UFRN), who is also one of the researchers linked to the RIDC NeuroMat. Schizophrenic patients may present psychosis, loss of contact with reality that causes delusions, hallucinations and incoherent speech, among other symptoms. The diagnosis of these patients, however, can take six months to be closed and can be reviewed several times throughout their lives by different specialists, since there are no biomarkers to attest this mental disorder. "What we measure today to diagnose schizophrenia are the patients' responses in a questionnaire. Although important, this method is highly subjective. Therefore, patients with schizophrenia are treated in a variety of ways, by multiple methods and usually with combinations of drugs", said Sidarta." Agência FAPESP website, 08/2018. (In Portuguese.)

Mathematics of the brain: a NeuroMat op-ed

What does Mathematics have to do with Brain Biology? This is the question that NeuroMat's director, Antonio Galves, asks on his first post as a contributor to the "Science & Mathematics" blog of the Brazilian newspaper

Reduced functional connectivity within the primary motor cortex of patients with brachial plexus injury

D. Fraiman, M. F. Miranda, F. Erthal, P. F. Buur, M. Elschot, L. Souza, S. A. R. B. Rombouts, C. A. Schimmelpenninck, D. G. Norris, M. J. A. Malessy, A. Galves and C. D. Vargas

This study aims at the effects of traumatic brachial plexus lesion with root avulsions (BPA) upon the organization of the primary motor cortex (M1). Nine right-handed patients with a right BPA in whom an intercostal to musculocutaneous (ICN-MC) nerve transfer was performed had post-operative resting state fMRI scanning. The analysis of empirical functional correlations between neighboring voxels revealed faster correlation decay as a function of distance in the M1 region corresponding to the arm in BPA patients as compared to the control group. No differences between the two groups were found in the face area. We also investigated whether such larger decay in patients could be attributed to a gray matter diminution in M1. Structural imaging analysis showed no difference in gray matter density between groups. Our findings suggest that the faster decay in neighboring functional correlations without significant gray matter diminution in BPA patients could be related to a reduced activity in intrinsic horizontal connections in M1 responsible for upper limb motor synergies.

D2 dopamine receptor regulation of learning, sleep and plasticity

A.S.C. França, B. Lobão-Soares, L. Muratori, G. Nascimento, J. Winne, C.M. Pereira, S.M.B. Jeronimo and S. Ribeiro

Dopamine and sleep have been independently linked with hippocampus-dependent learning. Since D2 dopaminergic transmission is required for the occurrence of rapid-eye-movement (REM) sleep, it is possible that dopamine affects learning by way of changes in post-acquisition REM sleep. To investigate this hypothesis, we first assessed whether D2 dopaminergic modulation in mice affects novel object preference, a hippocampus-dependent task. Animals trained in the dark period, when sleep is reduced, did not improve significantly in performance when tested 24 h after training. In contrast, animals trained in the sleep-rich light period showed significant learning after 24 h. When injected with the D2 inverse agonist haloperidol immediately after the exploration of novel objects, animals trained in the light period showed reduced novelty preference upon retesting 24 h later. Next we investigated whether haloperidol affected the protein levels of plasticity factors shown to be up-regulated in an experience-dependent manner during REM sleep. Haloperidol decreased post-exploration hippocampal protein levels at 3 h, 6 h and 12 h for phosphorylated Ca2+/calmodulin-dependent protein kinase II, at 6 h for Zif-268; and at 12 h for the brain-derived neurotrophic factor. Electrophysiological and kinematic recordings showed a significant decrease in the amount of REM sleep following haloperidol injection, while slow-wave sleep remained unaltered. Importantly, REM sleep decrease across animals was strongly correlated with deficits in novelty preference (Rho=0.56, p=0.012). Altogether, the results suggest that the dopaminergic regulation of REM sleep affects learning by modulating post-training levels of calcium-dependent plasticity factors.

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O Centro de Pesquisa, Inovação e Difusão em Neuromatemática está sediado na Universidade de São Paulo e é financiado pela FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo).

 

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