Сопоставление После эффектов Theta всплеск раздражения на человека слуховой коры с функциональной визуализации

Summary

Слуховые обработки является основой речи и музыки, связанные с обработкой. Транскраниальной магнитной стимуляции (ТМС) успешно используется для изучения когнитивных, чувствительных и двигательных систем, но редко применяется на прослушивание. Здесь мы исследовали TMS в сочетании с функциональной магнитно-резонансную томографию, чтобы понять функциональная организация слуховой коры.

Abstract

Auditory cortex pertains to the processing of sound, which is at the basis of speech or music-related processing¹. However, despite considerable recent progress, the functional properties and lateralization of the human auditory cortex are far from being fully understood. Transcranial Magnetic Stimulation (TMS) is a non-invasive technique that can transiently or lastingly modulate cortical excitability via the application of localized magnetic field pulses, and represents a unique method of exploring plasticity and connectivity. It has only recently begun to be applied to understand auditory cortical function ².

An important issue in using TMS is that the physiological consequences of the stimulation are difficult to establish. Although many TMS studies make the implicit assumption that the area targeted by the coil is the area affected, this need not be the case, particularly for complex cognitive functions which depend on interactions across many brain regions ³. One solution to this problem is to combine TMS with functional Magnetic resonance imaging (fMRI). The idea here is that fMRI will provide an index of changes in brain activity associated with TMS. Thus, fMRI would give an independent means of assessing which areas are affected by TMS and how they are modulated ⁴. In addition, fMRI allows the assessment of functional connectivity, which represents a measure of the temporal coupling between distant regions. It can thus be useful not only to measure the net activity modulation induced by TMS in given locations, but also the degree to which the network properties are affected by TMS, via any observed changes in functional connectivity.

Different approaches exist to combine TMS and functional imaging according to the temporal order of the methods. Functional MRI can be applied before, during, after, or both before and after TMS. Recently, some studies interleaved TMS and fMRI in order to provide online mapping of the functional changes induced by TMS ^5-7. However, this online combination has many technical problems, including the static artifacts resulting from the presence of the TMS coil in the scanner room, or the effects of TMS pulses on the process of MR image formation. But more importantly, the loud acoustic noise induced by TMS (increased compared with standard use because of the resonance of the scanner bore) and the increased TMS coil vibrations (caused by the strong mechanical forces due to the static magnetic field of the MR scanner) constitute a crucial problem when studying auditory processing.

This is one reason why fMRI was carried out before and after TMS in the present study. Similar approaches have been used to target the motor cortex ^8,9, premotor cortex ¹⁰, primary somatosensory cortex ^11,12 and language-related areas ¹³, but so far no combined TMS-fMRI study has investigated the auditory cortex. The purpose of this article is to provide details concerning the protocol and considerations necessary to successfully combine these two neuroscientific tools to investigate auditory processing.

Previously we showed that repetitive TMS (rTMS) at high and low frequencies (resp. 10 Hz and 1 Hz) applied over the auditory cortex modulated response time (RT) in a melody discrimination task ². We also showed that RT modulation was correlated with functional connectivity in the auditory network assessed using fMRI: the higher the functional connectivity between left and right auditory cortices during task performance, the higher the facilitatory effect (i.e. decreased RT) observed with rTMS. However those findings were mainly correlational, as fMRI was performed before rTMS. Here, fMRI was carried out before and immediately after TMS to provide direct measures of the functional organization of the auditory cortex, and more specifically of the plastic reorganization of the auditory neural network occurring after the neural intervention provided by TMS.

Combined fMRI and TMS applied over the auditory cortex should enable a better understanding of brain mechanisms of auditory processing, providing physiological information about functional effects of TMS. This knowledge could be useful for many cognitive neuroscience applications, as well as for optimizing therapeutic applications of TMS, particularly in auditory-related disorders.

Protocol

Протокол разделен на двухдневную сессию (не обязательно подряд). В первый день состоит из МРТ локализатор составлен с анатомической и функциональной МРТ сканирование, чтобы определить для каждого участника областей, которые будут направлены с TMS. Второй день состоит в том, МРТ сессии п?…

Discussion

Мы описываем протокол объединения форума TMS и МРТ для исследования функциональной организации слуховой коры. В следующих разделах мы будем обсуждать методологические факторы необходимо учитывать при проведении такого подхода.

Приобретение и сроки пост-TMS сессии фМРТ

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Materials

Material Name	Tipo	Company
Transcranial magnetic stimulation	Magstim super Rapid2 stimulator, Rapid-2 Plus One Module	Magstim Ltd., Wales, UK
Coil for magnetic stimulation	MRI-compatible 70 mm figure-of-eight-coil	Magstim Ltd., Wales, UK
Magnetic resonance imaging	3-T Siemens Trio scanner, 32-channel Head Coil	Siemens, Inc., Germany
Frameless Stereotaxy	Brainsight	Rogue Research Inc., Montreal, Canada
Optical measurement system	Polaris Spectra	Northern Digital Inc, Ontario, Canada
Multi-jointed arm for coil holder	Standard	Hybex Innovations Inc., Anjou, Canada
MRI-Compatible Insert Earphones	Sensimetrics, Model S14	Sensimetrics Corporation, MA, USA