Página 1 dos resultados de 1985 itens digitais encontrados em 0.008 segundos

## Avaliação de metodologia de coleta e analíse de solventes/misturas de solventes no ar em ambiente de trabalho: metanol em mistura MEG (Metanol 33% Etanol 60% e Gasolina 7%); Evaluation of methodology of sampling and analysis of solvents in the air in the workplace. Methanol in a MEG mixture (Methanol 33%, Ethanol 60%, and Gasoline 7%

Cardoso, Luiza Maria Nunes
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Relevância na Pesquisa
37.43%

## MEG-1 and MEG-2 Are Embryo-Specific P-Granule Components Required for Germline Development in Caenorhabditis elegans

Leacock, Stefanie W.; Reinke, Valerie
Fonte: Genetics Society of America Publicador: Genetics Society of America
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.33%
In Caenorhabditis elegans, germ granules called P granules are directly inherited from mother to daughter and segregate with the germ lineage as it separates from the soma during initial embryonic cell divisions. Here we define meg-1 and meg-2 (maternal-effect germ-cell defective), which are expressed in the maternal germline and encode proteins that localize exclusively to P granules during embryonic germline segregation. Localization of MEG-1 to P granules depends upon the membrane-bound protein MES-1. meg-1 mutants exhibit multiple germline defects: P-granule mis-segregation in embryos, underproliferation and aberrant P-granule morphology in larval germ cells, and ultimately, sterility as adults. The penetrance of meg-1 phenotypes increases when meg-2 is also absent. Loss of the P-granule component pgl-1 in meg-1 mutants increases germ-cell proliferation, while loss of glh-1 decreases proliferation. Because meg-1 is provided maternally but its action is required in the embryonic germ lineage during segregation from somatic lineages, it provides a critical link for ensuring the continuity of germline development from one generation to the next.

## Microtesla MRI of the human brain combined with MEG

Zotev, Vadim S.; Matlashov, Andrei N.; Volegov, Petr L.; Savukov, Igor M.; Espy, Michelle A.; Mosher, John C.; Gomez, John J.; Kraus, Robert H.
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.3%
One of the challenges in functional brain imaging is integration of complementary imaging modalities, such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). MEG, which uses highly sensitive superconducting quantum interference devices (SQUIDs) to directly measure magnetic fields of neuronal currents, cannot be combined with conventional high-field MRI in a single instrument. Indirect matching of MEG and MRI data leads to significant co-registration errors. A recently proposed imaging method-SQUID-based microtesla MRI-can be naturally combined with MEG in the same system to directly provide structural maps for MEG-localized sources. It enables easy and accurate integration of MEG and MRI/fMRI, because microtesla MR images can be precisely matched to structural images provided by high-field MRI and other techniques. Here we report the first images of the human brain by microtesla MRI, together with auditory MEG (functional) data, recorded using the same seven-channel SQUID system during the same imaging session. The images were acquired at 46 microtesla measurement field with pre-polarization at 30 mT. We also estimated transverse relaxation times for different tissues at microtesla fields. Our results demonstrate feasibility and potential of human brain imaging by microtesla MRI. They also show that two new types of imaging equipment-low-cost systems for anatomical MRI of the human brain at microtesla fields...

## BOLD Responses in Human Auditory Cortex Are More Closely Related to Transient MEG Responses Than to Sustained Ones

Gutschalk, Alexander; Hämäläinen, Matti S.; Melcher, Jennifer R.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.3%
Blood oxygen level dependent–functional magnetic resonance imaging (BOLD–fMRI) and magnetoencephalographic (MEG) signals are both coupled to postsynaptic potentials, although their relationship is incompletely understood. Here, the wide range of BOLD–fMRI and MEG responses produced by auditory cortex was exploited to better understand the BOLD–fMRI/MEG relationship. Measurements of BOLD and MEG responses were made in the same subjects using the same stimuli for both modalities. The stimuli, 24-s sequences of click trains, had duty cycles of 2.5, 25, 72, and 100%. For the 2.5% sequence, the BOLD response was elevated throughout the sequence, whereas for 100%, it peaked after sequence onset and offset and showed a diminished elevation in between. On the finer timescale of MEG, responses at 2.5% consisted of a complex of transients, including N1m, to each click train of the sequence, whereas for 100% the only transients occurred at sequence onset and offset between which there was a sustained elevation in the MEG signal (a sustained field). A model that separately estimated the contributions of transient and sustained MEG signals to the BOLD response best fit BOLD measurements when the transient contribution was weighted 8- to 10-fold more than the sustained one. The findings suggest that BOLD responses in the auditory cortex are tightly coupled to the neural activity underlying transient...

## Multimodal imaging of repetition priming: Using fMRI, MEG, and intracranial EEG to reveal spatiotemporal profiles of word processing

McDonald, Carrie R.; Thesen, Thomas; Carlson, Chad; Blumberg, Mark; Girard, Holly M.; Trongnetrpunya, Amy; Sherfey, Jason S.; Devinsky, Orrin; Kuzniecky, Rubin; Dolye, Werner K.; Cash, Sydney S.; Leonard, Matt K.; Hagler, Donald J.; Dale, Anders M.; Halgr
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.3%
Repetition priming is a core feature of memory processing whose anatomical correlates remain poorly understood. In this study, we use advanced multimodal imaging (functional magnetic resonance imaging (fMRI) and magnetoencephalography; MEG) to investigate the spatiotemporal profile of repetition priming. We use intracranial electroencephalography (iEEG) to validate our fMRI/MEG measurements. Twelve controls completed a semantic judgment task with fMRI and MEG that included words presented once (new, ‘N’) and words that repeated (old, ‘O’). Six patients with epilepsy completed the same task during iEEG recordings. Blood-oxygen level dependent (BOLD) responses for N vs O words were examined across the cortical surface and within regions of interest. MEG waveforms for N vs O words were estimated using a noise-normalized minimum norm solution, and used to interpret the timecourse of fMRI. Spatial concordance was observed between fMRI and MEG repetition effects from 350–450ms within bilateral occipitotemporal and medial temporal, left prefrontal, and left posterior temporal cortex. Additionally, MEG revealed widespread sources within left temporoparietal regions, whereas fMRI revealed bilateral reductions in occipitotemporal and left superior frontal...

## Localization of Broca’s area using verb generation tasks in the MEG: Validation against fMRI

Pang, Elizabeth W.; Wang, Frank; Malone, Marion; Kadis, Darren S.; Donner, Elizabeth J.
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.37%
Functional MRI (fMRI) is routinely used to non-invasively localize language areas. Magnetoencephalography (MEG) is being explored as an alternative technique. MEG tasks to localize receptive language are well established although there are no standardized tasks to localize expressive language areas. We developed two expressive language tasks for MEG and validated their localizations against fMRI data. Ten right-handed adolescents (μ=17.5 years) were tested with fMRI and MEG on two tasks: verb generation to pictures and verb generation to words. MEG and fMRI data were normalized and overlaid. The number of overlapping voxels activated in fMRI and MEG were counted for each subject, for each task, at different thresholding levels. For picture verb generation, there was 100% concordance between MEG and fMRI lateralization, and for word verb generation, there was 75% concordance. A count showed 79.6% overlap of voxels activated by both MEG and fMRI for picture verb generation and 50.2% overlap for word verb generation. The percentage overlap decreased with increasingly stringent activation thresholds. Our novel MEG expressive language tasks successfully identified neural regions involved in language production and showed high concordance with fMRI laterality. Percentage overlap of activated voxels was also high when validated against fMRI...

## Measuring functional connectivity using MEG: Methodology and comparison with fcMRI

Brookes, Matthew J.; Hale, Joanne R.; Zumer, Johanna M.; Stevenson, Claire M.; Francis, Susan T.; Barnes, Gareth R.; Owen, Julia P.; Morris, Peter G.; Nagarajan, Srikantan S.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.3%
Functional connectivity (FC) between brain regions is thought to be central to the way in which the brain processes information. Abnormal connectivity is thought to be implicated in a number of diseases. The ability to study FC is therefore a key goal for neuroimaging. Functional connectivity (fc) MRI has become a popular tool to make connectivity measurements but the technique is limited by its indirect nature. A multimodal approach is therefore an attractive means to investigate the electrodynamic mechanisms underlying hemodynamic connectivity. In this paper, we investigate resting state FC using fcMRI and magnetoencephalography (MEG). In fcMRI, we exploit the advantages afforded by ultra high magnetic field. In MEG we apply envelope correlation and coherence techniques to source space projected MEG signals. We show that beamforming provides an excellent means to measure FC in source space using MEG data. However, care must be taken when interpreting these measurements since cross talk between voxels in source space can potentially lead to spurious connectivity and this must be taken into account in all studies of this type. We show good spatial agreement between FC measured independently using MEG and fcMRI; FC between sensorimotor cortices was observed using both modalities...

## Emergence of Synchronous EEG Spindles From Asynchronous MEG Spindles

Dehghani, Nima; Cash, Sydney S.; Halgren, Eric
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.39%
Sleep spindles are bursts of rhythmic 10–15 Hz activity, lasting ~0.5–2 s, that occur during Stage 2 sleep. They are coherent across multiple cortical and thalamic locations in animals, and across scalp EEG sites in humans, suggesting simultaneous generation across the cortical mantle. However, reports of MEG spindles occurring without EEG spindles, and vice versa, are inconsistent with synchronous distributed generation. We objectively determined the frequency of MEG-only, EEG-only, and combined MEG-EEG spindles in high density recordings of natural sleep in humans. About 50% of MEG spindles occur without EEG spindles, but the converse is rare (~15%). Compared to spindles that occur in MEG only, those that occur in both MEG and EEG have ~1% more MEG coherence and ~15% more MEG power, insufficient to account for the ~55% increase in EEG power. However, these combined spindles involve ~66% more MEG channels, especially over frontocentral cortex. Furthermore, when both MEG and EEG are involved in a given spindle, the MEG spindle begins ~150 ms before the EEG spindle and ends ~250 ms after. Our findings suggest that spindles begin in focal cortical locations which are better recorded with MEG gradiometers than referential EEG due to the biophysics of their propagation. For some spindles...

## Using joint ICA to link function and structure using MEG and DTI in schizophrenia

Stephen, JM; Coffman, BA; Jung, RE; Bustillo, JR; Aine, CJ; Calhoun, VD
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.37%
In this study we employed joint independent component analysis (jICA) to perform a novel multivariate integration of magnetoencephalography (MEG) and diffusion tensor imaging (DTI) data to investigate the link between function and structure. This model-free approach allows one to identify covariation across modalities with different temporal and spatial scales [temporal variation in MEG and spatial variation in fractional anisotropy (FA) maps]. Healthy controls (HC) and patients with schizophrenia (SP) participated in an auditory/visual multisensory integration paradigm to probe cortical connectivity in schizophrenia. To allow direct comparisons across participants and groups, the MEG data were registered to an average head position and regional waveforms were obtained by calculating the local field power of the planar gradiometers. Diffusion tensor images obtained in the same individuals were preprocessed to provide FA maps for each participant. The MEG/FA data were then integrated using the jICA software (http://mialab.mrn.org/software/fit). We identified MEG/FA components that demonstrated significantly different (p < 0.05) covariation in MEG/FA data between diagnostic groups (SP vs. HC) and three components that captured the predominant sensory responses in the MEG data. Lower FA values in bilateral posterior parietal regions...

## Good practice for conducting and reporting MEG research

Gross, Joachim; Baillet, Sylvain; Barnes, Gareth R.; Henson, Richard N.; Hillebrand, Arjan; Jensen, Ole; Jerbi, Karim; Litvak, Vladimir; Maess, Burkhard; Oostenveld, Robert; Parkkonen, Lauri; Taylor, Jason R.; van Wassenhove, Virginie; Wibral, Michael; Sc
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.3%
Magnetoencephalographic (MEG) recordings are a rich source of information about the neural dynamics underlying cognitive processes in the brain, with excellent temporal and good spatial resolution. In recent years there have been considerable advances in MEG hardware developments and methods. Sophisticated analysis techniques are now routinely applied and continuously improved, leading to fascinating insights into the intricate dynamics of neural processes. However, the rapidly increasing level of complexity of the different steps in a MEG study make it difficult for novices, and sometimes even for experts, to stay aware of possible limitations and caveats. Furthermore, the complexity of MEG data acquisition and data analysis requires special attention when describing MEG studies in publications, in order to facilitate interpretation and reproduction of the results. This manuscript aims at making recommendations for a number of important data acquisition and data analysis steps and suggests details that should be specified in manuscripts reporting MEG studies. These recommendations will hopefully serve as guidelines that help to strengthen the position of the MEG research community within the field of neuroscience, and may foster discussion in order to further enhance the quality and impact of MEG research.

## Single-subject-based whole-brain MEG slow-wave imaging approach for detecting abnormality in patients with mild traumatic brain injury

Huang, Ming-Xiong; Nichols, Sharon; Baker, Dewleen G.; Robb, Ashley; Angeles, Annemarie; Yurgil, Kate A.; Drake, Angela; Levy, Michael; Song, Tao; McLay, Robert; Theilmann, Rebecca J.; Diwakar, Mithun; Risbrough, Victoria B.; Ji, Zhengwei; Huang, Charles
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.3%
Traumatic brain injury (TBI) is a leading cause of sustained impairment in military and civilian populations. However, mild TBI (mTBI) can be difficult to detect using conventional MRI or CT. Injured brain tissues in mTBI patients generate abnormal slow-waves (1–4 Hz) that can be measured and localized by resting-state magnetoencephalography (MEG). In this study, we develop a voxel-based whole-brain MEG slow-wave imaging approach for detecting abnormality in patients with mTBI on a single-subject basis. A normative database of resting-state MEG source magnitude images (1–4 Hz) from 79 healthy control subjects was established for all brain voxels. The high-resolution MEG source magnitude images were obtained by our recent Fast-VESTAL method. In 84 mTBI patients with persistent post-concussive symptoms (36 from blasts, and 48 from non-blast causes), our method detected abnormalities at the positive detection rates of 84.5%, 86.1%, and 83.3% for the combined (blast-induced plus with non-blast causes), blast, and non-blast mTBI groups, respectively. We found that prefrontal, posterior parietal, inferior temporal, hippocampus, and cerebella areas were particularly vulnerable to head trauma. The result also showed that MEG slow-wave generation in prefrontal areas positively correlated with personality change...

## Source localization of MEG generation using spatio-temporal Kalman filter; Source localization of magnetoencephalography generation using spatio-temporal Kalman filter

Desai, Neil U
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 41 leaves; 2023006 bytes; 2022779 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
27.35%
The inverse problem for magnetoencephalography (MEG) involves estimating the magnitude and location of sources inside the brain that give rise to the magnetic field recorded on the scalp as subjects execute cognitive, motor and/or sensory tasks. Given a forward model which describes how the signals emanate from the brain sources, a standard approach for estimating the MEG sources from scalp measurements is to use regularized least squares approaches such as LORETA, MNE, VARETA. These regularization methods impose a spatial constraint on the MEG inverse solution yet, they do not consider the temporal dynamics inherent to the biophysics of the problem. To address these issues, we present a state-space formulation of the MEG inverse problem by specifying a state equation that describes temporal dynamics of the MEG sources. Using a standard forward model system as the observation equation, we derive spatio-temporal Kalman filter and fixed-interval smoothing algorithms for MEG source localization.To compare the methods analytically, we present a Bayesian derivation of the regularized least squares and Kalman filtering methods. This analysis reveals that the estimates computed from the static methods bias the location of the sources toward zero. We compare the static...

## Temporal and spatial properties of shape processing in the human visual cortex : combined fMRI and MEG adaptation; Zeitliche und räumliche Eigenschaften in der Objektverarbeitung im visuellen Cortex des Menschen : kombinierte fMRI und MEG-Adaptationsstudien

Huberle, Elisabeth
Tipo: Dissertação
EN
Relevância na Pesquisa
37.23%
Recent studies have shown that global information about shapes is processed in both early ventral (i.e. V1, V2, Vp, V4) and higher occipitotemporal visual areas (i.e. Lateral Occipital Complex/LOC). However, the temporal and spatial properties of shape processing across visual areas in the human brain are largely unknown. The present thesis addressed this question in a combined fMRI and MEG study, that made use of the complimentary spatial and temporal resolution of the two techniques. An event-related adaptation paradigm was applied, in which lower neural responses are observed for two identical than two different consecutivelypresented stimuli. The stimuli were shapes, that consisted of collinear Gabor elements. To investigate the temporal properties of shape processing, the interstimulus interval between the two consecutively-presented stimuli was manipulated (ISI: 100 vs. 400 msec). The results showed adaptation for both the short and the long ISI in the LOC, but only for the short ISI in early visual areas. Further, the spatial properties (Local vs. Global) were tested by changes in the local orientation of the Gabor elements or different global changes. Strong fMRI adaptation effects to local changes were observed in early visual areas (V1...

## Identifikation von neuromagnetischen Korrelaten verschiedener Stufen sprachlicher Verarbeitung mit der Technik der Magnetoenzephalographie; Grundlage für einen klinischen Einsatz des MEG zur Lokalisation sprachgebundener Aktivitäten im Rahmen der funktionellen Neuronavigation; Neuromagnetic correlates of different stages in language processing; Basis for the clinical use of MEG for the localization of language-related activities in functional neuronavigation

Henseler, Ilona Konstanze
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
27.33%
In mehreren Studien wurde bereits die Technik der Magnetoenzephalographie (MEG) eingesetzt, um die Sprachverarbeitung bei Gesunden zu erforschen. Der Großteil dieser Studien konzentrierte sich allerdings auf einen einzigen Schritt im Verarbeitungsprozess. Im Gegensatz dazu wurde in der vorliegenden Studie ein experimentelles Stimulationsparadigma zusammengestellt und getestet, mit dem in nur einer Messsitzung eine Vielzahl neuronaler Antworten, die verschiedene Teilprozesse sprachlicher Verarbeitung repräsentieren, mit der Technik des MEG identifiziert werden kann. Dieses Vorgehen erlaubt die Untersuchung der zeitlichen und räumlichen Beziehungen einzelner Hirnantworten zueinander. Zudem könnte ein Paradigma, das eine umfassende Darstellung sprachassoziierter neuronaler Aktivitäten innerhalb einer Messsitzung ermöglicht, in Zukunft zu einem nützlichen Werkzeug im Rahmen der funktionellen Neuronavigation werden. In den durchgeführten Experimenten wurden 16 gesunde Probanden (8 Männer, 8 Frauen) mit dem neu konzipierten Stimulationsparadigma in einem 151-Kanal MEG-System untersucht. Hierbei konnten zahlreiche biomagnetische Hirnantworten identifiziert werden, die umschriebene Schritte im Sprachverarbeitungsprozess repräsentieren. So wurden Aktivitäten aufgezeichnet...

## Development of a new correlation for estimating pool boiling heat transfer coefficient of MEG/DEG/water ternary mixture

Fonte: Association of the Chemical Engineers Publicador: Association of the Chemical Engineers
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.1%
Pool boiling heat transfer coefficient of monoethylene glycol (MEG), diethylene glycol (DEG) and water ternary mixtures has been experimentally measured up to heat flux 114 kW/m2 at various volumetric concentrations of MEG and DEG. As expected, heat transfer coefficient was strongly taken as a direct function of heat flux. Existing well-known correlations are shown to be unable to predict the acceptable values for the tested ternary mixtures, particularly at different concentrations of MEG and DEG. Furthermore, a new modified correlation is developed on the basis of the Stephan - Preußer correlation that predicts the values of heat transfer coefficients with absolute average error of about 7% that is reasonable and acceptable values in compare to other existing correlations.; M.M. Sarafraz, S.A. Alavi Fazel, Y. Hasanzadeh, A. Arabshamsabadi, S. Bahram

## EEG-MEG Integration Enhances the Characterization of Functional and Effective Connectivity in the Resting State Network

Muthuraman, Muthuraman; Moliadze, Vera; Mideksa, Kidist Gebremariam; Anwar, Abdul Rauf; Stephani, Ulrich; Deuschl, Günther; Freitag, Christine M.; Siniatchkin, Michael
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.33%
At the sensor level many aspects, such as spectral power, functional and effective connectivity as well as relative-power-ratio ratio (RPR) and spatial resolution have been comprehensively investigated through both electroencephalography (EEG) and magnetoencephalography (MEG). Despite this, differences between both modalities have not yet been systematically studied by direct comparison. It remains an open question as to whether the integration of EEG and MEG data would improve the information obtained from the above mentioned parameters. Here, EEG (64-channel system) and MEG (275 sensor system) were recorded simultaneously in conditions with eyes open (EO) and eyes closed (EC) in 29 healthy adults. Spectral power, functional and effective connectivity, RPR, and spatial resolution were analyzed at five different frequency bands (delta, theta, alpha, beta and gamma). Networks of functional and effective connectivity were described using a spatial filter approach called the dynamic imaging of coherent sources (DICS) followed by the renormalized partial directed coherence (RPDC). Absolute mean power at the sensor level was significantly higher in EEG than in MEG data in both EO and EC conditions. At the source level, there was a trend towards a better performance of the combined EEG+MEG analysis compared with separate EEG or MEG analyses for the source mean power...

## The MEG Spectrometer at PSI

Cattaneo, Paolo Walter; collaboration, for the MEG
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.86%
The MEG experiment is designed to search the Lepton Flavor Violating process $\mu \to e^+\gamma$ \cite{mori-1999,meg2007-baldini}. This search requires a high intensity muon beam stopping in a thin target with the maximum rate compatible with the background from combinatorial events. The events are analyzed by a high resolution and fast liquid xenon calorimeter and by a spectrometer composed by an array of ultra-light drift chambers (DCH) for momentum measurement and a double layered timing counter (TC) for measuring the $e^+$ time. The design parameters and performance of the spectrometer during the 2008 physics run are described.; Comment: Presented at the 1st Conference on Technology and Instrumentation in Particle Physics, Tsukuba, 2009 (TIPP09). To be published by Nuclear Instrument & Methods in Physics Research

## A limit for the mu -> e gamma decay from the MEG experiment

MEG collaboration; Adam, J.; Bai, X.; Baldini, A.; Baracchini, E.; Barchiesi, A.; Bemporad, C.; Boca, G.; Cattaneo, P. W.; Cavoto, G.; Cecchet, G.; Cei, F.; Cerri, C.; De Bari, A.; De Gerone, M.; Doke, T.; Dussoni, S.; Egger, J.; Galli, L.; Gallucci, G.;
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.86%
A search for the decay mu -> e gamma, performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of BR(mu -> e gamma) < 2.8 x 10**-11 (90% C.L.). This corresponds to the measurement of positrons and photons from ~ 10**14 stopped mu-decays by means of a superconducting positron spectrometer and a 900 litre liquid xenon photon detector.; Comment: 13 pages, 9 figures. v2: improved estimate of photon reconstruction efficiency

## First Result From The MEG Experiment

Baracchini, Elisabetta; Collaboration, for the MEG
Tipo: Artigo de Revista Científica
We present the first results from the MEG experiment for the search of the Lepton Flavour Violating decay $\mu^+ \to e^+ \gamma$ . LFV decays are forbidden in the SM and highly suppressed in any minimal SM extension with tiny neutrino masses. On the other hand, several SUSY, GUT and ED models beyond the SM predict the $\mu^+ \to e^+ \gamma$ rate at a level experimentally accessible. Hence, the MEG experiment will be able either to provide an incontrovertible evidence of physics beyond the SM or to significantly constrain the parameter space of SM extensions.; Comment: 6 pages, 1 figure, 45 Rencontres de Moriond Electroweak proceedings