Detection of activity from the amygdala with magnetoencephalography (original) (raw)
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MEG Study of Amygdala Responses during the Perception of Emotional Faces and Gaze
… Conference on …, 2010
The uncovering of the time course of amygdala activation is a challenge for non invasive electromagnetic brain imaging methods. Here, we propose a new method to detect the activation of this deep brain structure with magnetoencephalography (MEG). The originality of our model is to use a realistic anatomical and electrophysiological model of the neocortex and amygdala, together with distributed source imaging performed simultaneously throughout the cortical surface and the amygdala volume. In a first step, we analyzed the extent to which simulated activation of the amygdala may result in detectable MEG signals. This simulation study demonstrated that MEG is sensitive to amygdala sources. Then, our method was applied during an experimental protocol where fearful and neutral faces with direct and averted gaze were presented. Such stimuli are known to activate the amygdala from fMRI and intracranial EEG studies. Early peaks of amygdala activity were detected at 100 and 160ms post-stimulus onset. This shows an amygdala contribution to the first stages of face processing.
Magnetoencephalography (MEG) and electroencephalography (EEG) were the Cinderellas of neuroimaging. On the one hand they are endowed with unparallel temporal resolution, while on the other they are in theory unable to uniquely determine the generators, even when a complete and exact set of measurements is available. Yet, study after study from our laboratories and others demonstrate that with modern hardware and software a very accurate estimate for the generators can be derived, at least from the MEG data. In this work we first review briefly theoretical arguments and the methods of source reconstruction. We then list experimental evidence for localization accuracy of a few millimeters from real MEG data using magnetic field tomography and a recent phantom study where a number of these techniques have been compared. We then put in context the accepted view of the electrophysiological basis of the EEG and MEG signal generation, adding caveats that must be considered given our incomplete knowledge of the anatomy and electrophysiology. We finally present results for processing of facial information that link the localization measures derived from MEG to the fMRI data at one end and invasive electrophysiology at the other and put them in the proper neurophysiological context.
Evoked amygdala responses to negative faces revealed by adaptive MEG beamformers
Brain Research, 2008
Adaptive beamformer analyses of magnetoencephalograms (MEG) have shown promise as a method for functional imaging of cortical processes. Although recent evidence is encouraging, it is unclear whether these methods can both localize and reconstruct the time course of activity in subcortical structures such as the amygdala. Fourteen healthy participants (7 women) performed a perceptual matching task of negative emotional faces (angry and fearful) and geometric shapes that was designed for functional magnetic resonance imaging (fMRI) studies to maximize amygdala activation. Neuromagnetic data were collected with a 275-channel whole-head magnetometer, and event-related adaptive beamformer analyses were conducted to estimate broadband evoked responses to faces and shapes across the whole brain in 7mm steps. Group analyses revealed greater left amygdala activity to faces over shapes, both when face-matching and shape-matching trials were presented in separate blocks and when they were randomly intermixed. This finding was replicated in a second experiment with 7 new participants (3 women). Virtual sensor time series showed clear evoked responses in the left amygdala and left fusiform gyrus in both runs and experiments. We conclude that amygdala activity can be resolved from MEGs with adaptive beamformers with temporal resolution superior to other neuroimaging modalities. This demonstration should encourage use of MEG for elucidating functional networks mediating fear-related neural phenomena that likely unfold rapidly in time across cortical and subcortical structures.
Magnetoencephalography as a research tool in neuroscience: state of the art
The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry, 2006
Magnetoencephalography (MEG) is a noninvasive neuroimaging method for detecting, analyzing, and interpreting the magnetic field generated by the electrical activity in the brain. Modern hardware can capture the MEG signal at hundreds of points around the head in a snapshot lasting only a fraction of a millisecond. The sensitivity of modern hardware is high enough to permit the extraction of a clean signal generated by the brain well above the noise level of the MEG hardware. It is possible to identify signatures of superficial and often deep generators in the raw MEG signal, even in snapshots of data. In a more quantitative way, tomographic images of the electrical current density in the brain can be extracted from each snapshot of MEG signal, providing a direct correlate of coherent collective neuronal activity. A number of recent studies have scrutinized brain function in the new spatiotemporal window that real-time tomographic analysis of MEG signals has opened. The results have ...
Magnetoencephalography in studies of human cognitive brain function
Trends in Neurosciences, 1994
Magnetoencephalography provides a new dimension to the functional imaging of the brain. The cerebral magnetic fields recorded noninvasively enable the accurate determination of locations of cerebral activ@ with an uncompromized time resolution. The first whole-scalp sensor arrays have just recently come into operation, and significant advances are to be expected in both neurophysiological and cognitive studies, as well as in clinical practice. However, although the accuracy of locating isolated sources of brain activity has improved, identification of multiple simultaneous sources can still be a problem. Therefore, attempts are being made to combine magnetoencephalography with other brainimaging methods to improve spatial localization of multiple sources and, simultaneously, to achieve a more complete characterization of different aspects qf brain activi& during cognitive processing. Owing to its good time resolution and considerably better spatial accuracy than that provided by E E G, magnetoencephalography holds great promise as a tool for revealing informationprocessing sequences of the human brain.
Amygdala responses to valence and its interaction by arousal revealed by MEG
International Journal of Psychophysiology, 2013
It is widely accepted that the amygdala plays a crucial role in the processing of emotions. The precise nature of its involvement is however unclear. We hypothesized that ambivalent findings from neuroimaging studies that report amygdala's activity in emotions, are due to distinct functional specificity of amygdala's sub-divisions and specifically to differential reactivity to arousal and valence. The goal of the present study is to characterize the amygdala response to affective stimuli by disentangling the contributions of arousal and valence. Our hypothesis was prompted by recent reports claiming anatomical sub-divisions of amygdala based on cytoarchitecture and the functional maps obtained from diverse behavioral, emotional, and physiological stimulation. We measured magnetoencephalography (MEG) recordings from 12 healthy individuals passively exposed to affective stimuli from the International Affective Picture System (IAPS) collection using a 2 (Valence levels) × 2 (Arousal levels) design. Source power was estimated using a beamformer technique with the activations referring to the amygdala sub-divisions defined through probabilistic cytoarchitectonic maps. Right laterobasal amygdala activity was found to mediate negative valence (elicited by unpleasant stimuli) while left centromedial activity was characterized by an interaction of valence by arousal (arousing pleasant stimuli). We did not find a main effect for amygdala activations in any of its sub-divisions for arousal modulation. To the best of our knowledge, our findings from non-invasive MEG data indicate for the first time, a distinct functional specificity of amygdala anatomical sub-divisions in the emotional processing.
A new approach to neuroimaging with magnetoencephalography
Human Brain Mapping, 2005
We discuss the application of beamforming techniques to the field of magnetoencephalography (MEG). We argue that beamformers have given us an insight into the dynamics of oscillatory changes across the cortex not explored previously with traditional analysis techniques that rely on averaged evoked responses. We review several experiments that have used beamformers, with special emphasis on those in which the results have been compared to those observed in functional magnetic resonance imaging (fMRI) and on those studying induced phenomena. We suggest that the success of the beamformer technique, despite the assumption that there are no linear interactions between the mesoscopic local field potentials across distinct cortical areas, may tell us something of the balance between functional integration and segregation in the human brain. What is more, MEG beamformer analysis facilitates the study of these complex interactions within cortical networks that are involved in both sensory-motor and cognitive processes. Hum. Brain Mapp 25:199–211, 2005. © 2005 Wiley-Liss, Inc.
Magnetoencephalography in the study of brain dynamics
Functional Neurology, 2014
To progress toward understanding of the mechanisms underlying the functional organization of the human brain, either a bottom-up or a top-down approach may be adopted. The former starts from the study of the detailed functioning of a small number of neuronal assemblies, while the latter tries to decode brain functioning by considering the brain as a whole. This review discusses the top-down approach and the use of magnetoencephalography (MEG) to describe global brain properties. The main idea behind this approach is that the concurrence of several areas is required for the brain to instantiate a specific behavior/functioning. A central issue is therefore the study of brain functional connectivity and the concept of brain networks as ensembles of distant brain areas that preferentially exchange information. Importantly, the human brain is a dynamic device, and MEG is ideally suited to investigate phenomena on behaviorally relevant timescales, also offering the possibility of capturing behaviorally-related brain connectivity dynamics.
Brain Research Bulletin, 2007
Magnetoencephalography (MEG) was used to record the dynamics of amygdala neuronal population activity during fear conditioning in human participants. Activation during conditioning training was compared to habituation and extinction sessions. Conditioned stimuli (CS) were visually presented geometric figures, and unconditioned stimuli (US) were aversive white-noise bursts. The CS+ was paired with the US on 50% of presentations and the CS− was never paired. The precise temporal resolution of MEG allowed us to address the issue of whether the amygdala responds to the onset or offset of the CS+, and/or the expectation of the initiation or offset of the an omitted auditory US. Fear conditioning elicited differential amygdala activation for the unpaired CS+ compared to the CS−, extinction and habituation. This was especially robust in the right hemisphere at CS onset. The strongest peaks of amygdala activity occurred at an average of 270 ms in the right and 306 ms in the left hemisphere following unpaired CS+ onset, and following offset at 21 ms in the left and 161 ms in the right (corresponding to an interval of 108 ms and 248 ms after the anticipated onset of the US, respectively). However, the earliest peaks in this epoch preceded US onset in most subjects. Thus, the activity dynamics suggest that the amygdala both differentially responds to stimuli and anticipates the arrival of stimuli based on prior learning of contingencies. The amygdala also shows stimulus omission-related activation that could potentially provide feedback about experienced stimulus contingencies to modify future responding during learning and extinction.