Magnetoencephalography Lab (MEG) offers unique opportunities to address research objectives that are core to the NICoE mission. Using noninvasive recordings of brain activity with millisecond temporal resolution, MEG can provide an understanding of the physiological basis of post-concussive symptoms and psychological health conditions such as post-traumatic stress disorder (PTSD), anxiety, or depression.

Understanding the link between functional impairments and neurophysiological alterations can help to identify and evaluate treatment strategies to improve cognitive and emotional functioning for patients affected by traumatic brain injury (TBI) and psychological health conditions. 

Background

Brain function is determined by the coordinated activity of ensembles of neurons bound together by virtue of neuronal oscillations (brainwaves) of various frequencies and at various spatial scales (local, global). Brain dysfunction can be conceptualized as an alteration of this coordinated activity (oscillations) and disorganization of these neuronal networks.

Modern MEG scanners use large arrays of superconductive sensors arranged in a helmet-like shape that can noninvasively measure the magnetic field generated by the electrophysiological activity of the brain with temporal resolution in the order of milliseconds. By measuring a direct effect of neuronal currents in the brain, either during rest or during the performance of cognitive tasks, MEG recordings can help characterize activity within specific brain regions, as well as the functional connectivity between these regions. Such undertakings are fundamental in order to understand the emergence of brain neural networks and changes in these networks with pathology, and to identify and evaluate interventions including pharmacological treatments, transcranial magnetic stimulation (TMS) or relaxation techniques.

Equipment

The NICoE MEG lab is equipped with an Elekta VectorView™ whole-head biomagnetometer system (Elekta Neuromag, Helsinki, Finland). The unit has 102 triplet sensors inside a cryogenic vacuum-insulated container. The MEG system, patient bed and patient chair are housed in a double-layer magnetically shielded room (figure 1). MEG electronics outside the magnetically shielded room record and process the sensor signals with millisecond temporal resolution. The data acquisition system collects and routes the data to the main acquisition computer. The MEG system is also equipped with capabilities for simultaneous recordings of high-density electroencephalography (EEG). The built-in EEG subsystem comprises an interface for electrodes, the computer controlled preamplifier unit, an isolation amplifier and the data acquisition unit. 

Recordings can be performed both in seated or supine positions, during rest or sleep or during performance of cognitive tasks. During the recording sessions, the operator monitors and communicates with the patient via the video and intercom systems.

A 3D Polhemus digitizer is used to register the position of external localization indicators and an additional set of head surface points that allow the co-registration of the functional MEG data with structural magnetic resonance images (MRI). Stimulus presentation software allows for programming complex sequences of auditory, visual and somatosensory stimuli. Multiple data analysis and source modeling software packages are also available including the Elekta Neuromag software, Freesurfer, Brainstorm, MNE, and in-house custom MATLAB software on multiple Windows and Linux platforms.

Research Overview

The research conducted in the MEG lab uses novel experimental paradigms to better understand the neurobiology of TBI and psychological health conditions, such as PTSD and depression. Research scientists at the NICoE are mapping brain activity from noninvasive recordings of the magnetic fields produced when brain cells communicate with one another while research participants are at rest or performing cognitive tasks. The brain activity can be estimated with millisecond temporal resolution and can be displayed on either orthogonal images of the brain or on the cortical surface determined from MRI (figure 2). Compared to EEG, MEG source mapping is less sensitive to signal distortions caused by the complex layering of head tissues, with highly heterogeneous conductivity profiles that cannot be measured with precision. 

Published Research Involving the MEG

• Post-traumatic stress disorder is associated with alterations in evoked cortical activation during visual recognition of scenes 
  NeuroImage: Clinical 31, 102752.
  Mihai Popescu, Elena-Anda Popescu, Thomas J. DeGraba, John D. Hughes
• Altered modulation of beta band oscillations during memory encoding is predictive of lower subsequent recognition performance in post-traumatic stress disorder
  NeuroImage: Clinical, 25, 102154.
  Mihai Popescu, Elena-Anda Popescu, Thomas J. DeGraba, John D. Hughes
• Post-traumatic stress disorder is associated with altered modulation of prefrontal alpha band oscillations during working memory
  Clinical Neurophysiology, 130(10), 1869-1881
  Mihai Popescu, Elena-Anda Popescu, Thomas J. DeGraba, David J. Fernandez-Fidalgo, Gerard Riedy, John D. Hughes
• Activation of dominant hemisphere association cortex during naming as a function of cognitive performance in mild traumatic brain injury: Insights into mechanisms of lexical access
  NeuroImage: Clinical, 15, 741-752
  Mihai Popescu, John D. Hughes, Elena-Anda Popescu, Judy Mikola, Warren Merrifield, Maria DeGraba, Gerard Riedy, Thomas J. DeGraba
• Reduced prefrontal MEG alpha-band power in mild traumatic brain injury with associated posttraumatic stress disorder symptoms
  Clinical Neurophysiology, 127(9), 3075-3085
  Mihai Popescu, John D. Hughes, Elena-Anda Popescu, Gerard Riedy, Thomas J. DeGraba