Imaging tools and stimulation technologies that enable safe exploration of the living human brain.
Core Resources Available for Psychiatric Neuroimaging Research
The Psychiatric Neuroimaging Research Program studies the human brain by using imaging techniques and stimulation technologies that can enhance brain function. At the center of the program is a partnership with the Athinoula A. Martinos Center for Biomedical Imaging – located adjacent to the Psychiatric Neuroimaging Program space at the MGH Charlestown Navy Yard. Research facilities include:
Measuring connectivity in the human brain requires new tools. One approach to measuring white-matter connectivity is based on diffusion imaging techniques such as diffusion tensor imaging (DTI) and diffusion spectrum imaging (DSI). However, conventional scanners are not engineered to optimize measurement of white-matter tracks in the human brain. Funded by the NIH Human Connectome Project, MGH developed with Siemens the human connectome scanner – the first scanner of its kind specifically designed to measure brain connectivity using ultrahigh gradient strength. With a gradient strength of 300 mT/m, the Connectome scanner was delivered to MGH and officially installed on September 20, 2011. The MGH-UCLA arm of the Human Connectome Project seeks to unravel the full connectivity map of the human brain using the Connectome Scanner.
Electroencephalography (EEG) involves recording electrical activity across the scalp to estimate activity within the brain. EEG, like MEG described below, has extremely high temporal resolution (milliseconds) and is thus useful for monitoring dynamic changes in neuronal activity and high-frequency oscillatory activity. Differences in EEG recordings have been suggested as candidate biomarkers for detection of risk for neuropsychiatric illness. High density EEG (128-channels) is available in the MEG facility to be recorded in isolation or combined with MEG for simultaneous source estimation. EEG is also available in the context of TMS (below) for combined TMS stimulation and simultaneous scalp recording. Computer-controlled visual, auditory, somatosensory stimulation, and response monitoring systems are available. A comprehensive suite of analysis software allows smooth integration of MEG, EEG, MRI, and functional MRI data.
Eye movements provide a window into cognition. The neural control of eye movements is well-understood from basic research studies. Eye movements thus provide direct physiologic measures that are useful in individuals who have difficulty with verbal responses. The eye tracking resources provide investigators in the psychiatric neuroimaging research program state-of-the-art eye tracking using a head-mounted EyeLink II video based eye tracking system with a 500 Hz sampling rate for behavioral studies. Eye tracking is also available in both the mock and actual MRI scanners using an ISCAN system with a 32 Hz camera. In MEG, it is possible to record the horizontal and vertical components of eye movements using bipolar EOG electrodes. These combined resources allow paradigms to be developed in the behavioral laboratory and ported to experiments that simultaneously measure eye movements during functional neuroimaging.
The first images of brain function using intrinsic Magnetic Resonance Imaging (MRI) signals were obtained at MGH in 1991. The psychiatric neuroimaging research group was founded within a few years and began utilizing functional MRI to develop probes of brain systems important to mental illness, a central theme of the program that continues today. Locally available facilities include three research-dedicated Siemens TIM Trio 60 cm MRI scanners, equipped with 12- and 32-channel head coils, EPI, second-order shimming, CINE, MR angiography, diffusion, perfusion, and spectroscopy capabilities. Special purpose scanners include the Connectome scanner optimized for ultrahigh gradient strength to measure brain connectivity (above) and high field (7.0T) human MRI to measure structure and function with sub millimeter resolution (below). To facilitate advanced behavioral paradigms, an assortment of audio, visual, and sensory stimuli equipment available include eye tracking, respiratory monitoring, and a variety of behavioral response devices. Support facilities include a mock magnet for acclimating participants, especially children, behavioral testing rooms, and clinical exam rooms.
The galvanic skin response (GSR), also sometimes called the skin conductance response (SCR), measures the electrical conductance of the skin, which varies as a function of physiological arousal. The GSR is an important physiological tool for gauging a person’s response to conditioning and extinction that is independent of awareness. For example, a person may show an elevated GSR to a room or object they have previously experienced as dangerous even if they have no conscious knowledge of this lingering association. Available is an integrated Coulbourn Instruments isolated skin conductance coupler. This system is integrated with behavioral computers to allow stimulus delivery and participant response recording. Software for analyzing the resultant data is also available.
High field MRI affords the ability to image the structure and function of the brain at sub-millimeter resolution. Housed adjacent to the psychiatric neuroimaging program is a unique high field 7.0 T MRI. The whole-body magnet was built by Magnex Scientific (Oxford, UK), and the conventional MRI console, gradient drivers and patient table were provided by Siemens. Integration of these components and the design and construction of RF coils were performed by MGH in collaboration with Siemens. The 7.0 T whole body magnet is augmented with an 80mT/m, 800 T/m/s slew rate head gradient set for echoplanar imaging and 2nd and 3rd order resistive shim coils under computer control. With its high performance gradient set, the system can provide better than 100-µm structural resolution and 900-µm functional resolution. The system is shielded by 460 tons of steel.
Electrical activity in the brain provides a view of the rapid neural dynamics that control brain function. The principal sources of magnetoencephalography (MEG) are synchronous synaptic currents in the cerebral cortex similar to those that give rise to the EEG signal. Under special circumstances, activity in the cerebellum as well as in certain subcortical structures can be detected. MEG provides a dynamic view of neural activity with millisecond resolution and thus is complementary to functional MRI which has good spatial but poor temporal resolution. The locally available facility is equipped with the Neuromag Vectorview system, comprising 306 MEG channels (2 planar gradiometers and a magnetometer at each of 102 sites) and 128 EEG channels, located within an Imedco magnetically shielded room, with a shielding factor of approximately 250,000 at 1Hz. Computer-controlled visual, auditory, and somatosensory stimulation systems as well as behavioral response monitoring are available in the laboratory. A comprehensive suite of analysis software allows smooth integration of MEG, EEG, MRI, and functional MRI data.
Breathing, while essential to human life, can introduce dramatic task related effects in functional neuroimaging data. Effects of breathing may be deliberate to study respiratory-related neural pathways or to study cerebrovascular responses via inhaled gases (e.g., carbon dioxide induced cerebral vasodilatation). The effects of breathing may also serve as unintended confounds in neuroimaging data. The respiratory physiology faculty, staff and facilities serve as a resource to address neuroimaging hypotheses related to respiration and/or address respiratory related sources of variance in neuroimaging data. Facilities include MRI-compatible human breathing systems capable of safely delivering and monitoring hyper/hypocapnic, hyperoxic/hypoxic gas mixtures. Resources also include a knowledge base and algorithms for implementing respiratory variables in neuroimaging analyses.
Positron emission tomography (PET) allows safe molecular imaging of neurotransmitter systems and other neuronal events relevant to psychiatric illness, but cannot obtain the detailed structural images and dynamic functional information provided by MRI. The first combined MR-PET system in the US was installed at the MGH Athinoula A. Martinos Center in 2010. The system is a 3T Siemens TIM Trio 60 cm (RF coil ID) 32-channel MRI with a PET insert camera employing APD photodiode detectors and is capable of simultaneous recording of the MR and PET image in the brain. The PET system consists of a gantry with 32 detector cassettes, gantry handling device with cable handling function, cooling system, acquisition electronics module, processing reconstruction station and power supply cabinet. Combined with an innovative radiochemistry group, the PET facility provides an array of approaches to measure neurotransmitter systems and is exploring markers of neurogenesis and epigenetic machinery.
Transcranial Magnetic Stimulation (TMS) activates the brain via electromagnetic induction. It is suitable for modulating activity in the cerebral cortex. TMS is a powerful research tool because it allows determining causal relations between brain areas and their functional roles. TMS can be applied with millisecond temporal precision and with a spatial accuracy of ~7-20 mm depending on the coil type. TMS can be recorded simultaneously with EEG/EMG, and functional MRI. The available facility is equipped with a Magstim Super Rapid stimulator and a 70-mm figure-of-eight coil, Nexstim eXimia Navigated Brain Stimulation (NBS) frameless neuronavigator, and Nexstim eXimia EEG system comprising 60 EEG and 6 EMG channels. A potentially important application of TMS is as a therapy for psychiatric illness. When combined with functional neuroimaging approaches that can localize brain systems in an individual, TMS may be guided to stimulate functional networks in ways that promote brain health.