Functional MRI in the Investigation of Blast-Related Traumatic Brain Injury

The current combat operations in Iraq and Afghanistan have involved U.S. military personnel in major ground combat and hazardous security duty. Studies are needed to systematically assess the mental health of members of the armed services who have participated in these operations and to inform policy with regard to the optimal delivery of mental health care to returning veterans. We studied members of four U.S. combat infantry units (three Army units and one Marine Corps unit) using an anonymous survey that was administered to the subjects either before their deployment to Iraq (n=2530) or three to four months after their return from combat duty in Iraq or Afghanistan (n=3671). The outcomes included major depression, generalized anxiety, and post-traumatic stress disorder (PTSD), which were evaluated on the basis of standardized, self-administered screening instruments. Exposure to combat was significantly greater among those who were deployed to Iraq than among those deployed to Afghanistan. The percentage of study subjects whose responses met the screening criteria for major depression, generalized anxiety, or PTSD was significantly higher after duty in Iraq (15.6 to 17.1 percent) than after duty in Afghanistan (11.2 percent) or before deployment to Iraq (9.3 percent); the largest difference was in the rate of PTSD. Of those whose responses were positive for a mental disorder, only 23 to 40 percent sought mental health care. Those whose responses were positive for a mental disorder were twice as likely as those whose responses were negative to report concern about possible stigmatization and other barriers to seeking mental health care. This study provides an initial look at the mental health of members of the Army and the Marine Corps who were involved in combat operations in Iraq and Afghanistan. Our findings indicate that among the study groups there was a significant risk of mental health problems and that the subjects reported important barriers to receiving mental health services, particularly the perception of stigma among those most in need of such care. Copyright 2004 Massachusetts Medical Society

Functional neuroimaging and electrophysiological studies have documented a dynamic baseline of intrinsic (not stimulus- or task-evoked) brain activity during resting wakefulness. This baseline is characterized by slow (<0.1 Hz) fluctuations of functional imaging signals that are topographically organized in discrete brain networks, and by much faster (1-80 Hz) electrical oscillations. To investigate the relationship between hemodynamic and electrical oscillations, we have adopted a completely data-driven approach that combines information from simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Using independent component analysis on the fMRI data, we identified six widely distributed resting state networks. The blood oxygenation level-dependent signal fluctuations associated with each network were correlated with the EEG power variations of delta, theta, alpha, beta, and gamma rhythms. Each functional network was characterized by a specific electrophysiological signature that involved the combination of different brain rhythms. Moreover, the joint EEG/fMRI analysis afforded a finer physiological fractionation of brain networks in the resting human brain. This result supports for the first time in humans the coalescence of several brain rhythms within large-scale brain networks as suggested by biophysical studies.

A previous report of correlations in low-frequency resting-state fluctuations between right and left hemisphere motor cortices in rapidly sampled single-slice echoplanar data is confirmed using a whole-body echoplanar MRI scanner at 1.5 T. These correlations are extended to lower sampling rate multislice echoplanar acquisitions and other right/left hemisphere-symmetric functional cortices. The specificity of the correlations in the lower sampling-rate acquisitions is lower due to cardiac and respiratory-cycle effects which are aliased into the pass-band of the low-pass filter. Data are combined for three normal right-handed male subjects. Correlations to left hemisphere motor cortex, visual cortex, and amygdala are measured in long resting-state scans.