A team of researchers from the University of Maryland have developed a new imaging technique that can identify the specific changes in neural communication as a result of mild traumatic brain injury (mTBI). The researchers state that this information could help explain why many patients with a diagnosis of mTBI will experience physical, cognitive, and behavioural symptoms that may persist. The opensource study is published in the journal Brain Connectivity.
The Centers for Disease Control and Prevention (CDC) estimates that each year 1.7 million people sustain a traumatic brain injury (TBI) which results in 275,000 hospitalizations and 52,000 deaths. TBI is caused by an exterior mechanical force applied to the skull causing damage to the brain tissue and resulting in short and long term cognitive impairments, functional disability, or behavioural maladjustment.
Previous studies show that the majority of TBI cases, approximately 75%, are diagnosed as mild TBI (mTBI). However, even among patients diagnosed with a ‘mild injury,’ many experience physical, cognitive, and behavioural deficits, resulting in a limited ability to return to work and reduced quality of life. As a consequence of these injuries, the patients and family members are left with a large emotional burden and the nation incurs an immense financial burden, estimated to cost annually between $62-$78 billion, which includes both direct and indirect costs.
The team state that there has been a great deal of interest in recent years in the use of resting state fMRI (rs-fMRI) to investigate alterations in neural communication in mTBI patient populations. Following mTBI, earlier resting state fMRI studies have noted reduced interhemispheric functional connectivity and increased thalamo-cortical functional connectivity. However, the majority of the research probing altered resting state functional connectivity in the mTBI population has focused on alterations to the default mode network (DMN), a set of regions in the brain that are deactivated during task related activities while demonstrating increased activity during rest conditions.
Past studies have noted reduced functional connectivity within the DMN as well as increased functional connectivity between the DMN and its anticorrelated task positive network, also referred to as the executive network.
The current study employs the imaging technique known as resting state functional magnetic resonance imaging (rs-fMRI). Instead of relying on a single frequency range to analyze functional connectivity in the brain, the researchers measured multiple frequency ranges using a technique known as discrete wavelength decomposition.
The team imaged sixty-three patients using rs-fMRI across multiple frequency ranges, 31 patients where neurologically intact subjects serving as a control population and 32 patients where diagnosed with mTBI. All participants were over the age of 18. The current study demonstrated for the first time ever that rs-fMRI can effectively be used to assess the effect of mTBI on the communication within the DMN.
The data findings also showed alterations in functional connectivity in patients during the acute and chronic stages of injury, differences between the two groups, and recovery of connectivity over time. The results showed DMN connectivity progressively changes during the first 6 months following injury, which is suggestive of either compensatory reorganization or disrupted network communication due to potential structural damage.
The team surmise that the consequences of head injury are difficult to detect with conventional CT and MRI diagnostic methods. This is especially true in the weeks to months following the traumatic event. They go on to add that they are on the forefront of developing a new MRI technique to pinpoint brain injury in the critical window after the traumatic event has occurred.
Visualization of the anatomy of the default mode network (DMN) regions of interest (ROIs) along with the respective Montreal Neurological Institute (MNI) coordinates. The ROIs are shown in standard space overlaid on the MNI template. PCC: Posterior cingulate cortex (PCC). MPFC: Medial prefrontal cortex. RLP: Right lateral parietal. LLP: left lateral parietal. LITG: Left inferior temporal gyrus. RITG: Right inferior temporal gyrus. LPHG: Left parahippocampal gyrus. RPHG: Right parahippocampal gyrus. Investigation of Multiple Frequency Ranges using Discrete Wavelet Decomposition of Resting State Functional Connectivity in Mild Traumatic Brain Injury Patients. Gullapalli et al 2015.