Functional imaging and related techniques: An introduction for rehabilitation researchers

Over the past 25 years, techniques to image brain structure and function have offered investigators in the cognitive neurosciences and related fields unprecedented opportunities to study how human brain systems work and are connected. Indeed, the number of peer-reviewed research articles using these techniques has grown at an exponential rate during this period. Inevitably, investigators have become interested in mapping neuroplastic changes that support learning and memory using functional neuroimaging, and concomitantly, rehabilitation researchers have become interested in mapping changes in brain systems responsible for treatment effects during the rehabilitation of patients with stroke, traumatic brain injury, and other brain injury or disease. This new rehabilitation research and development arena is important because a greater understanding of how and why brain systems remap in the service of rehabilitation will lead to the development of better treatments. At the same time that functional neuroimaging methods have been developed, new structural neuroimaging techniques also have been added to the tool box of rehabilitation researchers. For example, diffusion tensor imaging (DTI) and related magnetic resonance (MR) techniques offer the ability to assess human white matter pathways in vivo. Not only can these techniques be used to estimate the integrity of a given volume of white matter, but they also can be used to trace fiber tracts within the brain. This latter development is exciting because most of what we know (or at least thought we knew) about the connections of the human cortex has actually come from research on nonhuman primates, leaving questions especially about the phylogenetically newer portions of the cortex. In the rehabilitation arena, a better understanding of how the brain’s connections are damaged could help us to predict what treatments are best for different research subjects and, eventually, might be useful in selecting the best treatment strategies for individual patients. Because the newer functional and structural neuroimaging techniques have enormous implications for rehabilitation research and development, it is highly desirable that rehabilitation researchers be able to evaluate the usefulness of the techniques for rehabilitation research and that the consumers of rehabilitation research (i.e., clinicians and researchers) be able to evaluate research findings that have applied the techniques. The purpose of this article is to discuss functional and structural imaging techniques used in rehabilitation research. We will not cover routine clinical MR or x-ray computerized tomography (CT) images. Rather, we will concentrate on a variety of techniques used most frequently, though not necessarily exclusively, in research settings. The article will consist of two main sections: (1) Because of the extraordinary versatility or MR techniques, the large number of MR techniques will be discussed first. (2) Subsequently, other functional neuroimaging techniques will be discussed, including: Positron Emission Tomography (PET), Magnetoencephalography/Magnetic Source Imaging (MEG/MSI), Near Infrared Spectroscopy (NIRS), Transcranial Magnetic Stimulation (TMS), and Electroencephalography/Evoked Potentials (EEG/EPs). For each imaging modality, we will give a brief explanation of the modality, its uses/potential uses in rehabilitation research, its strengths and limitations, and an example of research in the area.