Methods
Magnetic Resonance Imaging (MRI) is a tool that allows us to visualize different aspects of brain function and anatomy. Individuals lie on a scanner bed and high-resolution pictures of their brain are taken using a high magnetic field.
Functional MRI enables us to measure brain activity indirectly by detecting changes in the concentration of oxygen in the blood. When you are flexing your fingers, regions in your brain that control movement (i.e. motor cortex) are in use and thus oxygen and blood flow also increases to that region. The signal we measure is called BOLD – blood-oxygenation-level dependent.
Figure 1: Motor brain regions are active when we listen to musical rhythms.
Figure 1: Motor brain regions are active when we listen to musical rhythms.
Diffusion MRI allows us to examine white matter of the brain. Using tractography analyses, we can visualize white matter anatomical connections. For example, we can look at the corticospinal tract, which connects motor cortex with the spinal cord, and is often affected in individuals with stroke. In particular, we can assess the integrity of these white matter pathways and this can be used as a marker of disease.
Figure 2: Integrity of corticospinal tract is important for stroke recovery.
Figure 2: Integrity of corticospinal tract is important for stroke recovery.
Resting state fMRI is a technique that allows us to measure how well the BOLD response is correlated across time in different brain regions. We measure this when the brain is ‘resting’, that is, when the participant is not performing a task. Resting state fMRI enables us to gain an understanding for which brain regions are interacting together in a network. These resting state networks (or patterns of brain connections) can be changed by learning, and as well by a disease and thus can be a marker of brain health.
Figure 3: Neural activity between left and right motor cortex are temporally coupled.
Figure 3: Neural activity between left and right motor cortex are temporally coupled.
Transcranial magnetic stimulation (TMS) and Transcranial direct current stimulation (TDCS) are both non-invasive tools that allow us to stimulate the brain through the scalp when subjects are awake. TMS uses a rapidly changing magnetic field to induce a weak electric current; TDCS uses a small electric direct current. Both tools can be used to facilitate or inhibit neural activity. In individuals with stroke, we can apply these tools to excite stroke-affected brain regions. In contrast, sometimes the stroke can cause over-activity in healthy brain regions for which these tools can be used to dampen or inhibit. TMS can also be used to look at how different brain regions influence each other.
The Optotrak Certus is a motion-capture system that allows us to precisely evaluate movements. Markers or infrared emitting diodes, are attached to a person and a sensor detects motion of these markers in real time. This enables us to determine the speed, accuracy and efficiency of how someone with a stroke moves their arm. We can also evaluate the degree to which movements are coordinated.
Electrogoniometers enable us to measure changes in joint range of motion during movement. An electrogoniometer consists of a spring cable joining two segments. Each segment is attached to a body part (i.e. arm and forearm) with the spring cable going across a joint (i.e. elbow). As the elbow joint moves, the spring bends or extends. The tension or strain placed on the spring results in a change in resistance, which is measured in volts and then converted to joint angles.
Thus motion capture systems and electrogoniometers allow us to quantify how movements have been affected by stroke and whether they have improved after a therapy.
Thus motion capture systems and electrogoniometers allow us to quantify how movements have been affected by stroke and whether they have improved after a therapy.