After a stroke, which is a brain injury caused by a disruption of blood flow, damage can occur to a part of the brain called the prefrontal cortex (PFC). The PFC is located at the front of the brain and is involved in planning and controlling movement. This damage can disrupt the brain's communication networks that are essential for coordinating movement and processing sensory information, a process known as sensorimotor integration. This disruption can lead to problems with the function of the ankle.
This exploratory study used a technique called functional near-infrared spectroscopy (fNIRS) to investigate brain activity in people who were in the subacute phase of stroke recovery, which is the period from a few days to a few months after the stroke. fNIRS is a non-invasive method that measures changes in blood flow and oxygen levels in the brain by shining near-infrared light through the scalp. These changes indicate which parts of the brain are active.
The research had three main goals. First, to see if brain activity in the PFC was different during three distinct tasks involving the paretic ankle, which is the ankle on the side of the body weakened by the stroke. Second, to see if there were differences in activity between the brain's left and right sides (hemispheres). Third, to examine the relationship between any imbalance in brain activity between the two hemispheres and the person's functional recovery.
The study involved nine participants. The researchers used fNIRS to measure blood flow changes in both sides of the PFC while the participants performed three tasks. The first task was active movement, where the participants moved their own ankle up (dorsiflexion) and down (plantarflexion). The second was passive movement, where a researcher moved the participant's ankle up and down for them. The third was somatosensory stimulation, where a sensation was applied to the ankle to stimulate the sense of touch and body position.
To measure the participants' physical function, the researchers used a standard clinical test called the Fugl-Meyer Lower Extremity (FMLE) assessment. They also calculated a laterality index, which is a score that quantifies the degree of imbalance in brain activity between the two hemispheres.
When comparing the three different tasks, the study found no differences in the level of PFC activation. There were also no differences in activation levels when comparing the left and right hemispheres of the brain.
However, the study did find a potential relationship between the imbalance of brain activity and the participants' physical function. A greater imbalance between the two hemispheres during the passive movement and sensory stimulation tasks appeared to be associated with poorer scores on the sensory and motor sections of the FMLE test.
The results suggest that these specific ankle-related tasks may not cause different levels of brain activity in either side of the prefrontal cortex on its own. The findings do indicate that the balance of PFC activity between the two brain hemispheres in response to sensory information and passive movement might be connected to a person's clinical sensory and motor function. This imbalance could potentially serve as a useful measurement for tracking a person's recovery after a stroke.
