MRI study shows how FA disrupts communication for brain regions
Scans show reduced connectivity linked to more severe disease
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Brain scans of people with Friedreich’s ataxia (FA) revealed reduced communication between the frontal cortex and the cerebellum, two-interconnected brain regions involved in planning and coordinating voluntary movement, a pattern that was tied to greater physical disability and cognitive difficulties.
At the same time, connections within the cerebellum and between the cerebellum and other brain regions increased, which researchers said suggests potential compensatory mechanisms in the presence of progressive structural damage.
The study, “Fronto-Cerebellar Connectivity Disruptions and Functional Reorganization in Friedreich’s Ataxia: A Structural and Resting-State fMRI Study,” was published in NeuroImage.
FA is a progressive disorder marked by the hallmark symptom of ataxia, or loss of muscle control and coordination. MRI scans of FA patients have shown that the spinal cord, brainstem, and cerebellum shrink or change as the disease progresses. Some of these changes can appear before symptoms become severe.
Yet structural changes alone do not fully explain why symptoms vary so much among individuals. Researchers now think that changes in how different parts of the brain communicate also play an important role.
Combined scans provide clearer picture
A research team in Germany combined structural MRI with functional MRI (fMRI), a technique that measures brain activity and connectivity. Their goal was to obtain a more complete picture of how FA affects brain networks and identify imaging markers to track the condition and help guide the development of more targeted treatments.
The researchers performed both types of brain scans on 37 adults, 20 of them women, with FA and 41 healthy controls matched by sex and age. Participants were tested at rest without engaging in active tasks.
On structural MRI scans, people with FA consistently showed shrinkage of the brainstem and cerebellum. Parts of the thalamus, which help relay information in the brain, were also smaller. And fluid-filled spaces in the brain appeared larger, indicating tissue loss.
When the team compared these findings with clinical data, greater shrinkage in the cerebellum and related areas was associated with more severe disease, longer duration, and poorer performance on movement and coordination tasks. Cognitive difficulties were also linked to structural changes in the brainstem, cerebellum, and thalamus.
In fMRI scans, the team found a complex pattern. Some brain regions, especially those involved in voluntary motor control, showed increased activity. Other areas, including parts of the temporal and visual regions, showed reduced activity.
A functional connectivity analysis revealed that connections between the cerebellum and frontal brain regions (fronto-cerebellar) involved in planning and movement were generally weaker in FA patients. In contrast, communication within the cerebellum itself and between some other brain regions was stronger.
Weaker communication between the cerebellum and motor-related areas corresponded with greater disability and poorer performance on coordination and speech tasks. Conversely, stronger connections between regions, such as the thalamus and striatum, were observed at more advanced stages. Similar patterns were also associated with longer disease duration.
In cognitive assessments, reduced fronto-cerebellar connectivity was associated with difficulties in attention, processing speed, and word generation. Stronger connections within the cerebellum were associated with poorer short-term memory performance. In contrast, stronger connections between the cerebellum and memory-related areas (such as the hippocampus) were associated with better performance on some cognitive tasks. This same pattern was also associated with more mood symptoms.
The pattern of stronger memory-related connections but weaker frontal connections “may reflect compensatory functional enhancement that could help sustain function in the presence of progressive structural damage and clinical impairment,” the team wrote.
The changes in the brain’s structure and communication were closely connected. For example, greater loss of brain tissue in certain areas was associated with weaker connections between the frontal regions and the cerebellum. More severe damage in the brainstem, cerebellar white matter, and thalamus was associated with increased connectivity within the cerebellum and between the cerebellum and the cerebrum (the uppermost part of the brain).
“Our findings offer a coherent and clinically meaningful account of how [FA] affects brain function at rest,” the researchers wrote. They said they “support the view that [FA] is best understood as a distributed network disorder, in which degeneration of cerebellar efferents [nerve fibers originating from the cerebellum] disrupts long-range integration, while additional circuits may be recruited, potentially reflecting adaptive reorganization as disability progresses.”
