Symptoms of cognitive impairment, such as changes to thinking and memory, in people with established diseases such as MS, can be detected using cognitive tests. But these tests are less useful in people who have more subtle changes to their thinking and memory, such as those with clinically isolated syndrome (CIS). CIS is a precursor to MS, where people have experienced only one clinical attack. These people may show only tiny signs of declining cognition, and many of the verbal and written cognitive tests available lack the sensitivity to detect these small changes. Another way to test cognition is through cognitive eye movement tasks. Eye movement tasks can test a range of cognitive functions including attention, memory and decision making.
A special type of magnetic resonance imaging (MRI) called functional MRI can also be used to look at changes that cause a decline in cognition. A functional MRI measures brain activity using blood flow – when a particular region of the brain is in use, there is increased blood flow. Even people who have no obvious cognitive impairment show changes in the amount of brain activity during a functional MRI. So this approach may be useful to investigate cognitive impairment in people with CIS.
A team of Australian researchers led by Ms Sanuji Gajamange, a postgraduate scholar funded by MS Research Australia, and Dr Scott Kolbe, aimed to understand how changes in the brain may contribute to cognitive impairment in people with CIS. They did this by looking at changes in cognition using functional MRI and cognitive tests, including eye movement tasks. Published in PLoS One, the team recruited 18 people with CIS and 17 people without CIS. The researchers had them complete eye movement tasks during a functional MRI and looked at the brain activity during these tasks. The advantage of eye movement tasks is that they don’t cause head motion that can lead to unreliable results, unlike written and verbal tests. The researchers looked at two different eye movements – they had the participants direct their gaze towards a target and away from a target as accurately and quickly as possible. The participants also completed cognitive tests commonly used in the clinic as a comparison.
The eye movement task results showed little difference in cognition between people with and without CIS – both had similar response times. Yet the participants with CIS showed a slightly higher error rate for the task that involved them looking away from a target. The researchers also found that the results were similar to the cognitive tests available in the clinic.
Even though there was no major cognitive impairment in participants with CIS, the researchers found that they had stronger brain activation than those without CIS for this task. This task is much more demanding compared to the task of looking towards a target, and it’s possible that people with CIS need more effort to stop themselves from looking at the target.
These exciting findings suggest that changes in brain activity are responsible for small changes in cognition in the very early stages of MS. While further studies with a larger number of people will be needed, cognitive eye movement tasks in combination with a functional MRI could potentially be used as a diagnostic tool for CIS, along with other cognitive tests. This will hopefully allow for early intervention to prevent the onset of MS or slow down its progression.