Post-stroke acute dysexecutive syndrome: Experts shed light on this little-understood condition

For the first time, researchers have measured the physical evidence of diminished neural processing within the brain after a stroke.

Many people after suffering from minor stroke recover well if they receive prompt treatment. But sometimes, some stroke patients experience a kind of subtle brain fuzziness. They may not be able to grasp ideas or multitask as they did earlier. Conversations may also go over their head at times. This happens even though there are no clinical signs of trauma and these symptoms may often be overlooked both by patients and doctors.

But this is actually a medical condition called post-stroke acute dysexecutive syndrome (PSADES). This is a cognitive dysfunction that people commonly experience after suffering from even minor strokes. The symptoms appear soon after the stroke occurs. While it correlates to having dead tissue lesion(s) in the brain left behind by the stroke, it does not seem to be related to the location of the lesion(s). Fortunately, PSADES gradually improves in the months after recovery. But what has been going on inside the brain during this time?

Diminished neural processing of the brain after stroke

Stroke patients have reported these cognitive difficulties to their doctors for a long time. Until now, the evidence of this problem has mostly been anecdotal. A new study by University of Maryland, Johns Hopkins University and New York University researchers for the first time provides measurable physical evidence of diminished neural processing within the brain after a stroke. It suggests that PSADES is the result of a global connectivity dysfunction. The paper, "Poststroke acute dysexecutive syndrome, a disorder resulting from minor stroke due to disruption of network dynamics," has just been published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Any lesion in the brain can disrupt cognitive connectivity

According to researchers, it is usually thought that certain parts of the brain are responsible for specific functions, but, in reality, the entire brain is needed to think clearly and complete tasks. In this study, they show how a small lesion anywhere can disrupt the cognitive network and result in a global dysfunction.

The researchers used magnetoencephalography (MEG) to look at the brain functioning of patients who recently experienced minor strokes. This is a non-invasive neuroimaging technology that employs very sensitive magnetometer sensors to make high-speed recordings of naturally occurring magnetic fields produced by electrical currents inside the brain. The subject typically sits under or lies down inside the MEG scanner, which resembles a whole-head hair drier. Once inside the scanner, patients had their magnetic fields recorded as they completed word and picture matching tasks. These tasks all involved memory, memory search or identification. In some tasks the patient needed to speak the answer, while others required them to press a "yes" or "no" button. An age-matched control group of people who had not suffered a stroke also completed the tasks and were recorded. Then the two sets of MEG recordings were compared.

Stroke patients' brains are more subdued

The stroke patients' recordings exhibited distinct characteristics that were different from the control group. For example, the signals within their brains were noticeably more subdued, appearing more like rolling hills rather than mountain peaks. This is an indicator that the brain is processing less efficiently. The stroke patients also took about twice as long as the control group to complete the tasks. In addition, they were not able to modulate their brain activity at different stages of performing the tasks, a further indicator of neural sluggishness. These patterns of inefficient processing suggest a dysfunction in the brain's distributed network -- a disruption of the network's dynamics.

But questions remain

But after a review six months later, researchers were surprised to see that most patients not only performed better on the tests, but also anecdotally reported their symptoms of impairment had largely resolved. However, surprisingly, the scans themselves looked relatively the same. Why symptoms improved while the recordings did not look very different is a mystery. Researchers say that they do not know the neural mechanisms that allowed the patients to improve. It could be that new neural communication routes have formed, to bypass the sluggish pathways. Or it could be that older, less used, communication pathways have been repurposed. Further studies will help to unlock this question.

(With inputs from Agencies)