Eye-opening apraxia is a neurological condition that prevents people from voluntary opening their eyes. Although people with stroke often experience this, little is known about it. Now, by comparing brain scans, researchers have found unique patterns showing that most lesions related to eye-opening apraxia occur in a specific area of the brain’s right hemisphere. The method and new knowledge could potentially expand understanding of the brain’s network connections and their significance in studying other neurological conditions.
For most people, opening their eyes is the simplest of tasks. People with eye-opening apraxia completely lose the ability to voluntarily open their eyes. Surprisingly common, it affects up to 5–6% of people with severe stroke and has a general prevalence of 59 per million population, yet the neural basis of the condition is unknown, which can have severe consequences.
“Some doctors mistakenly believe that these people with stroke are in a coma, whereas in reality, they just cannot open their eyes. Since activation is crucial for stroke recovery, this can delay rehabilitation. We therefore decided to try to determine what causes this so we can better identify the condition and prevent misunderstandings about their consciousness level,” explains Daniel Kondziella, a neurologist and Clinical Research Associate Professor from the Department of Neurology at Rigshospitalet in Copenhagen.
Giving priority to the relevant stimuli
To solve the mystery, researchers analysed the brains of 27 people with eye-opening apraxia after stroke and compared them with control groups of 20 people with aphasia – inability to speak and/or understand – and 45 people with hemiballismus – uncontrollable movements. Both conditions also occur frequently after stroke, so the researchers hoped to find those that were specific to eye-opening apraxia.
“We used a technique called lesion network mapping in which we use magnetic resonance imaging (MRI) to identify functionally connected brain areas affected by specific lesions – or brain injuries. This can provide a clearer picture of which brain networks are involved in various neurological disorders,” says Pardis Zarifkar, PhD from the Department of Neurology at Rigshospitalet.
Lesions were mapped by comparing them with a very precise standard – a brain atlas created via MRI data from 966 healthy adults in the Harvard Dataverse. The researchers’ analysis showed that most lesions associated with eye-opening apraxia occurred in the right hemisphere – whereas, for example, those with aphasia had them on the left side, and despite relative anatomical heterogeneity, the injuries clearly pointed somewhere.
“The network study points out that the injuries occur in the anterior and posterior of the brain’s insula area, which activates behavioural responses to stimuli by detecting, filtering and setting priorities for relevant stimuli among the many competing inputs received throughout the day,” explains Pardis Zarifkar.
Important not to go astray
Being able to control the opening and closing of the eyelids voluntarily requires getting different parts of the nervous system and eye muscles to work together. To move the eyelids, two muscles, orbicularis oculi and levator palpebrae superioris, must both be active. Additionally, the Müller’s tarsal muscle helps to lift the eyelid. Since the brain’s insula is responsible for emotions, taste, hunger and body awareness, the link between eyelid opening and the insula appears convincing.
“This may not necessarily be what we had expected a priori, but it is in accordance with the gut feeling that these things could be involved. The insula is crucial for decision-making. Therefore, we are not completely surprised that the insula is linked to voluntary eye opening,” explains Daniel Kondziella.
The new knowledge does not lead to any new type of rehabilitation for people with eye-opening apraxia, since the condition often disappears after a few days among people with stroke, but being aware that what may appear to be coma is actually something completely different can be extremely significant.
“Coma is a condition that requires investigation, clarity and a diagnosis, so it is important not to go astray and instead determine that the condition is eye-opening apraxia. And clearly, the more you talk to these patients, the more they are stimulated and the more they sit up instead of lying in bed and are mobilised, the more you help the brain reorganise networks so that the body starts functioning again,” says Daniel Kondziella.
May benefit treatment for other conditions
The new experience with the use of lesion network mapping as a method is just as important as the new knowledge about eye opening. The method can be used to study the brain’s functional organisation. It enables specific damaged areas of the brain to be linked and the resulting changes in behaviour or function to be observed in a way that has not previously been possible.
“By assessing how these lesions affect various cognitive or motor functions, we can better draw conclusions about the brain’s network connections and understand which regions are crucial for specific tasks. This helps to reveal not only the function of individual brain areas but also their interactions within neural networks and therefore our understanding of the brain’s complex architecture,” says Pardis Zarifkar.
Therefore, the research in eye-opening apraxia may prove to benefit the understanding of other conditions.
“There are good parallels to other coma mimics such as cognitive motor dissociation: people who are completely paralysed in their motor output. They cannot squeeze a hand, stick out their tongue or the like. When you put them in a special type of scanner, they still show voluntary brain activity in response to questions. It is important to find these patients and try to restore communication. There is still a long way to go, but the new method gives us important knowledge to move forward,” concludes Daniel Kondziella.
