Houston, Texas, USA : Some brain-injured people left with disorders of consciousness — unable to communicate or respond, such as people in a coma — nevertheless show normal brain responses to spoken language as measured through the scalp by electroencephalography (EEG). Functional magnetic resonance imaging (fMRI) studies also show that such patients retain the ability to carry out repeated mental imagery tasks, as demonstrated in earlier studies.
The findings reported in Current Biology on November 29 suggest that EEG might offer a cost-effective and efficient means to identify patients who are cognitively aware but unable to respond, a condition known as cognitive motor dissociation (CMD). More broadly, the researchers say, they underscore the importance of rethinking the way patients with severe brain injury are assessed.
“These findings emphasize the urgency to screen and identify patients who may be trapped in their heads and treated as unconscious,” says Nicholas Schiff, a professor of neuroscience in the Feil Family Brain and Mind Research Institute at Weill Cornell Medicine, New York, NY. “They also highlight how important it is that resources be developed to bring greater medical infrastructure and efforts to enhance communication with such persons.”
Brain activity rises and falls with the variation in sound pressure produced by speech. This variation of sound pressure is known as the speech envelope. The brain follows this envelope with matched electrical activity that arises with a time delay of around a tenth of a second in healthy people.
In the new study, the researchers set out to study the natural speech envelopes (NSEs) of 13 healthy controls in comparison to 21 people with a severe brain injury. Those brain-injured patients in the study had widely varying patterns and types of structural brain injuries.
Healthy controls listened to a portion of Alice’s Adventures in Wonderland by Charles Lutwidge Dodgson. Those with brain injury heard stories and recollections about their own lives prior to the injury spoken by family members. The researchers measured the time delay of electrical activity in the brain that followed that continuously spoken language.
Their studies found that normal time delays were preserved in brain-injured patients with high-level cognitive functions as independently assessed using fMRI. Those patients included people without any reliable means of communication.
“Our findings confirm that patients who harbor the cognitive capacity to carry out fMRI mental imagery tasks are biologically different and show the integrity of cortical speech processing mechanisms in their EEG signals,” says Schiff, who has stock options with Enspire DBS Therapy, Inc., a company focused in revitalizing stroke recovery to restore motor functions for hemiplegic stroke patients.
The findings suggest that the NSE may be used as a screening tool to help stratify patients with severe brain injuries and identify those patients who show only covert evidence of command following utilizing neuroimaging or electrophysiological methods that demand high levels of cognitive function, according to the researchers.
EEG is “cost effective and efficient and may be adapted for continuous tracking of recovery over time,” the researchers write. “Once identified, patients with evidence of command-following activity can be tested to determine whether they can modulate the NSE response with attention to speech stimuli to guide auditory brain-computer interfaces to restore communication and reveal the fullness of their consciousness.”
Schiff says that his team hopes to test the NSE as a measure to screen large numbers of patients for hidden cognitive capacities. They also plan to work toward developing new methods to help those patients they’ve already identified as having high levels of cognitive function improve their ability to interact with the outside world.
Citation: Current Biology, Braiman et al.: “Cortical Response to the Natural Speech Envelope Correlates with Neuroimaging Evidence of Cognition in Severe Brain Injury” Cell. DOI: 10.1016/j.cub.2018.10.057
A second study found that EEG and fMRI may detect consciousness in patients with acute, severe traumatic brain injury
EEG, fMRI may detect consciousness in patients with acute, severe traumatic brain injury
The use of functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) may be able to identify ICU patients with severe traumatic brain injuries who have a level of consciousness not revealed by the standard bedside neurological examination. A report from Massachusetts General Hospital (MGH) investigators, published in the journal Brain, is the first to test such an approach in acutely ill patients for whom critical decisions may need to be made regarding the continuation of life-sustaining care.
“Early detection of consciousness and brain function in the intensive care unit could allow families to make more informed decisions about the care of loved ones,” says Brian Edlow, MD, of the Center for Neurotechnology and Neurorecovery in the MGH Department of Neurology, co-lead and corresponding author of the study. “Also, since early recovery of consciousness is associated with better long-term outcomes, these tests could help patients gain access to rehabilitative care once they are discharged from an ICU.”
The standard bedside neurological examination of patients with serious brain injuries may inaccurately indicate that a patient is unconscious for several reasons. The patient may be unable to speak, write or move because of the effects of the injury itself or sedating medications, or a clinician may misinterpret a weak but intentional movement as a reflex response. Studies have suggested that the rate of misclassifying conscious patients as unconscious could be as high as 40 percent. While previous studies have used fMRI or EEG to detect this sort of “covert consciousness” in patients who have moved from acute-care hospitals to rehabilitation or nursing care facilities, no such study had previously been conducted in ICU patients.
The current study enrolled 16 patients cared for in MGH intensive care units after severe traumatic brain injury. Upon enrollment, eight were able to respond to language, three were classified as minimally conscious without language response, three classified as vegetative and two as in a coma. fMRI studies were conducted as soon as patients were stable enough for the procedure, and EEG readings were taken soon afterwards, ideally but not always within 24 hours. A group of 16 healthy age- and sex-matched volunteers underwent the same procedures as a control group.
The screenings were taken under three experimental conditions. To test for a mismatch between participants’ ability to imagine performing a task and their ability to physically express themselves – what is called cognitive motor dissociation – participants were asked to imagine squeezing and releasing their right hand while in the fMRI scanner and while EEG readings were being taken. Since it is known that certain areas of the brain can respond to sounds even when an individual is asleep or under sedation, participants also were exposed to brief recordings of spoken language and of music during both fMRI and EEG screenings. Those tests were designed to detect activity in areas of the brain that are part of the higher-order cortex, which interprets the simple signals processed by the primary cortex – in this instance not just detecting a sound but potentially recognizing what it is.
Of the eight patients who were classified as unable to respond to language in the bedside examination, evidence of covert consciousness based on the hand-squeeze exercise was found in four, including the three originally classified as vegetative. In two additional patients, higher-order cortex activity was seen in response to either language or music. While higher-order cortical activity doesn’t prove that a patient is conscious, Edlow notes, finding a response in those structures could have implications for a patient’s eventual recovery.
He also stresses that negative responses to these tests should not be taken as predicting a low likelihood of recovery. Not only did about 25 percent of the healthy controls have no detectable brain response during the hand squeeze imagery test, but one of the comatose patients who had no responses to language, music or motor imagery during the early fMRI and EEG tests went on to have an excellent recovery 6 months later. In fact, no associations were found between early brain responses and long-term outcomes, which could relate to the small size of the study or the fact that several patients were sedated during the fMRI and EEG tests.
“It is also difficult to measure the false-positive rate for stimulus-based fMRI and EEG tests in these patients, since there is no definitive, gold-standard test to diagnose their level of consciousness,” explains Edlow, who is an assistant professor of Neurology at Harvard Medical School. “Much more work needs to be done to determine the utility of these techniques for detecting consciousness in patients with severe traumatic brain injuries. Based on these results, our team at the MGH Laboratory for NeuroImaging of Coma and Consciousness is working on improving the accuracy of these tests, and we are planning a larger follow-up study in the near future.”
Citation for second study : Brian L. Edlow et al, Early detection of consciousness in patients with acute severe traumatic brain injury, Brain. DOI: 10.1093/brain/awx176.
A third study found that brain scans may help predict recovery from coma
Brain scans may help predict recovery from coma
Brain scans of people in a coma may help predict who will regain consciousness, according to a study published in Neurology, the medical journal of the American Academy of Neurology. The study looked at connections between areas of the brain that play a role in regulating consciousness.
For the study, 27 people in a coma with severe brain injuries were compared to 14 healthy people of the same ages. All of the participants had functional magnetic resonance imaging (fMRI) scans taken of their brains. For those in a coma, the scans were conducted after any sedative drugs were out of their systems. Three months after their injuries, four of the people with coma had recovered consciousness. The others remained in a minimally conscious state or a vegetative state at three months.
All of the comatose people had significant disruption in the connections between brain areas and the posterior cingulate cortex. These changes were the same whether the brain injury was due to trauma or to lack of oxygen, such as from cardiac arrest.
The researchers found that the coordination of activity between the posterior cingulate cortex and the medial prefrontal cortex was significantly different between those who went on to recover from the coma and those who remained in a minimally conscious state or a vegetative state. The coordination between the two brain areas was the same for the healthy participants and those who regained consciousness.
Study author Stein Silva, MD, PhD, of the French national research institute, INSERM U825, in Toulouse, said that more research is needed before these results can be used to guide decisions about people in comas.
“We need to do more studies with larger numbers of patients to substantiate these results, but the findings are promising,” Silva said. “We could be able to predict better who is more likely to recover from a coma and eventually develop innovative networks-based personalized treatments for people with brain injuries.”