January
16
If Your Brain Could Speak
As neuroscientists, we spend much of our time staring at brain signals trying to decipher what the brain is “telling” us. We draw conclusions about memories, actions and even emotions from patterns of neural activity. In a very metaphorical sense the data “speaks to us”, it answers our questions, begs us to ask more, and occasionally tells us when we had a dumb idea. But what if neural activity could actually be a tool for communication? Evidence for this idea comes from a growing field of research that uses neuroimaging to study patients who have lost their ability to speak.
Communicating with recovering coma patients
Acute brain injuries can arise from physical traumas to the head or a stroke that cuts off oxygen to the brain. As a result, many patients will enter a coma or a state of prolonged unconsciousness [1]. The trajectory of recovery varies considerably across patients but a proportion of patients will eventually awaken from their coma. A surprisingly difficult question to answer is whether or not these “awake” patients are conscious and aware of themselves and their surroundings. Physicians look for two key signs that a patient is conscious: 1) the patient is visibly awake (i.e. open eyes) and 2) the patient is aware and able to respond to commands (i.e. “raise your hand if you hear me.”). Patients that are unable to respond to these types of commands are considered to be in a vegetative state. In the vegetative state, the brain manages to preserve reflexive responses and execute many of the bare necessities for life (i.e. breathing, sleeping, etc.) without assistance. But its cognitive abilities seem to stop there [2,3].
A unique set of patients, however, appear to get stuck in a “grey zone”, or a state of minimal consciousness in which they are conscious of these instructions yet unable to produce the requested response [4]. Without any way to communicate with the outside world, these patients appear clinically identical to a vegetative state patient. A critical question is whether there are other ways to determine consciousness without access to speech and overt behaviors.
Dr. Adrian Owen was the first researcher to propose using neural activity as a tool to examine these patients. His approach required finding a mental task that would prove conscious awareness. There are many cognitive processes that fly below the radar of our conscious awareness and occur automatically. For instance, although we might pretend not to recognize our ex in the grocery store, one glance at that face will have us singing Whitney Houston’s “I Will Always Love You” on the drive home. Facial recognition, language processing, and several other cognitive processes occur automatically and can be detected in neural activity. In fact, even healthy patients that are heavily sedated will show neural activity in response to language [5].
Other processes, such as mental imagery, however, require a conscious cognitive process, and Owens and colleagues discovered that they could use mental imagery as a “consciousness test.” The researchers instructed minimally conscious patients to imagine specific actions (i.e. playing tennis or walking through their house). Using fMRI to observe the patients’ neural activity, they were able to determine when patients were imagining one scenario versus the other [2]. In fact, the pattern of activation when a patient was imagining an action (i.e. imagining playing tennis) versus spatial navigation (i.e. walking around their house) looked almost identical to patterns of activation observed in healthy volunteers performing the same imagery tasks.
This data was critical because it demonstrated the ability of these patients to perform a conscious process: understand and respond to external instructions via mental imagery. Further, these imagery tasks have now been used to create a simple yes/no channel of communication. Patients using mental imagery for communication have been able to respond to an impressive set of biographical questions. For instance, patients have accurately reported whether or not they have brothers or sisters and even the last place they were prior to the accident that left them in their critical condition [2]. To date, researchers estimate that about 20% of “vegetative” patients are living life in the grey zone, covertly conscious to the world happening around them [6].
Allowing Coma Patients to Assert Their Will
Using patterns of neural activity, we can attempt to decrypt the mind’s “black box” and infer residual cognitive abilities in coma patients. But to what extent can we use this tool? Though widely debated, some have suggested that if patients can voluntarily modulate neural activity to indicate a simple “yes” or “no”, then patients can weigh in on important decisions regarding their medical care. Perhaps most controversial, some suggest that patients could even be asked whether or not they want to continue living given their current condition [2]. This could alleviate the burden and stress as families are sometimes tasked with trying to guess what that person would have wanted. However, it raises important ethical questions. For instance, without fluent conversation, how can physicians ensure that a patient indicating they want to be taken off life support 1) has a comprehensive understanding of the medical situation, and 2) is in an emotional state that would allow for a level headed decision? A few physicians, however, have used these mental imagery tasks to grant patients some input on their therapy and living situation. For instance, one patient was able to indicate that they were not in any pain and that they still enjoyed watching hockey while in the hospital bed [2].
Beyond its important potential for medical decisions, we could also delve into more sci-fi-esque scenarios. For instance, one could imagine the makings of a great mystery novel in which a coma patient could even provide witness testimony. For instance, if their brain injury (heaven forbid) was the result of a crime, could patients indicate if the accused was in fact at the scene? Where the crime happened? Which item was the weapon of choice?!
The Logistics
Although the prospect of communicating with coma patients via neuroimaging is intriguing, the technique is far from becoming a standard tool in medicine. fMRI, the most reliable method, is both expensive and difficult to use on patients who have suffered a severe injury. Because fMRI scanners function like a giant magnet, it is not safe to scan patients that have metal in their body including any screws or metal plates that may have been placed in their body as a result of the injury. Contrary to fMRI, EEG is a portable tool and better suited for a patient population. While several studies use EEG to conduct imagery tasks in coma patients, current work suggests that fMRI is still the superior method for these purposes (perhaps due to the improved spatial resolution you get with fMRI). Functional near-infrared spectroscopy (fNIRS) is currently the most user friendly technology available for this type of work. It is both portable and relatively cheap. A few studies have verified similar results of imagery tasks when patients have responded using fNIRS [2].
In conclusion, the information we infer from patterns of neural activity may have utility beyond answering questions about how the brain works. Neuroimaging by no means allows us to “read minds” but it may eventually help to inform our decisions when treating patients who have lost their ability to speak.
Works Cited
[1] https://www.mayoclinic.org/diseases-conditions/coma/symptoms-causes/syc-20371099
[2] Owen, A.M. The Search for Conciosuness. Neuron, 102(3):526-528, 2019.
[3]http://www.scholarpedia.org/article/Vegetative_state#Minimally_conscious_state
[4] Peterson, A., & Owen, A. M. (2019). Confronting the grey zone after severe brain injury. Emerging Topics in Life Sciences, 3(6), 707-711.
[5] Davis, M. H., Coleman, M. R., Absalom, A. R., Rodd, J. M., Johnsrude, I. S., Matta, B. F., … & Menon, D. K. (2007). Dissociating speech perception and comprehension at reduced levels of awareness. Proceedings of the National Academy of Sciences, 104(41), 16032-16037.
[6] Kondziella, D., Friberg, C. K., Frokjaer, V. G., Fabricius, M., & Møller, K. (2016). Preserved consciousness in vegetative and minimal conscious states: systematic review and meta-analysis. J Neurol Neurosurg Psychiatry, 87(5), 485-492.
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