Vagus Nerve Stimulation Promotes brain Activity in Persistent Vegetative State Patients.
By Kelsi Cottrell
· Patients who are in a persistent vegetative state have a low chance of regaining consciousness after one year of PVS status.
· Vagus nerve stimulation increases cortical brain signals and metabolic brain activity.
· Ethical implications of patients regaining minimal consciousness need to be considered before giving recently comatose patients rights to treatment decisions.
Of all the medical conditions, the coma reigns as one of the most tenacious medical mysteries; humans have yet to effectively treat all the intricacies of this complex mental state. Previously, the outcome of this condition was definitive, but a new therapy utilizing stimulation of the vagus nerve provides evidence that progress can be made towards reversing the coma. The ambiguous state of being, caused by the coma, traps the patient in a purgatory between conscious and dead – forcing families and physicians to make difficult ethical decisions for a person who is physiologically alive, with a beating heart and functioning organs, but unable to determine the treatment they would like to receive. After one year of being classified as within a Persistent Vegetative State (PVS), or coma, it is highly unlikely that the patient will ever regain consciousness.
There are two levels of recovery from a PVS: recovery of consciousness and recovery of function. Recovery of consciousness describes an awareness of self and environment, coupled with voluntary responses to external stimuli. Recovery of function requires cognition of a higher level such as the ability to communicate with others, learn new tasks, and participate in complex activities.
In certain PVS cases, it is difficult to determine if the patient has experienced recovery of consciousness because this level of awareness can occur without external manifestation. For example, a patient can emerge from a PVS and become aware of their environment, without demonstrating any evidence that they know where they are or who they are with. Recovery of function means the patient provides evidence of being cognitive because it requires a visceral response, such as movement or vocalization, that can be recognized from simple interaction with the patient.
A new PVS therapy is being tested that utilizes stimulation of the vagus nerve, the longest cranial nerve in the body, to bring patients out of their vegetative state. The vagus nerve originates in the medulla oblongata, the lowest aspect of the human brain and positioned directly above the spinal cord. The nerve travels down through the neck and throat and continues all to the abdomen, innervating, or connecting to, vital organs along its path. The medulla oblongata is arguably the most important part of the brain, responsible for autonomic, or non-voluntary, bodily functions. Some of these functions are arousal, sleep, and body movement – capacities that are compromised when trapped in a vegetative state.
Vagus nerve stimulation was performed on a man who had been in a PVS for fifteen years. The procedure was conducted using an electrical device surgically implanted into the man’s neck that wrapped around the nerve. The device transmitted an electric current, stimulating specific areas of the brain.
Nerves communicate information through the body by using electrical current. When the electrical potential across the nerve cell membrane reaches a certain voltage, this depolarization creates a current the sends a signal to the receiving nerve. In this experiment, the implanted device administered stimulation by producing current, causing the vagus nerve to send signals to targeted areas of the brain. The device operated over the course of six months and reached a maximum electrical intensity of 1.5 milli-Amperes.
The results of this experiment showed that stimulation of the vagus nerve increased the cascade of cortical signals, found in the cortex of the brain, as well as metabolic brain activity. In other words, this new brain activity was translated into behavioral improvement, reported by both the clinicians and family members of the PVS patient. These improved behaviors included tracking objects with his eyes and staying awake while listening to stories. The patient was also able to develop responses to simple requests, like turning his head, but took ample time to complete them.
Like all recoveries associated with patients trapped in persistent vegetative states, vagus nerve stimulation sparks ethical questions regarding the psychological effects of making a brain-injured patient aware of their condition through the minimal awareness this therapy produces. Angela Sirigu, a chief researcher for vagus nerve therapy, is hoping this minimal awareness could allow patients to decide the course of treatment that is right for them; the two most significant options being continual care or euthanasia.
Rights to treatment decisions are out of reach for these minimally aware patients, especially when doctor-assisted suicide is on the table. This unnatural practice is only legal in six states and requires two oral requests fifteen days apart, a witnessed written request, and a complete psychiatric evaluation. It seems premature that Sirigu would suggest that minimally aware patients who have completed vagus nerve stimulation would have the option of choosing doctor assisted suicide when the requirements to receive this end of life care are so steep. The goal of this treatment is to help patients begin the recovery process, not become aware enough to end their life.
The coma may will continue to challenge the medical community in the years to come, however, therapies being developed, such as vagus nerve stimulation; however, therapies being developed will provide inspiration for researchers who wish to optimize treatment for this condition. Vagus nerve stimulation will be further tested and in time scientists may create an entirely successful treatment that reverses a patient’s vegetative state and helps them regain pre-brain injury level cognition. Previously, the families of PVS patients had minimal hope for the awakening of their comatose loved one; now they have vagus nerve therapy - new scientific evidence that progress can be made.