Locked-In Syndrome and PVS: Implications for Brain = Behavior

This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

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Biology 202
2002 First Paper
On Serendip

Locked-In Syndrome and PVS: Implications for Brain = Behavior

Gavin Imperato

During our first few class sessions, I became very intrigued by the brain = behavior idea and the I-function. I kept searching for what I thought to be an easy way to approach these complicated issues. We discussed extensively the example of Christopher Reeve, as someone with an intact I-function, but who has lost a certain element of connectedness between total I-function control and his actual body. I became very interested in how the I-function and brain = behavior interrelate. I thought that looking into some information about the persistent vegetative state and the locked-in syndrome would yield a satisfying and definitive answer once and for all. Is a brain still a brain without the I-function? I found no definitive answer, but I was able to convince myself of the "less-wrongness" of the brain = behavior idea.

I first looked into the persistent vegetative state. Below I have reproduced a somewhat technical explanation of how PVS patients are believed not to have an I-function:

Three lines of evidence suggest that PVS patients are "noncognitive, nonsentient, and incapable of conscious experience [12]." First, motor and eye movement, and facial expressions in response to stimuli occur in stereotyped patterns rather than learned reactions. Second, positron emission tomography reveals cerebral glucose metabolism at a level far below those who are aware or in locked in states. PVS levels are comparable to those in deep general anesthesia and as such are totally unaware and insensate. Third, neuropathological examinations of PVS patients show "lesions so severe and diffuse [12]" that it would be almost impossible, giving our current understanding of neural anatomy and function, to have any sort of awareness. (1) [see site for references within]

As the above passage clearly indicates, patients in PVS lack an I-function. They are totally removed from the world of perceptive experience Ė they are simply not there. A PVS patient goes through normal periods of sleep and wakefulness, can "grind their teeth, swallow, smile, shed tears, grunt, moan, or scream" (2). When I discovered this, I was quite puzzled. I didnít understand how someone who is ostensibly not in control of such actions, could exhibit behavior that in my everyday life I observe to be a clear indication of emotion and feeling. These are things that seemed to me should to be absent from the lives of people with this syndrome.

What troubled me I later found out, was simply the fact that these things are remarkably similar to things we might normally think are clear evidence of the I-function. So, my problem with the I-function then became the following: if a human being has no I-function then does brain still equal behavior? It seemed very interesting to me that that the things a PVS patient can do donít require a functioning mind to do them. That is, the brain, even when seriously injured, can control a range of functions within the body, even when the patient has no awareness, no sense of self, and is for all intents and purposes, "not there." I put the last phrase in quotes to highlight it as the first thing that came to my mind when thinking about the relationship between brain, mind, and body in a PVS patient. The body of a PVS patient seemed to me almost like an unmanned vehicle, like a plane on autopilot. Things are happening, but no one is at the controls. The body has lost its I-function, and yet continues to function.

The dynamic relationship between brain, behavior, and the I-function also surfaced in our discussion of paralysis and Christopher Reeve. Intrigued by the fact that despite an almost total disconnection with his body, Christopher Reeve exhibits all the complex manifestations of an intact I-function. How can the I-function still be there, but the ability to control all of oneís body be gone? This seemed to contradict what I learned about PVS patients, who have no I-function, but nonetheless behave with the gesturing of normal healthy humans. Christopher Reeve exhibits the reverse of this scenario. I had discovered at this point that there is evidence beyond the shadow of a doubt that there can be no I-function in patients with PVS. However, I was not as convinced about patients with locked-in syndrome. I wondered if finding more out about patients with this condition could help me to understand more about the brain = behavior idea and the I-function.

The locked-in syndrome describes a condition in which a person is "unable to communicate orally or gesturally due to paralysis of motor pathways" (3). There are numerous grades of this syndrome, with Christopher Reeve as an example of someone who has much of his ability to communicate orally still intact. In Christopher Reeveís case, it seemed obvious to me that an I-function was intact. However, when did the I-function cease to exist? Some patients with more serious cases of the locked-in syndrome can be fully awake, and aware of what is happening around them, but are unable to effect even the most minor response (4). I was initially unsure of what to make of these patients. How could one objectively determine if these patients had an I-function? What if an I-function were present, and we just could not prove it? In looking at more sites on the web, I found that there are numerous new technologies being tested which can help in both the diagnosis and therapy of patients are with varying degrees of this syndrome. One such technology is called the Eyegaze Communication System and is used as both a therapeutic and diagnostic device (5). The technology employed here relies on tracking movement in the patients eyes, and this can be a tremendously valuable asset when this is one of the only types of motion that can be generated by the patient. Even if the movement is small, it can be used to determine if the patient can in fact respond to commands using his or her limited motor output abilities. The goal of this technology is essentially to harness as much power as one can from the limited amount of output the patient can generate, and to in turn translate this power into meaning and purpose. Even with small eye movements, we can determine if the I-function is present. A patient can be instructed of a set of motions that will convey meanings.

Another such device I read about is a thought translation device that was developed by researchers who noted that it is often very difficult to evaluate a patientís level of consciousness and awareness when he or she is locked-in and unable to participate in human communication (6). The researchers of this particular study were surprised to find that their belief in a hierarchy of complexity information processing in humans was not validated. Patients in the study often demonstrated complex abilities in the absence of rudimentary ones. Formerly I would have espoused this as clear evidence that brain does not equal behavior. However, when came upon this information, I realized that there is in fact a gray area here that scientists donít completely understand. We donít know everything that goes on the brain, but this certainly does not damage the credibility of the brain = behavior model; it simply makes it a little more of a challenge to think of it as still "less wrong."

This led me to the observation that we as humans are naturally attuned to macroscopic and simplistic demonstrations of behavior to prove that our I-functions are intact. In reality, testing for the existence of the I-function in these types of patients is an enormous challenge. So, in my quest to simplify the questions we had been asking in class, I made things more complicated. Overall, the activity of the brain is something that is taken for granted in conscious individuals. It seems odd that people can be vegetative and do so little, yet still be alive. It also seems strange that patients can exhibit a range of behaviors (even laughing) which would normally suggest some sort of cognition when in fact they have no sense of self. The discoveries began to make me feel more comfortable with the brain = behavior notion.

My initial thinking on these subjects was affected by my finding something inherently unsettling when any idea surfaced that would challenge the fact that the I-function is in control at all times. I did not think that the brain = behavior idea could hold when there was no I-function present. It seems a fairly natural human feeling to want to know that one is able to have control over oneís own behaviors and actions all the time. The idea that our brain is in control when "we" are not is unnerving. I found the fact that biological processes can occur without any problem in PVS patients and patients with the locked-in syndrome to be a very difficult concept to grasp. What originally seemed to be a manageable foray into the big question of does brain = behavior turned into something more complicated than I would have thought. In the end, I am much more comfortable with the idea of brain = behavior, having read extensively that documentable neurophyisiological happenings can give satisfactory explanations of the behavior of persons with PVS or in a locked-in state. I know believe that even in patients who are vegetative or locked-in, brain does equal behavior regardless of I-function status.


1)UPENN bioethics site

2) independent patient resource site

3) The Locked-In-Syndrome by Philippe Van Eeckhout.

4) medical summary of conditions and examinations, E. Valenstein & S. E. Nadeau.

5) Use of an Eye-Operated Eyegaze Communication System in Locked-In Syndrome, by: James E. Chapman, M.D.

6) Results and Reflections on the Boundaries of Consciousness, Niels Birbaumer.

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