LATENT LEARNING?: If some vegetative patients can be shown to acquire conditional learning, should their status be reevaluated?
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In patients who have survived severe brain damage, judging the level of actual awareness has proved a difficult process. And the prognosis can sometimes mean the difference between life and death.
New research suggests that some vegetative patients are capable of simple learning—a sign of consciousness in many who had failed other traditional cognitive tests. The findings are presented in a paper today in Nature Neuroscience (Scientific American is part of the Nature Publishing Group).
To decide whether patients are in a minimally conscious state (MCS), in which there is some evidence of perception, or intentional movement or have sunk into a vegetative state (VS), where there is neither, doctors have traditionally used a battery of tests and observations, many of which require some subjective interpretation, such as deciding whether a patient's movements are purposeful—to indicate a sullied feeding tube, for example—or just random.
"We want to have an objective way of knowing whether the other person has consciousness or not," says Mariano Sigman, senior study author and director of the Integrative Neuroscience Laboratory at the University of Buenos Aires.
Previous neuroimaging work had surprised doctors by showing that some vegetative patients, when asked to imagine performing physical tasks such as playing tennis, still had activity in premotor areas. In other patients, verbal cues sparked language sectors.
"It's really quite appalling that we don't have better techniques to evaluate cognitive and brain states on these individuals," says Joy Hirsch, a professor of neuroscience and psychology at Columbia University, who wasn't involved in the study.
Recent research has revealed that about 40 percent of vegetative state diagnoses is incorrect. That startling statistic reinforced the need for better tools to measure that which often eludes quantification—consciousness.
Training the mind
To study the ability of VS and MCS patients to learn via classical conditioned response, researchers built off the work of 19th-century Russian psychologist Ivan Pavlov, who famously conditioned his dogs to salivate at the ring of a bell by associating the sound with the presentation of food. In this case, they sounded a tone, which was followed about 500 milliseconds later with a light puff of air to the eye, a mild adverse stimulus. The air puff would cause a patient to blink or flinch his or her eye as a natural reaction, but after repeated trials over the course of half an hour, many of the patients would begin to anticipate the puff, blinking an eye after only hearing the tone.
If two stimuli are delivered at exactly the same time, even less conscious organisms, such as snails, can be conditioned to equate the stimuli. But delaying the second stimulus by more than 200 milliseconds is enough to demonstrate some learning, says Tristan Bekinschtein, lead study author and a researcher at the Impaired Consciousness Research Group at the University of Cambridge. To make that association, as brief as the time gap is, he says, "You need conscious processing."
To demonstrate the extent to which the vegetative and minimally conscious patients showed consciousness, the researchers also performed the test on people under general anesthesia (specifically, on patients who were on propofol for an endoscopic procedure). These individuals, considered to be entirely lacking awareness, showed no sign of learning.
What was more, current designation of either vegetative or minimally conscious did not determine how well patients learned. Some of those who were minimally conscious didn't learn as well as some who were classified as vegetative and vice versa. "I think there's some consensus that there is a [need for] revision in the way these patients are classified," Sigman says.
The new detection of learning also opens up questions about when patients should be classified as being in a persistent vegetative state—in which emergence isn’t predicted to be likely—as Terri Schiavo was determined to be at the time. Decisions to take people off of life support are often based in part on doctors' predictions of recovery and assessments of consciousness. If "someone shows the patients can learn," Bekinschtein says, "I think it would be a very clear argument" to keep them alive.
New signs of recovery
The findings might also have practical applications for patient recovery. At the outset, says Bekinschtein, "We wanted to test for capacity to learn and capacity for conscious processing." But once the study was underway, they found that learning ability and speed was about 86 percent accurate in predicting the extent of recovery within the next year.
"If you think about that in a subtle way," he says, "that they can change their brain network—[showing] some plasticity—it implies that there's room for at least some recovery."
Other researchers in the field are encouraged by the results. "This is a really important study," Hirsch says. "We don't know a lot about the neurocircuitry that is involved in classical conditioning," she says, but "the use of a learning paradigm to predict whether a patient would [recover] is a possibly important idea."
The researchers hope that similar tests will be widely adopted by hospitals all over the world. Functional magnetic resonance imaging (fMRI) machines and other diagnostic tests can be expensive and hard to come by in many places, the authors note. Much of the testing was completed in Argentina, where imaging capabilities can be less available than in the U.S. or U.K. For this test, "you just need two wires, and it costs $100," Sigman says. "In practical terms, it has strong implications."
Hirsch, who is also the director of Columbia's Program for Imaging and Cognitive Sciences, still thinks that "functional imaging is by far the tool of choice" because it can reveal "cognitive processes that are latent in these patients that aren't visible through [traditional] bedside tests."
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20 Comments
Add CommentAmazing, and I think its about time our scientists started paying attention to this issue, as I know if I was in a vegetative state with some consciousness and had some chance of recovery, I would want that chance. It is important to note that a vegetative state should not be confused with Brain Death, where there is no brain activity due to necrosis, as being in a vegetative state does not allow for organ donation.
Reply | Report Abuse | Link to thisThis research is meaningful.
Reply | Report Abuse | Link to thisThis research is meaningful.
Reply | Report Abuse | Link to thisI would be curious if the patients who were under anesthesia and given the test (who showed no signs of learning) had any rememberance or subconscious reaction to the tone after coming out of anesthesia...
Reply | Report Abuse | Link to thisMy dad was declared a veg. I listened to the docs and signed a DNR but declined to remove the tube and instead moved him to a nursing home. A number of months later, he woke up. He eventually came home. He lived around 7 more years until the VA bureaucracy decided he could take the cheaper "blue pill" instead of allowing his doctor to do the immediate surgery she wanted to do (to get at an infection in his jaw and then surgery on his heart). She got three appeals, he got a bottle of pills and 10 days later a massive heart attack. I wonder if they called that panel she appealed to a "death panel"? I do.
Reply | Report Abuse | Link to thisAnd to think this came out right after the exciting results of "Scanning Dead Salmon in fMRI "
Reply | Report Abuse | Link to thishttp://prefrontal.org/files/posters/Bennett-Salmon-2009.pdf
http://www.wired.com/wiredscience/2009/09/fmrisalmon/
How long had the salmon been dead?
Reply | Report Abuse | Link to thisCould the results be due to remining neural activity in a newly deceased organism?
How long had the fish been dead?
Reply | Report Abuse | Link to thisI wonder if the activity noted could be due to the residual neural firing of a newly deceased organism.
This is an interesting study that basically extends the bedside neurologic exam to include testing for conditioned responses. A good idea. Drawbacks to the current methodology include: 1- Performing a decent (thoughtful and time consuming) physical examination in the era of imaging is a lost art. And 2- A substantial number of putatively vegetative patients may be locked in, that is unable to respond even with cranial nerves. It is clear that a more proximal CNS output should be sought as the conditioned response.
Reply | Report Abuse | Link to thisBy the way, learning during anesthesia is not only possible it is fairly well studied. It clearly occurs, but this is a different phenomenon from explicit recall of events. For those of you awaiting surgery, you may also wish to contemplate that certain anesthesia techniques are intended not to prevent suffering but instead to block the transfer of the suffering cognitive trace from the short term to the long term memory registers. If a tree falls in the forest...
Cognitive processes are independent of consciousness. The problem is with the ability to communicate cognition within the neural system or between neural functions and self-consciousness or consciousness and the external environment.
Reply | Report Abuse | Link to thisAnimals and plants are dumb because we are unable to communicate with them. Humans are dumb because we fail to communicate with certain levels of cognition.
"How long had the fish been dead?"
Reply | Report Abuse | Link to thisWell they bought it at the grocery store, so it probably got caught, killed, put on ice until the fishing boat got to port, sent to market and so on. I think it was a "fresh fish" in the sense that it was not yet a spoiled fish, so probably not much residual neural firing of a newly deceased organism.
The fish fMRI study is about statistical analysis and how it can be used to generate misleading derivative data. The authors advise on how to prevent future fMRI studies from accidentally reporting the kind of garbage data that they reported on purpose.
Reply | Report Abuse | Link to thisAre we reinventing the wheel again? My father died twice, the first time intensive care was able to revive him. My grandmother died and her spirit refused to leave the house for over 14 years. My wife talks about 5 prior lives.
Reply | Report Abuse | Link to thisThere are medical cases recorded where a person died and when revived later, told of seing and hearing what happened to him while brain dead. Thus mind as separate from the brain, sees and hears and as a physical life enity evolves the physical parts of the body as they have in the spirit form.
Having been in a two week coma after a cerebral hemorrhage suffered in late January of 1986, I cannot say wha my capacity for learning was while comatose, but suffice ity to say that I went on to succeed in college after some degree of recovery upon release from the hospital and graduated in 1999 with a GPA of 3.54, not bad for what some ableistic folks misnamed "a mental veggie who would never even walk again" - got out of the wheelchair in 6 months after waking up, too. I tend to agree with former Surgeon General C. Everett Koop who suggested we should always err on the side of protcting life - where there's life, there's hope!
Reply | Report Abuse | Link to thisUpon my cerebral hemorrhage in January of 1986, the prognosis was that I would die within 3 days, then that I was soomed to bcoming a mental vegetable who would never walk again. By the grace of God, I woke up from that coma in 2 weeks, rose from the wheelchair within 6 months and went on to graduate from college in 1999 for a B.A. attained magna cum laude, GPA 3.54. While I could nnot tell you how much I was capable of learning during the comatose phase, it's clear that the potential existed nonetheless. I agree with former Surgeon General C. Everett Koop who believed we should always err on the side of protecting life . Terri was cruelly deprived of her chance to recover by a man who was in a hurry to marry someone else - the state should never have indulged that crime gainst humanity - Terri deserved to be protected and hder right to life respected.
Reply | Report Abuse | Link to thisI believe with all of my heart that Michael Schiavo got away with legal murder, and the State of Florida is be held accountable, along with the useless media.
Reply | Report Abuse | Link to thisI will always believe that Michael Schiavo got away with legal murder, and the State of Florida and the useless media are to be held accountable, along with the blind judges that presided over this case at numerous hearings and with blatant evidence to err on the side of life. Shame on them.
Reply | Report Abuse | Link to thisthis research is very meaningful due to brain damage. you might get in a wreck and hit your head really hard, hard enough to make you a vegtable and you have a chance to recover due to some consiousness and they are declaring you brain dead when you may still have the chance to recover.
Reply | Report Abuse | Link to thisYes, Michael wanted to deprive Terri of medical help (antibiotics for an infection) years before he was finally allowed to mandate her death. In fact, it was shortly after his financial award was funded. You would have thought that this would have precluded him being Terri's representative immediately. In any case, for a long time I displayed a bumper sticker that said, BETTER FED THAN DEAD. Those are still my sentiments. I don't even think we have to prove how much brain activity was going on in her head. She had been living without unusual medical procedures for 15 years. (A feeding tube is not an unusual piece of equipment.) She had a RIGHT TO LIFE--period. Sarita
Reply | Report Abuse | Link to thisThis is encouraging. My older brother has been in what they term PVS for 4 weeks now. I will say the medical professionals prognosis is not positive, but we, his family, have faith and believe that he will wake up. Faith in glory and power of our Father will make this happen.
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