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Showing entries tagged eeg.  Show all entries

December 4, 2011

Phantom Limb Pain and Cortex Reorganization

Feeling pain in the arm that you lost in an accident? Does your arm you lost in the war itch terribly? This sensation of feeling like a lost limb is still attached to the body is known as a phantom limb pain (PLP). The purpose of this study was to identify plastic changes in the somatosensory and motor cortex in patients with and without phantom limb pain. Most sensations regarding these phantom limbs are painful as if the limb was contorted into an awkward position. Although in many cases the complaint is pain, some patients experiencing a phantom limb experience sensations such as itching, burning, or feeling as though the limb is too short. Although PLP is more common in the early stages following an amputation, some have reported pain for years after. It was previously discovered that PLP had a strong correlation with representational plasticity in the somatosensory cortex; however, its correlation with the plasticity in the motor cortex was unknown. This experiment used methods such as Transcranial Magnetic Stimulation (TMS) of the motor cortex, and neuroelectric source imaging of the somatosensory cortex to study the correlation of plasticity in these cortices.

In this study, participants included five upper-limp amputees experiencing PLP and five upper-limb amputees experiencing no PLP. A German version of the West Haven- Yale Multidimensional Pain Inventory was used to evaluate each patient's stump and limb pain. To test for motor reorganization, focal TMS was delivered from a magnetic stimulator through an 8-shaped magnetic coil. The leads were positioned to cause currents to flow approximately perpendicular to the central sulcus, optimally causing the largest peak-to-peak motor evoked potential in each muscle. In patients experiencing PLP, a map of outputs determined by neuroelectric source imaging of EEGs done showed significantly larger motor-evoked outputs on the side lacking the arm than the side with the remaining arm, whereas excitability in the motor neurons of amputees remained unchanged. Since it was previously known that motor reorganization in amputees takes place at a cortical level, the leap was made that. "It is likely that cortical mechanisms are also responsible for the differences in reorganization observed in both patient groups (Karl, Anke et. al., 2011)."

While these findings support the notion that increased plasticity is present in the motor cortex of PLP patients, the evidence used to support this main point is presented in a very odd fashion. Immediately following this claim about cortical mechanisms and presenting supporting evidence, they state that their results "do not rule out the possibility of additional subcortical reorganization." This statement is saying that other factors could be causing or contributing to the claims being made by their research, thus making the research inconclusive as a whole. Another problem with the research methods is that the patient's amputations all occurred at different times. Some more recent than others, which could have a profound effect on the plasticity levels reached at the time of testing.
All in all the research conducted further supports already claimed notions, while having no real additions of any validity or originality. These limitations could be reduced by choosing patients who's amputations occurred within the same month. The potential that could be reached through studies similar to this are immense, but further research needs to be conducted in order to draw on more valuable conclusions.

The Journal of Neuroscience, 15 May 2001, 21(10): 3609-3618;
Posted by      Madelyn K. at 8:29 PM MST

December 3, 2011

Buried Alive: Finding cognizance in unresponsive patients

It's a horrible thought, one that undoubtedly haunts people's nightmares: the idea of being buried alive. The idea that someone might be taken against their will and forced, alive, into the depths of the earth, is terrifying. Personally, I have a similar but slightly altered phobia: asylums. The thought of being held against my will and, by physical or pharmaceutical restraints, forced to submission, scares the bejeebies out of me.

Many people in hospital rooms all over the world are facing a fate not unlike these scenarios. Over the years, evidence has accumulated that many of the people diagnosed as being in a persistent vegetative state, or coma, are at least somewhat conscious. That is, these people are trapped inside their own bodies - awake, but in such a state of unresponsiveness that they are thought to be in a coma! These people are not a small minority, either. In fact, as many as 43% of people diagnosed as vegetative are later reclassified as at least minimally conscious.

A new paper published in the November 10th issue of The Lancet outlines a very accessible new method for accurately diagnosing these people. Doctors used "bedside" electroencephalography (EEG) to look at the brains of sixteen vegetative patients. The doctors asked the patients to envision producing simple motor actions at precise times. Three of the patients "were found to be aware and capable of substantially and consistently modulating their EEG responses to command". The study was designed so that any response by the patients required higher order "top down" brain function - meaning that responsiveness was indicative of at least some level of cognizance.
This study is very important, not for it's novelty, but for it's practical implications. Functional magnetic resonance imaging (fMRI) has been used for a while to recognize cognizance in unresponsive patients. In fact, EEG has also appeared in the literature as recognizing cognition in individual unresponsive patients. This study is important in that the doctors used a group of patients (rather than a single patient) to show that EEG can be used as an effective replacement for fMRI.

For unresponsive patients, there are a number of potential hurdles that that make using fMRI difficult or impossible: cost, scanner availability, the physical stress associated with traveling to a suitably equipped fMRI facility, movement artifacts, and interference from metal implants (present in many brain damaged patients) are all serious hindrances to using fMRI. EEG, on the other hand, is much less expensive, is unaffected by metal implants and, possibly most importantly, can be done at the bedside. The method introduced in this study can both bring brain imaging to patients who do not have access, and can supplement or replace the current system of diagnosing a vegetative state.
Currently, vegetative state is diagnosed by a team of specialists who use the coma recovery scale-revised (CRS-R) to access the patient's auditory, visual, motor, oromotor, communication, and arousal functions. This method is highly subjective and prone to misdiagnosis. Each of the patients in this study, including the three cognizant patients, met the CRS-R requirements for vegetative state.

While the prospects of this study are exciting, there are limitations, say the authors. Of the twelve healthy controls in the study, only 9 (75%) were capable of producing brain activity that met the study's criteria for responsiveness. This means that, while using EEG can recognize cognizance, its failure to do so is not indicative of a lack of cognizance.

The authors of the study say that this method can lead to new technologies that allow the patient to interact with their environment and loved ones in meaningful ways. For some patients, this study might be the first step in regaining some form of freedom, some sort of escape from the prison of their bodies.

article link:
Edited by      Kyle K. at 4:41 AM MST
Tags: coma, eeg, vegetative

October 23, 2011

Will this Blog Affect How you Read the Rest?

It's intuitive that memory and perception are linked, but the underlying neural mechanisms for this interaction are still unclear. The article "Biasing Perception by Spatial Long-Term Memory" (Summerfield et al.) from the Oct. 19th issue of The Journal of Neuroscience sheds some light on this problem. Their experiment links previous visual perception and subsequent long-term memory generation to increases in brain activity, improved behavioral performance and enhanced perceptual functioning in a recall type task.

This linkage was uncovered by putting subjects through visual identification tasks. The tasks involved finding a gold key, which was inserted into a complex picture after a random short period of time. The subjects were put through 160 trials in one day. These trials were setup in a precise manner that enabled the experimenters to strictly focus on the task and relevant results. EEG recordings, reaction time, accuracy, and optic focus were measured. The next day the subjects were put through the task again. With a number of the trials replicating the previous picture and key location exactly.

The experimenters analyzed the results prior to the experiment and eliminated the outliers and bad trials. The results demonstrate "anticipatory spatial biases were triggered by long-term memory" (5). Long-term memory affects the early stages of visual perceptual processing. The experimenters recorded increases in brain wave activity that mimicked the activity seen in trials where the subjects correctly identified the key on the first day. So when the same picture and key placement were used on the second day the brain wave activity of the first day was replicated before the stimulus was presented. This anticipatory affect is due to the long-term memory prepping the visual system for the expected target.

This study is helpful in generating a greater understanding of how powerful our long-term memory is. It inadvertently points to the possibility of problems that may arise when people find themselves in similar scenarios. The long-term memory bias was beneficial in the case of the study (faster reaction times), but these preconceived ideas may send some down the wrong path in a different scenario. The long-term memory's influence on perception may promote greater speed and fluidity in simple tasks, but what other assumptions and conclusions will it lead people to jump to. Is long-term memory bias causing people to make quick irrational decisions based on what worked last time? What other aspects of perception and action are being affected by long-term memory bias? To what extent do scenarios have to be similar to allow for this anticipation effect? Is this evolutionary adaption losing utility in a world that requires more imagination, understanding, critical thinking, and thoughtful interaction due to technological innovation and globalization?

All these questions and many more are on the cusp of discovery. This article uncovers a key building block to deciphering this neural pathway. Their use of EEG demonstrates the utility of this technique to answer questions about spatial and long-term memory. Applying this technique to novel scenarios will increase our knowledge of memory's role in biasing perception.

The Journal of Neuroscience October, 19th 2011
Posted by      Charlie S. at 9:31 PM MDT
Tags: eeg, learning, memory

July 31, 2011

Taking A Brake: Making Driving Easier/Safer Through Neuroscience

It appears as though we're going back to the future, again, through the help of neuroscience. This time around, there is no time travel involved...just brain waves. A group of German researchers have recently used drivers' brain signals to assist in automated car braking, resulting in quicker reaction times and a potential solution to prevent thousands upon thousands of car accidents each year caused by human error.

The braking system is actually quite simple: through an EEG connected to the scalp and with modern traffic sensors equipped in most luxury cars today, the scientists could detect a driver's intention to break nearly 130 milliseconds faster than they would manually braking themselves. This 130-millisecond difference is phenomenal in that it nearly circumvents all the 'thinking' a human has to do to perform the same braking action.

Crunching Numbers: At 100 km/h, this means that the automated braking system would spare the average driver approximately 12 feet in space compared to manual breaking, which is just about the size of a standard compact vehicle. The twelve feet of distance gained by the driver could be the difference between a minor fender bender and a fatal car crash, or even no car accident at all.

But, this arising technology certainly isn't foolproof. For this reason, the scientists at Berlin Institute for Technology added a second component to their braking system: EMG. Instead of relying on brain signals for car braking, they also use human leg muscles for the same purpose. The scientists measure leg muscle tension associated with braking and are able to sense when a person is going to brake before their legs even reach the brake pedal. Thus, adding another safety dynamic to the overall automatic braking system.

Unfortunately, this technology is still new and undergoing initial testing. Most trials are conducted through simulations and computer programs and haven't been integrated into real working vehicles.

According to the lead author of the study: "We are now considering to test the system online in a real car however if such a technology would ever enter a commercial product, it would certainly be used to complement other assistive technology to avoid the consequences of false alarms that could be both annoying and dangerous." I think it is important to note that under no circumstances are the scientists trying to replace human function, they are only trying to strengthen and improve it.

The thought of automated braking and driving is actually kind of frightening. Where should we draw the line in terms of technology replacing what we do as humans? Are there any caveats that we simply can't predict with this automated driving technology?

As far as I'm concerned, I would love for this technology to gain funding and respect in the scientific community. But until we actually know what we're doing with it, I'd prefer for it to remain on computer simulations until I know I can trust my life or other people's lives with it.

Sources: (Full Text PDF Available on Website)
Posted by      Jordan E. at 10:54 PM MDT
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