High Altitude Climbers at Risk for Brain Bleeds

New magnetic resonance imaging (MRI) research shows that mountain climbers who experience a certain type of high altitude sickness have traces of bleeding in the brain years after the initial incident, according to a study presented at the annual meeting of the Radiological Society of North America (RSNA).

High altitude cerebral edema (HACE) is a severe and often fatal condition that can affect mountain climbers, hikers, skiers and travelers at high altitudes—typically above 7,000 feet, or 2,300 meters.

HACE results from swelling of brain tissue due to leakage of fluids from the capillaries. Symptoms include headache, loss of coordination and decreasing levels of consciousness.

"HACE is a life-threatening condition," said Michael Knauth, M.D., Ph.D., from the University Medical Center’s Department of Neuroradiology in Goettingen, Germany. "It usually happens in a hostile environment where neither help nor proper diagnostic tools are available."

Dr. Knauth and colleagues at the University Hospitals in Goettingen and Heidelberg, Germany, compared brain MRI findings among four groups of mountaineers: climbers with well documented episodes of HACE; climbers with a history of high altitude illness; climbers with a history of severe acute mountain sickness (AMS); and climbers with a history of isolated high altitude pulmonary edema (HAPE), a life-threatening accumulation of fluid in the lungs that occurs at high altitudes. Two neuroradiologists assessed the brain MRI findings without knowing the status of the mountaineers and assigned a score based on the number and location of any microhemorrhages.

"In most cases, these microhemorrhages are so small that they are only visible with a special MRI technique called susceptibility-weighted imaging," Dr. Knauth said. "With this technique, the microhemorrhages are depicted as little black spots."

The MRI results showed brain microhemorrhages almost exclusively in HACE survivors. Of the 10 climbers with a history of HACE, eight had evidence of microhemorrhages on MRI. The other two had uncertain results. Only two of the remaining 26 climbers were positive for microhemorrhages.

"It was previously thought that HACE did not leave any traces in the brains of survivors," Dr. Knauth said. "Our studies show that this is not the case. For several years after, microhemorrhages or microbleeds are visible in the brains of HACE survivors."

(Photo: Mitch Barrie (Flickr))

A 3-D Light Switch for the Brain

A new tool for neuroscientists delivers a thousand pinpricks of light to a chunk of gray matter smaller than a sugar cube. The new fiber-optic device, created by biologists and engineers at the Massachusetts Institute of Technology (MIT) in Cambridge, is the first tool that can deliver precise points of light to a 3-D section of living brain tissue. The work is a step forward for a relatively new but promising technique that uses gene therapy to turn individual brain cells on and off with light.

Scientists can use the new 3-D “light switch” to better understand how the brain works. It might also be used one day to create neural prostheses that could treat conditions such as Parkinson’s disease and epilepsy. The researchers describe their device in a paper published today in the Optical Society’s (OSA) journal Optics Letters.

The technique of manipulating neurons with light is only a few years old, but the authors estimate that thousands of scientists are already using this technology, called optogenetics, to study the brain. In optogenetics, researchers first sensitize select cells in the brain to a particular color of light. Then, by illuminating precise areas of the brain, they are able to selectively activate or deactivate the individual neurons that have been sensitized.

Ed Boyden, a synthetic biologist at MIT and co-lead researcher on the paper, is a pioneer of this emerging field, which he says offers the ability to probe connections in the brain.

"You can see neural activity in the brain that is associated with specific behaviors," Boyden says, “but is it important? Or is it a passive copy of important activity located elsewhere in the brain? There’s no way to know for sure if you just watch.” Optogenetics allows scientists to play a more active role in probing the brain’s connections, to fire up one type of cell or deactivate another and then observe the effect on a behavior, such as quieting a seizure.

Unlike the previous, 1-D versions of this light-emitting device, the new tool delivers light to the brain in three dimensions, opening the potential to explore entire circuits within the brain. So far, the 3-D version has been tested in mice, although Boyden and colleagues have used earlier optogenetic technologies with non-human primates as well.

A better brain implant: Slim electrode cozies up to single neurons

A thin, flexible electrode developed at the University of Michigan is 10 times smaller than the nearest competition and could make long-term measurements of neural activity practical at last.

This kind of technology could eventually be used to send signals to prosthetic limbs, overcoming inflammation larger electrodes cause that damages both the brain and the electrodes.

The main problem that neurons have with electrodes is that they make terrible neighbors. In addition to being enormous compared to the neurons, they are stiff and tend to rub nearby cells the wrong way. The resident immune cells spot the foreigner and attack, inflaming the brain tissue and blocking communication between the electrode and the cells.

The new electrode developed by the teams of Daryl Kipke, a professor of biomedical engineering, Joerg Lahann, a professor of chemical engineering, and Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Engineering, is unobtrusive and even friendly in comparison. It is a thread of highly conductive carbon fiber, coated in plastic to block out signals from other neurons. The conductive gel pad at the end cozies up to soft cell membranes, and that close connection means the signals from brain cells come in much clearer.

"It’s a huge step forward," Kotov said. "This electrode is about seven microns in diameter, or 0.007 millimeters, and its closest competitor is about 25 to 100 microns."

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Brain satnav helps surgeons travel to a tumour

SATNAV is good at finding the easiest route to where you want to go. Now a version for the brain could allow a flexible probe to take the safest route to reach deep tissue. Together, the algorithm and probe could provide access to brain tumours that were previously deemed inoperable.

When surgeons want to take a biopsy from deep inside the brain, they face a problem - how to get there without damaging the brain tissue en route. Flexible needles are one solution. Ferdinando Rodriguez y Baena at Imperial College London and colleagues created such a probe in 2009, basing the design on the needle-like ovipositor that female wasps use to deposit eggs inside trees.

Just like the wasp’s ovipositor, the probe has a number of interlocking flexible shafts, each of which can slide independently of the others. The probe naturally sticks to the soft brain tissue, providing traction, which means that when one of the shafts slides further into the tissue the probe will flex. By controlling the relative movement of each shaft it is possible to send the probe snaking along a path through the tissue.

Rodriguez y Baena’s team has now begun to think about exactly which paths are best to take. “Some areas of the brain are more important than others and we needed a way to decide what route caused the least amount of damage to vital areas,” says team member Seong Young Ko at Chonnam National University in Gwangju, South Korea. “You would want to stay well away from major blood vessels and sensory areas, for example.”

The team has now developed an algorithm to direct the probe around these obstacles. It considers three factors: the distance from the scalp to the desired brain tissue, the proximity of the route to vital areas such as blood vessels or nerve bundles, and the accumulated risk along the way.

There is controversy over how to rate the importance of different parts of the brain, so the team tested the algorithm by giving arbitrary levels of importance to different areas. It revealed the path which should theoretically bring the least risk to a patient. Ko presented the algorithm at the BioRob 2012 conference in Rome, Italy, last month.

"The ability to take a curved path through the brain, selecting the most forgiving route to avoid critical regions, represents an intriguing breakthrough," says Katrina Firlik, a neurosurgeon in Greenwich, Connecticut, who was not involved in the research. "It could not only enhance safety but might even expand the surgical repertoire to include cases currently deemed inoperable."

That is the hope, says Ko. So far the probe has only been tested in animal tissue, but he says the goal is to use the algorithm to guide the safe implantation of electrodes deep in the brain and to improve the safety of taking biopsies from hard-to-reach tumours.