February 23, 2009

Towards Wireless Brain Computer Interface: Light Activation of Neurons Via Nanoparticles

Light rather than electrical current: The inner or outer surfaces of glass micropipettes can be coated with nanoparticles of a narrow-band-gap semiconductor. When visible or near-infrared light is used for excitation, these micropipettes (labeled PE Stim in the image) can activate nearby neurons (labeled *) in brain tissue without the damage associated with electrical stimulation.

Case Western University researchers use light to activate brain circuits with nanoparticles. fMRI [Function Magnetic Resonance Imaging] would be a candidate read method for the wireless brain interface. This would be a precise write method.

By using semiconductor nanoparticles as tiny solar cells, the scientists can excite neurons in single cells or groups of cells with infrared light. This eliminates the need for the complex wiring by embedding the light-activated nanoparticles directly into the tissue. This method allows for a more controlled reaction and closely replicates the sophisticated focal patterns created by natural stimuli.

The electrodes used in previous nerve stimulations don't accurately recreate spatial patterns created by the stimuli and also have potential damaging side effects.

In principle, the researchers should be able to implant these nanoparticles next to the nerve, eliminating the requirement for wired connections. They can then use light to activate the particles.

The researchers' paper, "Wireless Activation of Neurons in Brain Slices Using Nanostructured Semiconductor Photoelectrodes," is the first report of brain stimulation using light-activated semiconductor nanoparticles. This research study was published in Angewandte Chemie, a premier chemistry journal. The journal also highlighted the study as a "hot paper."

This study used brain slices to show that light can trigger neural activity. The next step is to see if this innovative technology can be used to stimulate longer pathways within the intact brain. Clinical development of the technology could lead to new methods to activate specific brain regions and damaged nerves.

"The long-term goal of this work is to develop a light-activated brain-machine interface that restores function following nerve or brain impairments," Strowbridge says. "The first attempts to interface computers with brain circuitry are being done now with complex metal electrode stimulation arrays that are not well suited to recreating normal brain activity patterns and also can cause significant damage."

Currently light is being used in the study to drive neural activity in a minimally invasive manner, without requiring electrical wires.

Scientists have demonstrated microscopic, real-time imaging of the deepest regions of the brain in a freely moving mouse

“This advance should have profound impact on the field of neurological research,” said Uwe Maskos, D.Phil., a lab chief at the Institut Pasteur (Paris, France). “Never before have we been able to see the deep reaches of the brain at the cellular level while an animal is moving freely. Gaining understanding of neurological activity throughout the brain is vital to understanding normal brain function and the kinds of alterations that lead to neurological disorders. We now have visual, microscopic access to the living, working brain that we’ve never had before. We can now bridge the gap between processes at the cellular, organ, and animal level.”

Cellvizio uses in vivo cellular imaging, a new endoscopic imaging approach that is improving both diagnostic rates, as well as the time needed to diagnose the condition. Cellvizio is the first and only confocal microscopy system that is compatible with most endoscopes and allows physicians to view live tissue inside the body at the cellular level in dynamic, real-time images at 12 frames per second. To date, over 2,000 of these procedures have been completed.

Cellvizio, the world’s smallest microscope, is the first system designed to provide live images of internal human tissues at the cellular level during endoscopic procedures. This new method, known as probe-based confocal laser endomicroscopy (pCLE), allows physicians to pinpoint and remove diseased tissue with endoscopic tools on the spot, or in more serious cases, send the patient directly to surgery.

Synthetic telepathy project was funded by DARPA

State of the art electrical connection to the brain/neurons:
Moritz's system, though, uses only 12 moving electrodes – just 50 micrometres wide – to seek out and connect to just a single neuron. This produces a much simpler and tidier output signal.

After being inserted into the brain's motor cortex, the device can sense where the strongest signal is coming from, and move the electrodes towards it.

Piezoelectric motors can move the 12 electrodes in small 1-micrometre increments and will back off when necessary to avoid damaging nerve cells.

In the latest development in the field of neuroimaging, researchers have watched the brain of someone watching an image, and were actually able to perform reasonable reconstructions of the image.

Features of what someone is looking at will correlate with activity in specific areas of the visual cortex. Others have drawn precisely that inference and met with moderate degrees of success; the authors of the new paper cite previous results where researchers have identified small (3 x 3 pixel) images with over 50 percent accuracy simply by following the activity of the visual cortex.

The new work significantly ups the ante by moving to 10 x 10 pixel black-and-white images, which are big enough to represent alphabetic characters. It also introduces a few methodological twists that improve its accuracy. The authors start out by showing subjects 10 x 10 images that represent random noise while using fMRI equipment to track activity in the visual cortex. After collecting a series of data, they set machine learning algorithms loose on the data; these recognized areas of the cortex that were consistently activated by elements in the image. Although this activity largely correlated with a retinal map, there were enough differences that the authors' method was more accurate.

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