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One of my readers suggested that I give reports on recent scientific conferences, and the state-of-the-art in various fields in which I do research. In June I attended the Neural Interfaces Conference in Salt Lake City, Utah, where participants discussed both the latest in brain to machine interfacing, as well as the electrodes, devices, and computers used to perform those interfaces.
In recent months I've seen developments which indicate that the field of neuroscience is not very far from developing effective "bionics". Sometime in the next year. The first patient will be fitted with an upper limb prosthetic– a bionic arm – and will wear it for six months to a year. The means to record and decode the neural signals that control normal muscle movement have been around for at least two decades. However, does not been until recently that we have risked implanting recording electrodes in humans to do this task. One of the great drawbacks of bionic interfacing is that we still don't have a very good technique for creating a two-way connection and allowing the patient to actually "feel" using a prosthetic limb.
One of the biggest drawbacks to the implantation of recording electrodes has been that they eventually become encapsulated by glial cells and scar tissue. Once this happens the electrodes become less capable of recording and the recordings become less precise. This is one of the major reasons why the patients who initially test our new bionic limbs will only have the use of them for very short period of time. However, some remarkable new techniques have been developed over the past several years which may make metal recording electrodes obsolete.
The first technique uses a system very similar to that which I reported previously, as a future direction for developing a prosthetic for the retina. Healthy retina cells containing pigment called rhodopsin which changes its shape when exposed to light. The rhodopsin embedded in cell membranes of a "rod" or "cone" causes the cell to react to light by opening ion channels, much the same way neurons react to chemical and electrical stimuli. The new field of "optogenetics" inserts similar chemicals collectively termed "opsins" into cells to make them sensitive to specific wavelengths of light. In the retina, this technique can be used to rebuild the light-sensitive cells that have been damaged by disease. However, in other brain areas, it can be used to insert the capability of stimulating cells using light instead of electricity. The advantage to using optogenetics as a means of providing an interface from the machine back to the brain, is that the fiber-optic implants used to present the light stimulus are much less likely to produce inflammation and lead to scar tissue formation and encapsulation of the electrode. The disadvantage is that multiple electrodes using fiber optics do not yet exist, and the technique for inserting the opsins into brain cells is still subject to some controversy.
However, the second exciting new technique still uses light, but instead of requiring a specialized molecule inserted into the neuron, it relies on infrared wavelengths, which produce a very small amount of heat focused on single neurons. It was shown at the conference, that the amount of infrared energy required to activate a neuron was considerably less than what would produce a measurable heating of the tissue around the infrared light source. Thus, it may turn out to be possible to stimulate neurons using light, with or without specialized opsins. With these two techniques at our disposal, what is needed now is a better way to record neural activity, and to many of the same scientists using both optogenetics and infrared stimulation are looking for alternative recording techniques. him. By the time the next conference is held in two years, I expect that even this problem will be solved.
In Friday's blog, I will provide a brief update on medicinal Cannabinoids, followed by a couple more book reviews and even a convention report over the next several weeks. I am still open to suggestions on topics that readers would like to see covered in The Lab Rats' Guide to the Brain.
Until next time, if you have a question about the brain, don't be afraid to ask!