Wiring the Brain at the Nanoscale

Working with platinum nanowires 100 times thinner than a human hair -- and using blood vessels as conduits to guide the wires -- a team of U.S. and Japanese researchers has demonstrated a technique that may one day allow doctors to monitor individual brain cells and perhaps provide new treatments for neurological diseases such as Parkinson's.

Neuroscientist Rudolfo Llinas and his colleagues envision an entire array of nanowires being connected to a catheter tube, which could then be guided through the circulatory system to the brain. Once there, the nanowires would spread into a kind of bouquet, branching out into tinier and tinier blood vessels until they reached specific locations. (Zina Deretsky, NSF)

The researchers explain that it is becoming feasible to create nanowires far thinner than even the tiniest capillary vessels. That means nanowires could, in principle, be threaded through the circulatory system to any point in the body without blocking the normal flow of blood or interfering with the exchange of gasses and nutrients through the blood-vessel walls.

In a proof-of-principle experiment, the team first guided platinum nanowires into the vascular system of tissue samples, and then successfully used the wires to detect the activity of individual neurons lying adjacent to the blood vessels.

Already, the researchers note, physicians routinely use arterial pathways to guide much larger catheter tubes to specific points in the body. This technique is frequently used to study blood flow around the heart, for example.

Following the same logic, the researchers envision connecting an entire array of nanowires to a catheter tube that could then be guided through the circulatory system to the brain. Once there, the wires would spread into a "bouquet," branching out into tinier and tinier blood vessels until they reached specific locations. Each nanowire would then be used to record the electrical activity of a single nerve cell or small groups of them.

If the technique works, it would be a boon to scientists who study brain function. Current technologies, such as positron emission tomography (PET) scans and functional magnetic resonance imaging (fMRI), have revealed a great deal about how neural circuits process, say, visual information or language. But the view is still comparatively fuzzy and crude. By providing information on the scale of individual nerve cells, or "neurons," the nanowire technique could bring the picture into much sharper focus.

The nanowire technique also could greatly improve doctors' ability to pinpoint damage from injury and stroke, localize the cause of seizures, and detect the presence of tumors and other brain abnormalities. Better still, the nanowires could deliver electrical impulses as well as receive them. So the technique has potential as a treatment for Parkinson's and similar diseases.

One challenge is to precisely guide the nanowire probes to a predetermined spot through the thousands of branches in the brain's vascular system. According to the researchers, a promising solution is to replace the platinum nanowires with new conducting polymer nanowires. Not only do the polymers conduct electrical impulses, conductive, they change shape in response to electric fields, which would allow the researchers to steer the nanowires through the brain's circulatory system. Polymer nanowires have the added benefit of being 20 to 30 times smaller than the platinum ones used in the reported laboratory experiments. They also will be biodegradable, and therefore suitable for short-term brain implants.

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