Tag Archives: nerve cells

Robot limbs to plug into the brain with light

Imagine a bionic arm that plugs directly into the nervous system, so that the brain can control its motion, and the owner can feel pressure and heat through their robotic hand. This prospect has come a step closer with the development of photonic sensors that could improve connections between nerves and prosthetic limbs.

Existing neural interfaces are electronic, using metal components that may be rejected by the body. Now Marc Christensen at Southern Methodist University in Dallas, Texas, and colleagues are building sensors to pick up nerve signals using light instead. They employ optical fibres and polymers that are less likely than metal to trigger an immune response, and which will not corrode.

The sensors are currently in the prototype stage and too big to put in the body, but smaller versions should work in biological tissue, according to the team.

The sensors are based on spherical shells of a polymer that changes shape in an electric field. The shells are coupled with an optical fibre, which sends a beam of light travelling around inside them.

The way that the light travels around the inside of the sphere is called a “whispering gallery mode”, named after the Whispering Gallery in St Paul’s Cathedral, London, where sound travels further than usual because it reflects along a concave wall.

The idea is that the electric field associated with a nerve impulse could affect the shape of the sphere, which will in turn change the resonance of the light on the inside of the shell; the nerve effectively becomes part of a photonic circuit. In theory, the change in resonance of the light travelling through the optical fibre could tell a robotic arm that the brain wants to move a finger, for instance.

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Pulses of light spark muscle movement

Pulses of light might one day restore normal muscle activity in people with cerebral palsy or paralysed limbs. That’s the hope of researchers now using the technique to control the leg muscles of mice.

The work is part of a growing field called optogenetics, and used light-activated proteins from photosynthetic algae to switch nerve cells on and off. The latest study is the first to apply the technique to the peripheral nervous system, which controls voluntary movements.

Karl Deisseroth of Stanford University, and colleagues, inserted into mice the gene which codes for the algal protein ChR2, which caused the protein to attach itself to the surface of nerve cells. After anaesthetising each mouse, they optically stimulated its sciatic nerve – which runs from the lower back to the lower limb – using a cuff lined with light-emitting diodes. They measured the resulting contractions in the Achilles tendon.

Stimulating muscles with electrical impulses has allowed paralysed people to walk. But electrical signals activate large, fast-twitch nerve fibres before small slow-twitch ones – the opposite of what happens naturally. This makes people walk with jerky, robotic movements which quickly become exhausting.

In contrast, the light pulses reproduced the “natural firing order” of nerves in the mice, says team-member Scott Delp, also at Stanford. The team is hopeful that the technique could work in humans to restore movement to paralysed limbs, or counter the muscle spasticity characteristic of cerebral palsy.

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Scientists find link in humans between nerve cell production & memory

Production of new nerve cells in the human brain is linked to learning and memory, according to a new study from the University of Florida. The research is the first to show such a link in humans. The findings, published online and in an upcoming print issue of the journal Brain, provide clues about processes involved in age- and health-related memory loss and reveal potential cellular targets for drug therapy.

The researchers studied how stem cells in a memory-related region of the brain, called the hippocampus, proliferate and change into different types of nerve cells. Scientists have been unsure of the significance of that process in humans.

“The findings suggest that if we can increase the regeneration of nerve cells in the hippocampus we can alleviate or prevent memory loss in humans,” said Florian Siebzehnrubl, Ph.D., a postdoctoral researcher in neuroscience in the UF College of Medicine, and co-first author of the study. “This process gives us what pharmacologists call a ‘druggable target.'”

Over the past two decades, several studies have shown that new nerve cells are generated in the hippocampus. In animal studies, disrupting nerve cell generation resulted in the loss of memory function, while increasing the production of new nerve cells led to improved memory.

To investigate whether the same is true in humans, the UF researchers, in collaboration with colleagues in Germany, studied 23 patients who had epilepsy and varying degrees of associated memory loss. They analyzed stem cells from brain tissue removed during epilepsy surgery, and evaluated the patients’ pre-surgery memory function.

In patients with low memory test scores, stem cells could not generate new nerve cells in laboratory cultures, but in patients with normal memory scores, stem cells were able to proliferate. That showed, for the first time, a clear correlation between patient’s memory and the ability of their stem cells to generate new nerve cells.

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