Saturday, 31 March 2012

Vestibular Organs Provide Movement Guidance System.

The vestibular organs in the inner ear, which this study speaks of transmit their information through the eighth cranial nerve to the vestibular nuclei in the brainstem, which form massive connections to the cerebellum, which is part of this neurological 'movement guidance system' via its cortical connections.  This is why vestibular stimulation forms such an important part of the Snowdrop programme.

With thanks to 'Medical News Today.'

 Anyone who's had to find his or her way through a darkened room can appreciate that nonvisual cues play a large role in our sense of movement. What might be less apparent is that not all such cues come from our remaining four senses. 

In a finding that broadens our understanding of human movement control, researchers at the Institute of Neurology in London have shown that the inner-ear vestibular organs provide what is essentially an on-line movement guidance system for maintaining the accuracy of whole-body movements. 

The vestibular organs are commonly thought of as sensors that serve balance, the control of visual gaze, and higher spatial functions, such as navigation. However, because these organs respond to head movements, such as accelerations, they also have the potential to signal the accuracy of any voluntary movement that causes the head to move in space. The brain may then use that information for movement control in the same way that it uses sensory feedback information from the eyes, muscles, and skin to assess and adjust a limb movement as it is being executed. 

In the new work, appearing in the August 9 issue of Current Biology, Brian Day and Raymond Reynolds of University College London show that the brain uses signals from the vestibular organs to make on-line adjustments to whole-body voluntary movements. The researchers were able to show this by precisely stimulating the vestibular sensory nerves through the skin while volunteers performed a simple upper-body movement. The researchers found that the stimulus altered the normal vestibular response to the upper-body movement and automatically caused the subjects to adjust their movement speed--and did so in a predictable way that depended on how the vestibular sensory nerves were stimulated. As one might expect when perturbing the guidance system, the effect of the nerve stimulation was only apparent in connection with body movement; the same stimulus had almost no effect when the subjects were stationary. 

The authors of the study point out that this vestibular mechanism of movement control may be especially valuable when other senses become less reliable--such as in the dark--or for complex, high-precision whole-body movements, such as those of the gymnast or circus performer. 

The researchers include Brian L. Day and Raymond F. Reynolds of University College London. The Medical Research Council funded this work. 

Day et al.: "Vestibular reafference shapes voluntary movement" Publishing in Current Biology, Vol. 15, 1390-1394, August 9, 2005. DOI 10.1016/j.cub.2005.06.036

Thursday, 29 March 2012

Stimulated neurons produce more connections.

As the brain develops, neurons reach out randomly to form new connections, only a small number of which take hold. How the brain chooses which connections to keep and which to prune back appears to be governed by which branches have the most electrical activity.  This is a finding that could help to explain not only how early environmental experiences guide brain development, but how those environmentally experiences can be utilised as a treatment principle for brain injured children. 
Stephen Smith, professor of molecular and cellular physiology at the Stanford University School of Medicine, immersed 3-day-old zebra fish in a breathable, jelly like substance that kept the fish alive but immobile. The researchers could then focus video cameras on the fish's developing brain to watch how the branches of individual neurons grew and shrank over time. 

It turns out that determining which of the branches will grow follows an age-old axiom: The squeaky neuron gets the grease. "Louder neurons drown out their quieter neighbours," Smith said. 

Working out this seemingly simple rule took some technical finesse. Smith created zebrafish with a few brain cells that made a protein which prevented them from firing their normal electrical signals. These cells were also engineered to produce a protein that glowed green under the appropriate light. 

He looked for green neurons in the immobilized fish to see how their branches fared compared with neighboring neurons that fired normally. The green neurons didn't compete well.

Although the poorly-firing green neurons still formed extensive branching structures, which the researchers call the neuron's arbor, most of those branches eventually receded while neighboring neurons formed a large number of stable connections. When the fish were five days old, the green neurons had a smaller, less complex arbor than those of neighboring neurons

They gave those losing neurons a fighting chance through another molecular twist, managing to silence some neurons near the green, quietly-firing cells. When that was done, the green cells were able to compete successfully and formed longer, more complex arbors. 

Although this work specifically examined the brains of fish, Smith said the same rules likely apply to all neurons, including those in the human brain. 
Neurons that fire regularly while learning to recognize a new person's face, for example, will form larger arbors with more connections that help retain that memory for the future. Likewise, neurons stimulated by engaging toys or experiences will probably create larger arbors than similar neurons in less exciting conditions.  This is good news for children on the Snowdrop programme, who are exposed to highly enriched environments, which encourage their brain cells to develop larger arbors with more connections.