Is Axon Guidance by Attraction and Repulsion, or by a Roll of the Dice?

Attractants and repellants guide axons to their targets.  On its journey, a migrating axon may be confronted with multiple attractive and repulsive guidance cues.  This presents a conundrum. How does the axon avoid a tug-of-war between attractants and repellants?  Does the strongest cue win?  Can one cue negate the effects of another?  Can an axon switch its responsiveness to cues until they all match?  

Our study suggests that the key to understanding this problem may lie within the realm of probability theory.

A Random Walk into the Genetics of Axon Guidance

The man claimed he was a wizard and had cast the “spell of attraction” on the target.  Now the target would guide his arrow to the mark.  So we gave the man a broken arrow and watched to see if this arrow could hit the target.  The man took the arrow and flung it at the target.  Indeed, this arrow too could hit the target. 

The Attraction of Axons; the Moth or the Spider?

An axon is attracted towards its target by guidance cues.  A moth flies towards the source of a pheromone.  A spider is sucked across the floor towards the nozzle of a vacuum cleaner.  Is the attraction of an axon towards its target more like the movement of the moth or the spider?

Axon Guidance Meets Statistical Physics

The proposition that the response of an axon to guidance cues is a random walk provides a different perspective of axon guidance.

For the most part, Biologists like deterministic models, i.e. cause and effect.  From the deterministic point-of-view, axon guidance is caused when axon outgrowth activity occurs at the site where the neuron detects an external attractive guidance cue. 

But what if the direction of axon outgrowth activity were to rapidly fluctuate in different directions?  

Random Walks, the Brain Initiative, and the Genius of Einstein's Brain

Over a four-month period in 1905, Einstein published a series of remarkable papers that changed our conception of time and space.


Even more remarkable is the instrument that enabled Einstein to unlock the mysteries of time and space.  His brain.