Randomly wired?
A fluorescence microscope reveals the largely random network,
that neurons
form in a culture dish. An international team of scientists, led by researchers
from the MPI for
Dynamics and Self-Organization, investigated whether nerve cells
in the brain
wire randomly.
© Manuel
Schottdorf, MPI for Dynamics and Self-Organization
(November 23, 2015) The
brain is not relying on random-wiring, but self-organized neural networks for
visual information processing
Our brain is a mysterious machine. Billions of nerve cells
are connected such that they store information as efficiently as books are
stored in a well-organized library. To this date, many details remain unclear,
for instance the set of rules that governs the connections between nerve cells
and the organization of information therein. An international team led by
scientists of the Max Planck Institute for Dynamics and Self-Organization in
Göttingen has now shed new light on these long-standing questions and found
that networks are not governed by randomness. Some scientists considered this
possibility for the organization of the brain, because randomly connected
networks work well in computing applications. To test the random wiring
hypothesis, the team examined whether the brain is using random connections to
process visual stimuli. To this end, they calculated predictions that rely on
the random wiring hypothesis and compared the results with precision
measurements of the cortical architecture in various mammals. The result:
random connections do not suffice to explain the observed layout of the brain.
The scientists conclude that initially random connections in the visual cortex
are reorganized to a precisely determined layout using self-organization. Random
wiring, in the end, plays a small role.
Nerve cells in the human brain are densely interconnected
and form a seemingly impenetrable meshwork. A cubic millimeter of brain tissue
contains several kilometers of wires. A fraction of this wiring might be
governed by random mechanisms, because random networks could at least
theoretically process information very well. Let us consider the visual system:
In the retina, several million nerve cells provide information for more than
100 Million cells in the visual cortex. The visual cortex is one of the first
regions of the brain to process visual information. In this brain area, various
features as spatial orientation, color and size of visual stimuli are processed
and represented. The way information is sent may be comparable to a library, in
which books can easier found if they are sorted not only alphabetically by
title, but also by genre and by author. In a library, books are spread to
different shelves, but typically not randomly. Similarly, various facets of
visual perception are represented separately in the visual cortex. And the
organization of this representation might be random. Mathematical modeling
suggested that randomly distributed information is very well suited to separate
features, in fact, better and better the more features are concerned.