f**d
发帖数: 768 | 1 ScienceDaily (May 1, 2011) — For more than 50 years, a dominating
assumption in brain research was that nerve cells in the cortex of the
brain are organised in the form of microscopically small columns.
Subsequently, it became a textbook standard that connections are created
predominantly between nerve cells within these columns. In a review
article for the journal Frontiers in Neuroscience, Clemens Boucsein
and colleagues from the Bernstein Centers in Freiburg and Berlin show
that this view has to be revised: input from cells that lie outside this
column plays a much more important role than hitherto assumed.
It was one of the great discoveries of the 20th century in the
neurosciences that nerve cells lying on top of each other in the
cortex react to the same stimulus -- for example edges of different
orientation that are presented to the eye. Investigations of the
connectivity between nerve cells further supported the assumption that
these column-like units might constitute the basic building blocks of
the cortex. In the following decades, much research was conducted on
cortical columns, not least because the investigation of long-range
connections within the brain is a very complicated affair.
But now, these assumptions about a columnar cortex structure come
under scrutiny. New experimental techniques allow the tracing of
connections over long distances. Boucsein and his colleagues at the
University of Freiburg refined a technique to use laser flashes to
specifically activate single nerve cells and to analyse their
connections. These experiments led to surprising results: less than half
of the input that a cortical nerve cell receives originates from
peers within the same column. Many more connections reached the cells
from more distant, surrounding regions.
The experiments also revealed that these horizontal connections
operate very accurately in terms of timing. To the scientists, this is
an indication that the brain may use the exact point in time of an
electrical impulse to code information, a hypothesis that is gaining
more and more experimental support. These new insights into structure
and function of the brain suggest that the idea of a column-based
structure of the cortex has to be replaced with that of a densely
woven tapestry, in which nerve cells are connected over long distances.
Journal Reference:
1.Boucsein C, Nawrot MP, Schnepel P and Aertsen A. Beyond the cortical
column: abundance and physiology of horizontal connections imply a
strong role for inputs from the surround. Front. Neurosci., 5:32 DOI:
10.3389/fnins.2011.00032 |
|
