Freiburg and Berlin, Germany. Most of the input to a cortical nerve cell in the brain travels horizontally over long distances from distant regions, a new discovery that changes our basic understanding of brain structure.

The emerging picture is that of cortical structures that resemble a densely woven tapestry that resists unraveling from its initial configuration. The connections are part of a very accurate (and interwoven) timing scheme, indicating the importance of synchronizing the electrical impulses that code information and maintaining the stability of the brain's organization.


A primary assumption in brain research for more than 50 years was that nerve cells in the cortex of the brain are organised in the form of microscopically small columns. It became a textbook standard that connections are created predominantly between nerve cells within these columns. However, a review article in the journal Frontiers in Neuroscience shows input from cells that lie outside this column plays a much more important role than previously assumed.

The large mass of the cerebral cortex site on the cerebellum, the bottom of the brain which acts as a kind of stable foundation for the cortical structures above it. It was one of the great 20th century discoveries in the neurosciences that nerve cells lying on top of each other in the cortex react to the same stimulus (e.g., edges of different orientation that are presented to the eye).

Investigations into 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, considerable research was conducted on the cortical columns, not least because the investigation of long-range connections within the brain is a very complicated affair that knits together and coordinates all of the neural processes essential to managing our physiology.

Depending on sex and age, there are 15–33 billion neurons in the human cerebral cortex, each linked with up to 10,000 synaptic connections. There are roughly one billion synapses in each cubic millimeter of cerebral cortex. The axons, long protoplasmic fibers, carry high speed train deliveries of signal pulses (action potentials) to specific recipient cells in distant parts of the brain or body.

Clemens Boucsein and colleagues from the Bernstein Centers for Computational Neuroscience (BCCN) in Freiburg and Berlin have used new experimental techniques allow the tracing of these long-distnce connections, placing the assumptions about a columnar cortex structure under scrutiny.

The Boucsein group 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.

Arbitrary revisions to such a structure, once formed, becomes more than the rearrangement of roughly geometric parts, helping to explain how fresh neuron growth, or repair and regeneration processes, can occur without changing the basic and preset architecture of the brain.

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