Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
Personal tools
Log in

Working faster in a team

Date: 15.03.2011

Groups of neurons in the cerebral cortex can process and transmit signals that are significantly faster than has been assumed for a long time. For this astonishing experimental finding scientists from the Max Planck Institute for Dynamics and Self-Organization (MPIDS) and from the Bernstein Center for Computational Neuroscience of Göttingen University have now for the first time found an explanation. Their theoretical calculations show, that only the velocity, with which a single neuron initiates its nerve impulses, limits a group's speed of communication. A population of neurons can therefore handle several hundreds of elementary stimuli per second. The researchers from Göttingen describe their results in the journal Physical Review Letters.

Fig. 1 Neurons in the cerebral cortex receive tousands of synaptic inputs from other cells. This so-called "synaptic bombardment" leads to a wildly fluctuating electrical current into the cell. credits: MPIDS, background: Thomas Dresbach/University Göttingen

Fig. 1 Neurons in the cerebral cortex receive tousands of synaptic inputs from other cells. This so-called "synaptic bombardment"leads to a wildly fluctuating electrical current into the cell. credits: MPIDS, background: Thomas Dresbach/University Göttingen

Every neuron in the cerebral cortex is permanently „under fire“: It constantly receives electrical pulses, so-called spikes, from approximately 10000 other nerve cells. At the same time, each neuron generates and passes on only approximately ten pulses per second. After each sent pulse, every neuron requires a short time-out: If in direct succession to emitting a spike of its own further pulses “hit”, the cell, it is not yet receptive again and cannot process this new information. The neuron falls silent. Until now, scientists therefore assumed that the cerebral cortex can only handle signals with frequencies of up to 20 Hertz. But recent experiments showed that groups of neurons can react much faster. They can make do with signals of up to 200 Hertz. Until now, an explanation for this phenomenon was missing.

„In order for a theoretical model to be able to explain this behavior, the dynamics of the electrical currents through the cell membrane must be accounted for precisely”, says Prof. Dr. Fred Wolf from MPIDS. When a spike reaches a neuron, an electrical voltage builds across its membrane. Because of the multitude of incoming pulses, this voltage fluctuates permanently. But only when it exceeds a certain value, does the neuron react by firing off a spike of its own. This process of spike initiations takes only fractions of a millisecond.

For the first time, the scientists from Göttingen were now able to incorporate this complicated process into a model that directly calculates the response of a population of neurons to an incoming signal. “If the population no longer transmits an outgoing signal, this indicates that the incoming pulses were too fast and overburdened the neurons”, Dr. Wei Wei from MPIDS explains the fundamental idea of the model. The researchers' calculations show, that by no means does the duration of the required time-out limit the speed of neuronal communication. Instead, while one neuron is recovering, another one can step into the breach. An upper limit for the processing speed depends, however, on the much shorter time scale of spike initiation. As a consequence, teams of neurons can easily receive and transmit signals with frequencies up to several hundred Hertz.

The new results might be of great importance for the field of developmental neurobiology. For a long time researchers have known, that in infants and newborn animals visual stimuli only lead to new links between neurons after a certain age. „The very first stimuli hardly change the architecture of the neuron network“, explains Prof. Dr. Siegrid Löwel, neurobiologist at the University of Göttingen. With the help of the new results this phenomenon could be explained in principle. The creation of new links only works reliably, if the neurons can react as fast and precisely as possible to incoming information. If it were experimentally shown, that the neurons of newborns cannot process signals of the same speed as adults can, this would offer an explanation for the onset of the brains learning ability.

Fig. 2 Prof. Dr. Siegrid Löwel, Dr. Wei Wei, and Prof. Dr. Fred Wolf discussing the new results. Credits: MPIDS

Fig. 2 Prof. Dr. Siegrid Löwel, Dr. Wei Wei, and Prof. Dr. Fred Wolf discussing the new results. Credits: MPIDS

 

 

Original publication:

Wei Wei and Fred Wolf: 
Spike Onset Dynamics and Response Speed in Neuronal Populations 
Physical Review Letters, 106, 088102 (2011)
doi: 10.1103/PhysRevLett.106.088102

 

 

For further information please contact:

Dr. Birgit Krummheuer, press office 
Max Planck Institute for Dynamics and Self-Organization 
Tel.: +49 551 5176-668 
E-Mail: birgit.krummheuer@ds.mpg.de

Dr. Wei Wei 
Max Planck Institute for Dynamics and Self-Organization 
contact: follow this link

Prof. Dr. Fred Wolf 
Max Planck Institute for Dynamics and Self-Organization, University Göttingen, and Bernstein Center for Computational Neuroscience 
contact: follow this link