Every movement and every thought requires the passing of specific information between networks of nerve cells.

To improve a skill or to learn something new entails more efficient or a greater number of cell contacts.

Until now, astrocytes were thought to have their main role in the development and nutrition of the brain's nerve cells. The new findings improve our comprehension of how the brain learns and remembers. They could also aid in the basic research of diseases such as epilepsy and the amyotrophic lateral sclerosis (ALS).

To live is to learn: Even fruit flies can learn to avoid detrimental odors and also in humans, most abilities are based on what we learn through practice and experience. Thus we are able to perform both fundamental processes such as walking and speaking and also master complex tasks such as logical reasoning and social interactions.

Learning at the cellular level

In order to learn something, i.e. to process new information, nerve cells grow new connections or strengthen existing contact points. At such contact points, the synapses, information is passed from one cell to the next.

Once a synapse is created, new information has a means to be passed on and the information is learned. Enhancing an acquired skill through practice is then accomplished by strengthening the synapses involved. Incoming information elicits a much stronger response in the downstream nerve cell when passing through a strengthened synapse, as compared to a "normal" synapse.

At the cellular level, this can be envisioned as follows: At a synapse, the two communicating nerve cells do not come in direct contact but are separated by a small gap. When incoming information reaches the synapse, glutamate is released into the gap.

These transmitter molecules cross the gap and bind to special receptors in the downstream nerve cell. This in turn prompts the downstream cell to pass on the information. In a strengthened synapse, the informing cell releases more glutamate into the synaptic gap and/or the informed cell is more efficient at binding the glutamate. As a result, information transmission is significantly enhanced.

"Some contact points between nerve cells (red) are surrounded by star-shaped cells known as astrocytes (green). It is now shown that via ephrinA3/EphA4 interactions, astrocytes influence the communication between nerve cells by removing the transmitter molecule glutamate. This so far unknown activity also has implications for the ability to learn. (Credit: Max Planck Institute of Neurobiology / Schorner, Klein & Paixão)"

Source: Max Planck Society