Friday, December 30, 2011

Brain uses 'glue cells' to form memories

Scientists have long thought that we use neurons, the cells that make up the wiring of the brain, for all of the brain's functions. The other commonly found cell type, glial cells, were thought to be supporting the neurons in keeping the brain structure intact. Hence the name glial, which is Greek for glue. Researchers from the Tel Aviv University have shown, however, that glial cells play an essential role in memory formation. While the role of glial cells in supporting the brain's wiring have been investigated previously, the Israeli researchers reveal how they are able to function in concert with neurons.

Neurons are specialized cell types that communicate by long wires by which they are connected to each other. Electrical signals are used for communication, and the whole network of neurons and their connections is thought to be enough for the brain to function. Scientists in Tel Aviv have shown that glial cells serve as regulators in this process. They decide which messages are to be sent forward, and which can be discarded. Glial cells also decide when information is passed on, which gives them an important role in the process of learning and memory.

The researchers made their discovery after they observed that there are much more glial cells than neurons in the hippocampus, an area of the brain that is important in memory formation. Because of their abundance, it suggested that these cells have a more profound role than merely providing structural support. Indeed, without the glial cells acting on neurons, the brain would probably become overloaded with information, which would impair memory formation and learning.
Red = neurons. Green = glial cells
Curing brain diseases
With the new found role of glial cells, scientists may be able to develop new therapies for brain diseases, such as epilepsy. During an epileptic seizure, neurons fire an excessive amount of signals throughout the brain, which leads to an overload. By allowing glial cells to more closely regulate neuronal activity, such seizures may be prevented. Additionally, the scientists note that neurodegenerative diseases, of which Alzheimer's and Parkinson's are examples, are related to dysfunctioning glial cells.

Forming memories
The brain needs more than just the hippocampus to form memories. Storing and retrieving them is governed by the actions of many brain parts, and their mechanism of action is not yet fully understood. Recently, scientists found a set of genes that play a role creating the connections that enable us to remember things. Studying a protein called kibra revealed on a cellular level how memories are created. Additionally, a lack of memory cells, for example due to brain diseases, can be countered by electrically stimulating parts of the brain.

Paradigm shift
Long have scientists thought that glial cells do nothing more than provide structural support, which also explains their name: they 'glue' the brain together, so that neurons can function by communicating with each other. A possible role of glial cells in neurotransmission has only been suggested more recently. Previous studies have revealed that these glue-like cells play an important role in the plasticity of the brain, which is its capability to modify the existing wiring by making new connections and breaking down the old ones. This is important for the ever-changing collection of memories that our brain has.

The Israeli scientists have now shown, with the aid of computer models, that neurons require the aid of glial cells in properly conducting signals for the formation of memories and to facilitate learning. It is likely that the future will reveal what role glial cells play in other parts of the brain, as their role as moderator of neuronal signals seems something that is prevalent throughout the entire brain.

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