Brain activity once thought to be background noise is actually required

EPFL researchers have made an important discovery about the brain. The team says that a form of neuron-to-neuron communication previously dismissed as background noise is actually required to keep nerve junctions intact as animals age. Their finding suggests defects in this type of neural communication could contribute to neurodegenerative disorders and other conditions of the brain.

Neurons typically communicate using fast electrical signals that regulate the release of neurotransmitters, which are described as the chemical messengers of the brain. Once an electrical signal is transmitted across the neuron, they cross a juncture with another neuron known as a synapse to release droplets filled with neurotransmitters that pass the information on to the next neuron. That type of neuron-to-neuron communication is known as evoked neurotransmission.

Scientists know that the synapses can release some neurotransmitter droplets even in the absence of electrical impulses, something known as miniature release events or minis. Studies have shown that minis have an important function. One of those functions is to support the development of synapses and ensure that the synapses are connected. Researchers wanted to determine if the minis could play a role in a mature nervous system and investigated neuron control movement in fruit flies.

As insects age, their synapses began to break up into smaller fragments, which also happens in aging mammals, including people. As the nerve junctions broke down, both evoked and miniature neurotransmission were dampened, leading to motor problems in the flies, including reduced ability to climb the walls of a plastic vial. The team assessed the effects of stimulating or inhibiting the evoked and miniature neurotransmission and saw that synapses aged prematurely when both types were blocked.

The team believes this could be related to neurological diseases that are associated with old age. The discovery is contrary to the long-standing idea of neuroscience. Researchers say that the idea has long been that the structure of a synapse breaks down, leading to a functional change in the synapse. However, the researchers found it's actually the other way around. The team also found increasing the frequency of minis kept synapses intact and preserved the motor ability of middle-aged flies.