As any athlete or musician can attest, practicing makes a difficult task easier. In fact, repeating an activity can take us to a point where we a no longer conscious of what we're doing; we've perfected the task so we no longer think actively about it. This kind of efficiency also happens in brain cells, researchers from the University of Pittsburgh, Pennsylvania, have found, and this efficiency can led to some surprising brain activity.

Neurobiologist Peter Strick and his colleagues reported in Nature Neuroscience that extensively practicing a given motor skill reduces metabolic activity in the cerebral cortex responsible for managing that skill, while the number of firing nerve cells remains the same as if the skill were just being learned.

Experimenting with 10 monkeys, the researchers measured their brain activity as they learned a task for the first time, and as they spent up to six years honing that task. During the initial learning period, the monkeys (like nearly all animals) depending on visual cues to perform the task. Once fully trained, the monkeys relied on internally generated instructions. Strick measured two types of brain activity; the firing of single neurons in the brain, and the absorption of a variant of sugar, called 2-deoxyglucose, that's commonly used to measure brain metabolism.

While it's known that the motor cortex is larger among well-trained professional musicians and that structure and function of the brain can be altered by training and expertise, the relationship between metabolism and nerve cell activity was unknown.

What the researchers found, was quite surprising. Instead of increased metabolism (2-deoxyglucose uptake), they found instead that practiced monkeys used dramatically less 2-deoxyglucose, indicating an efficiency increase in brain metabolism. Just as surprising, nerve cell activity did not vary between practiced monkeys and those just starting to learn a task.

This efficiency, the researchers think, comes from changes that happen at nerve cells before the synapse (the connection to an adjacent nerve cell). Therefore, an "upstream" nerve cell can better control the activities of cells it contacts through its synapse, and make a more efficient (or less efficient) system. Some of these changes could be changes in the effectiveness of a synapse's transmission, relocation of synapses to better sites, and more streamlined coordination of synaptic activity.

While the study was conducted in monkeys, it has several implications for humans and even clinical diagnoses. "Low activation is not always a sign of low neuronal activity," they warned. Their study, then, is a new caution for interpreting functional imaging results, like fMRI or PET scans. A "slacker brain" may instead be a far more efficient one.