Not getting enough sleep could be changing your brain, European researchers say.
Sleep deprivation can lead to connectivity changes in the brain, according to a German study.
It is thought sleep regulates the connective strength between neurons, which is important for learning and memory.
Scientists from the University Medical Center Freiburg put this theory to the test by comparing the brain activity of 20 participants after one night of sleep and one night of little sleep.
They applied magnetic pulses to the brain's motor cortex, which is the area of the brain responsible for controlling movement.
The researchers found the strength of the pulse needed to stimulate a muscle response in the left hand was much lower for participants who had had minimal sleep.
This suggests brain excitability was higher after lack of sleep, lead researcher Christoph Nissen says.
Sleep-deprived participants also performed poorly in a word-pair memory task and their blood samples had reduced levels of BDNF, a protein that regulates how effectively neurons communicate with each other.
Sleep-deprived brains were also less able to rewire themselves - which is important for forming memories and mastering new skills - and did worse on a short-term memory test.
The researchers say the results give greater insight on the mechanisms through which loss of sleep leads to poor memory performance.