Almost everyone has trouble sleeping once in a while – worries from the day have a tendency to stick in your brain and spill over into the night, and keep you from mentally taking the break your brain needs to recharge.
But for 15% of American adults, not being able to sleep is a chronic problem that can interfere with memory and concentration. And according to the latest research, the reason may have to do with the way their brains work.
Dr. Rachel Salas, an assistant professor of neurology at Johns Hopkins University School of Medicine, and her colleagues studied how plastic, or adaptable, the brains of 18 insomniacs and 10 good sleepers were, using a technique called transcranial magnetic stimulation. Through electrodes placed around the skull, the team could precisely and painlessly deliver electromagnetic currents to specific parts of the brain. TMS is approved by the Food and Drug Administration to treat depression and migraines by disrupting the circuits that can lead to symptoms of those conditions. Salas found that TMS could have a similar role in helping insomnia patients.
To determine brain plasticity, she measured brain activity with electroencephalograms (EEG) while she pulsed each participant in an area of the brain that controls the thumb muscle, and observed in which direction – left, and up, for example – the thumb moved by default when targeted. Without TMS, she then asked the participants to reverse the default movement when prompted – so if their thumbs moved to the left and upward, the volunteers were supposed to move their thumb to the right and downward. Salas and her team figured that given the memory problems and concentration issues people with insomnia showed in previous studies, that they would do less well in performing this task than the good sleepers – in other words, that they would make more mistakes or have trouble even learning the task to begin with.
To their surprise, however, that wasn’t the case. Reporting in the journal Sleep, the group found that the insomniacs showed enhanced brain activity compared to the good sleepers. In fact, those with insomnia showed more plasticity in picking up the new task.
That supports the prevailing theory of why some people may be chronically bad sleepers. Studies suggest that the brains of insomniacs may be in a constant “on” state, continuing to operate at high levels even when it’s supposed to be dialing down to recharge at night. When insomniacs are finally able to drift off, for example, their brain activity is layered with more waking, or arousal patterns than those of good sleepers. “Their brain waves look different from good sleepers,” she says. “Traditionally in normal sleep, the brain waves slow down, become more synchronous and get into a nice delta wave for sleep. Insomniacs may get into delta sleep, but they have other faster rhythms riding on top of their EEG.”
Insomniacs also tend to show higher levels of the stress hormone cortisol, and more metabolism, or activity in the brain overall, compared to good sleepers. So while the plasticity was surprising, it wasn’t totally unexpected, says Salas. “It fit with the whole story of dysregulation of arousal in insomniacs. The light switch is on, so there is increased excitability and that could be running this increased plasticity.”
For now, it’s still not clear which came first – whether insomniacs tend to have more active brains, which robs them of sleep, or whether the chronic sleep disruptions lead to a state of hyperarousal. Salas hopes to explore that question in more in-depth studies, and figure out whether the plasticity has its limits too. “When you give an insomnia patient an easy task, they may do well, just as well as a good sleeper,” she says. “The minute you give them something more complicated, that’s where they start to break down. We hope to give insomniacs in a future study a more complicated task to see how the brain adapts and changes.”
But now that she and her colleagues have shown that the brains of people with insomnia may be over-excited, that could lead to new studies targeting this hyperarousal as a potential treatment. Whether TMS or medications that lower levels of the brain’s excitatory agent, glutamate, are used, Salas is optimistic that the latest understanding of what’s keeping insomniacs up at night could help them to dial down their brains and get some sleep.