The human brain is somewhat similar to a rudimentary radio with five channels. Electrical signals from neurons coordinate across the brain, generating oscillations known as brain waves. In a way, the brain changes its channels as we go about our day to match our internal state of mind to outside requirements-though at any point, the channels can bleed over.
There’s a mysterious outcast: a frequency called theta waves. For decades, these waves have taunted neuroscientists trying to decipher their functions. Theta waves seem to help mice navigate mazes, but also support memory in humans.
By finding the driving source of theta waves, we could potentially enhance them-using neurostimulation or other methods-to slow cognitive decline. Thanks to Xbox and some virtual mall shopping, a team led by Dr. Arne Ekstrom from the University of Arizona dug deep into what drives theta waves.
The study recruited people with epilepsy who already had electrodes implanted into their brains to hunt down the source of seizures. The brain has a way of internally generating theta waves using memory, said the team.
Using electroencephalography, we can record the speed and sequence of brain activity and capture its relative pace. Like calm or stormy, choppy waters, these brain oscillations rise and fall at different frequencies, each representing a different state of mind.
Beta waves, for example, spark when the brain is completely engaged-for example, when you’re intrigued by a conversation. Alpha waves are slower, and usually present when you’re sitting down and ready for a rest. These waves are larger in amplitude and cycle even slower at 3 to 12Hz per second.
These waves are tentatively linked to creativity-ideas or solutions suddenly come to you-or when you’re daydreaming or meditating. While we’re awake theta waves are mostly found in the hippocampus, a brain region critical for both memory and navigation.
So it’s no surprise that the waves appear in mice and rats as they try finding their way across complex mazes, suggesting they help integrate sensations and movement as the rodents explore a new environment. What is surprising is that the waves also appear in completely still humans challenged with memorizing lists of words or pictures.
In another, artificially enhancing theta waves with an off-the-shelf entrainment device-which uses a combination of sound and lights to stimulate certain brain wave bands-increased memory performance for recalling words in 50 volunteers.
So what is it that theta waves do? Do they help guide us as we navigate the world? Or do they help us lay down precious memories?
Each already had up to 17 electrodes implanted in their brains to search for the source of seizures. The brain wave analyses came back with a clear answer. Both navigation and mental simulation sparked theta waves, becoming stronger as the trials progressed.
Simply remembering the route-without any movement-generated far larger waves that lasted longer. It seems that memory is a far stronger driver for theta waves compared to simple navigation, said the team.
Theta waves seem to naturally occur in the brain even without outside stimulation, supporting the idea that they’re internally generated in the brain and integral for memory.
With memory closely knitted to theta waves, it’s possible to tap into the unique frequencies and improve memory during aging or in patients with dementia or other mental disorders.
Researchers are already exploring different brain stimulation methods-from electrical to magnetic-with initially promising results.
Perhaps more broadly, the study adds to a recent trend that explores brain waves as a novel route for treating difficult neurological disorders, including Alzheimer’s and stroke.