A new study shows that electrical stimulation deep in the brain contributes to the growth of new neurons. Dr. Andres Lozano, Canada Research Chair in Neuroscience, and Scellig Stone, neurosurgery resident and PhD candidate at U of T, have discovered that brain stimulation often used in therapy for patients with Parkinson’s disease leads to increased neuron growth.
The original surgical procedure was practiced for over 15 years and consisted of placing a battery into the patient’s chest (similar to a pacemaker), drilling a hole in their skull, and stimulating the electrical circuits within the brain to alleviate the patient’s brain malfunctions. Most often, brain disorders cause neurons to be either over- or underactive.
By using a similar system of electrodes, Lozano and Stone were able to regulate neuronal activity. “[While] we could see that the patient’s symptoms got better, we could not see whether or not new cells were being born in the brain,” says Lozano. Additionally, the human brain is a difficult environment for observing neurons and their functions.
Thus researchers applied the same stimulation to mice in an area of the brain called the hippocampus. “[Through this electrical stimulation] we could increase the normal production of neurons by two to three times,” says Lozano. By placing wires within the mouse, the electrical stimulation could be switched on or off, and thus controlled neuron production. “We are [also] able to show that the new neurons seem to grow normally. [They] integrate into circuits of the brain and appear to be involved in memory functions,” says Lozano.
Old neurons were distinguished from new ones by labelling the new DNA with a genetic marker. All neurons made after this injection incorporate the genetic marker into their DNA, while the old ones did not. “When a neuron is made, DNA has to be used. If a new cell is born, the DNA [within it] will have this label, [therefore] we can identify which cells are new,” explains Lozano.
Lozano and Stone tested the activity of the newly created neurons by teaching mice to find a platform in what is called the Morris water maze. Once the mouse learned the task, the mouse was taken away, the water was clouded, and the mouse reintroduced to find the platform once more. “We found that during the task, while they were remembering, the new neurons became active.”
While electrical brain stimulation has already been performed on 60,000 people in order to control the tremors and rigidity associated with Parkinson’s disease, the ability to induce neuron production was unknown to the neurosurgery field. “It’s been known for 15 to 20 years that the adult brain, under certain conditions, can increase or decrease the number of neurons made. For example, exercise increases the number of neurons created in the brain, [while] stress decreases [their production]. When we applied electrodes to circuits within the brain, we found that we could stimulate neuron growth.”
In the future, this research will be extended to prove whether having a greater number of neurons is beneficial or detrimental to one’s health. While researchers suspect that new neurons help store and acquire memory, it is difficult to come to such conclusions because other changes in the brain’s chemistry may be responsible for a similar outcome.
Although the mice used in the research didn’t have memory disorders, the researchers assumed that if neuron growth is proven beneficial it could help not only patients with Parkinson’s and Alzheimer’s disease, but also those with memory impairment, epilepsy, and depression.
