Can you imagine a world without our smartphone or laptops ? Electricity is essential to the
world.
Even our brain cells, neurons, communicate with electricity.
Can you control the brain using this same electricity ? Yes and we are going to talk
about deep brain stimulation.
Deep brain stimulation, is an implantable device that directly stimulate the brain in
Parkinson’s disease, a movement disorder.
Parkinson’s derived from the death of dopamine producing or dopaminergic neurons in the substantia
nigra.
The substantia nigra is a part of the basal ganglia, a collection of the brain that control
movement through their connection with the motor cortex.
Therefore when the neurons in the substantia nigra die, the individual may be hypokinetic
or low movement state which is commonly seen in Parkinson’s disease.
The clinical features are : tremor, which is an involuntary shakiness and it’s a resting
tremor.
There is rigidity, a relative stiffness of the arm, bradykinesia, slowed movements, hypokinsia
lessened movements, akinesia absence of movement, and these three last symptoms result from
difficulty to initiate movements.
The treatment can’t stop the degeneration, the main strategy is to increase the dopamine
signaling in the brain.
Levodopa can pass through the brain barrier and be transformed into dopamine.
But, after few years of levodopa treatments patients present dyskinesias, which are unvoluntary
movements.
In 1987, the neurosurgeon Dr Benabid and neurologist Dr Pollak, started the implantation of electrodes
and the electrical stimulation in the brain of Parkinsonian patients.
And guess what ? It works, it allows to reduce motor symptoms of Parkinsonian patient’s
and also by reducing the dopaminergic treatment, it reduces dyskinesias.
The deep brain stimulation was born and targeted a small nucleus in the brain, part of the
basal ganglia system, the Subthalamic nucleus.
As we switch the program of our TV, the neurologist decide to switch off or switch on this part
of the brain.
Switching on the stimulation inhibits the nucleus.
As a radio station, the neurologist can choose the frequency, only high frequency stimulation
improves motor symptoms.
Deep brain stimulation is continuous, it never stops, but some years after stimulation, it
can lead to side effects caused by the deep brain stimulation itself.
This is where research is needed to better understand the Subthalamic nucleus.
So in research center as at the brain and spine institute or ICM, patients came three
days after the implantation of deep brain stimulation electrodes.
Scientists record the brain activity through this same electrodes during resting state,
walking or even during movement.
Through these electrodes we can record local field potential, which is the activity of
neurons population.
By recording this activity, we can measure different parameters as frequency of the signal
(theta, alpha, beta, or even gamma) and we can measure the increase or decrease in the
time during an action for example.
The goal is to find a biomarker in the electrophysiological activity in Parkinson’s.
Indeed, recording in this nucleus showed increased activity in beta during resting state, and
was correlated with patients’ motor symptoms.
Using brain-machine interface, scientist tried to improve deep brain stimulation and to stimulate
only when necessary, it is called adaptive deep brain stimulation.
They used beta activity as a trigger of the stimulation, it showed improvements of the
motor symptoms, but still more research is needed to make it real in everyday life of
patient’s.
Deep brain stimulation is not only for Parkinsonian patients, by changing the region of the electrodes
for example in the circuitry involved in memorization, it may improve Alzheimer’s disease.
There is a future in deep brain stimulation to help more patients with neurological disease,
but still more research is needed.