DES and mapping

In this video, we give you a few more details about we map the brain areas in question with direct electrical stimulation and how electricity is the language of the brain. Different parts of the brain communicate by transmission of electrical signals. That’s why we use electrical stimulation to activate or to inhibit brain functions, such as motor function and language. By electrical stimulation of the brain of, for example, the motor cortex, it is possible to activate the function. You can see the effects when the muscle of the patient contract. That’s what we do in motor mapping. To elicit a movement, a certain level of stimulation is needed.

The lowest level of stimulation intensity in which a contraction or a movement occurs is called the stimulation threshold. This stimulation threshold differs per individual. So when we start with language mapping, we first determine the individual stimulation threshold on the motor cortex.

In language testing, eliciting an answer by stimulation is not possible. We cannot make a patient speak by simply stimulating an area. So the only thing we can do now is to disturb the electrical activity of the brain. That is called inhibition, which results in language disturbances. Cortical and subcortical inhibition of language is more complicated than stimulation of the motor cortex and motor pathways. The reason why is not straightforward, and precise details about the underlying mechanisms are still unknown. The probes we used to stimulate the brain are bipolar or monopolar. We use the bipolar probe for language testing. As stimulation parameters, we can choose the pulse width, amount of pulses, frequency, and intensity. These stimulation parameters are important.

For example, high frequency stimulation evokes less seizures compared to the low frequency stimulation, better known as Penfield methods. Yet, we still use the Penfield methods because in our experience, it is the most effective method for language mapping. The maximal contact duration of the probe on the brain is four seconds. Safety comes first in stimulation. This means you have to stimulate enough to disturb the function, and on the other hand, make sure you don’t overstimulate and risk damage to function or elicit an epileptic seizure. Now that you’ve been introduced to the method itself, let us put it into practice in the operating theatre in the next videos.