Deep Brain Stimulation (DBS) and Temporal Interference Stimulation (TIS)

Through the application of electrical stimulation to the brain, it is possible to modulate neural activity. Deep Brain Stimulation (DBS) and Temporal Interference Stimulation (TIS) are two types of electrical stimulation researched at 4Brain. The main aim behind our research is to find electrical stimulation paradigms and parameter combinations that are able to modulate neural activity and bring therapeutic well-being to patients suffering from a variety of neurological disorders. Although these techniques have the potential to treat many neurological disorders, at 4Brain we focus our efforts on researching DBS and TIS as possible treatments for epilepsy.

Deep Brain Stimulation (DBS)

DBS is a established invasive therapy for the treatment of neurological diseases, such as Parkinson’s disease (PD). It consists of an invasive procedure where a stimulating electrode is implanted in the region of interest (ROI) of the brain. Along with the electrode, but at the level of the chest a neurostimulator is also implanted. Connecting the electrode implanted in the brain and the neurostimulator in the chest is a lead wire. Through current-controlled biphasic square pulses applied at the ROI of the brain electrical stimulation interacts with neuronal activity. The interaction between the electrical stimulus and neuronal activity is dependent on the parameter values of the electrical stimulus. In the case of DBS there are 4 main parameters that can be tuned. Phase duration, also known as pulse width which determines the duration of the positive and negative phases of the pulse. Interphase gap, which corresponds to the time gap between the negative and positive phase. Stimulus amplitude, which determines the amount of current injected into the tissue. Finally inter-pulse interval which is determined by pulse-rate or frequency and corresponds to how often the stimulus repeats itself. By modifying these parameters, along with the placement of the electrode it is possible to determine how this approach can be used to interface with neuronal activity and treat neurological disorders.

Temporal Interference Stimulation (TIS)

TIS, unlike the previously explained DBS, is a novel noninvasive approach that is able to target deep brain structures without activating the overlying cortex. It consists on the placement of two electrode pairs at the skull connected to a current controlled stimulator. In this case instead of square biphasic pulses, sinusoidal waves are used to interact with neurons. Specifically, out of each electrode pair a high frequency (kHz) sinusoidal wave is outputted. The waves are outputted at a slightly different frequency from each other. Although these waves by themselves cannot interact with neural activity because of their fast nature, when they interfere and add constructively a new amplitude modulated waveform is created that has a beat envelope exactly at the difference of frequency between both high-frequency sine waves. Since the beat envelope is of much lower frequency neurons are capable of sensing it, and through this beat envelope is how neural activity can be modulated. By adjusting electrode placement and current amplitudes it is possible to non-invasively target different brain regions without having to go through an invasive procedure. Just like in DBS, the interaction between the electrical stimulation and the neuronal activity is also parameter dependent. In TIS, there are two main parameters that can be adjusted. Carrier waves frequency, which corresponds to the frequency of both sinusoidal waves and also determine the beat envelope frequency. Amplitude, which corresponds to the injected current through the sine waves and determines the envelope amplitude. By modifying these parameters it is possible to research the parameter-dependent effects of this therapy and its potential to treat neurological disorders.