Within DOC-Stim we developed three cognitive protocols for DOC patients and one movement protocol. One using vibrotactile stimulation, one with functional electric (FES) stimulation and the third one with transcranial direct current stimulation (tDCS).
Vibrotactile protocol:
The vibrotactile stimulation protocol uses 7 tactile stimulators that can be distributed all over the patient’s body. The protocol is for assessment and communication of a patient. While the protocol is running, the seven stimulators will generate short vibration bursts in randomized order. By counting each vibration burst on the selected target stimulator, the processing in the human’s brain will create an EEG pattern that can be detected by the BCI, hence the system knows on which stimulator the patient was focusing on.The protocol has two modes: assessment mode and communication mode. The first one is for assessing the status of consciousness of a patient, the second to generate an easy means of communication for people without any voluntary motor control. During an assessment session a user is told on which target stimulator he or she shall focus on. If the system detects that the patient is focusing on those locations, it can be concluded that she or he is able to understand and follow instructions, hence there is consciousness in the patient. If an assessment run was successful one can continue to a communication run. In the communication mode, the system does not tell the user on which stimulator he or she shall focus, instead the patient’s voluntary selection of one stimulator expresses the answer she or he wants to give. This means, before asking a question, the experimenters gives each of the two target stimulators a distinct meaning, e.g. “YES” or “NO” or “Monday” or “Tuesday”. Now, the experimenter explains the question and the two answering options to the patient, for example the question could be “Should I switch on the radio?”. The answer could be to focus on the stimuli one feels on the left hand for the answer “YES, please switch on the radio”, or focus on the stimuli one feels on the right hand for “NO, please don’t”.
tDCS protocol_
tDCS stands for transcranial direct current stimulation and is one of DOC-Stim’s new stimulation approaches for rehabilitation of DOC patients. A meta- analysis revealed just in November 2020 that tDCS improves attention/vigilance and shows a small trans-diagnostic effect on working memory. This paradigm makes use of these effects. tDCS provides a constant current for several minutes between two selected electrode positions. Depending on the polarity it can increase or decrease the excitability of neurons, and hence can increase or
decrease learning and rehabilitation. With the DOC-Stim system stimulation can be done during or before running protocols for example the new vibrotactile one. By using the stimulation, the rehabilitation effect will be increased.
Resting state EEG protocol:
The resting state analysis is for assessment only, not for rehabilitation. Several studies showed that biomarkers from resting state EEG can provide useful information about the status of a patient. After the acquisition of ten minutes of resting state EEG, the Delta Alpha Ratio (DAR) and the Power Ratio Index (PRI) are calculated. In Task 3.7 we show correlations between functional scales and those parameters.
Movement protocol:
The movement protocol is for rehabilitation of DOC patients. If a patient tries to perform motor movements, the according brain areas will be active, no matter if the motor movement is really performed or not. Some scientists speculate that the motor output in some patients is blocked, this means that the function of motor areas in the brain is intact, but the motor commands don’t reach the periphery. With the BCI technology we track the intention to perform movements and close the feedback loop by using FES to contract the peripheral muscles. That way, the information about the movements gets fed back via afferent nervous pathways to the motor cortex. This rehabilitation protocol shall improve the rehabilitation success of DOC patients. During a session a patient is asked to try 80 movements and will receive feedback if brain areas are activated.
