DEVELOPMENT AND EVALUATION OF A VISUAL NEUROFEEDBACK SYSTEM: A TRANSCRANIAL DOPPLER APPROACH

The aim of this study is to develop a visual TCD-based neurofeedback system and assess its efficiency on healthy subjects by setting up an adequate experimental design. Neurofeedback is a non-invasive technique based on the idea of monitoring brain activity and providing feedback in real-time to the subject, to allow him/her to self-regulate their brain functions to reach a certain goal. Brain activity assessment was conducted using a Transcranial Doppler (TCD), a non-invasive ultrasound method employing low-frequency waves (2MHz) to investigate blood flow velocity in major brain arteries. Specifically, the middle cerebral arteries (MCAs) of each hemisphere were detected and the difference in flow between the two arteries was used to build a lateralization index. This index was employed to drive the feedback animation developed using the node-based program TouchDesigner; it consisted in a sphere moving horizontally, to the right or to the left according to the current lateralization. Various cognitive tasks were employed to induce functional hyperemia, preferentially increasing perfusion in one hemisphere of the brain, and producing observable lateralization on the feedback system, with the sphere moving towards the corresponding side. The experiment designed in this study comprises four sessions, where each subject undergoes a 15-minute training phase followed by a 10-minute test phase. During training, participants are encouraged to explore mental activities and cognitive tasks that efficiently influence the movement of the sphere. Subsequently, the test phase evaluates participants’ ability to move the sphere in the right or in the left direction, as indicated by visual cues on-screen within predefined time intervals. After data acquisition and analysis through Spike software and MATLAB, the results highlighted an increase in the average accuracy of the test through sessions, suggesting that subjects were progressively gaining more control over the sphere’s movement via training. The final goal of further studies is to employ this developed program in brain-computer interface (BCI) applications, possibly to achieve control over external communication devices.