Neurofeedback (NFB) is a broadly used method that enables individuals to self-regulate one or more neurophysiological parameters. In the case of electroencephalography (EEG) the parameters most often used so far are slow cortical potentials (SCPs), coherence training and frequency training. Protocols based on these measures have been applied to many clinical populations exhibiting abnormal EEG patterns including schizophrenia, insomnia, dyslexia, drug addiction, autistic spectrum disorder and attention deficit/hyperactivity disorder (ADHD). Today, the most widely used neurofeedback protocol for the ADHD population is based on the theta/beta ratio (TBR). However more recent studies have failed to replicate this finding of elevated TBR as a diagnostic feature in ADHD, which was also confirmed in a meta-analysis. These divergent results motivate the need for research to explore new markers to diagnose and treat ADHD. In a recent study, Férat and colleagues proposed EEG microstate analysis as a new framework to study ADHD. Microstate analysis models spontaneous EEG as a sequence of states defined by recurring appearance of a given distribution of scalp potentials. The authors observed a significantly increased contribution of one specific state commonly referred to microstate D in the ADHD population compared to healthy subjects. This state is often associated with attentional functions and brain regions in the dorsal attention networks are involved . It would therefore be interesting to study the causal link between this microstate and attention by manipulating this biomarker with neurofeedback. In this context, a recent study by Hernandez and colleagues has already demonstrated that healthy participants were able to control such brain microstates by neurofeedback. The aim of the present study is to test whether patients with ADHD are also capable of self-regulating their microstate dynamics.

In the light of recent findings on EEG microstate and the ADHD population, the hypothesis is that microstate D could be a potential functional biomarker of ADHD. To test it, the proposal is to modulate this microstate using a neurofeedback training protocol directly targeting microstate parameters. According to the main hypothesis, changes in microstate parameters should be correlated with change in attentional and impulsive behaviour. To answer this question, a two-session study was designed, where participants will perform a continuous performance task (CPT) before and after 30 minutes of microstate-based neurofeedback training. During one of the sessions participants will be trained to upregulate microstate parameters, while during the other one, they will be trained to downregulate the same parameters. Intra- and across-section statistical contrasts, both in terms of brain activity changes and behavioural performance, should provide evidence to evaluate the impact of microstate changes relative to behaviour. In addition, and according to a large number of studies on ERP components in ADHD patients the recording of event related potentials (ERPs) during the behavioural task could help us understand the neurophysiological changes linked to attention and impulsivity measures.