In the last years Brain Computer Interface (BCI) technology has benefited from 
the development of sophisticated machine leaning methods that let the user 
operate the BCI after a few trials of calibration. One remarkable example is the 
recent development of co-adaptive techniques that proved to extend the use of 
BCIs also to people not able to achieve successful control with the standard BCI 
procedure. Especially for BCIs based on the modulation of the Sensorimotor 
Rhythm (SMR) these improvements are essential, since a not negligible percentage 
of users is unable to operate SMR-BCIs efficiently. In this study we evaluated 
for the first time a fully automatic co-adaptive BCI system on a large scale. A 
pool of 168 participants naive to BCIs operated the co-adaptive SMR-BCI in one 
single session. Different psychological interventions were performed prior the 
BCI session in order to investigate how motor coordination training and 
relaxation could influence BCI performance. A neurophysiological indicator based 
on the Power Spectral Density (PSD) was extracted by the recording of few 
minutes of resting state brain activity and tested as predictor of BCI 
performances. Results show that high accuracies in operating the BCI could be 
reached by the majority of the participants before the end of the session. BCI 
performances could be significantly predicted by the neurophysiological 
indicator, consolidating the validity of the model previously developed. Anyway, 
we still found about 22% of users with performance significantly lower than the 
threshold of efficient BCI control at the end of the session. Being the 
inter-subject variability still the major problem of BCI technology, we pointed 
out crucial issues for those who did not achieve sufficient control. Finally, we 
propose valid developments to move a step forward to the applicability of the 
promising co-adaptive methods.