Implications of brain plasticity to brain-machine interfaces operation a potential paradox?

The adult brain has the remarkable ability to plastically reorganize itself in order to record memories (experiences), to add abilities, and to learn skills, significantly expanding the carnet of resources useful for facing and solving the unpredictability of any daily life activity, that is, artistic and cultural activities. Brain plasticity also plays a crucial role in reorganizing central nervous system's networks after any lesion, being it sudden and localized, or progressive and diffuse, in order to partly or totally restore lost and/or compromised functions. In severely affected neurological patients unable to move and to communicate with the external environment, technologies implementing brain-machine interfaces (BMIs) can be of valuable help and support. Subjects operating within a BMI frame must learn how to produce a meaningful signal for an external reader; how to increase the signal-to-noise ratio at a level which makes it suitable for rapid communication with the machine; and how to improve the speed and specificity (bit rate) of signal production as a new language for governing and controlling a machine. Since it is of absolute importance for the patient to be able to maintain such a skill for a prolonged lapse of time (i.e., until his/her lost abilities are restored by a therapy and/or a different technology), neurophysiological phenomena at the base of plastic changes are obviously of remarkable importance within any BMI and are the content of the present chapter.