Bidirectional brain-machine interfaces (BMIs)

How does the technology work? Balance explanation with depth of technical detail

Explain how bidirectional brain- machine interfaces (BMIs) work, what it does, and its significance. 

Can use :

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5145890/

https://www.frontiersin.org/articles/10.3389/fnins.2016.00563/full

or any website found information on this.