BCI (brain-computer interfaces) is a technology being looked into by companies such as VALVE and Facebook. This technology allows people to get readable information from your brain. Collected in the right way you can essentially read people's emotions.
This can make a big difference in the entertainment and healthcare industries. For video games BCI could read when people are getting bored and turn up the difficulty or find out how scared someone is. For tv shows or movies it could tell the developer when someone has a reaction. For healthcare the technology can be used to communicate with the brain directly. This bypasses the normal neuromuscular pathways.
This technology is basically just another peripheral like a mouse or keyboard, but much more advanced. It is concerning what companies could do with the data gathered from this technology. They could have access to your emotions and eventually maybe even your thoughts. Advertising could become exactly what you need. If you dislike a certain company they can send you articles about how they aren't doing anything wrong. Eventually if this technology ever gets the ability to write signals to your brain they could start literally brainwashing you.