Meanwhile, AI is enhancing the capabilities of wearable consumer products that record signals from outside the brain. Ethicists worry that, left unregulated, these devices could give technology companies access to new and more precise data about people’s internal reactions to online and other content.

Farahany says that moving beyond the motor cortex is a widespread goal among BCI developers. “All of them hope to go back further in time in the brain,” she says, “and to get to that subconscious precursor to thought.”

Last year, Andersen’s group published a proof-of-concept study5 in which internal dialogue was decoded from the parietal cortex of two participants, albeit with an extremely limited vocabulary. The team has also recorded from the parietal cortex while a BCI user played the card game blackjack (pontoon)6. Certain neurons responded to the face values of cards, whereas others tracked the cumulative total of a player’s hand. Some even became active when the player decided whether to stick with their current hand or take another card.

Before a car crash in 2008 left her paralysed from the neck down, Nancy Smith enjoyed playing the piano. Years later, Smith started making music again, thanks to an implant that recorded and analysed her brain activity. When she imagined playing an on-screen keyboard, her brain–computer interface (BCI) translated her thoughts into keystrokes — and simple melodies, such as ‘Twinkle, Twinkle, Little Star’, rang out.

For Smith, it seemed as if the piano played itself. “It felt like the keys just automatically hit themselves without me thinking about it,” she said at the time. “It just seemed like it knew the tune, and it just did it on its own.”

In unpublished work, researchers at Synchron have found that, like Andersen’s team, they can decode a type of preconscious thought with the help of AI. In this case, it’s an error signal that happens just before a user selects an unintended on-screen option. That is, the BCI recognizes that the person has made a mistake slightly before the person is aware of their mistake.

Marcello Ienca, a neuroethicist at the Technical University of Munich in Germany, says that EEG can detect small voltage changes in the brain that occur within hundreds of milliseconds of a person perceiving a stimulus. Such signals could reveal how their attention and decision-making relate to that specific stimulus.