The experiment involved participants utilizing specialized equipment including sensors and earbuds. On September 24, one participant sleeping at home induced lucid dreaming, a state in which you are aware that you are dreaming. It is apparently a trainable skill, although I have only ever personally experienced it a handful of times throughout my life.
the lucid dreaming communication experiment itself is decades old now, people in lucid dreams have communicated to conscious scientists by moving their eyes in patterns to communicate with sleep scientists talking to the dreamer or playing sounds for them while in a lucid dream state to indicate the dreamers’ awareness and understanding of stimulus from the waking world.
The “first” they’re talking about is an extension of that phenomen, which is cool in its own right.
heres a recent article about similar sleep studies:
https://www.science.org/content/article/scientists-entered-peoples-dreams-and-got-them-talking