Animal brain-to-brain studies

The invasive BBIs that carry the most information are in animals, where both reading and writing use implanted electrodes. Pais-Vieira, Nicolelis and colleagues (2013) coupled two rats: an encoder rat performed a tactile or lever discrimination while its somatosensory or motor activity was recorded and delivered as intracortical microstimulation to a decoder rat, which used the stimulus to choose the same option well above chance — including a version in which encoder (in Brazil) and decoder (in the United States) were joined over the internet. Yoo et al. (2013) built a cross-species link, decoding human EEG and writing to a rat's motor cortex with focused ultrasound to move its tail.

These systems reach higher fidelity than non-invasive human BBIs because microstimulation writes a richer, better-localized signal than a TMS phosphene, but they are still narrow: the decoder animal's performance sits well below the encoder's, the transmitted variable is a low-dimensional task cue, and the animals are extensively trained on a fixed paradigm. They define the current invasive ceiling for the write side.