Cortico-cortical microstimulation write channel

The highest-fidelity write channel in animal BBIs is intracortical microstimulation (ICMS): patterned current delivered through implanted electrodes directly into the receiver's cortex, typically somatosensory or motor. Compared with a TMS phosphene, ICMS is far better localized and can encode graded, multi-site patterns, which is why invasive rat and monkey BBIs transmit richer task variables than any non-invasive human system.

Its promise is also its problem. Writing informative, naturalistic percepts requires solving the same open questions as sensory neuroprosthetics — how to encode information in stimulation patterns, avoid adaptation and off-target activation, and keep the interface stable and safe over time. Cortico-cortical write in humans is not demonstrated; it inherits every unsolved issue of chronic microstimulation, which is why human BBIs still rely on the coarse but non-invasive TMS channel.