The Food and Drug Administration placed a clinical hold on new patient implants in Neuralink's PRIME study following complications reported in connection with the trial's second participant, according to two people with knowledge of the regulatory action. Neuralink, when asked directly about the hold, neither confirmed nor denied its existence.
The second participant's neural implant is understood to have shifted position in the weeks following surgery — a complication referred to as device migration — significantly reducing the device's ability to detect and interpret neural signals. Neuralink had not previously disclosed the second participant's outcomes publicly. A person familiar with the matter said the second participant's performance had been "significantly below" the benchmark associated with the trial's first participant, who had demonstrated a typing rate of 40 words per minute using neural signals alone.
A clinical hold prevents a trial sponsor from implanting new participants until the FDA lifts the restriction. It is a regulatory mechanism used when the agency has identified a safety or device concern that requires resolution before enrollment can continue. Existing participants may continue using their devices during a hold. "A hold is not a termination," said a former FDA reviewer with knowledge of the agency's regulatory framework. "But it is a signal that the agency has seen something in the safety record that warrants stopping the clock."
Device migration is a known risk in implantable neural devices, having been documented in earlier generations of deep brain stimulation devices. Whether the migration in the PRIME study represents an isolated mechanical event or a design issue requiring modification of the device or the surgical protocol is the central question the FDA's hold is intended to resolve.
The divergence between the two participants' outcomes is particularly striking given that the first patient's widely publicised 40-words-per-minute result depended on the implant's electrodes remaining stably positioned in the motor cortex. Researchers who study brain-computer interfaces said the gap in results raised important questions about what determines implant stability and how reliably it can be maintained.
Neuralink's spokesperson said in a statement that the company was "committed to transparency in everything we do" and would share updates "through appropriate channels at the appropriate time." The spokesperson declined to address the existence of the clinical hold directly or to comment on the second participant's outcomes.
The combination of an undisclosed FDA clinical hold and undisclosed complications in the second participant was described by bioethics researchers as inconsistent with the standards of transparency expected of clinical trial sponsors and, in their view, likely to invite closer regulatory scrutiny going forward.