Personality change and psychological continuity
Writing to the brain is not hypothetical: therapeutic stimulation already changes mood, motivation and impulse control. Reports around deep brain stimulation include patients who become elated, disinhibited, or subtly different in ways that outlast the immediate therapeutic effect. Philosophically this engages psychological continuity — the idea that personal identity over time is carried by overlapping chains of memory, personality and psychological connectedness. An intervention that alters those chains raises a real, not merely rhetorical, question about whether the person before and after is continuous in the way that matters.
Authenticity: 'more myself' versus 'not myself'
The striking empirical finding is that patients report interventions in opposite directions. Some say a stimulator made them 'finally myself again' — lifting a depression that had buried their real personality. Others feel 'this isn't me,' estranged from choices the device seemed to enable. Authenticity cannot therefore be read off the biology; the same physical change can be experienced as restoration or as alienation.
Two philosophical pictures compete. An essentialist view says there is a true self to be uncovered, and an intervention is authentic if it reveals it. An existentialist view says the self is made through endorsed choices, and an intervention is authentic if the person can integrate and own its effects. For design and clinical practice, the existentialist framing is more actionable: it directs attention to whether the patient can reflectively endorse the change, and whether they retain the ability to adjust or reverse it, rather than to an unobservable 'real me'.
Consent when capacity is impaired
Here the ethics bites hardest, because of the population Volume I introduced: the people for whom BCI is most transformative — late-stage ALS, locked-in syndrome, severe paralysis — are often the least able to give standard informed consent. Some cannot speak or move enough to signal understanding; the very BCI under evaluation may be their emerging communication channel. Informed consent under impaired capacity is thus not an edge case in BCI research; it is close to the central case.
Consent is best treated not as a one-time signature but as a process with several safeguards, each of which a protocol can specify.
- Capacity assessment matched to the modality — evaluate understanding through whatever reliable channel the person has, including an already-working communication BCI.
- Surrogate and advance directives — decisions made with a proxy and, ideally, with the person's own prior expressed wishes when current capacity is uncertain.
- Ongoing (dynamic) consent — re-affirm willingness over the study's life, since both capacity and the device's role in the person's life change.
- A real right to withdraw — withdrawal must be genuinely available and not punished by loss of a communication channel the person now depends on.
Therapeutic misconception and the research relationship
A specific, well-documented risk is the therapeutic misconception: a research participant believes an experimental BCI is primarily meant to help them, when its primary purpose is to produce generalisable knowledge. Under the pressure of severe illness the confusion is understandable and easy to reinforce accidentally — enthusiastic recruitment, hopeful language, the sheer intimacy of a brain implant. The ethical obligation is repeated, concrete honesty: this is a study, it may not benefit you, here is what happens when it ends.
Ownership, explantation and abandonment
The most concrete identity-and-justice problem arrives at the end of a study. When a trial concludes, funding lapses, or a company folds, what happens to a participant whose implant has become part of how they speak, move, or feel themselves? Explantation carries surgical risk and can remove a capacity the person now relies on; leaving the device in requires someone to maintain it. The community increasingly frames this under post-trial obligations: the duty to plan, before implantation, for continued access, maintenance, or a humane and supported wind-down.
This connects identity to justice and back to Guide 5's governance. A device woven into someone's sense of self is not a gadget you can simply switch off at the end of a grant; abandonment is a distinctive harm, and avoiding it is a foreseeable duty that belongs in the trial design, the budget, and the regulatory expectations — not in an afterthought once the paper is published.