The futuristic ethical concerns already mentioned arise in the long-term future. We define this era as when BCIs are routinely used to augment human brains, giving users perceptual, cognitive and motoric abilities that may greatly exceed those of the unenhanced, and transforming emotional life as well. At this point, cyborgs will differ radically from unenhanced humans. One concern is that they will view us as a different, and inferior, life form, much as we now regard chimpanzees (Warwick, 2003). Loss of individuality is another long-term future scenario. If BCIs are used for direct brain-to-brain contact, this would enable new modes of communication but also lead to the possible replacement of individual mental lives by a network in which individual brains are mere nodes (Warwick, 2003).

Thoughts, feelings and memories that can be stored and shared as bits of data will not degrade as readily as human brain tissue. While other prosthetics such as artificial hips or heart valves can replace failing bodily structures, BCIs offer the first possibility of increased longevity of a person's consciousness. Immortality may even be possible (McGee and Maguire, 2007).

These BCI scenarios lead to interesting questions about what it means to be human. Would we be human if we could see infrared light, memorize a phone book, or cause others to move by willing them to with our own mind? Would we be human if we ceded the role of smartest beings on earth to others, or would those enhanced beings be humanity's new form? Would we be human if our minds never operated independently from others'? If they operated for eternity? These questions raise the more general question of what it means to be human, and also the question of whether being human by any particular definition has intrinsic value. Although these questions are age-old, they arise with a new urgency in connection with advanced BCIs (McGee and Maguire, 2007).

BCIs could eventually bring about tectonic societal shifts. The effects of cochlear implants on deaf culture (Tucker, 1998) may presage the impact of BCIs on all aspects of human culture that are adapted to current human capabilities rather than the augmented, networked capabilities of future cyborgs. Global political trends such as the Arab Spring, attributed in part to social networking, could be distant harbingers of the effect of wide bandwidth BCIs that enable the sharing of thoughts and feelings among groups of individuals.

The ethical challenges of the medium term will be largely free of the existential and metaphysical dimensions just discussed, such as ceding dominion of the earth to others, merging our identities into a global network, or questioning the meaning and value of being human. Yet the emergence of these medium-term challenges will depend on BCI technology advancing significantly beyond its current state and therefore do still have a science fiction flavor. We take the defining feature of the medium-term to be the availability of BCI therapies for a wide range of human afflictions.

One set of ethical issues at this point will concern barriers to delivery of BCI therapies. One barrier is likely to be economic. The cost of BCIs in the coming decades is hard to predict, as is future societal support for universal access, but we can anticipate some degree of inequity in access to BCIs. Patient acceptance of implants, in particular the bioethicists' “yuck factor” (Niemelä, 2011) may also prevent or slow delivery of BCI therapies.

Another issue with a degree of bioethical precedent concerns control of the BCI (Jebari and Hansson, 2013). Therapies vary in how much control patients have. How much adjustment or programming of a BCI by the patient will be feasible, and with what risks and benefits? An aspect of control with much less precedent concerns the possibility of BCI hacking, that is, the possibility that a third party, unbeknownst to patient and healthcare provider, would deliver inputs to a patient's brain or read brain states (Denning et al., 2009). Although safeguards against such interventions could of course be designed into any system, experience with current information technology shows that no system can ever be made entirely invulnerable to such attacks. This raises the dire prospect of hacking into systems controlling human thought, feeling and behavior.

Finally, as BCIs are adopted more widely for therapeutic use, enhancement uses will likely follow. The ethics of enhancement is a well-explored area in bioethics and neuroethics more specifically (Parens, 2000; Farah et al., 2014). However, compared to the effects of drugs, which only modulate function within existing brain networks, the addition of new sensory, action and computational devices has the potential to more radically enhance human capabilities.

The transition from therapy to enhancement is evident in many areas of medicine: from neuropsychiatry, where attention-boosting drugs are used by college students to enhance their focus and improve their grades (Sussman et al., 2006), to plastic surgery, where techniques developed to reconstruct injured faces are now commonly used to enhance the attractiveness of the uninjured. Therapeutic implantation of BCIs for only mildly impaired individuals could provide a bridge between therapy and enhancement uses of BCI. Another pathway along which BCIs could transition from therapy to enhancement is by the addition of enhancing BCIs for someone who is already undergoing therapeutic implantation for a serious disorder, for example increasing the range of wavelengths perceived by someone with impaired vision.

Compared with the challenges awaiting us in the medium and long-term, which are currently speculative, we are now faced with a set of ethical challenges that are clear and present. How we respond to these challenges will determine the path we take to the medium- and long-term challenges of BCIs. One set of ethical challenges concerns clinical trials—how trials are conducted and which indications are pursued. Economic considerations of course shape these decisions, and the ethical issue is how these considerations will be balanced by other considerations. Will BCIs be developed only for the most profitable applications, leaving numerous “orphan” medical conditions unaddressed? How will an emphasis on profitability shape the future of BCI technology, by advancing technology for certain applications over others?

A related set of immediate challenges concerns ownership of products during research and development. The finances of pharmaceutical research and development has been identified as an impediment to discovery and innovation (Cohen, 2005), as well as a disincentive for scientific objectivity and transparency (Goldacre, 2013). Given the extensive collaboration of academic and other publicly funded researchers with privately held device manufacturers, how should we design intellectual property agreements, clinical trials and regulation to maximize innovation and patient benefit?

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.