Neurosurg Focus 28 (5):E25, 2010 Brain-computer interfaces: military, neurosurgical, and ethical perspective *IVAN S. KOTCHET K OV , B.A., BR I AN Y. HWANG , B.A., GEOFFRE Y APPEL B OOM , M.D., CHR is TOPHER P. KELLNER , M.D., AN D E. SAN D ER CONNOLL Y JR., M.D. Department of Neurological Surgery, Columbia University College of Physicians and Surgeons, New York, New York Brain-computer interfaces (BCIs) are devices that acquire and transform neural signals into actions intended by the user. These devices have been a rapidly developing area of research over the past 2 decades, and the military has made significant contributions to these efforts. Presently, BCIs can provide humans with rudimentary control over computer systems and robotic devices. Continued advances in BCI technology are especially pertinent in the military setting, given the potential for therapeutic applications to restore function after combat injury, and for the evolving use of BCI devices in military operations and performance enhancement. Neurosurgeons will play a central role in the further development and implementation of BCIs, but they will also have to navigate important ethical questions in the translation of this highly promising technology. In the following commentary the authors discuss realistic ex- pectations for BCI use in the military and underscore the intersection of the neurosurgeon’s civic and clinical duty to care for those who serve their country. (DOI: 10.3171/2010.2.FOCUS1027) KE Y WOR ds • brain-computer interface • military neurosurgeon • ethics • brain-machine interface RAIN -COMPUTER interfaces, also called brain-ma- tential applications of BCIs have greatly exceeded the chine interfaces or neural interface systems, rep- current state of the technology. Nevertheless, practical resent a direct communication pathway between and clinically useful BCIs are increasingly becoming a Bthe brain and an external device.18,32,59 The devices used reality, and this has important implications for neuro- for the BCI acquire brain signals such as an EEG rhythm surgeons practicing and conducting research in military or electrophysiological recordings of neuronal firing settings. Our aim in this commentary is to use an un- and translate them into commands intended by the user. derstanding of current achievements in the field of BCIs Brain-computer interfaces accomplish this through novel to discuss realistic expectations for future adaptation of output pathways that do not use the normal conduits of BCI systems in military settings and to highlight the the nervous system.32 complex role of military neurosurgeons in the further During the past 40 years, BCIs have rapidly pro- expansion of this technology. The implications of neu- gressed from mere neuroscientific theory into a rudimen- rosurgical BCI implantation for restoring function to in- tary yet highly promising technology. Increasing levels jured soldiers as well as the potential to enhance military of brain-derived control have been attained in nonhuman training and operations are considered from an ethical primates and in humans.13,21,32,48,50,51,54,55 Moreover, rapid perspective. In the context of our national duty to support progress of supporting technologies from the fields of those who serve our country, we reinforce the importance computational neuroscience, biomaterial engineering, of physician beneficence and nonmaleficence in any BCI and computer processing have significantly contributed application, alongside responsible and just distribution of to the ongoing development of BCIs. Importantly, an the technology. ever-increasing understanding of motor, cognitive, and sensory functions through cortical mapping has led to improvements in device designs as well as a wider gamut State of BCI Technology at Present of possible BCI applications.32,42,43 For BCIs to translate the user’s intentions accurately Media hype and popular imagination regarding po- into actions, “learning” must take place on both ends of the interface: the user must modulate his or her brain sig- nals to improve performance of the BCI, while the device Abbreviations used in this paper: BCI = brain-computer interface; DARPA = Defense Advanced Research Projects Agency; ECoG = must identify, interpret, and adapt to the neural signals electrocorticography; EEG = electroencephalography. that are most predictive of the desired output. This is * Mr. Kotchetkov and Mr. Hwang contributed equally to this achieved through feedback and fine-tuning mechanisms work. that are similar to those used when learning a new mo- Neurosurg Focus / Volume 28 / May 2010 1 Unauthenticated | Downloaded 10/05/21 02:43 PM UTC I. S. Kotchetkov et al. FIG. 1. Three classes of BCIs: their anatomical locations, advantages, and limitations. tor task.32 Some BCI designs rely on a training phase in at the cortical surface placed either above or below the which the subject performs a designated task and a com- dura mater.10,32,40,48 Platforms that belong to the latter 2 putational algorithm is employed to select the neuronal classes require neurosurgical implantation. signals that best correlate with execution of that task. A Using an EEG-based system, humans with motor de- code is generated for each command that can subsequent- bilities, including those that result from spinal cord injury ly be used for control of an external device.31,39,40 Alter- or amyotrophic lateral sclerosis, have been able to control natively, a real-time adaptive algorithm can be employed a computer cursor in 2 dimensions.29,60 This technology during the learning phase to concurrently select for the has also been used by motor-intact individuals to com- signals that are most predictive of the user’s intentions mand robots to manipulate objects, and has the potential by continuously refining them based on comparisons of to be applied in operating limb prosthetics.3 The EEG de- past and intended trajectories.40,54,60 Recordings from vices, however, are fundamentally limited by their signal larger populations of neurons, or neuronal ensembles, are content, which does not convey information about com- generally the preferred source for extracting useful and ponents of movement such as position and velocity, and relevant information to guide appropriate activity.2,6,40 Al- recordings are prone to interference from the electromyo- though input from a single neuron can result in success- graphic activity of cranial musculature.10,32 ful BCI control,7,22 averaging neuronal signals over many Invasive BCIs, on the other hand, can acquire more trial sessions is often necessary for predicting behavior,46 informative signals that enable higher performance lim- and therefore synthesizing the electrical firing of neuronal its.50 For instance, human patients with locked-in syn- ensembles can remove the variability associated with us- drome are able to move cursors on a 2D keyboard to ing the input of a single neuron.2,40 As the user learns to communicate using typed messages after undergoing im- operate the BCI, neuronal plasticity leads to a tuning of plantation of electrodes that attract growth of myelinated ensemble signals such that activity in more discrete popu- nerve fibers.24,25 With the aid of a 96-microelectrode ar- lations of neurons becomes the best determinant of action ray that records signals from primary motor cortex, tet- commands.8,30 raplegic patients have been able to move a 2D cursor as Depending on the source from which they derive well as to execute basic control over robotic devices, such their neural signals, BCIs can be classified into those that as opening and closing a prosthetic hand, years after their use noninvasive, invasive, and partially invasive platforms initial spinal cord injury.21 Subsequent reports on tetraple- (Fig. 1). Electroencephalography, which obtains electri- gic patients who were enrolled in a pilot clinical trial of cal signals from the scalp, has been the dominant method BCIs have demonstrated modest improvements in cursor of recording used for noninvasive BCIs due to its rela- control, thereby achieving greater functionality for practi- tive safety and practical technical requirements. Invasive cal tasks.13,26 BCIs retrieve signals from single-neuron recordings via More recently, ECoG has proven to be a useful tool in microelectrodes implanted in the cortical layers. Partially detecting input signals for BCIs.33,51 Unlike EEG, ECoG invasive BCIs use ECoG readings that come from sensors can detect high-frequency gamma wave activity that is 2 Neurosurg Focus / Volume 28 / May 2010 Unauthenticated | Downloaded 10/05/21 02:43 PM UTC Brain-computer interfaces: military, neurosurgery, and ethics the product of smaller cortical ensembles and correlates multijointed robotic arm to exert variable grip strength with discharge of action potentials from cortical neu- and perform 3D movements to feed themselves.55 These rons.19,32 Because they are not embedded in brain paren- results have been achieved with motor prostheses, which chyma, ECoG electrodes inflict less damage to the cortex continuously process cortical signals to guide movement and also experience less signal deterioration than invasive and speed.48 Their counterparts, communication prosthe- electrodes.32,34 In patients with intractable epilepsy who ses, which extract information from higher cortical ar- required invasive monitoring, ECoG signals have been eas about intended goals, have also been successful and used for 2D movement control at a level of performance promise to enhance