Brain Computer Interface

Science Times Editorial Brain computer interface devices (BCI) detect and translate neural activity into command sequences for computers and prostheses. That is, electrodes recording from the brain are used to send information to computers so that mechanical functions can be performed. As a developing field, BCI has gained the attention of scientists and clinicians alike. This is reflected by the sharp increase in the number of BCI-related publications. BCI devices aim to restore function in patients suffering from loss of motor control, as in the case of stroke, spinal cord injury, multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). If successful, BCI will broaden the repertoire of neurosurgical treatments available to patients previously treated by non-surgical specialists. This editorial reviews some of the hurdles facing BCI in the context of two papers in the current issue of Clinical Neurophysiology. BCI as a field remains in its infancy. Indeed, researchers are divided over many fundamental issues, such as the optimal methods of neural sampling, neural decoding, and command output functions. The gamut of sampling methods ranges from noninvasive electroencephalographs (EEG) to surgically implanted microelectrode arrays. Less invasive methods spare patients a costly, painful surgery. This benefit, however, comes at the expense of spatial and temporal fidelity, which results in poor signal extraction. As a consequence, less invasive methods are frequently associated with lengthy training periods (i.e. weeks to months) before even minimal neural control may be achieved. On the other hand, invasive methods offer excellent signal to noise ratios but carry the risks associated with implanted hardware. Researchers further debate which neural signal to utilize for BCI applications. Non-invasive BCI devices, for example, have measured the μ, α and β rhythms of the EEG, slow cortical potentials and the P300 evoked response. The P300 is a late positive component occurring in response to talkrelevant stimuli (1). The P300 has shown promise as a keystroke pointer allowing subjects to communicate at a rate of one word per minute (4). Two recent papers from Clinical Neurophysiology underscore the current advances in BCI, while also shedding light on its current obstacles. Piccione and colleagues studied a non-invasive BCI application in paralyzed patients and healthy controls (2). They used a P300 potential as a cortical control switch during a visual task where patients guided a graphically depicted ball towards a target. In the final analysis, the P300-driven BCI system showed good performance on established BCI criteria (4). A second investigation, Sellers and Donchin compared P300 responses between patients with amyotropic lateral sclerosis (ALS) and normal controls (3). Using a 'yes/no' recognition task, two of the ALS patients were able to reliably answer with P300 responses. These studies demonstrated 'proof of concept' using BCI to convert neural signals into computer command sequences. These independent investigations also underscore some of the current limitations facing BCI development. First, BCI devices attempt to assist those with severe motor deficits. Unfortunately, BCI performance was poorest in patients with the greatest clinical deficits. This may reflect global dysfunction in patients with cerebrovascular disease or demylinating processes. Second, the nature of the scalp recordings obtained in the present studies required training periods of weeks to months. This intensive training may prove prohibitive in debilitated patients. Third, P300 driven BCI algorithms function on a binary system—they yield 'yes/no' commands only. The system is therefore limited to one degree of freedom. The field of BCI is growing at a rapid pace. BCI devices may offer neurosurgical options to patients historically beyond the scope of neurosurgery. Neurosurgeons possess the insight and technical ability to promote BCI research. Look for exciting new articles on this subject in future issues of Neurosurgery. RICHARD G. ELLENBOGEN, M.D., F.A.C.S. PRINCIPAL, SCIENCETIMES TIMOTHY H. LUCAS, II., M.D.