An accurate, low-cost BCI (brain-to-computerinterface) can help realize the science-fictionideal in which there’s no need to speak,gesture, or type into a keyboard to communicatewith machinery: You just think—andthe machine responds. BCI technology is notjust the domain of sci-fi junkies: An obvioususe for BCI control is in medical therapeuticequipment for paralyzed patients or forresearch into brain conditions, such as Parkinson’s disease or epilepsy.Other possible applications include game-control interfacesand military equipment. For example, the Defense Advanced ResearchProjects Agency’s bionic-arm project to improve the stateof the art for prosthetics partially funded research into BCIs at theUniversity of Utah. Plus, the growing use by the military of remotelypiloted aircraft highlights the potential the military sees for BCI. An accurate, low-cost BCI (brain-to-computerinterface) can help realize the science-fictionideal in which there’s no need to speak,gesture, or type into a keyboard to communicatewith machinery: You just think—andthe machine responds. BCI technology is notjust the domain of sci-fi junkies: An obvioususe for BCI control is in medical therapeuticequipment for paralyzed patients or forresearch into brain conditions, such as Parkinson’s disease or epilepsy.Other possible applications include game-control interfacesand military equipment. For example, the Defense Advanced ResearchProjects Agency’s bionic-arm project to improve the stateof the art for prosthetics partially funded research into BCIs at theUniversity of Utah. Plus, the growing use by the military of remotelypiloted aircraft highlights the potential the military sees for BCI.

The brain is a 3-lb bag of fluids andneurons that communicate by firing offtiny electrical pulses. There are severalways to track these electrical signals:One requires going beneath the skulland implanting electrodes onto or intothe brain itself. This approach is riskybusiness and so far has found use onlyfor therapeutic purposes—for example,for the study and treatment of epilepsy.Another method, ECOG (electrocorticography),dates back to the 1950s.It places electrodes directly on the exposedsurface of the brain but still beneaththe skull to record electrical activityfrom the cerebral cortex.

More recent work by researchersat the University of Utah uses siliconelectrodes the size of baby aspirin thatfloat above the brain but still underthe skull. In microECOG, the devicecomprises an array of electrodes ratherthan just one (Figure 1 and Figure 1 (left) also shows two micro-ECOG arrays, each with 16 microelectrodesthat connect to microwires that pass through the orange and greentubes. Photo-editing software outlinedthe electrodes in the figure. Figure 1 (right) shows one microECOG arraywith 32 microelectrodes that connectswith microwires entering through aclear tube at the bottom of the figure.The green wires connect to the large,conventional ECOG electrodes. More recent work by researchersat the University of Utah uses siliconelectrodes the size of baby aspirin thatfloat above the brain but still underthe skull. In microECOG, the devicecomprises an array of electrodes ratherthan just one (and Reference1 ). The researchers placed arraysof tiny electrodes between the skulland the brain. They found that theseelectrodes can accurately detect thebrain’s signals that control arm movements.Surgeons placed two kinds ofmicroECOGs on the brains of severelyepileptic patients. Parts of the patients’skulls had been temporarily removedfor placement of the larger ECOG electrodes,which locate and treat the brainarea responsible for epileptic seizures.These larger, metallic, button-likeelectrodes are numbered in the figure.also shows two micro-ECOG arrays, each with 16 microelectrodesthat connect to microwires that pass through the orange and greentubes. Photo-editing software outlinedthe electrodes in the figure.shows one microECOG arraywith 32 microelectrodes that connectswith microwires entering through aclear tube at the bottom of the figure.The green wires connect to the large,conventional ECOG electrodes.

ECOG and microECOG are intermediatesteps between electrodes thatpenetrate the brain and EEG (electroencephalography),which places electrodesoutside the skull on the scalp.Compared with the risky, surgical natureof ECOG, EEG is a relatively simpleprocedure that relies on electrodesanchored through an adhesive to thescalp. However, to reach electrodes onthe scalp, the brain’s electrical signalsmust travel through the skull. Boneconductivity is low, and signals attenuaterapidly. By the time the brain’s signalsmake it through the surroundingmembrane, skull, skin, and hair, thesealready-faint signals are vanishinglysmall. EEGs for medical purposes useelectrodes that require a conductivejelly that can be messy to apply and remove.These medical-grade EEG-sensorsystems can cost tens of thousandsof dollars, keeping research into BCIswithin the realm of academia and medicalresearch (Figure 2 ). ECOG and microECOG are intermediatesteps between electrodes thatpenetrate the brain and EEG (electroencephalography),which places electrodesoutside the skull on the scalp.Compared with the risky, surgical natureof ECOG, EEG is a relatively simpleprocedure that relies on electrodesanchored through an adhesive to thescalp. However, to reach electrodes onthe scalp, the brain’s electrical signalsmust travel through the skull. Boneconductivity is low, and signals attenuaterapidly. By the time the brain’s signalsmake it through the surroundingmembrane, skull, skin, and hair, thesealready-faint signals are vanishinglysmall. EEGs for medical purposes useelectrodes that require a conductivejelly that can be messy to apply and remove.These medical-grade EEG-sensorsystems can cost tens of thousandsof dollars, keeping research into BCIswithin the realm of academia and medicalresearch ().

However, the lucrative gaming market,in which thought control of gamesis a novel gimmick, and military applicationsare driving the interest in BCIdevices, which are starting to appearat prices far below the tens of thousands of dollars you can expect to payfor medical-research-quality EEG. Recently,products such as Emotiv’s Epocand NeuroSky’s Mindset have becomeavailable for approximately $150 to$300.

How likely is it that EEG-based headsetscan contribute to robust BCI-hardwareapproaches? Following a BCI workshopearly this year at the MassachusettsInstitute of Technology, Rod Furlan, SingularityUniversity founder, summarizedhis thoughts on invasive versus noninvasiveBCIs (Reference 2). “As noninvasiveinterfaces are generally limited toreading brain states, it is unlikely theywill be able to evolve into robust inputand output solutions,” he said. “Consensusamong the experts in the room wasthat EEG is probably a dead end because,while it provides great temporal resolution,its maximum achievable spatial resolutionwill probably fall short of the requirementsof future applications.”

Tan Le, co-founder and president ofEEG-headset maker Emotiv, explainsthe human brain, the limitations ofEEG, and Emotiv’s approach (Reference3). “Our brain is made up of billionsof neurons, around 170,000 kmof combined axon length,” she says.“When these neurons interact, thechemical reaction emits an electricalimpulse, which can be measured. Themajority of our functional brain is distributedover the outer surface layer ofthe brain. To increase the area that’savailable for mental capacity, the brainsurface is highly folded. This foldingpresents a significant challenge for interpretingsurface electrical impulses becauseeveryone’s cortex is folded differently.Even though a signal comes fromthe same functional part of the brain, bythe time the structure has been folded,its physical location is very different betweenindividuals, even identical twins.

“[Emotiv created] an algorithm that‘unfolds’ the cortex [to] map the signalcloser to its source and make it able towork across a mass population. EEGmeasurements typically involve a hairnet with an array of sensors. The Emotivheadset is a 14-channel, high-fidelityEEG-acquisition system and requiresno scalp prep [and] no conductive gel. Itonly takes a few minutes to put on andfor the signals to settle. It’s wireless andcosts only a few hundred dollars.”

Pull it out of the box, connect it toyour PC, place it on your head, spenda few moments on the canned exercisesthat let the headset algorithms learnyour brain-wave pattern, and you canbegin manipulating virtual images onyour PC with your brain (Figure 3 ).Pretty neat, huh?

Hacker Cody Brocious thought so,too. New to the world of BCI, Brociouswas impressed by the simplicity of theEmotiv device, and he wanted to delvedeeper. He asked for donations withinthe hacker community to buy oneand quickly raised the money. He discoveredthe key to the encrypted datacoming over the USB connection andbuilt a decryption routine. So far, his libraryof code hacks to the device justpulls raw data from the unit; there’s noability to filter the signals or tell whichsensor corresponds to each data stream.Brocious created Cody’s Emokit project,an open-source library for readingdata directly from the headset, and posted about his project on the Emotiv user forum, which thecompany runs (Reference 4).

Emotiv officials didn’t like the fact that Brocious hadcracked the encryption and posted his library. They claimedthat doing so could force the company out of business (Reference5). Emotiv sells a $700 developer’s version of the headset that allows access to the data, but it is not an open environment;the company controls access. Apparently, Emotivis working to close the encryption hole and thus end Cody’sproject.

Other approaches

Alternatives to EEG exist for measuring small signals onthe surface of the head. One such technology, EOG (electrooculography),employs eye polarization. The back of theeye is more negative than the front of the eye because of thelarge populations of neurons on the retina. As the eye moves,the electric field surrounding the eye also moves. Electrodeson the left and right side of the face and above and below theeyes can measure these fields. An electrode behind the earserves as a reference voltage.

Waterloo Labs comprises a group of engineers at NationalInstruments that builds and documents electronics projectsusing the company’s components. Its implementation ofan EOG-measurement device that controls the Mario videogame provides a good example of the design challenges ofacquiring small differential signals in a noisy environment,such as the head (Figure 4 ). Waterloo Labs comprises a group of engineers at NationalInstruments that builds and documents electronics projectsusing the company’s components. Its implementation ofan EOG-measurement device that controls the Mario videogame provides a good example of the design challenges ofacquiring small differential signals in a noisy environment,such as the head ( Reference 6 ). A National InstrumentsRIO (rapid input/output) single-board computer performsthe signal processing for the EOG. A custom daughterboardperforms signal acquisition, amplification, filtering, and digitization().

The inputs to the EOG are the bipotential signals measuredat the electrodes; these signals are smaller than thoseof background environmental noise, such as RF-communicationsignals or 60-Hz ac-mains noise. Fortunately, each electrodepicks up the same noise, making the interference thecommon signal. Amplifying the difference between the electrodesand rejecting everything common to them yield theEOG’s signal. The Waterloo Labs engineers used an AnalogDevices 8221 instrumentation amplifier because of its lownoise and high common-mode rejection.

Whenever metal, such as that composing an electrode,touches an electrolytic solution, such as human skin, a potential difference—the half-cell potential—results. The 8221 amplifiesthe half-cell potential along with theEOG signal. If the amplifier’s gain istoo high, the half-cell potential swampsthe EOG’s signal. The half-cell potentialcannot overpower a gain of 10,which is enough to distinguish it fromthe noise. The circuit next uses a highpassRC filter set to 0.1 Hz to reject thehalf-cell voltage. Without the half-cellconstant, the circuit can further amplifythe signal, carefully adding no noiseback in after all that work rejecting it.It uses two low-noise, high-offset amplifiersto keep the signal clean. The finalstage uses a lowpass filter set to 50 Hzto remove any high-frequency noise,including 60-Hz ac-mains voltage, andthen an ADC.

As for electrical isolation, the EOGreceives its power from a 9V battery, soit has no dangerous voltages. However,the video-game controller, the TVdisplay, and the RIO all use 120V wallpower, so if there’s a short in the transformer,the EOG user will get a 120Vjolt of electricity across the face. Toavoid this painful scenario, the circuituses an isolated AD7401 ADC thatmagnetically couples the signal across adielectric gap so that there is no electricalconnection between the EOGand the RIO. The AD7401 can withstand120V wall power for an indefiniteamount of time and more than 3000Vfor as long as a minute.

You can reachTechnical EditorMargery Connerat 1-805-461-8242and .