for instance , in 1999 , john chapin s laboratory at hahnemann university in philadelphia and my own laboratory at duke university collaborated in the first experimental demonstrations of a brain - machine interface in animals . in these experiments
, rats learned to use the combined electrical activity of a handful of cortical neurons to move a robotic arm in order to obtain a water reward . around the same time ,
niels birbaumer at the university of tbingen in germany reported how completely paralyzed patients learned to use brain - derived signals ( recorded though a classic method known as electroencephalography , or eeg ) to write messages on a computer screen . even in its initial version ,
this brain - computer interface was the only way for these locked - in patients to communicate with the external world .
it was an early indication of bmis significant potential as new rehabilitation tools . in subsequent years
, further animal experiments with bmis indicated that monkeys could learn to employ the combined electrical activity of hundreds of their cortical neurons to move multiple degree - of - freedom robotic arms , entire humanoid robots , and even avatar limbs and bodies without the need for any overt movement of their own bodies .
soon , initial clinical studies also reported that patients could rely on bmis to control the movements of computer cursors and robotic arms .
as the bmi field rose to the forefront of modern neuroscience , the possibility of establishing a bidirectional dialogue between brains and artificial devices was also realized . in 2011 , through a technique called cortical electrical microstimulation , my laboratory was able to deliver simple  tactile messages  directly into the brains of monkeys .
every time one of our monkeys used its brain activity to move a virtual hand to scan the surface of a virtual sphere , a simple electrical wave , proportional to the virtual texture of the touched object , was immediately delivered to the animal s primary somatosensory cortex , an area known to be fundamental for the definition of one s tactile perceptions .
after a few weeks of training , by taking advantage of this direct and continuous inflow of tactile information into their brains , a pair of monkeys became capable of discriminating the fine texture of the virtual objects by using their virtual hands , as if they were using their own biological fingertips .
we called this new paradigm a brain - machine - brain interface ( bmbi , figure 1 ) .
in 2009 , as a direct result of this auspicious first decade of bmi research , the duke university center for neuroengineering and the edmond and lily safra international institute of neuroscience of natal ( els - iinn , in brazil ) jointly created a nonprofit research consortium called the walk again project . by the end of 2012 , the walk again project received a grant from the brazilian government to assemble a large international research team of roboticists , neuroscientists , engineers , and computer scientists .
this international team joined with a brazilian multidisciplinary rehabilitation team , composed of physicians , psychologists , and physical therapists , to take on a very ambitious project : designing and implementing the first bipedal robotic exoskeleton whose movements could be controlled directly by human - brain activity .
the central goal of the first phase of project was to allow paraplegic patients suffering from severe spinal - cord lesions to use their eeg activity to control the exoskeleton s leg movements ( figure 2 ) and , in so doing , regain lower - limb mobility .
in addition to restoring basic locomotion behaviors , the exoskeleton would be the first in its class to provide continuous sensory feedback to the user in the form of artificial tactile and proprioceptive signals . in december 2013 , a group of eight patients suffering from complete and incomplete spinal - cord lesions started the training process required for achieving proficiency in controlling a brain - controlled robotic exoskeleton .
four months later , all eight were capable of commanding the exoskeleton with their brain activity alone , and all had regained the sensation of walking in a laboratory setting .
the feeling of walking again was even more realistic in these patients because of the addition of two innovative technologies in the design of our exoskeleton .
the first was a new type of artificial tactile sensor known as artificial skin , developed by gordon cheng at the technical university munich .
these sensors were distributed across key locations of the exo s legs and feet to detect the device s movements and contact with the ground .
the second was an ingenious haptic display , created by hannes bleuler s laboratory at the cole polytechnique fdrale de lausanne ( epfl ) in switzerland , that allowed the tactile feedback signals generated by the arrays of the artificial sensors to be delivered to the skin of a patient s forearms .
for the haptic display to work properly , patients had to wear a special shirt containing a linear array of small vibromechanical elements in the distal half of each sleeve while walking with the brain - controlled exoskeleton .
to celebrate a major first step toward the development of a new generation of neuroprosthetic devices , one of our patients , juliano pinto , who is paralyzed from the mid - chest down , was invited to help our team demonstrate our exoskeleton s enormous potential before the opening match of the 2014 fifa world cup in brazil on june 12 .
for the first time in history , a human subject showed that a brain - controlled exoskeleton could be used to initiate the kicking of a soccer ball .
the demonstration was witnessed by 70,000 fans at the itaquero stadium and an estimated 1 billion people watching on tv .
seconds after executing this historic kick , juliano reported to us that he clearly felt his leg moving in the air during the moment at which the exo s foot made contact with the surface of the ball . according to juliano s perception , it was his own body , not the exo , that executed the kick .
the effort and complexity required to pull off that world cup demonstration well exemplifies the current state of the art of bmis . over the last 15 years ,
and although the case has been made that bmis offer concrete hope for the future development of a variety of new neurorehabilitation tools , we are still a few years away from being able to produce neuroprosthetic devices that patients can routinely use outside well - controlled laboratory conditions . certainly ,
at this point , we are very far from the braincaps imagined by science - fiction writers like clarke .
despite the uncertainty , recent experiments combining bmis with cortical electrical microstimulation effectively open the doors for more daring adventures .
indeed , i could almost bet that clarke himself would have enjoyed the opportunity to be present when miguel pais - vieira , a portuguese postdoctoral fellow in my lab , demonstrated the operation of the first brain - to - brain interface designed to link two animals brains directly ( figure 3 ) .
first proposed in my 2011 book beyond boundaries : the new neuroscience of connecting brains with machines  and how it will change our lives , our brain - to - brain interface ( btbi ) paradigm , reported in 2013 , allowed a pair of rats to transmit and receive rudimentary mental sensorimotor messages . in one of the published experiments , the first rat of the pair , known as the encoder ,
was trained to use its facial whiskers to determine the diameter of a computer - controlled aperture placed inside a behavioral box . from trial to trial , the aperture could assume two distinct diameters , classified as narrow ( x mm ) or wide ( y mm ) .
the encoder s job was to use its facial whiskers to correctly judge the aperture s diameter and then indicate its value by placing its snout in one of two holes located in a nearby chamber .
if the encoder nose - poked in the hole corresponding to the correct aperture diameter , it received a water reward .
as the encoder used its facial hair to evaluate the opening s diameter , electrical activity recorded from neurons located in its somatosensory cortex was combined and transmitted , via cortical electrical microstimulation , to the brain of a second rat , the decoder , located in a different behavioral box .
the decoder had no access to an aperture , so its facial whiskers were useless in solving the task and getting water . yet to receive such a reward , the decoder also had to indicate , by nose poking , the diameter of the aperture touched by the encoder . to do that , the decoder had to rely solely on the simple neural message being transmitted to its brain by electrical microstimulation .
after a bit of training , decoder rats became capable of using our brain - to - brain interface to successfully perform this task way above chance level .
this indicated that the brain of a decoder rat could make sense of the messages broadcasted by its associated encoder rat .
interestingly , since the encoder received an extra reward allotment every time a decoder was able to correctly indicate the aperture s diameter , encoder rats adapted their behavior and cortical activity to make it easier for their counterpart to complete the task , particularly after the latter committed a series of trial errors .
that further suggested to us that these rat dyads had established a new form of communication , despite the fact that neither animal was aware of its counterpart s existence . as an extra proof of the effectiveness of this btbi
, we repeated these tactile - discrimination experiments by using an encoder rat placed in a laboratory in the els - iinn , in natal , brazil , while the decoder rat performed its trick in my lab at duke university , in the u.s . despite the distance and
the use of an average internet connection , the brain - to - brain interface worked as well as it did when the two animals were in the same laboratory . in a final test of our btbi , decoder rats used neuronal signals provided by the motor cortex of encoder rats to choose which of two levers to press , without ever seeing the visual cues that instructed the encoders to make the same decision in the first place .
in other words , the brain - to - brain connection between the encoder and decoder rats allowed the latter to correctly make a motor decision based on visual cues experienced only by its encoder partner . during the past year , two other laboratories published studies involving brain - to - brain architectures .
moreover , a press release from a group at the university of washington indicated that the group had established a functional link between human subjects brains by combining two noninvasive techniques : eeg to record brain activity in the first subject ( encoder ) and transcranial magnetic stimulation ( tms ) to deliver an eeg - triggered signal to the second subject s ( decoder s ) brain . since the group has not yet published a full scientific report , it is difficult to evaluate what was really achieved .
if anything , the limited description ( and video clip ) provided in the press release did not fully support the claim that a true functional communication between human brains occurred .
this is because , essentially , the encoder s eeg activity was simply used to trigger a magnetic stimulus in the decoder s motor cortex .
as expected , every time this magnetic stimulation was delivered , the decoder subject produced an involuntary body movement . yet
as such , i do not see how two brains shared a true message in this paradigm . on the other hand ,
the potential methodology for doing so was unveiled , and that was certainly enough to cause a significant media and public response .
we are currently investigating what kinds of social behaviors and global patterns of neuronal activity emerge when groups of animal brains are allowed to collaborate directly , through the employment of different types of brain - to - brain interfaces .
the central task of each of these animal brainets is to optimize the combination of neuronal activity , sampled from multiple brains simultaneously , into a supranervous system that is responsible for attaining a common behavioral goal , such as identifying a complex tactile pattern or moving an elaborate virtual limb .
the results of these studies , which are currently under review for publication , mostly focus on how btbis can enhance social interactions between animals and whether brainets could operate as a new type of computational architecture , like some sort of non - turing biological computer .
in addition , these experimental paradigms allow one to study whether , in a still - distant future , artificial interfaces like these may be used to functionally reconnect brain areas where communication may have been disrupted by brain damage , such as that produced by strokes or other neurological disorders . right now
however , seeking such a path has become a hallmark of our laboratory during the past decade . during this period ,
we have successfully translated similarly abstract basic - science ideas into potential new therapies for untreatable epilepsy , parkinson s disease , and disabling paralysis .
all of these therapies are currently undergoing clinical testing worldwide . as exciting as these animal research projects are , none of them come close to competing with the fictional wonders of clarke s braincaps .
, nobody would ever consider it ethically or medically acceptable to implant nanotubes or other types of electrodes in healthy human subjects for the purpose of testing a btbi , as suggested by clarke .
but even if , years or decades from now , better noninvasive technology enables us to record large - scale brain activity in real - time , at the millisecond scale , and then another efficient , noninvasive method might be used to deliver brain - derived messages to another human brain , it is highly unlikely that such a btbi would lead to the emergence of a fluid and efficient form of human communication , as long as we rely on digital computers to mediate this task . nor
do i believe that there will be a day in which braincap - like technologies will allow us to upload vast and complex information packets  like a new language or a large amount of scientific knowledge , as clarke describes in his book  into our brains , or to download all our memories or personal experiences into some sort of digital storage media .
apart from tasks such as motor control for which bmis can become very useful , mimicking higher - order brain functions , such as knowledge acquisition , memory storage , performance of cognitive tasks , and even consciousness , may be beyond the reach of binary logic , the basis from which all digital computers operate , no matter how simple or elaborate .
an interesting corollary of this view is that we need not worry about the forecast that , in the near future , a  really smart  digital computer / machine will supplant human nature or intelligence . in all likelihood
, this day will never come because , in a more - than - convenient arrangement , our most intimate neural riddles seem to have been properly copyright - protected by the very evolutionary history that generated our brains , as well as the very complex emergent properties that make it tick .
as such , neither evolution nor neurobiological complexity can be effectively simulated by digital computers and their limited logic . in the end
, this may not be so bad . like commander poole , as much as i would love to take advantage of a brand - new braincap  minus the nanotubes  to learn a few new intellectual tricks in a hurry , from the perspective of someone living in the early 21st century ( not the 31st ) , it is very difficult to imagine that any of us at this juncture in our history would , in good faith , feel comfortable in surrendering our final frontier of individual privacy , knowing that there is a chance , no matter how insignificant it may be , that an uninvited snoop may , nevertheless , want to take a peek .
 editor s note : every memory that we have , act that we perform , and feeling that we experience creates brainstorms  interactions of millions of cells that produce electrical signals . 
 neuroscientists are now able to record those signals , extract the kind of motor commands that the brain is about to produce , and communicate the commands to machines that can understand them and facilitate movement in the human body . 
 research in this area has the potential to help paraplegics and others suffering from spinal - cord injuries to control machines with their thoughts and to bolster their ability to get around . 