Brain to Brain Interfaces

Estimated Reading Time: 10 minutes 

In last week’s blog post, we had a look at the question whether it is actually possible to alter one’s memory or even implant new recollectionsThis week, we continue to ask the exciting questions: Is it actually possible to directly transfer one’s experiences into another person’s brain?

“Case sat in the loft with the dermatrodes strapped across his forehead, watching motes dance in the diluted sunlight that filtered through the grid overhead. A countdown was in progress in one corner of the monitor screen. […] Then he keyed the new switch.

The abrupt jolt into other flesh. Matrix gone, a wave of sound and color…. She was moving through a crowded street, past stalls vending discount software, prices feltpenned on sheets of plastic, fragments of music from countless speakers. Smells of urine, free monomers, perfume, patties of frying krill. For a few frightened seconds he fought helplessly to control her body. Then he willed himself into passivity, became the passenger behind her eyes.” (page 55 – 56)

This short excerpt from the 1984 novel “Neuromancer” by William Gibson describes “simstim” – a technology allowing a person to experience the world through somebody else’s body. In the novel, simstim works through stimulation of the brain and nervous system through technical devices, which receive input from a live broadcast of another person’s sensory experiences … What a great merging of neuroscience and technology! Although William Gibson does not describe how simstim works in detail, I was fascinated from the beginning.

Mankind’s current attempts at rudimentary “simstim” technology: Virtual Reality.  wikimedia Public Domain

The two main characters of the novel use this technology to be directly aware of the other’s physical situation and to support each other with cyberspace skills from a distance. It soon becomes apparent that in the world of Neuromancer, simstim provides a large venue for both entertainment and business. Ordinary people pay to be hooked up into the sensory experiences of simstim stars to share their life; instead of merely watching sports, you can actually experience the adrenaline of a climber on top of a mountain or a soccer player about to score.

While doing some further research on simstim, I stumbled upon this article from 2009 dedicated to the 25th birthday of William Gibson’s great novel. The author of the blog post reviews some of the technologies described in the world of Neuromancer and lists simstim under the category of “Not gonna happen soon”.

But is that true? Let’s consider the possibility of simstim in our real world while reviewing some recent developments in an exciting new field of neuroscience – brain to brain interfaces.

What are Brain to Brain Interfaces?

In some ways, brain to brain interfaces (BtBIs) are very close to simstim. BtBIs establish a link between two brains, enabling their direct communication without the need for signals to pass through the conventional route of sensory organs and the peripheral nervous system1. To exchange information between brains, we need devices that can record the output of the brain and devices that can feed input into a brain. Thus, BtBIs can be seen as the extension of Brain Computer Interfaces (BCIs; the “Output”) and Computer Brain Interfaces (CBIs; the “Input”). And if you start to get confused with these abbreviations, don’t worry, because that’s pretty normal3. Some people refer to BCIs as Brain Machine Interfaces (BMIs), Mind Machine Interfaces (MMIs), or Direct Neural Interfaces (DNIs).

Output Devices

We will stick to Brain Computer Interfaces (BCIs) defined as neural devices that “enable communication without movement”3, relying on direct measures of brain activity and on intentional control of the user.

In simple terms, this means: brain activity is measured (e.g. with electroencephalography ; EEG). At the same time, an online process extracts features from the data that is just being recorded. In a last step, the extracted features are translated into discrete signals that can be used as input for a computer program.

Ideas about BCIs have been circulating since 19734, but most research is quite recent:

  • In 2008, Meel Velliste and colleagues implanted a device into a monkey’s brain, which allowed the monkey to control a robotic arm to feed itself5.
  • Moving a wheelchair using EEG recordings via electrodes loosely connected to the skull is possible, although there are still many challenges6.
  • Most recently (2015), a group of researchers developed a tiny electrode array, which can be injected into the brain through a minimally invasive procedure7. This might be the first step towards neural dust, micro-sized sensors that record permanently from the brain and transmit signals wirelessly.

BCIs can take diverse forms depending on their degree of invasiveness, the method used to pick up neural data, and finally their application.

Input Devices

The counterpart of a BCI needs to pick up signals from the outside world, translate them into a neural code that can be understood by the brain, and feeds this code into our central nervous system. Let’s call these neural devices Computer Brain Interfaces (CBIs) and remember the following: BCIs = output from brain and CBIs = input into brain.

One example of a successful CBI is the cochlear implant. Cochlear implants work by using a sophisticated computer chip to pick up environmental noises and stimulate the cochlear nerve arccordingly. This enables hearing for people who would otherwise be hard of hearing.

However, just as BCIs, CBIs can take many forms and can be invasive or non-invasive. Some methods that are currently used in BtBI research are:

  • Focused Ultra Sound (FUS)
    • FUS is used in neurosurgery for removing tumors by delivering a highly energetic acoustic signal to regions within the brain. For CBIs, FUS is used at an intensity below the energy threshold required to remove tissue, but still at a sufficient intensity to evoke neuronal responses.
  • Transcranial Magnetic Stimulation (TMS)
    • TMS is a non-invasive method that relies on electromagnetic induction of neuronal activity. A “coil” near the participant’s skull sends magnetic impulses into the skull to modulate neuronal activity. However, TMS has a low penetration depth compared with FUS.
  • Implanted Electrode Arrays
    • Small electrode arrays can be implanted beneath the skull to electrically stimulate the surrounding neurons directly, but this procedure is highly invasive.

Now we are well prepared to tackle the original goal of this post: the Brain to Brain Interfaces, which combine BCI and CBI into one device that can read information from one brain and feed it into another brain, and vice versa.

What can we (currently) do with BtBIs?

Research on BtBIs is very nascent, and so it is still quite easy to get a comprehensive overview about the projects conducted so far. I would like to present to you four studies in the order of how I subjectively experience their level of intensity.

The first study to link two different brains was published by Pais-Vieira in 20132. They implanted micro-electrodes in the brains of two rats that were sitting in separate cages without means of communication besides the BtBI. One rat acted as the receiver rat and could only solve a puzzle with crucial information from the transmitter rat. The same experiment was also repeated using an Internet transmission of the data and thus two experimental rats became the first living beings to communicate directly via the Internet.

In the same year, Yoo and colleagues8 took it one step further: A human could control the tail movement of an anaesthetized rat, thus effectively creating the first interspecies BtBI. The setup wasn’t even as complicated as you might imagine: The human could look at a visual stimulus that would alter his brain activity picked up by EEG. This alteration was translated into FUS pulses by a computer, which were directed into the motor cortex of the rat, which would then involuntarily move its tail. All of this with a 94% accuracy rate and a mean time delay of 1.59 seconds!

Two further studies linked two humans to play a ‘mind guessing game’ or to mind-control finger-movement9–11 but believe it or not, there is something even more exciting: Some studies have already gone further than to simply link two brains – they have linked multiple brains12,13 to create an “organic computer”, which they called a “brainet”. One of these studies linked four different rat brains and used the resulting single brainet for classifying stimuli13. According to the authors, the brainet had a better accuracy than single rats doing the task. The other study linked the brains of three monkeys in order to control a virtual avatar arm in a task that requires the arm to move to a certain position12 … wow.

Ethical Implications

I could imagine that half of the readers are either fascinated or terrified by BtBIs by now, and perhaps you are moving in between those two anchor points (be sure to visit the survey at the end of the blogpost!).

There are, of course, plenty of reasons to be careful about BtBIs, and considering that there are so few experimental papers on BtBIs so far (less than ten as I write this blog post), there is already a number of papers addressing the ethical implications. To give you a break from reading, I have summarized the main arguments from two papers that I particularly liked1,14 using a mindmap.

Ethical Implications
Ethical Implications with BtBIs [Source: Stefan Appelhoff, Licensed under Attribution-NonCommercial-ShareAlike 4.0 International]

Evaluation, Outlook, and Conclusion

With this blogpost, we set out to re-evaluate somebody’s statement that simstim is “not gonna happen soon”. To do that, I have reviewed some of the BtBI literature so far, but I have a confession: I don’t think that BtBIs and simstim as imagined by William Gibson are that comparable after all. They are both referring to the direct connection between two humans and, in some way, to the old dream (or nightmare?) of “mind-reading”. However, I believe that BtBIs will develop into something far more complex than simstim and they will quite likely revolutionize the way we interact in society.

Some thoughts in that direction:

  • Accessing the Internet directly with your brain
  • Linking two brains bi-directionally for silent communication irrespective of distance
  • Linking an animal to a human so that the human can have augmented senses. For example, rescue-personnel collaborating with rescue animals14
  • Transferring memories so that teaching will have a completely new meaning
  • Exchanging emotions directly

Kyriazis provides a particularly interesting perspective15, making a case for the global brain. Taking brainets that connect three or four different brains one step further could mean that, at some point, all of humanity will be directly connected. Humanity could merge into a single entity experiencing global emotions and decision-making faculties. For his case of the global brain, Kyriazis draws on a comparison of a human brain to the Internet. In his words:

“The conceptual similarities with the human brain are remarkable. Both networks exhibit a scale-free, fractal distribution, with some weakly-connected units, and some strongly-connected ones which are arranged in hubs of increasing functional complexity. […] Both networks are “small worlds” which means that information can reach any given unit within the network by passing through only a small number of other units. This assists in the global propagation of information within the network, and gives each and every unit the functional potential to be directly connected to all others.”

Barrett Lyon / The Opte Project – Visualization of the routing paths of the Internet. [Source:, Licensed under a Creative Commons Attribution-NonCommercial 4.0 International License]
 What a collection of inspiring ideas! Let’s leave it at that for today, and close with a quote by Miguel Nicolelis, one of the key players in BtBI research:

“Where this is going? We have no idea … we’re just scientists, paid to be children and to go to the edge and discover what is out there.”

Interactivity: Questionnaire

What do you think about these futuristic topics? If simstim existed, would you try it? How do you judge the ethical implications of BtBIs? I have set up a short questionnaire (~4 min) for you to answer. Stay tuned for an update of this article, where I’ll post the results of the survey!

EDIT: The questionnaire is now closed. You can see the results here.

Academic References

  1. Hildt, E. What will this do to me and my brain? Ethical issues in brain-to-brain interfacing. Front. Syst. Neurosci. 9, 17 (2015).
  2. Pais-Vieira, M., Lebedev, M., Kunicki, C., Wang, J. & Nicolelis, M. A. L. A Brain-to-Brain Interface for Real-Time Sharing of Sensorimotor Information. Sci. Rep. 3, 1319 (2013). doi:10.1038/srep01319
  3. Brunner, C. et al. BNCI Horizon 2020: towards a roadmap for the BCI community. Brain-Computer Interfaces 2621, 1–10 (2015).
  4. Vidal, J. J. Toward direct brain-computer communication. Annu. Rev. Biophys. Bioeng. 2, 157–80 (1973).
  5. Velliste, M., Perel, S., Spalding, M. C., Whitford, a S. & Schwartz,  a B. Cortical control of a robotic arm for self-feeding. Nature 453, 1098–1101 (2008). doi:10.1038/nature06996
  6. Kaufmann, T., Herweg, A. & Kübler, A. Toward brain-computer interface based wheelchair control utilizing tactually-evoked event-related potentials. J. Neuroeng. Rehabil. 11, 1–17 (2014). doi: 10.1186/1743-0003-11-7
  7. Oxley, T. J. et al. Minimally invasive endovascular stent-electrode array for high-fidelity, chronic recordings of cortical neural activity. Nat. Biotechnol. (2016). doi:10.1038/nbt.3428
  8. Yoo, S. S., Kim, H., Filandrianos, E., Taghados, S. J. & Park, S. Non-Invasive Brain-to-Brain Interface (BBI): Establishing Functional Links between Two Brains. PLoS One 8, 2–9 (2013).
  9. Rao, R. P. N. et al. A direct brain-to-brain interface in humans. PLoS One 9, (2014).
  10. Stocco, A. et al. Playing 20 questions with the mind: Collaborative problem solving by humans using a brain-to-brain interface. PLoS One 10, 1–15 (2015).
  11. Grau, C. et al. Conscious brain-to-brain communication in humans using non-invasive technologies. PLoS One 9, 1–6 (2014).
  12. Ramakrishnan, A. et al. Computing Arm Movements with a Monkey Brainet. Sci. Rep. 5, 10767 (2015). doi:10.1038/srep10767
  13. Pais-Vieira, M., Chiuffa, G., Lebedev, M., Yadav, A. & Nicolelis, M. A. L. Building an organic computing device with multiple interconnected brains. Sci. Rep. 5, 11869 (2015). doi:10.1038/srep11869
  14. Trimper, J. When ‘I’ becomes ‘We’: ethical implications of emerging brain-to-brain interfacing technologies. Front. Neuroeng. 7, 4 (2014). 10.3389/fneng.2014.00004
  15. Kyriazis, M. Systems neuroscience in focus: from the human brain to the global brain? Front. Syst. Neurosci. 9, 7 (2015). 10.3389/fnsys.2015.00007


2 thoughts on “Brain to Brain Interfaces

  1. I enjoyed your article! Great “mindmap.”

    It will be exciting to see how increasingly specific neural stimulation protocols (e.g., optogenetics – slated for human trials**) and large-scale recording devices*** push the boundaries of BTBI technology.




    1. Hi J.B. Trimper, I am glad you liked the article!

      Thanks for sharing these two links, the one about optogenetics as a treatment for a kind of degenrative blindness sounds particularly exciting. Since the article you posted was from February, I tried to find news on this matter, but the latest update is only from March:

      Seems like we will have to wait for some more time to learn more about the outcome.


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