Cryptography: Enigma Applied to Neuroscience

One of the main struggles of neuroscience today is to decipher the neural code, in other words the language of the brain that is translated into real-world movement.

This is a key step to be able to program devices that allow issues such as paralysis to be treated and to produce a new generation of prostheses for some. In December of last year, it was cryptographydiscovered that United States researchers had achieved promising results with a brilliant decryption technique similar to those used by the Allied forces crypt-analysts in order to defeat Enigma.

Up until now the typical method used by neuroscience to try to decipher the brain’s code that controls mobility was to process the neuronal as well as motor activity and then compare both in order to identify the underlying code thereof. This is an equivalent situation we. Speaking from a cryptographic point of view to comparing an encrypted message with its decrypted version to attempt to identify the coding system or key being used.

This approach however requires time and a sizable volume of data for analysis. Returning to the comparison with classical cryptography – in particular with the technique of frequency analysis, it is easier to identify which symbols or letters appear more often—basically those that encode the often-used letters of the alphabet—the bigger the length of the encrypted message.

Very recently a team of neuroscientists from the Georgia Tech Institute and University of Pennsylvania have implemented an alternative approach to all of this. Much like the cryptographic techniques used by Polish cryptanalysts and by their British cohorts, led by Alan Turing, to decipher the daunting German encryption machine known as Enigma.

It is an approach based almost entirely on the analysis of the encrypted messages which has now also succeeded in decoding neuronal activity. The irony of this is that as the head of the study, Konrad Kording at first they did not realize they were engaging in cryptography. “We were basically trying to solve a problem that we already knew existed. We became aware of it when we brainstormed to figure out what we were doing exactly.” he goes on to say.

A Fissure to Penetrate the Enigma

In the late 1920’s, when the German military began using the Enigma machine to codify their messages, they established a protocol that involved a day key as well as a “message key”. The day key was used to code the message keys which was composed of three letters – with which each communication was initiated; from that moment the message key was the one that solely encrypted the transmission. In order to avoid errors in receiving the message, the German armed forces typed the message key twice in a row. The Polish cryptanalyst Martin Rejewski noticed that the first and fourth, second and fifth, as well as the third and sixth letters of each message respectively encoded the same letter of the original alphabet – whatever these were – and independently of the content of the message. He had thus successfully identified a pattern, a pattern that then served as a shortcut to break Enigma.

During World War 2, Alan Turing as well as other British cryptographers faced a more advanced version of Enigma machine which was manned by forewarned operators. The real achievement of Turing was to detect the existence of “cribs”: fragments of original text which were associated with a piece of encrypted text. Though not easy to visualize, it is best understood with this example: Turing realized that every single day, the very first thing in the morning, the German military issued a weather report. He correctly sensed that the German word “wetter” would lead the text in question. Essentially realizing that the first six letters of the encrypted message – whatever they may be –  would be translated as “wetter.” This permitted him to establish an association between the encrypted message and the subsequent decryption  independently of the contents of the communication, which then became a fissure through which to penetrate Enigma.

Secret Patterns in Neural Activity

Unintentionally, the neuro-scientists from the University of Pennsylvania and the Georgia Tech Institute moved forward in a similar way: identifying and searching for patterns that were repeated in all neural transmissions so that they could be associated with a specific message or command.

If we apply the cryptographic analogy above it involves starting from the hypothesis that all the motor messages have moving parts in their structure that are repeated over and over. Something like:  “right arm-elevate-20°”, “left leg-bend-75°”… In the words of the researchers, “basically what we did was map the key neural signals that the neural activity registers in order to find hidden patterns that may then be associated with a command of movement.”

This stunning achievement would make available to all a language to program cerebral devices that would enable us to restore the mobility in people with major injuries or disease.

Olé Crypto,


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