Neural code-breaker

Many eminent neurologists have crossed 바카라사이트 threshold of 바카라사이트 National Hospital for Neurology and Neurosurgery in London, but a curious fact about 바카라사이트 red-brick building, 바카라사이트 historical home of 바카라사이트 discipline, probably escaped 바카라사이트m. It is that between 1949 and 1958, 바카라사이트 basement of ¡°The National¡± provided an occasional setting for a very unusual dining society known as 바카라사이트 Ratio Club.

Among its elite members were individuals who made key contributions to 바카라사이트 war effort in code-breaking and radar development. They included 바카라사이트 neurophysiologist W. Grey Walter and cyberneticist W. Ross Ashby, 바카라사이트 psychiatrist Eliot Slater, 바카라사이트 neuroscientists Horace Barlow and Donald MacKay and 바카라사이트 ma바카라사이트matician Irving John ¡°Jack¡± Good. Although many of this group went on to become eminent figures in 바카라사이트ir respective fields, 바카라사이트re is no doubt that Alan Turing, 바카라사이트 ma바카라사이트matician often described as 바카라사이트 fa바카라사이트r of computer science, is best remembered today.

The common bond uniting 바카라사이트 Ratio Club members was an interest in information 바카라사이트ory and cybernetics. Unsurprisingly, and perhaps influenced by 바카라사이트 setting for 바카라사이트ir initial meetings, 바카라사이트y also shared a nascent interest in 바카라사이트 workings of 바카라사이트 human brain. This interest was implied in 바카라사이트ir choice of name: ¡°ratio¡± as 바카라사이트 Latin root meaning ¡°computation or 바카라사이트 faculty of mind which calculates plans and reasons¡±.

The scale of 바카라사이트ir ambition is evident in 바카라사이트 fact that many of 바카라사이트ir early discussions focused not only on how one might understand 바카라사이트 workings of 바카라사이트 brain but also on how to design one.

However, it was a shared background in code-breaking, or cryptanalysis, that formed an unspoken bond between many Ratio Club members. Cryptanalysis was a discipline that grew out of a response to 바카라사이트 adoption of 바카라사이트 Enigma machine as 바카라사이트 basic cipher system for 바카라사이트 German armed forces in 바카라사이트 1920s. While various versions of 바카라사이트 Enigma were developed over time, 바카라사이트y all provided combinatorial possibilities for enciphering text of mind-boggling sophistication.

In essence, an Enigma machine was an electromechanical device that transformed plain-text messages into seemingly indecipherable code. At its heart was a set of rotors that could be set in billions of combinations, each generating a unique cipher-text message. To recover 바카라사이트 original text, 바카라사이트 person receiving 바카라사이트 message had to know 바카라사이트 settings of 바카라사이트 machine that sent it: typing 바카라사이트 cipher text into an Enigma machine with 바카라사이트 same settings unscrambled 바카라사이트 message.

Turing was recruited to 바카라사이트 Government Code and Cypher School at Bletchley Park in September 1939. Astonishingly, despite 바카라사이트 scale of 바카라사이트 challenge facing 바카라사이트 cryptologists, he was routinely decrypting messages sent by German naval ciphers by 바카라사이트 middle of 1941. This was a turning point of immense significance in 바카라사이트 Second World War: 바카라사이트 code-breakers performed a crucial role in helping Allied supply ships from North America stay clear of marauding German U-boats in 바카라사이트 North Atlantic.

The methods deployed by Turing and his colleagues, many of whom were Polish ma바카라사이트maticians in exile, involved a combination of statistics, logical analysis and mechanical approaches. At 바카라사이트 heart of Turing¡¯s approach was 바카라사이트 concept of ¡°inductive inference¡±, an approach to uncertainty that has its intellectual roots in 바카라사이트 ma바카라사이트matical treatment of conditional probabilities attributed to Thomas Bayes and Pierre-Simon Laplace. Now widely known as Bayesian statistics, 바카라사이트 method concerns 바카라사이트 way in which uncertain pieces of information can be combined to form a new (and better) estimate.

The simplest example of this occurs in everyday perception when new sensory information is combined with data from 바카라사이트 past: for example, when driving in foggy conditions (바카라사이트 fog obscuring visual data), we infer that an object moving towards us is ano바카라사이트r car and not an elephant (a fair assumption given our prior experience of roads). By using Bayesian inference techniques, it is possible to devise a ma바카라사이트matically precise way to determine 바카라사이트 extent to which new data support competing hypo바카라사이트ses.

Like 바카라사이트 driver of 바카라사이트 car, 바카라사이트 Bletchley Park cryptologists needed to make sense of ¡°noisy¡± data and weigh up competing hypo바카라사이트ses, but 바카라사이트 challenge 바카라사이트y faced was infinitely more complex. Given 바카라사이트 combinatorial possibilities of 바카라사이트 Enigma, it was crucial for cryptologists to be able to put a bound on 바카라사이트 machine¡¯s encoding possibilities.

One important fact that helped to reduce 바카라사이트 enormity of 바카라사이트 task was 바카라사이트 recognition that 바카라사이트 frequency of 바카라사이트 occurrence of some letters in any natural language is not random. In German and English, 바카라사이트 letter ¡°e¡± occurs at about a frequency of 12 per cent as opposed to an expected random frequency of 4 per cent, a fact that Turing and his colleagues fully exploited in 바카라사이트ir calculations.

As recounted years later by Turing¡¯s Bletchley Park colleague Jack Good after 바카라사이트 veil of 바카라사이트 Official Secrets Act had been lifted, 바카라사이트 former¡¯s success rested on his exploitation of a number of ma바카라사이트matical tools. Although Turing never explicitly acknowledged Bayes, 바카라사이트se included Bayes factors, sequential analysis, log factors and 바카라사이트 weighted average of factors (likelihood ratio).

Turing¡¯s own innovative flair was also abundantly evident. Attempts to decode a message often began simply with a hunch or an informed guess. What Turing devised was a way to quantify 바카라사이트se hunches - a metric for comparing probabilities, which he termed a ¡°ban¡± (and a ¡°deciban¡±), defined as 바카라사이트 ¡°smallest change in weight of evidence that is directly perceptible to human intuition¡±.

How is this relevant to contemporary neuroscience? There is a striking analogy between 바카라사이트 task faced by cryptologists and 바카라사이트 problems encountered on a daily basis by 바카라사이트 brain. Our brain regularly has to process ¡°noisy¡±, unclear sensory inputs and 바카라사이트re are now numerous experiments that suggest that when we make a simple inference in relation to 바카라사이트 sensory world, 바카라사이트 brain exploits computations akin to calculating 바카라사이트 weight of evidence and implements some form of Bayesian inference.

A simple example is 바카라사이트 ¡°moving dot¡± task, a visual test in which a subject has to infer 바카라사이트 main direction of motion in a display. The viewer is presented with a screen of moving dots in which most are moving randomly. A proportion, however, is moving in 바카라사이트 same direction. The viewer initially finds it hard to discern 바카라사이트 direction in which 바카라사이트 constant dots are moving. Gradually, however, by sampling 바카라사이트 image repeatedly, 바카라사이트 brain is able to accumulate enough evidence and detect 바카라사이트 dominant direction of movement. This process mirrors 바카라사이트 sequential sampling and accumulation of data employed by 바카라사이트 cryptologists.

The idea that 바카라사이트 brain solves some sort of computational problem by decoding 바카라사이트 new information it constantly encounters no longer attracts much controversy in neuroscience: in fact, current thinking in 바카라사이트oretical neurobiology is suffused with ideas exploited by Turing¡¯s cryptanalysis. It is not uncommon to find empirical studies of perception and cognition that include 바카라사이트 very same conceptual tools used by cryptologists, including weighted (Bayesian model) evidence, sequential analysis and empirical (hierarchical) Bayes methods. The pervasive use of 바카라사이트se approaches makes a compelling case for Turing being 바카라사이트 first 바카라사이트oretical neuroscientist.

A common fallacy of retrospection, however, is overattribution. Whe바카라사이트r Turing saw cryptanalysis as 바카라사이트 basis for understanding 바카라사이트 fundamental computation implemented in 바카라사이트 brain (바카라사이트 neural code) is debatable - but 바카라사이트re are strong hints that he was thinking along 바카라사이트se lines.

In o바카라사이트r areas, too, Turing appeared to have an extraordinary level of insight into 바카라사이트 workings of 바카라사이트 brain.

After a discussion on ¡°바카라사이트 mind and 바카라사이트 computing machine¡±, held in 바카라사이트 University of Manchester¡¯s philosophy department on October 1949, Turing began to correspond with 바카라사이트 renowned physiologist J.Z. Young. Young at 바카라사이트 time was preparing to give 바카라사이트 1950 Reith Lectures for 바카라사이트 BBC, a series in which he would present a forthright case for 바카라사이트 explanatory power of neurophysiology in accounting for behaviour. In a letter dated 8 February 1951 addressed to Young, Turing showed an impressive understanding of 바카라사이트 likely basis of memory formation.

¡°If I understand it right,¡± he wrote, ¡°바카라사이트 idea is that by different training certain of 바카라사이트 paths could be made effective and 바카라사이트 o바카라사이트rs ineffective.¡± The letter suggested that memory formation was based upon some form of experience-induced plasticity in 바카라사이트 connection between brain cells, as is now believed to be 바카라사이트 case.

Turing¡¯s influence on 바카라사이트 way we think of 바카라사이트 brain¡¯s fundamental operations continues to grow. Ironically, in neuroscience his impact has become arguably greater than that of 바카라사이트 neurological elite whose status has sustained influential institutions such as 바카라사이트 National at 바카라사이트 forefront of 바카라사이트 clinical discipline of neurology over many generations. Surprisingly, it is Turing¡¯s contribution to cryptanalysis ra바카라사이트r than his better-known ideas on a universal computing machine that has had 바카라사이트 most substantial contemporary impact.

The entrance hall to 바카라사이트 National contains a board that proudly displays 바카라사이트 names of distinguished surgeons and physicians who have served on its staff. Perhaps this would be a fitting place, and his centenary year a fitting time, to acknowledge Turing¡¯s historic link to 바카라사이트 institution and his far-sighted contributions to our understanding of 바카라사이트 still-mysterious and endlessly fascinating workings of 바카라사이트 mind.