The Web-Brain Hypothesis
By Kristina Lerman
First created: April 12, 1998

In a previous essay I argued that the Internet can and should be thought of as an organism. What organism, or part of an organism, does the Internet best resemble? At first glance, the Internet, and more specifically the Web, resembles the human brain. It is a surprisingly robust metaphor, that could benefit the way we treat and use the Web. The idea that the Internet can be thought of as a brain, was first proposed a number of years ago (Source: Mayer-Kress and Barczys) when the Web was still in its infancy. The dramatic explosion in the size and complexity of the Internet in the intervening years, driven primarily by the growth of the Web, motivated me to reexamine the premise and to see what evidence might support it.

The Web and the Brain

It is generally accepted that most, if not all, functions of the brain, such as perception, thought, learning, are a result of its architecture as a highly connected network of neurons. All of communications between neurons occur at the specialized connections between them called synapses. The number and density of synaptic connections is very high in the brain --- each of approximately one trillion (1012) neurons in the human brain forms about 1000 synaptic connections and may receive even more. (Source: Kandel and Schwartz, Principles of Neural Science, 1985 (New York: Elsevier)) Though neurons themselves may be involved in information processing, most of what makes the brain perform its unique functions happens at the synapses. Synapses, the junctions between dendrites and axons of one neuron and the body of another neuron, mediate the signal transfer, or information transfer, between neurons through an electric current or release of neurotransmitters. Input received by the neuron, might in turn cause it to fire, that is to trigger information to flow to the neurons it is connected to. More importantly the chemical synapses, which constitute the majority of synapses in the brain, are plastic, that is their effectiveness at transmitting information from one neuron to the next may be modified for a long time by the history of previous activity. This kind of long term modification, or plasticity, of synapses is believed to be the underlying basis of the brain's ability to learn (Source: Kandel and Schwartz, ibid.). Moreover, new research indicates that the adult brain is capable of growing new cells in response to environmental stimuli (Source: Gould, McEwen, Tanapat, Galea, and Fuchs, J. of Neuroscience, 17 (Number 7), 1997; also Holzenberger, Jarvis, Chong, Grossman, Nottebohm, and Scharff, J. of Neuroscience, 17 (Number 18), 1997). This mechanism could also play a role in learning.

Organization of neurons is important as well - there are regions of the brain dedicated to specific purposes or activities. In other words, neighboring neurons often perform the same function. In addition these neurons are connected to others performing related functions. The evidence for this view is quite strong - localized damage to the brain, such as that caused by a stroke or a gunshot wound, makes a person lose a very specific function, e.g. the ability to name colors, while seemingly not affecting other faculties.

While the morphology and chemistry of neurons and synapses are indisputably complex, the details of structure and interactions are of less importance to the behavior of the brain as a whole. In other words, we may find other many-unit, highly interconnected systems which may exhibit interesting, brain-like behaviors on a large scale. Coexisting populations of interacting species, an ecosphere, might be one example of such a system, the Internet could be another. The Internet is made up of tens of millions of computers (Source: http://www.bitwise.net/~maclearn/shistory.html), that communicate with each other through electrical cables or wireless signals. The Web is made of Web servers and computers delivering Web pages, images and movies, to clients (surfers using Web browsers) using Hypertext Transfer Protocol (HTTP). In 1996, there were an estimated 400,000 Web servers delivering about 50 million pages (Source: Internet Archive). As of the beginning of 1998 the size of the Web was estimated to be about 300 million pages (Source: Steve Lawrence and Lee Giles, as reported on http://www.news.com/News/Item/0,4,20728,00.html?st, also see K. Bharat and A. Broder in http://www.research.digital.com/SRC/whatsnew/sem.html). This number is increasing by about 20 million pages per month (Source: K. Bharat and A. Broder, ibid.) as more and more human knowledge and experience is digitized. Each Web page as a rule contains hyperlinks, which users click on to navigate to other Web pages. The average number of hyperlinks per page is not known, but it must be significant, because hyperlinks are the primary mode of navigating the Web.

The Web as a Brain

I propose that it is useful to imagine Web pages in the role of neurons, and hyperlinks as synapses that direct the flow of information from one page to the next - in short, the brain as a metaphor for the Web. Each neuron receives a stimulus - either a voltage spike across the electrical synapse, or some amount of neurotransmitter released across the chemical synapse - and depending on its state and processing capacity, the neuron may in turn generate a signal that will be received by other neurons. I will postulate that the signal received by a web page is proportional to the number of "hits" or users seeing it. Depending on the content of the page, for example Web page author’s annotation of the outgoing hyperlinks, users may follow hyperlinks to other pages. The text (or pictures) in and around the hyperlink plays the role of the neuron’s presynaptic environment. If the text indicates that the page pointed to by the hyperlink is considered to be important by the author, the user is more likely to follow that link than another. As the page changes with time, the author may attach less (or more) importance to a hyperlink. Plasticity of the presynaptic environment plays a big role in the brain’s ability to learn.

Organization of web pages mirrors the structure of the brain. Pages on the same server, just like neurons in the same area of the brain, are more likely than not to deal with the same subject. Moreover, each page is connected through hyperlinks to other pages on similar subjects. As a matter of fact, the link structure that develops over time between Web pages on similar subjects is so information-rich that it has been used to identify authoritative information sources as well as communities of interest (Source: J. Kleinberg, Authoritative Sources in Hyperlinked Environment; D. Gibson, J. Kleinberg and P. Raghavan, Inferring Web Communities from Link Topology.)

In addition to simply responding to the external environment, the Web could well be undergoing long-term changes in the number of pages, or how the hyperlinks are stressed on a page - in other words, the Web could be learning. Hyperlinks on popular gateways to the Web, such as Yahoo, are plastic. Current events generate many hyperlinks, and if the event is especially newsworthy, the links will grow in number, their explanatory text might change, and with time they might be moved to a different portion of the site, though usually not disappear.