From: mike99 (mike99@lascruces.com)
Date: Wed Jan 11 2006 - 16:49:45 MST
Sejnowski's little essay (below) was published as part of the www.edge.org
"Dangerous Ideas" event. Although his idea is not original, some of his
argument are (at least to me).
Regards,
Michael LaTorra
TERRENCE SEJNOWSKI Computational Neuroscientist, Howard Hughes Medical
Institute; Coauthor, The Computational Brain [sejnowski101.jpg]
When will the Internet become aware of itself?
I never thought that I would become omniscient during my lifetime, but as
Google continues to improve and online information continues to expand I
have achieved omniscience for all practical purposes. The Internet has
created a global marketplace for ideas and products, making it possible for
individuals in the far corners of the world to automatically connect
directly to each other. The Internet has achieved these capabilities by
growing exponentially in total communications bandwidth. How does the
communications power of the Internet compare with that of the cerebral
cortex, the most interconnected part of our brains?
Cortical connections are expensive because they take up volume and cost
energy to send information in the form of spikes along axons. About 44% of
the cortical volume in humans is taken up with long-range connections,
called the white matter. Interestingly, the thickness of gray matter, just a
few millimeters, is nearly constant in mammals that range in brain volume
over five orders of magnitude, and the volume of the white matter scales
approximately as the 4/3 power of the volume of the gray matter. The larger
the brain, the larger the fraction of resources devoted to communications
compared to computation.
However, the global connectivity in the cerebral cortex is extremely sparse:
The probability of any two cortical neurons having a direct connection is
around one in a hundred for neurons in a vertical column 1 mm in diameter,
but only one in a million for more distant neurons. Thus, only a small
fraction of the computation that occurs locally can be reported to other
areas, through a small fraction of the cells that connect distant cortical
areas.
Despite the sparseness of cortical connectivity, the potential bandwidth of
all of the neurons in the human cortex is approximately a terabit per
second, comparable to the total world backbone capacity of the Internet.
However, this capacity is never achieved by the brain in practice because
only a fraction of cortical neurons have a high rate of firing at any given
time. Recent work by Simon Laughlin suggests that another physical
constraint -- energy--limits the brain's ability to harness its potential
bandwidth.
The cerebral cortex also has a massive amount of memory. There are
approximately one billion synapses between neurons under every square
millimeter of cortex, or about one hundred million million synapses overall.
Assuming around a byte of storage capacity at each synapse (including
dynamic as well as static properties), this comes to a total of 10^15 bits
of storage. This is comparable to the amount of data on the entire Internet;
Google can store this in terabyte disk arrays and has hundreds of thousands
of computers simultaneously sifting through it.
Thus, the internet and our ability to search it are within reach of the
limits of the raw storage and communications capacity of the human brain,
and should exceed it by 2015.
Leo van Hemmen and I recently asked 23 neuroscientists to think about what
we don't yet know about the brain, and to propose a question so fundamental
and so difficult that it could take a century to solve, following in the
tradition of Hilbert's 23 problems in mathematics. Christof Koch and Francis
Crick speculated that the key to understanding consciousness was global
communication: How do neurons in the diverse parts of the brain manage to
coordinate despite the limited connectivity? Sometimes, the communication
gets crossed, and V. S. Ramachandran and Edward Hubbard asked whether
synesthetes, rare individuals who experience crossover in sensory perception
such as hearing colors, seeing sounds, and tasting tactile sensations, might
give us clues to how the brain evolved.
There is growing evidence that the flow of information between parts of the
cortex is regulated by the degree of synchrony of the spikes within
populations of cells that represent perceptual states. Robert Desimone and
his colleagues have examined the effects of attention on cortical neurons in
awake, behaving monkeys and found the coherence between the spikes of single
neurons in the visual cortex and local field potentials in the gamma band,
30-80 Hz, increased when the covert attention of a monkey was directed
toward a stimulus in the receptive field of the neuron. The coherence also
selectively increased when a monkey searched for a target with a cued color
or shape amidst a large number of distracters. The increase in coherence
means that neurons representing the stimuli with the cued feature would have
greater impact on target neurons, making them more salient.
The link between attention and spike-field coherence raises a number of
interesting questions. How does top-down input from the prefrontal cortex
regulate the coherence of neurons in other parts of the cortex through
feedback connections? How is the rapidity of the shifts in coherence
achieved? Experiments on neurons in cortical slices suggest that inhibitory
interneurons are connected to each other in networks and are responsible for
gamma oscillations. Researchers in my laboratory have used computational
models to show that excitatory inputs can rapidly synchronize a subset of
the inhibitory neurons that are in competition with other inhibitory
networks. Inhibitory neurons, long thought to merely block activity, are
highly effective in synchronizing neurons in a local column already firing
in response to a stimulus.
The oscillatory activity that is thought to synchronize neurons in different
parts of the cortex occurs in brief bursts, typically lasting for only a few
hundred milliseconds. Thus, it is possible that there is a packet structure
for long-distance communication in the cortex, similar to the packets that
are used to communicate on the Internet, though with quite different
protocols. The first electrical signals recorded from the brain in 1875 by
Richard Caton were oscillatory signals that changed in amplitude and
frequency with the state of alertness. The function of these oscillations
remains a mystery, but it would be remarkable if it were to be discovered
that these signals held the secrets to the brain's global communications
network.
Since its inception in 1969, the Internet has been scaled up to a size not
even imagined by its inventors, in contrast to most engineered systems,
which fall apart when they are pushed beyond their design limits. In part,
the Internet achieves this scalability because it has the ability to
regulate itself, deciding on the best routes to send packets depending on
traffic conditions. Like the brain, the Internet has circadian rhythms that
follow the sun as the planet rotates under it. The growth of the Internet
over the last several decades more closely resembles biological evolution
than engineering.
How would we know if the Internet were to become aware of itself? The
problem is that we don't even know if some of our fellow creatures on this
planet are self aware. For all we know the Internet is already aware of
itself.
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