Human Neuron and Input/Output Count

Brain:
    1*10^11 neurons
    7*10^3 synapses per neuron
    (est) 7*10^14 synapses in adult (or 700 teraSynapse)
    (guess) 8bit synaptic signal == 7*10^14 bytes (or 5.6 petaBit of state)
    50/sec firing rate (40/s sync frequency, 200-1000 max)
    (guess) 50*7*10^14 synapse-neuron-fire/sec == 3.5*10^16 (or 35 petaFlop)
    (presume each synapse does a scale-and-sum operation)


Body:
    Spine:      1*10^9 neurons
    Intestines: 5*10^8 neurons


Sensory systems:
    Sight:      5*10^6 cones + 1.3*10^8 rods ~= 1.4*10^8 "pixels"
                 retinal ganglion cells -- 1*10^6
                 optic nerve fibers -- 1.2*10^6
                 lateral geniculate body -- 5.7*10^5 neurons

    Touch:      (swag) 3*10^6 sensors
                  nerve endings in hand = 1,300/in2
                  area of skin = 3,000 in2
                  tactile receptors in hand = 17,000

    Hearing:    8.8*10^2 sensor neurons
                inferior colliculus -- 3.9*10^5 neurons
                medial geniculate body = 5.7*10^5 neurons

    Taste:      (swag) 1*10^5 sensors
                  104 taste buds w/ 50-150 receptors each

    Smell:      1.2*10^6 sensors


Motor systems:  number of muscles ~= 800
                 (each muscle may have multiple motor-neuron drivers)


Some refs:

Brain Facts and Figures
http://faculty.washington.edu/chudler/facts.html

Information Processing in Human Body
http://vadim.oversigma.com/MAS862/Project.html

Moravec,H(1997)
When will computer hardware match the human brain?
http://www.transhumanist.com/volume1/moravec.htm


Drachman D (2005). "Do we have brain to spare?".
Neurology 64 (12): 2004-5.
doi:10.1212/01.WNL.0000166914.38327.BB. PMID 15985565.
The human brain has a huge number of synapses. Each of the 10^11 (one
hundred billion) neurons has on average 7,000 synaptic connections to other
neurons. It has been estimated that the brain of a three-year-old child has
about 1015 synapses (1 quadrillion). This number declines with age,
stabilizing by adulthood. Estimates vary for an adult, ranging from 1014 to
5 x 1014 synapses (100 to 500 trillion).


http://www.scholarpedia.org/article/Enteric_nervous_system
Large numbers of neurons are contained in the enteric nervous system, about
200-600 million in human. This is far more neurons than occurs in any other
peripheral organ and is similar to the number of neurons in the spinal
cord. 


http://faculty.washington.edu/chudler/facts.html
Number of neurons in human spinal cord = 1 billion
   Kalat, J.W., Biological Psychology, 6th Edition, 1998, page 24

Number of neurons in cochlear nuclei = 8,800 
Northern, J.L. and Downs, M.P.,
Hearing in Children, 5th edition,
Philadelphia: Lippincott Williams & Wilkins, 2002.

Number of neurons in inferior colliculus = 392,000
Northern, J.L. and Downs, M.P.,
Hearing in Children, 5th edition,
Philadelphia: Lippincott Williams & Wilkins, 2002.

Number of neurons in medial geniculate body = 570,000

Number of neurons in auditory cortex = 100,000,000

Total number of human taste buds (tongue, palate, cheeks) = 10,000
Number of receptors on each taste bud = 50-150
Boron, W.F. and Boulpaep, E.L.,
Medical Physiology. A Cellular and Molecular Approach,
Philadelphia: Saunders, 2003

Number of human olfactory receptor cells = 12 million
Shier, D., Butler, J. and Lewis, R.
Hole's Human Anatomy & Physiology,
Boston: McGraw Hill, 2004

Number of retinal receptor cells = 5-6 million cones; 120-140 million rods
Number of retinal ganglion cells = 800 thousand to 1 million
Number of fibers in optic nerve = 1,200,000
Number of neurons in lateral geniculate body = 570,000
Number of cells in visual cortex (area 17) = 538,000,000

Surface area of skin (adult human) = 3,000 in2 (~1.8 m2)
Schiffman, H.R.,
Sensation and Perception. An Integrated Approach,
New York: John Wiley and Sons, Inc., 2001

Number of tactile receptors in the hand = 17,000
Number of nerve endings in hand = 1,300 per in2


Information Processing in Human Body
Based on final project for MIT Class MAS 862 (1998) by Vadim Gerasimov
Corrected and updated in 2000-2006.
http://vadim.oversigma.com/MAS862/Project.html
The activity of the brain is equivalent to that of 1000 kHz processor with
40 Gbits of states. The corresponding processing power (channel capacity)
is C=4*1013 bit/s.   ???


When will computer hardware match the human brain?
Hans Moravec (Received Dec. 1997)
http://www.transhumanist.com/volume1/moravec.htm


Resonant synchronization in heterogeneous networks of inhibitory neurons
R. Maex, Erik De Schutter
http://www.tnb.ua.ac.be/publications/pub057/pub057.shtml
Neural Sync rate ~40Hz, firing rate 200-1000Hz


And some more to look at:

Boris Barbour, etal
What can we learn from synaptic weight distributions?
http://www.physicsforums.com/attachment.php?attachmentid=27574&d=1281897303

Rene Marois and Jason Ivanoff
Capacity limits of information processing in the brain
http://www.psy.vanderbilt.edu/faculty/marois/Publications/Marois_Ivanoff-2005.pdf