Encyclopedia of Computer Science and Technology

336 neural networkwebmd.com/stroke/news/20040415/Brain-Implants. AccessedOctober 5, 2007.Cooper, Huw, and Louise Craddock, eds. Cochlear Implants: APractical Guide. 2nd ed. Hoboken, N.J.: Wiley, 2006.Eisenberg, Anne. “What’s Next: Don’t Point, Just Think: The BrainWave as Joystick.” New York Times, March 28, 2002. Availableonline. URL: http://query.nytimes.com/gst/fullpage.html?res=9C01E7D8103BF93BA15750C0A96 49C8B63. AccessedOctober 5, 2007.Graham-Rowe, Duncan. “World’s First Brain Prosthesis Revealed.”New Scientist, March 12, 2003. Available online. URL: http://www.newscientist.com/article/dn3488.html. Accessed October5, 2007.He, Bin, ed. Neural Engineering. New York: Kluwer Academic,2005.“New Prosthetic Devices Will Convert Brain Signals into Action.”Science Daily, October 4, 2007. Available online. URL: http://www.sciencedaily.com/releases/2007/10/071003130747.htm.Accessed October 5, 2007.Experimental neural interfaces link nerve impulses to a computer,allowing users to control computers (and even remote robots) literallyby thinking.Human subject are now performing similar feats. Thenext step is to build robotic limbs that can be controlledby the person thinking in a certain way. Ideally, a personshould be able to think about clenching a hand or tappingan index finger and have the prosthetic hand replicate thosemovements. One obvious application for this technology isto enable quadriplegics who have little or no motion capabilityto control wheelchairs or other devices mentally.Future Brain ImplantsAs more is learned about the detailed functioning of neuronalnetworks inside the brain, “cognitive prosthetics” maybecome feasible. One example might be computer memorymodules that might act as a surrogate or extension ofhuman memory, perhaps helping compensate for loss ofmemory due to age or disease. (Early experiments on interfacingto the hippocampus, a part of the brain important forforming memories, have been underway since 2003.)Other possibilities might include processors that couldgive a person the ability to think about a mathematicalproblem and “see” the answer, or to search databases or theWeb simply by visualizing or thinking about the informationdesired.Further Reading“Brain Implants Move at the Speed of Thought.” WebMD MedicalNews, April 15, 2004. Available online. URL: http://www.neural networkWhen digital computers first appeared in the late 1940s, thepopular press often referred to them as “electronic brains.”However, computers and living brains operate very differently.The human brain contains about 100 billion neurons,and each neuron can form connections to as manyas a thousand neighboring ones. Neurons respond to electronicsignals that jump across a gap (called a synapse)and into electrodelike dendrons. The incoming signals formcombinations that in turn determine whether the neuronbecomes “excited” and in turn emits a signal through itsaxon. Clumps of neurons, therefore, act as networks that ineffect sum up incoming signals and develop a response tothem. That is, they “learn.”In a conventionally operated computer, the “neurons”(memory locations) are not inherently connected, and thecentral processing unit (CPU) uses arbitrary, interchangeablememory locations for storing data. Algorithms writtenby a programmer and implemented in instructions executedby the CPU impose cognition, to the extent one can speakof it in computers. In the brain, however, cognition seemsto be something that emerges from the cooperating activitiesand connections of the neurons in response to sensestimuli, and possibly the creation of agentlike entities, asdescribed in Marvin Minsky’s book The Society of Mind.Alan Turing and John von Neumann (see Turing, Alanand von Neumann, John) had established the universalityof the computer. That is, any calculation or logical operationthat can be performed at all can be performed by anappropriate computer program. This means that the “brain”model of a network of interconnected neurons can also beimplemented in a computer. During the 1940s, Warren S.McCulloch and Walter Pitts developed an electronic “neuron”in the form of a binary (on/off) switch that could belinked into networks and used to perform logical functions.During 1950s, Marvin Minsky, working at the MIT ArtificialIntelligence Laboratory (see Minsky, Marvin) furtherdeveloped these concepts, and Frank Rosenblatt developeda classic form of neural network called a Perceptron. Thisconsists of a network of processing elements (that is, func-