The human brain is a highly complex organ that is responsible for remarkably sophisticated behavior. In order to more fully elucidate the relationship between brain structure and function, investigators involved with attempting to understand the neuroscience of brain systems especially concerning cognition are testing large-scale simulations of brain structure and function. This is a particularly daunting challenge.
For example, there is the so-called, “Blue Brain Project” that involves the simulation of about one million neurons arranged in cortical columns. The design of this model incorporates significant biological detail that reflects known spatial relationships and neuronal connectivity data. Another example of a human brain-modeling project involving some 100 billion neurons has also been reported.
A limitation to these approaches has been that although they seek to model the complexity of brain organization they do not address the relationship between brain structure and brain function, i.e. human behavior. Dr. Chris Eliasmith and colleagues from the Centre for Theoretical Neuroscience from the University of Waterloo, Waterloo, Ontario in Canada has attempted examine this relationship. To do so, they have created a neuron model of 2.5 million neurons that focuses on the relationship between neuronal structure in the brain and the resulting human behavior.
Within this model, the inputs are represented by images of handwritten or typed characters. All the outputs are the movement of an “arm” that possesses appropriate physical properties such as mass, length and inertia. The designers of this model refer to it as “Spaun” – an acronym for Semantic Pointer Architecture Unified Network. Incorporated within Spaun are typical brain-related functions such as image recognition, serial working memory and learning. Furthermore, the eight tasks that Spaun performs are:
• Copy drawing
• Image recognition
• So-called three-armed bandit task in which it is required to determine which of the three possible choices results in the statistically greatest reward
• Successful reproduction of a list of any length
• Responding to questions
• Ability to create variables
• Simple reasoning.
The model is so structured that it represents the anatomical structure of the human brain as established by current brain research. Although a more detailed examination of the theoretical basis for this model is beyond the scope of this report, this kind of intensive work indicates the degree to which the apparent enigmas associated with high-order brain function are being methodically unraveled.