The heart is a pump. If it fails, an artificial heart can pump in its place. The lungs are balloons. When breathing is insufficient, a ventilator can inflate them. Mechanical models provide simple ways to understand organs and organ systems. They are also the basis of interventions that can be used when organs stop working. Is there a model for the brain?
Neurons and the nervous system function with inputs, processing and outputs. Neurons connect with each other to form circuits. They generate electric currents through action potential propagation. Myelinated axons can be likened to insulated wires. With all these characteristics, the brain can be thought of as a computer.
Neurons in isolation are capable of complex electrical activity. With numerous cell processes they are able to take in vast amounts of information, and every part of a neuron, from dendrites to cell body to axons, is capable of information processing. This allows neurons to be thought of as tiny computers, or as microchips within a larger supercomputer. Neurons are organized into cortical columns or nuclei in the brain, with each column or nuclei as a computational unit with a seemingly specific purpose. This forms the basis of a computer model that can be built from the bottom up, piece by piece, to simulate an entire human brain. This is the premise for the Blue Brain Project.
If it is successful, the Blue Brain Project promises to revolutionize neuroscience. Modelling the brain from the level of ion channels to neural networks, and the prospect of generating consciousness may present scientists with new ways of understanding how the brain works. In medicine, it may elucidate the etiologies and mechanisms of currently unexplainable neurological and psychiatric disorders. However, there is scepticism along with the excitement.
Can a computer ever match the brain’s complexity? Neurons are variable and diverse. They have different numbers and sizes of cellular processes and they have different distributions of ion channels and chemical receptors. In addition, these features change over time and experience as a result of neuroplasticity. How accurately can a computer describe and simulate the effects of ever changing neuron morphology? And can a giant computer ever be capable of processing and transmitting signals as fast as a one-and-a-half kilogram brain?
Most importantly, how closely does the brain resemble a computer? Yes, the nervous system has electrical properties. Yes, microchips can act as single neurons. And yes, configuring microchips to work together as neural networks does make sense. But where do glial cells fit in? Can a model that does not account for the presence and function of glial cells be a true representation of brain physiology?
Ultimately, the Blue Brain Project is an ambitious scientific endeavour to create a grand computational machine. Its success hinges on whether or not a ghost can be found to occupy it. And then, will it only be the ghost of a ghost?