With computing power doubling every 18 months, there is speculation that AI could be realised within 50 years. However, this projection could fail to materialise, as the true complexity of the human brain becomes better understood. The brain and spinal cord are made up of many cells, including neurons and glial cells. Neurons are cells that send and receive electro-chemical signals to and from the brain and nervous system. There are about 100 billion neurons in the brain, but there are many more glial cells, which provide support functions for the neurons,
Neurons are nerve cells that transmit nerve signals to and from the brain, at a speed up to 200 mph. The neuron consists of a cell body, or soma, with branching dendrites that act as signal receivers and a projection called an axon, which conduct the nerve signal. At the other end of the axon, the axon terminals transmit the electro-chemical signal across a synapse, which is the gap between the axon terminal and the receiving cell. The cell body contains the nucleus, which contains DNA plus other nuclear organelles and typically has anywhere between 1,000 to 10,000 synapses through which it communicates with other neurons, muscle cells and glands. However, there are many different types of neurons, which all differ in structure, e.g. the number of processes or axons. For example:
- Sensory neurons carry messages from the body's sense receptors,
e.g. eyes, ears, to the central
nervous system (CNS). These neurons have two processes,
but only account for 0.9% of all neurons.
- Moto-neurons carry signals from the CNS to the muscles and glands,
but have many processes originating from the cell body. Moto-neurons
account for 9% of all neurons.
- Inter-neuron cells form all the neural wiring within the CNS. These have two axons, instead of an axon and a dendrite. One axon communicates with the spinal cord, while the other communicates with either the skin or muscle.
Unlike most other cells, neurons cannot re-grow after damage, except neurons from the hippocampus. The glial cells make up the remaining 90 percent of the brain's cells, but are are nerve cells that don't carry nerve impulses. However, the various glial cells perform many important functions, including the digestion of parts of dead neurons, the manufacture of myelin for neurons plus provide both physical and nutritional support for neurons. Not surprisingly, there are still many fundamental questions that the proponents of AI science, both for and against, need to address, which we shall simply represent as follows:
How does the brain work as a physical system?
How does the mind work as a metaphysical system?
The brain is made up of biological matter, i.e. cells; as such it might be possible to described it in terms of a physical system analogous to computer hardware. So while it may be the most extraordinarily complex system, never the less it may be possible to eventually decipher its blueprint of operation. However, while the operation of the brain can be described in terms of the physical interactions between cells, the process of thought that we call the mind is more difficult to describe in just these terms. However, it may also be possible to extend the computer analogy and describe the mind as the software system operating within the brain's hardware. As a result, human intelligence and behaviour may just be a matter of developing the right algorithms and system programming. However, it is not difficult to see why so many paradigms and belief systems may collide at this point. Of course, those involved in the theological and philosophical sciences will continue to debate the metaphysical issues, but if we ask the physical sciences to adopt an agnostic position, the challenge for these sciences is to prove that a physical system can indeed develop metaphysical thought processes. As indicated, the human brain contains a mind-boggling 100 billion neurons in conjunction with over a trillion supporting cells. However, the sheer complexity of the brain is only realised after understanding that each neuron may support as many as 10,000 receptor branches called dendrites. Based on these numbers, it is estimated that the brain may contain in excess of 100 trillion (1014) connections. Other important aspects include the relationships between hormones and neural functions, and the sensory input and motor output functions. Somehow, over hundreds of millions of years, evolution has nurtured a sentient intelligence that may be potentially unique within the universe. Therefore, the replication of this feat may have to be revised as a longer-term goal of AI and not one that will automatically occur as a result of increased processing speed, as defined by Moore's Law. However, as an analogous task to that of mapping the human genome at the end of the 20th century, mankind could embark on a new endeavour in the 21st century by starting the process of accurately mapping the neural functions of the brain. See Scanners and Human Brain Project.
Early models tried to assign basic attributes such as speech and sight to specific centres within the brain. However, it is now realised that many functions of the human mind are reflective of the integrated operation of the brain as a whole. For example, our vision is an image projected onto each retina of the eye. This image is upside down, without depth of field and subject to a large blind spot caused by the optic nerve exiting the back of the eye. The real perception of vision is a construct of numerous discrete functions within the brain that uses previous visual experience laid down in our memory connections since birth. In this context, our perception of reality is but a construct of the mind not that dissimilar to dreams that can be thought of as an alternative reality.