Scientists and philosophers have puzzled over human consciousness for thousands of years. Those familiar with the Greek classics and the writings of Plato, Aristotle and Democritus will already have read a great deal about the arguments as to whether consciousness is a unique quality of human life or whether it is a purely abstract concept of little or no consequence.
Scientists are polarized around conflicting ideas which hinge on whether consciousness is a phenomenon associated with classical brain functioning, or whether it has aspects which cannot be explained entirely by electrical impulses traversing the synaptic connections between brain cells. Philosophers on the other hand have focused on the mind/brain problem. Is the mind simply a function of the brain, an epiphenomenon of little consequence, or is it a separate entity strongly associated with human consciousness? In other words do we actually determine our actions by first thinking about them, or do we react automatically and then persuade ourselves that we thought about our actions after the event. We know that some human reactions, like the 'flight or fight' response to threatening situations, are automatic, but it is a little scary to believe we are entirely robotic.
Are we taking a very homo centric viewpoint in believing that the brain is the location of consciousness? What about organisms that don't have a brain as such, are they simply not conscious? What does not conscious mean? Is it the same as being unconscious? Studies of 'unconscious' patients under anesthesia suggest that the unconscious state is a very variable state of consciousness and can involve receiving sensory information, such as pain, without having the ability to respond. Perhaps the brain is just another organ which over time has become specialized in receiving, categorizing and making sense of information received so that the human body as a whole can initiate an appropriate response.
Paramecium is a unicellular organism which has demonstrated the ability 'to learn' from contrived experiences in an experimental situation in a way that enables it to respond to subsequent changes in the experimental environment which correlate with its previous 'learned' experiences. In other words, the paramecium, which obviously does not possess any structure comparable to the human brain, still demonstrates some aspects of consciousness that we normally associate with human consciousness. If organisms which lack a brain are conscious then where is their consciousness located and what potential structures' exist across all life forms? Some eminent scientists like Emeritus Professor Roger Penrose have suggested that consciousness is located not in any particular organ but within each living cell. This idea suggests that all living things based on cells, even unicellular organisms, are conscious, although organisms like viruses, which are non cellular, may not be conscious.
Philosophers interested in the nature of human life sometimes refer to our dualistic nature, body and soul. Some religious philosophers go further and refer to our tripartite nature, body, soul and spirit. By definition the body would include the anatomy and physiology of all parts including the brain. Most scientists would stop short at this point and deny the existence of a soul. However many religious philosophers would define the soul as the mind, the emotions and the will and give this a separate existence beyond the confines of the human body. It is the soul which is believed to continue on beyond the death of the human body into an afterlife, the nature of which varies according to different spiritual beliefs. Those who believe in the existence of the spirit tend to define this as the God given part which enables human beings to communicate with their creator. Human consciousness could be a phenomenon associated with this concept of the human spirit and hence dependent on our beliefs as to whether it is important or otherwise.