In the preceding sections, I have provided comprehensive evidence that the vertebrate central nervous system, including that of humans, is organised as superimposed internal neural loops from the spinal cord to the cerebral cortex.
Thus, the human nervous system can be conceived of as a tall building with many floors. In a multi-floor building, there are internal connections between and within floors; any particular floor can function to some degree independently from other floors; and at each higher level, there is an increasing distance from the external world accessed via the ground floor.
We do not know how many levels are in this building, but I suggest that they correspond to the number of synaptic steps that separate the level of each neural loop from the external world, with the highest level loops becoming increasingly distant from the lowest neuromechanical loops (the “ground floor”), where all sensory inputs from the external world enter, and all motor outputs exit.
The primary consequence of this fundamentally hierarchical architecture is that all levels of the nervous system are connected to the outside world only via the ground floor of sensory inputs and motor outputs. This represents a bottleneck of how the brain, and thus the inner experiential being, is connected the external world.
This model emphasises that nothing of what happens in the external world enters the brain except via its sensory inputs while information about events within the body’s own internal organs reach the brain via visceral sensory inputs. Without sensory inputs to the brain, a person would be totally unaware of anything happening in both the external world and their own body.
Conversely, the output of any brain activity can only emerge at the one exit: via the final motor neurons in the spinal cord and brain stem. Without functioning motor neurons, a person is paralysed and, even if kept alive by artificial means, is unable to move and interact physically with the world.
What are some of the consequences of accepting the human brain as a multistorey neural building for our own existence?
For a start, every communication between individuals has to exit at the ground level of one person and can only be received at the ground level of the other.
How then subjective experiences can be shared to become objective?
Subjective experiences are assumed not to be directly shareable. This serious obstacle appears to represent the main reason why many thinkers consider states of consciousness to be a unique solipsistic condition.
Our experiences, even those regarded as “objective”, are primarily individual experiences. It is only because we share common neural process that we feel that what we share is objective. To be communicated, any idea needs to be brought back to the “common senses” (ie shared senses) of direct experience.
What do we do then about all those indirect experiences upon which most of our knowledge depends, even though we have no chance to directly experience them personally? For example, very few people have seen the far side of the moon. Instead, we must trust some graphic images (which are an “objective” means to transfer indirectly other people’s experiences) to accept how the hidden face of the moon looks.
Clearly, we are immersed in a world and interact with it from the very beginning of our existence. But even as we become increasingly autonomous as we mature, not only are we are dependant on other human beings, but we remain so throughout our lives. Then the problem of transforming experiences from the subjective to objective realms becomes the problem of understanding how personal experiences can be shared.
Additional consequences of the neural building
The proposal of the brain as a multistorey building is consistent with the history of a hierarchical view of human brain. In addition, it also resolves the apparent gap between body and mind (see Chapter 10).
It enables us to better establish the relations between neural levels, mental functions, and the graded nature of consciousness (see Chapter 11).
It helps to explain the evolutionary and developmental steps in the making of a self (see Chapter 12).
It helps to place us as individuals in the 4D universe (see Chapter 13).