Consciousness as Dynamic Activities of the Brains Reticular Activating System

As technology accelerated, brain and mind theorists eventually turned back to the brain-the three and a half pound lump of pinkish-gray "wonder tissue." Mathematician-philosopher Rene Descartes, who had defined the brain/mind duality by his statement "cogito, ergo sum," (I think, therefore I am) chose the brain's pineal gland as the site of consciousness. His choice was partly based on the fact that the pineal gland is a midline, single structure. Thus, unlike nearly all other brain regions it had no duplicate, and was therefore thought to be essential. Descartes' proposal was readily refuted by neurophysiologists but did start the search for a single site of brain consciousness. Since many researchers viewed the brain/mind as a hierarchical arrangement of information processing, the logical conclusion was that at a certain site or region all information was recognized and assimilated by the "Mind's Eye," the site of consciousness, the Grandfather neuron, or some manifestation of a hierarchical apex. Recently, most of the brain has been found to be involved with wide ("distributed") parallel files of information, memory, and cognition. Historically, however, many workers focused on the reticular activating system (RAS) as the neural substrate of consciousness.

Maintenance of consciousness depends to an important extent upon the RAS, an organized tangle of tiny interconnecting neurons extending from the top of the spinal cord up through the brain stem into the thalamus and hypothalamus. The RAS integrates collaterals from sensory and motor nerves, has direct lines to half a dozen major areas of the cortex and probably all of the nuclei of the brainstem, and sends fibers down the spinal cord where it influences the peripheral sensory and motor systems. Its function is to sensitize or awaken selective neurons and nervous centers and desensitize others such that it can regulate the activity and wakefulness of the entire brain. Anesthetic induction drugs such as sodium thiopental are thought to exert their effects largely on the RAS. Destructive lesions of this area also produce permanent sleep and coma, and stimulating the RAS electrically can wake up a sleeping animal. It can also regulate the activity of most other parts of the brain through its own internal electrical excitability and neurochemistry.

Figure 2.2: A group of associated neurons such as brain cortical pyramidal cells. The long axons and dendrites extending from cell bodies are on the ,order of a few microns (thousand nanometers) thick. Some lateral synaptic connections are evident. By Jamie Bowman Hameroff.

Although the RAS regulates wakefulness, the riddles of consciousness are unsolved. For example, high level integration and associative functions implicit to cognition occur predominantly in the cortex, structurally more evolved in advanced animals such as man. Conversely, the RAS is one of the oldest evolutionary parts of the nervous system and is relatively unchanged when compared among lower animals and humans. Jaynes observes that even if we had a complete wiring diagram, if we were aware of every transmitter in the nervous system, understood all of the billions or trillions of synapses, we could still not discern that a specific brain contained a consciousness like our own.

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