Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Reticular Formation

The reticular formation is a tangled, densely packed cluster of nerve cells containing mostly gray matter inter­laced with fibers of white matter. It is an anatomical region about the size of a little finger, extending through the central core of the brainstem, from the upper spinal cord, through the medulla oblongata and pons, into the midbrain. For the most part, the reticular formation is not distinctly identifiable as a discrete system of CNS nuclei. Rather, it communicates, via networks of interneurons with (1) afferent sensory pathways that course through this ana­tomical region, (2) sensory nuclei and motoneuronal cell groups located in the brainstem, and (3) neural pathways that operate through the autonomic nervous system. In addition, the reticular formation has elaborate connections with the thalamus and hypothalamus. (Schneck & Berger; Music Effect, 84)

 A single nerve trunk (e.g. the auditory nerve) contains about 30,000 total sensory nerve fibers. At 400 impulses per second a 30-thousand nerve-fiber trunk would produce an information flow into the CNS of about 12 million bits per second. (Schneck & Berger; Music Effect, 83)

 The interneurons of the reticular formation are very short, allowing messages to be relayed quickly from one nerve cell to the next. This allows it to function as sieve, continuously sifting through the mass of incoming data. Only those sensory inputs that the neural hardwiring construes to be essential, unusual, possibly dangerous, and/or in some sense "action-provoking" are passed along for further processing and forwarding to the higher levels of the brain. (Schneck & Berger; Music Effect, 84)

Reticular formation in the brain stem, a region involved in arousal, alertness, and vigilance. (LeDoux; Synaptic Self, 244)

Reticular formation neurons in the caudal ponds and medulla oblongata generally serve a premotor function in the sense that they integrate feedback sensory signals with executive commands from the upper motor neurons and deep cerebellum nuclei and, in turn, organize the efferent activities of lower visceral motor and certain somatic motor neurons in the brainstem and spinal cord. (Purves; Neuroscience, 398)

 Examples of this coordination of firing patterns include the smaller neurons that coordinate a broad range of motor activities that organize mastication, facial expressions, and a variety of reflexive orofacial behaviors such as sneezing, decoupling, yawning, and swallowing.  (FAPs) (Purves; Neuroscience, 398)

The reticular formation is best viewed as a heterogeneous collection of distinct neuronal clusters in the brainstem tegmentum that either modulate the excitability of distant neurons in the fore­brain and spinal cord, or coordinate the firing patterns of more local lower motor neuronal pools engaged in reflexive or stereotypical (FAPs) somatic motor and visceral motor behavior. (Purves; Neuroscience, 399)

The level of any conscious state in the brain rises and falls in response to the degree of electrochemical activation supplied by the reticular formation in the brainstem.  Overall brain activation level changes about 10 - 20% during sleep.  Consciousness is exquisitely sensitive to even slight changes in activation level.  A significant amount of information processing occurs even while we are completely unaware of it as in sleep. (Hobson, Consciousness, 67)

 The reticular formation influences the conscious mind not only by changing the level of activation but also by modulating the neural inputs and outputs, especially those arising and emanating from the spinal cord.  By altering the tension in our muscles and by focusing our internal awareness on one channel of data or another, we can transition into a more peaceful conscious state.  In this way we bring the reticular formation partially under the control of our will, probably via the prefrontal cortex. (Hobson, Consciousness, 68)

 The reticular formation begins in the medulla, just above the level of the spinal cord. The medulla programs many autonomic functions essential for consciousness as well as organizing posture and controlling head and neck positions.  The ponds and midbrain are the very center of the reticular system because they coordinate activation of the higher brain structures. (Hobson, Consciousness, 69)