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

Sensory Pathways



The processing of somatosensory and sound information involves the hierarchy of three pathways, in series, through which the information passes on its afferent journey through the CNS.

Macroscopic strategy of the brain: smells awful, so don't eat it; smells right, mate with it. (Llinás; I of the Vortex, 166)

Link to —  Sensory Pathways Diagram

Link to —  Cortical Layers Diagram


Reticular Formation information processing

At the first level of information-processing, the reticular formation, the afferent sensory action potentials travel through a web of neural networks, where they are progressively assembled into integrated, compound action potentials that deliver to the CNS a "state-of-the-controlled-system" message. Those messages destined for further processing arrive first at the reticular activating system, the "port-of-entry" into the brain. Recall further that the primary function of the RAS is to prevent information overload by acting as a preliminary, coarse sieve, a filter that serves to avoid overburdening the brain with extraneous data.

The reticular activating system (RAS) is the portal through which nearly all information enters the brain. (Smells are the exception; they go directly into your brain’s emotional area.) The RAS filters the incoming information and affects what you pay attention to,    how aroused you are,    and what is not going to get access to your brain.

For survival’s sake, your RAS responds to:    your name,    anything that threatens your survival,    and information that you need immediately. For instance, if you’re looking for a computer file that you’re sure you placed on your desk, your RAS alerts your brain to search for the name of the file or focus on one word in the filename to help you find it.

The RAS also responds to novelty. You notice anything    new and different. For leadership purposes, this includes anything out of the ordinary in day-to-day activities within your organization, attending to changes in your employees relative to production, mood, and interactions with others.

Reticular Activating System (RAS) Neuronal Circuits (Wikipedia, Reticular activating system)

The reticular activating system (RAS) is composed of several neuronal circuits connecting the brainstem to the cortex. These pathways originate in the upper brainstem reticular core and project through synaptic relays in the rostral intralaminar and thalamic nuclei to the cerebral cortex.

The neuronal circuits of the RAS are modulated by complex interactions between a few main neurotransmitters. The RAS contains both cholinergic and adrenergic components, which exhibit synergistic as well as competitive actions to regulate thalamocortical activity and the corresponding behavioral state.

The reticular activating system also helps mediate transitions from relaxed wakefulness to periods of high attention. There is increased regional blood flow (presumably indicating an increased measure of neuronal activity) in the midbrain reticular formation (MRF) and thalamic intralaminar nuclei during tasks requiring increased alertness and attention.

Thalamus processes all information except smell

Next, information that makes it through the reticular formation travels up the spinothalamic tract, to be input to the thalamus, which processes all information coming in to the CNS, except that derived from smell. Olfactory neurons go directly to the rhinencephalon, or "smell brain." The thalamus evaluates incoming information to establish a preliminary classification for it. In fact, certain areas of the thalamus are specialized to receive particular kinds of digitized information (Ornstein and Thompson 1984). Once classified, this information is immediately dispatched to two generic places: (1) the sensory regions of the, cerebral cortex, where it will be processed further, and, possibly, eventually stored elsewhere following delayed, conscious perception; and (2) the limbic to effect instantaneous responses to potential threats.

All sensory inputs to the neocortex are relayed through the thalamus, except for the olfactory sensory neurons, which project directly to the paleocortex. (LaBerge; Attentional Processing, 163)

Limbic System processing – Amygdala and Hippocampus

In the limbic system, the second level of information-processing, sensory inputs are fine-tuned through the process of stimulus-coding (Berger 2002; Berger and Schneck 2003; Schneck 1997; Schneck and Berger 1999). The coding "tags" the information to give it temporal/sequential significance for subsequent filing away in memory, and for recall (the somesthetic cortex will use this information later). More importantly, however, the limbic system evaluates the data that the thalamus has classified, to determine its potential threat to the safety of the organism. For the latter purpose, the data travels in series pathways, first through the amygdala, and second through the hippocampus. If the amygdala senses "threat," real or imagined, it issues forth a distress message, an "SOS" error signal, that mobilizes control systems into action; it also truncates any further processing by the hippocampus. These distress signals are in the form of outgoing motor (as opposed to incoming sensory) compound action potentials. Motor signals travel via hypothalamo-hypophysial and hypothalamo-autonomic pathways to trigger the release from target organs and tissues of corresponding neurotransmitters and hormones that elicit a "fight-or-flight" response.

Only when the amygdala sounds an "all clear" does information track next through the hippocampus, for additional stimulus-coding and processing en route to the "higher" centers in the cerebral cortex (Berger 2002; Schneck 1997).


There are three important things to remember, especially when evaluating the role of music in the human experience.

1. The road to higher cerebral centers travels first through the older paleoencephalon and, within the latter, first through the amygdala of the limbic system. In the words of Ornstein and Thompson (1984, p.24), "Emotions were here before we were."

2. As long as the amygdala is in "alert" perceived-threat mode, all roads lead to "fire stations, rescue squads, emergency services, and hospitals." Indeed, when active, the amygdala actually inhibits the activity of the hippocampus (but not the other way around), causing it to start to self-destruct (degenerate) if the amygdala-driven alert mode of information-processing persists for extended periods of time (Damasio and Moss 2001).

3. As long as the amygdala is in alert mode, all roads through the hippocampus to "universities, libraries, Institutions of Higher Learning," and cognitive cerebral centers are completely blocked. It is an exercise in futility to try to reason with anybody in a perpetual alert state. Instead, one must emote with a person in this state, which is why music is so effective as a driving function that "kicks" the system out of its perpetual fight-or-flight mode.

If the amygdala signifies that all is well, information filtered by the RAS, classified by the thalamus, and evaluated and prioritized by the limbic system passes on through the hippocampus to the cognitive regions of the cerebral cortex. Here, the final stop in the hierarchy of information-processing channels may be storage in tertiary memory, because the body always reserves the option to discard unwanted information at any step along the processing pathways. Once the information is in final memory, however, it is there forever, barring physical damage to the brain in the region where that data is stored.

To further the effectiveness of all physiological function, the body also operates according to two guiding principles (Schneck 1990, 2003a). First, it attempts to economize on energy expenditure. The more scientists learn about the physiology of the human body, the clearer it becomes that this organism operates according to a minimum-energy principle, an optimization scheme. All metabolic processes, mechanical outputs, feedback/ feedforward control mechanisms, and so on, take the path of least resistance in an attempt to optimize performance and at least minimize the rate of loss of usable energy.

Second, the body attempts to economize on the utilization of space for the storage and handling of raw materials and/or information. This it does in basically three ways:

1. It stores ingredients, not products. (Convergence Zones for Language)

2. It draws upon fractal principles to create complicated geometric shapes and configurations that fit neatly into tight quarters, yet maximize their functional capacity

3. It discards any and all information for which it has no perceived need. Unlike many, the human body is not a pack rat.



Taste can be simplified to four primitive chemical categories, and responses are monotonic to concentration.