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)

 

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.

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.

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 corresponding controlling 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 (Chapter 5).

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 principle1 an optimiza- I tion 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.

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.

All of what has been discussed in this chapter, the body does for one ultimate purpose: survival — of both itself and its species.

"All well and good," you might say. "That's great: 7-6-5-4-3-2-1, all in a neat package. But what happens if the organism's operating set-points somehow go awry? What if a person's perception of reality causes his or her body to be in a perpetual, amygdala-driven, fight-or-flight mode of operation? How does a clinician 'get through' to such an individual? How can he or she apply effective means of intervention to break that destructive behavioral mode? And, how can music help?" Read on!

 

Taste

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