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Originally posted 2021-05-13 15:22:27.

Nitrogen Narcosis Sedation and Consciousness

If you are a scuba diver, you may think you understand nitrogen narcosis. Sadly, what is taught in most scuba diving courses is mostly fiction. In this article, I will explain the reality of nitrogen narcosis sedation. To stay safe on your deeper dives, you need to know how the anesthetic effects of nitrogen progressively reduce your level of consciousness.

The commonly taught model of alcohol-like intoxication utterly fails to describe the profoundly nuanced cognitive effect upon the diver and, at worst, promotes divers towards a dangerous misbelief that they aren’t mentally impeded by narcosis on their deeper dives.

See also my article ‘Nitrogen Narcosis: Perceptions of Susceptibility’

The sedative effect of nitrogen narcosis degrades communication between different parts of the brain; especially in regard to accessing the different memory systems that enable higher levels of consciousness and cognition (anterograde amnesia).

Narcosis is essentially a slow progression through sedative effects towards unconsciousness as you go deeper (and the narcotic dose gets higher).

Nitrogen narcosis sedation described by impediments to Tulving’s “Three Component Model of Consciousness”

Before the use of helium became popularized and easily accessible for technical diving in SE Asia, I used to conduct very ‘deep air’ dives. These were frequently in the ranges of 70-90m  (230-300ft) depth.

The level of inert gas narcosis was, needless to say, exceptionally high. It is from those extreme experiences that I was able to assess and analyze the actual cognitive degradation that occurs from nitrogen narcosis sedation.

A cognitive model for nitrogen narcosis effect

It took me many years to find a cognitive model that suitably described mental functionality in a way that explained the progressive deterioration I had observed on my dives. That model was Endel Tulving’s three-component theory on consciousness.

Narcosis consciousness effect
Endel Tulving’s Three-Component Theory on Consciousness (1985)

Tulving describes three levels of consciousness (autonoetic, noetic, and anoetic) that were each reliant upon specific memory systems (episodic, semantic, and procedural).

As the sedative effect of nitrogen narcosis degrades communication with memory centers in the brain, the diver’s level of consciousness deteriorates; they lose profound cognitive abilities and – most importantly – lose the capacity to perceive that cognitive abilities are being lost.

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First Level Impediment – Autonoetic Consciousness and Episodic Memory

The first cognitive function to be degraded is the AUTONOETIC ability. This is essentially one’s metacognition; self-reflection, self-awareness, and self-diagnosis. It is the ability to perceive oneself and one’s own performance.

The degradation of autonoetic consciousness stems from an increasing inability to access EPISODIC memory – the personal experiences that a person normally uses to project their thoughts predictively or comparatively forwards and backward in time (“mental time travel“).

Autonoetic Consciousness: the capacity to be aware of one’s own existence as an entity in time.

Loss of autonoetic consciousness means that the diver rapidly becomes unable to recognize any mental impairment affecting them. This is why many divers deny that they suffer from narcosis effects. Unfortunately, the first thing they lose is the ability to diagnose themselves effectively.

Without episodic memory as a benchmark for unimpaired performance. As a result, it is impossible to recognize impaired performance.

One’s ability to make plans in advance also declines and ceases. As a result, cognition becomes restricted to “in-the-moment” reactions. This can be recognized as a profound limitation to situational awareness and has serious risk consequences.

Autonoetic nitrogen narcosis sedation

Likewise, degradation to episodic memory can be considered as a loss of ‘experience’. As such, the past lessons that a diver learns and holds in mind become inaccessible. As a result, nothing provides them with warnings or solutions based on similar events they’ve experienced before.

Episodic Memory: a type of long-term memory that involves conscious recollection of previous experiences together with their context in terms of time, place and associated emotions.

Loss of episodic memory will also cause a progressive amnesia effect during the dive. Furthermore, reducing communication to the episodic memory during the dive becomes a barrier to accessing existing memories. In addition, it also diminishes the ability for new episodic memories to be created.

Back when I conducted very deep air dives, it was common to experience complete amnesia of the dive once surfacing. At that time, we were doing dives to identify virgin shipwrecks. As a result, any information not recorded on slates during the dives was lost by the time we got back to the boat.

To a lesser extent, at shallower depths, I still notice that my fine-detail memory from a dive will be very unreliable. This is most easily recognized when the same sites are also dived using trimix. Only then, very precise memories will be retained after surfacing.

Second Level Impediment – Noetic Consciousness and Semantic Memory

As the sedative effect increases with depth, the diver’s NOETIC consciousness will start to decline.

Noetic Consciousness: awareness of facts, concepts, words, and meanings but not of any connection to one’s own experience. The capacity to recursively introspect on one’s own subjective experience through time.

Noetic consciousness involves the SEMANTIC memory. This is the long-term storage of learned facts and familiarity. The result of losing semantic memory is a diminished awareness of objects and events.

As a result, divers lose mental representation of the situation. They are not processing the mental connections needed to operate equipment or perform procedures when required.

Mental representation: the mental imagery of things that are not actually present to the senses, i.e. that are not currently seen or sensed by the sense organs.

Degradation of a diver’s ability to mentally represent their dive is a significant reduction to their diving competency.

Noetic nitrogen narcosis sedation

Mental representation is a definitive function of expertise. As such, it is a diver’s ability to mentally represent (or ‘visualize’) their dive in higher levels of detail. Obviously, that visualization is an important tool before, during, and after dives. As such, mental representation is a major factor enabling them to conduct more challenging dives.

The loss of semantic memory can also be directly recognized through increasing difficulties holding information immediately in mind: for instance, checking an SPG reading then quickly forgetting what the read was… and had to recheck it again shortly afterward.

Semantic Memory: the memory of meaning, understanding, general knowledge about the world, and other concept-based knowledge unrelated to specific experiences

The decline in noetic consciousness diminishes the ability to judge and react. Anything that is not directly stimulated by external events or objects will not be considered. Nothing can be ‘held in mind’.

Third Level Impediment – Anoetic Consciousness and Procedural Memory

If the diver continues to go deeper, increased inert gas partial pressure will start affecting their ANOETIC consciousness.

Anoetic Consciousness:  the rudimentary state of affective, homeostatic, and sensory-perceptual mental experiences, not involving or subject to intellectual or cognitive processes.  A state of knowledge or memory in which there is no consciousness of knowing or remembering. Anoetic consciousness is a corresponding kind of “unknowing knowing” in which one is aware of external stimuli but not of interpreting them.

Anoetic consciousness is the objective capacity to respond to direct stimulus. It is a person’s capacity to understand the outside world and external stimuli. Emotional cognition is considered at the level of anoetic consciousness.

This level of consciousness involves PROCEDURAL memory: the skills and procedures a person learns to perform over time.

Procedural memory: the system in charge of the encoding, storage, and retrieval of the procedures that underlie motor, visuospatial, or cognitive skills.

Losing anoetic consciousness means the diver will become steadily worse at equipment operation and following well-known procedures – if they have to be consciously recalled.

Anoetic nitrogen narcosis sedation

Skills, procedures, and protocols that have been deeper ingrained through substantial practice and experience may persist longer. This is a result of these functions becoming automated subconsciously in the working memory.

The unconscious ingraining of dive functions at higher levels of expertise may be an explanation of why some elite-level divers consider that they “adapt” to narcosis over time.

Eventually, as the nitrogen narcosis effect continues to increase, the diver would become unable to complete any type of mental or physical function. This is a type of ‘eyes open catatonia‘. Progress further and full unconscious occurs.

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Nitrogen narcosis sedation references:

  1. Memory and consciousness. Tulving, E. (1985). Canadian Psychology / Psychologie canadienne, 26(1), 1–12.

  2. Varieties of consciousness and levels of awareness in memory. Endel Tulving In A. D. Baddeley & Lawrence Weiskrantz (eds.), Attention: Selection, Awareness,and Control. Oxford University Press (1993)

  3. Varieties of Memory and Consciousness: Essays in Honor of Endel Tulving.Henry L. I. Roediger & Fergus I. M. Craik (eds.) – 1989 – Lawrence Erlbaum.
  4. Memory, Consciousness, and the Brain: The Tallinn Conference.Endel Tulving – 2000 – Psychology Pr.
  5. Episodic Memory and Autonoesis: Uniquely Human.Endel Tulving – 2005 – In Herbert S. Terrace & Janet Metcalfe (eds.), The Missing Link in Cognition: Origins of Self-Reflective Consciousness. Oxford University Press. pp. 3-56.


Andy Davis Technical Sidemount Wreck Diving Subic Bay Philippines RAID Courses Training

About The Author

Andy Davis is a RAID, PADI TecRec, ANDI, BSAC, and SSI-qualified independent technical diving instructor who specializes in teaching sidemount, trimix, and advanced wreck diving courses.

Currently residing in Subic Bay, Philippines; he has amassed more than 10,000 open-circuit and CCR dives over three decades of challenging diving across the globe.

Andy has published numerous diving magazine articles and designed advanced certification courses for several dive training agencies, He regularly tests and reviews new dive gear for scuba equipment manufacturers. Andy is currently writing a series of advanced diving books and creating a range of tech diving clothing and accessories.

Prior to becoming a professional technical diving educator in 2006, Andy was a commissioned officer in the Royal Air Force and has served in Iraq, Afghanistan, Belize, and Cyprus.

In 2023, Andy was named in the “Who’s Who of Sidemount” list by GUE InDepth Magazine.

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