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

Covington Theory of Consciousness

I’ll lay out here my theory of consciousness based upon my understanding of statements made by experts.

Consciousness -- an Emergent Property of Neuronal Network Activity

Consciousness is an emergent property of neuronal network activity in the brain.

Consciousness is spatially multiple yet effectively single at any one time.  It is an emergent property of noncommitted and divergent groups of neurons that is continuously variable with respect to and always entailing a stimulus epicenter. (Greenfield; Centers of Mind, 97)

Consciousness is the sustained, synchronized ~40 Hz electrical oscillation among the brain circuits. (Ratey; User's Guide to Brain, 136)

Brains can have consciousness as an emergent property. (Searle; Mystery of Consciousness, 13)

Consciousness is an emergent property arising from the self-organization of concurrently active but spatially distributed regions of the brain; there is no central organizer and no unique location where it comes into existence. (Johnston; Why We Feel, 124)

Consciousness is spatially multiple yet effectively single at any one time. It is an emergent property of non-specialized and divergent groups of neurons (gestalts) that is continuously variable. (Johnston; Why We Feel, 124)

Consciousness is an emergent property that depends upon activity within large neural gestalts (dynamic core), whose size is regulated by arousal. (Johnston; Why We Feel, 124)

Scientific meaning of emergent -  The whole may not be the simple sum of the separate parts. The whole can be understood from (1)  behavior of the parts plus (2) knowledge of how all the parts interact. (Crick; Astonishing Hypothesis, 11)

Allan Hobson has stated some Building Blocks of Consciousness.

 

Network of Neurons Interconnected via Synapses

Projection neurons and interneurons are major players in the neuronal network. Synaptic connection is via chemical neurotransmitters. Most of the rapid synaptic communication is via glutamate for excitation and GABA for inhibition.  Modulatory neurotransmitters, using their own special receptors, influence the excitability of neurons.

Human-type Consciousness

Human-type consciousness is mediated by a greatly expanded brain facility compared with other animals. Most prominent among these is a greatly expanded frontal cortex and the uniquely human Broca and Wernicke language areas. The hugely expanded frontal cortex, facilitating cognitive reasoning, thinking, planning and decision making has coevolved with the special language areas. Human-type consciousness is dependent upon the function of Core Consciousness.

 Core Consciousness

Core consciousness is a "convolution" of a mental image with the sense of self.

Primary consciousness (Core Consciousness) comprises sensation, perception, emotion, learning, geographic orientation, instinct, primary intention; all of these can be operationally defined in lower animals.  (Hobson; Consciousness, 84)

The terms primary/secondary, core/extended, core/human-type have been used to describe human consciousness as distinguished from the consciousness experience by animals. Here are paraphrases from Allan Hobson:

Primary components of consciousness are those experienced by all mammals, including human infants: sensation, perception, attention, emotion, instinct, movement. (Hobson; Consciousness, 16)

Secondary components of consciousness are those experienced only by adult humans: memory, thought, language, intention, orientation, volition. (Hobson; Consciousness, 17)

Consciousness -- "Convolution" of a Mental Image with the Sense of Self

Consciousness is a ‘convolution’ (my choice of word; it's hard to precisely convey the concept) of a current mental image with a neural network image of the self. The result is what Edelman calls the “remembered present” of consciousness.

This link will give my interpretation of Edelman's core consciousness:

 

 

 

 

 

 

 

 

 

Sense of self

Sense-of-self is the basis of consciousness.  The self is a neuronal network pattern of memory established by genetics together with embryonic and early childhood environmental experience.

The interaction of the neural network activity of a current mental image together with the neural network activity representing the self constitutes what Edelman calls the “remembered present” of consciousness.

The interaction of this current mental image neural network activity with the self neural network activity occurs in the dynamic core of the thalamocortical system.

Mental image

Mental images are the mental constructs we normally experience in consciousness. Neural patterns or neural maps or maps are the neural representation of the mental images.

Perception, Memory, Consciousness

Perception, memory, and consciousness are closely intertwined.  The basis for consciousness is "the self" comprised of the entire ensemble of neurons and their synaptic connections laid out by genetics and continually modified via neuronal plasticity through a lifetime of experience and interactions with the environment. A perception is the activation of a neural subnetwork within the self. A memory is the reactivation (or reconstruction) of a perception. 

Neuron assemblies

Basic unit of the selective process is not the individual neurons but the neuronal group. (Ratey; User's Guide to Brain, 142)

There are perhaps 100 million neuronal groups in the brain, and they range in size from 50 to 10,000 neurons. (Ratey; User's Guide to Brain, 142)

Because single neurons have small and uncertain effects on other neurons, the cortical description must be carried out in terms of stochastic neuronal populations rather than at the level of individual cells.

Neurons are only effective in groups, working toward a single goal, such as discriminating color or producing emotion. (Ratey; User's Guide to Brain, 142)

By virtue of their size, neuronal groups can compensate for individual cell deaths. (Ratey; User's Guide to Brain, 142)

Brain' s Three Topological Networks

The brain has three topological networks: (1) thalamocortical system, (2) parallel system through basal ganglia, cerebellum, and thalamus, (3) diffusely projecting modulatory neurons from the brainstem and midbrain.

Thalamocortical System

Intralamina nuclei of the thalamus receive and project long axons to many areas of the brain. Information flowing back and forth between the intralamina nuclei of the thalamus and the rest of the brain modulates itself, setting up a regular loop of electrical activity oscillating to a synchronized beat of ~40 Hz. This thalamocortical system of reentrant neuronal activity contains a dynamic core subnetwork that mediates consciousness. During waking there are large burst of electrical activity in every brain region, in addition to the steady 40 Hz oscillation. During non-dreaming sleep, the intralaminar nuclei are inactive; there is no 40 Hz oscillation. During dream sleep (REM sleep), the 40 Hz background oscillation returns, and is again accompanied by heavy regional activity, similar to that which occurs during waking.

Reentrant activity leading to recursion is a fundamental feature of thalamocortical activity, and indeed nearly all neural activity.  Reentrant activity is not simple feedback but functions in a network as recursive multiple pathways, which update cyclically on a time scale of tens to hundreds of milliseconds, rapidly converging to the dynamic core’s synaptically connected neuronal network mediating an instantaneous thought. This cyclical neural activity generates gamma (~40-Hz) oscillations in the normal waking state.

Research experiments indicate that humans perform near-optimal Bayesian inference in a wide variety of tasks, ranging from cue integration to decision making to motor control. This implies that neurons both represent probability distributions and combine those distributions according to a close approximation to Bayes' rule.

Parallel System through Basal Ganglia, Cerebellum, and Thalamus

A set of parallel, unidirectional chains link the cortex to a set of its appendages, each with a special structure -- the cerebellum, the basal ganglia, and the hippocampus. (Edelman; Universe of Consciousness, 45)

Nearly all regions of the neocortex project directly to the striatum, making the cerebral cortex the source of the largest input to the basal ganglia, by far. (Purves; Neuroscience, 418)

Of the cortical areas that innervate the striatum, the heaviest projections are from association areas in the frontal and parietal lobes, but substantial contributions also arise from the temporal, insular, and cingulate cortices. (Purves; Neuroscience, 418)

The fact that different cortical areas project to different regions of the striatum implies that the corticostriatal pathway consists of multiple parallel pathways serving different functions. (Purves; Neuroscience, 419)

Efferent neurons of the internal globus pallidus and substantia nigra pars reticulata together give rise to the major pathways that link the basal ganglia with upper motor neurons located in the cortex and in the brainstem. (Purves; Neuroscience, 423)

Diffusely Projecting Modulatory Neurons

Fan-out meshworks of diffusely projecting neuromodulatory neurons emanate from brain stem and midbrain nuclei. Reentrant circuits of the thalamocortical system are modulated by these neurotransmitters.

Modulatory neurotransmitters, operating in seconds, minutes or longer, often emanate from widely-projecting neurons clustered in sub-cortical ganglia. Chemical and functional changes in the synapses of neurons provide many of the short-term and longer-term changes such as memory in the brain function of neural networks.

Major modulatory systems of the brain. (1) noradrenergic, (2) adrenergic, (3) dopaminergic, (4) serotonergic, (5) cholinergic, (6) histaminergic. (Kandel; Principles of Neural Science, 890)

Small collections of neurons can deliver a dose of dopamine, norepinephrine, serotonin or acetylcholine to widespread regions of the brain including the cerebral cortex and basal ganglia.

Dopaminergic neurons send their axons to the nucleus accumbens, the striatum, and the frontal cortex, three structures thought to be involved in motivation.

Dynamic core

The Dynamic Core hypothesis formulated by Gerald Edelman is the fundamental neurobiological foundation of my concept of consciousness. The dynamic core is a constantly changing hierarchical web of reentrant neural activity (perhaps 10-20% of total neural activity) that mediates a mental pattern of thought at any one instant. The mental pattern supported by the dynamic core can be a thought pattern during the waking state, or it can be the thought pattern during the dreaming state. The thalamocortical activity begins prenatally and continues uninterrupted until death or until an abnormal state such as brain death.

Gestalts

Consciousness is an emergent property of nonspecialized and divergent groups of neurons (gestalts) that is continuously variable with respect to, and always entailing, a stimulus epicenter. Size of the gestalt, and hence the depth of prevailing consciousness, is the product of the interaction between the recruiting strength of the epicenter and the degree of arousal. (Greenfield; Centers of Mind, 104)

Hierarchy of Gestalts

The enormous associative capabilities of the dynamic core are ideal to link or hierarchically organize a series of preexisting unconscious routines into a particular sequence. (Edelman; Universe of Consciousness, 187)

Synchronization Binding of Gestalts

A group of neurons can contribute directly to conscious experience only if it is part of a distributed functional cluster that, through reentrant interactions in the thalamocortical system, achieves high integration in hundreds of milliseconds. (Edelman; Universe of Consciousness, 144)

Minimal Functionality Of Consciousness

At the current state of science, the minimal functionality required for consciousness is currently unknown.  There is much uncertainty in borderline areas such as Persistent Vegetative State.

Pulse-like behavior of neurons and the neural network

Thousands of dendrites comprise the input terminals of a neuron. Thousands of other neurons and their axons form synapses with these dendrites. Some of these input axons are excitatory, some are inhibitory, and some are modulatory. The neural signals incoming to the receptors are brief (a millisecond or so) and must be considered as pulses. If the summation of these incoming pulses exceeds a momentary threshold at the neuron’s soma, the neuron will “fire” a signal down its axon.

Stochastic nature of neuronal behavior

An individual neuron does not fire in a deterministic fashion. The thousands of synaptic inputs on the dendritic tree of a neuron function on a population basis to result in a probabilistic influence on the neuron’s firing. Assemblies of perhaps ~1000 neurons  within a volume of ~0.1 mm³ may be sufficiently correlated to comprise a physiologically meaningful neural signal.

Because single neurons have small and uncertain effects on other neurons, the cortical description must be carried out in terms of neuronal populations rather than at the level of individual cells. (Stevens; Cortical Theory, 242)

The overall stochastic nature of neuronal behavior suggests that the physiologically meaningful signal from cortex should be the average firing rates of a population of perhaps 100 to 1000 neurons near a particular cortical site. (Stevens; Cortical Theory, 243)

Bayesian Inference

Psychophysical experiments indicate that humans perform near-optimal Bayesian inference in a wide variety of tasks, ranging from cue integration to decision making to motor control. (“Bayesian Inference in Brain Functionality,” Nature Neuroscience, published online 22 October 2006)

Sensory Systems

Within each modality, sensory inputs are processed by activity in a constellation of cortical regions that analyze specific aspects of the stimuli to continuously update the dynamic neuronal network model of reality. (Llinás & Paré; Brain Modulated by Senses, 5)

Dreamlike state modulated by the senses

Dreaming and wakefulness are so similar from electrophysiological and neurological points of view that wakefulness may be described as a dreamlike state modulated by sensory input. (Llinás & Paré; Brain Modulated by Senses, 6)

Imagery and emotions of dreams are always with us, riding in our nonconscious, and we change state from waking to dreaming, this information is able to cross into consciousness. (Hobson; Dreaming as Delirium, 209)

Brain Functions as a Reality Emulator

The brain functions as a reality emulator to assist the animal with prediction and decisions to enhance survival.  In this process the brain performs near-optimal Bayesian inference to continuously update its dynamic neuronal network model of reality with the stream of input data from the senses.

Brain operates as a reality emulator. (Llinás; I of the Vortex, 13)

The brain constructs an explicit, multilevel, symbolic interpretation of parts of its environment.  (Koch and Crick; Neuronal Basis, 109)

Brain is a system whose processes create states of consciousness in response not only to sensory inputs but also to internal signals representing expectations based on past experiences.  (Logothetis; Window on Consciousness, 89)

Perception-action cycle is the circular processing of information between posterior and frontal cortices in the integration of sensory -- motor behavior, as well is in higher cognitive activities such as language. (Fuster; Cortex and Mind, 218)

Declarative memory functions to represent objects and events in the external world and the relationships between them.  (Squire & Kandel; Memory, 99)

The illusion of the brain's reality emulator is so powerful and ubiquitous that we come to believe that objects really are red, or hot, or bitter, or sweet, or beautiful, and we usually do not ask how or why we impose this structure on our physical world, or how the structure relates to our biological survival. (Johnston; Why We Feel, 13)

 

Memory Is Necessary for Consciousness

Memory is a central component of the brain mechanisms that lead to consciousness. (Edelman; Universe of Consciousness, 93)

Memory is not a single entity but is composed of different systems.  Only one of these systems is accessible to awareness, the declarative memory system. (Squire & Kandel; Memory, 159)

Cognitive psychologists subdivide short-term memory into two major components: immediate memory and working memory. (Squire & Kandel; Memory, 84)

Memory -- Declarative, Procedural, Emotional

Three major memory systems in the brain. (Eichenbaum; Neuroscience of Memory, 200)

Hippocampus and Memory

 

Working Memory

Working memory is a momentary network-assembly of neurons, principally in the frontal cortex, that interact with most other modular areas of the brain to perform the higher levels of sensory processing, to arrive at decisions, and to produce commands for movement. Working memory is intimately related to the ongoing neural activity of the thalamocortical system. The memory function of working memory may be located in the widely distributed synapses in the brain, with principally control-functions in the frontal cortex and the thalamocortical system (diagram).

Working memory, the dynamic core, and the thalamocortical system are intimately related as the mediators of consciousness.

Working memory is one of the brain's most sophisticated capacities and is involved in all aspects of thinking and problem-solving. (LeDoux; Synaptic Self, 175)

Consciousness serves as a mental workspace, a very powerful mechanism for registering the environment and relating it to past experience, which can in turn be used to model the present, and using that model, to simulate and hence to predict the future and planned further action. (Baddeley; Working Memory, 314)

Working memory includes: (1) the central executive, (2) the phonological loop, (3) the visuospatial sketchpad, and (4) the episodic buffer.  Working memory functions of the frontal cortex interact with the parietal and temporal cortex, along with subcortical areas such as the basal ganglia and limbic system. Working memory and the thalamocortical system are closely related to consciousness.

Attention and Consciousness

Attention is necessary for consciousness. (Baddeley; Working Memory, 311)

In the real world, multiple streams of information reach our awareness, some of it relevant, some not for the task at hand. With the inherent capacity limitations of working memory, it is essential that only representations of task-relevant information are generated and maintained. An important aspect of goal-directed behavior is understanding the neural mechanisms underlying how task-relevant versus task-irrelevant information is differentially processed. (Gazzaley; Top-down WM, 197)

The brains of complex organisms are threatened with information overload.  In primates, about one million nerve fibers leave each eye and carry on the order of 1 MB per second of raw information. The brain' s attention mechanisms function to select the information of current relevance to the organism.

Key brain structure involved in attention is the thalamus, a large collection of cells located atop the brainstem in the center of the upper brain. (Hobson; Consciousness, 59)

Vigilance—or sustained attention—ensures that goals are maintained over time. (Parasuraman; Attentive Brain, 7)

Four main projection systems have been identified as playing functional roles in arousal and attention: (1) cholinergic basal forebrain, (2) noradrenergic nucleus locus coerulus (LC), (3) dopaminergic median forebrain bundle, (4) serotonergic dorsal raphe nucleus. (Parasuraman; Varieties of Attention, 227)

 

Pain  -- -- Pleasure

All feelings contain some aspect of pain or pleasure as a necessary ingredient. (Damasio; Looking for Spinoza, 123)

Pleasure is a key factor in controlling the motivated behavior of humans. (Kandel; Principles of Neural Science, 1007)

 

Amygdala and Fear

Pleasure Pathway

Stimulation of the nucleus accumbens in humans elicits smiling, laughter, pleasurable feelings, happiness, even euphoria. (Cardoso; Hardwired for Happiness, 173)

Emotion, Cognition, Motivation

 

Emotion

Emotions are among the very oldest of the brain's properties. Limbic system, hypothalamus, and brain stem intervene in body regulation and in all neural processes on which mind phenomena are based. Emotions are linked to the motor aspects of FAPs by access through the amygdala and the hypothalamus and their connectivity with the brain stem.

 The limbic system consists of a number of subcortical structures which are active in emotions and which are tightly interrelated with cortical functions.  In recent years, some neuroscientists have included the prefrontal cortex as a member of the limbic system, since it is often heavily involved in emotional activity.

Basic Emotions

Although there is no consensus among experts, six so-called primary or universal emotions are often stated, for example: Happiness, Sadness, Fear, Anger, Surprise, Disgust.

Eight basic emotions: surprise, interest, joy, rage, fear, disgust, shame, anguish - controlled by 'hardwired' brain systems. (LeDoux; Emotional Brain, 112)

Secondary Emotions

Many secondary emotions could be proposed, such as the social emotion ‘embarrassment,’ although I don't think it's helpful to haggle over these possibilities.

We often evaluate the self and others from social comparisons. We feel envy when the target person has superior and self-relevant characteristics. Schadenfreude occurs when envied persons fall from grace.

Feelings

Conscious experiences of emotions -- the feelings. (LeDoux; Emotional Brain, 82)

A feeling is the perception of a certain state of the body along with the perception of a certain mode of thinking and of thoughts with certain themes. (Damasio; Looking for Spinoza, 86)

Higher order consciousness leads to a rich cognitive, affective, and imaginative domain -- feelings (qualia), thought, emotions, self-awareness, will, and imagination. (Edelman; Bright Air, 198)

Normal consciousness can take stock of emotions in the form of feelings, feelings can generate a new line of emotions that confers behavior. (Damasio; Feeling of What Happens, 101)

Conscious experiences, like sensations and feelings, evolved because they dictated a dynamic organization of the nervous system that could prioritize experiences and distinguish between environmental events or circumstances that had a real influence on biological survival. (Johnston; Why We Feel, 127)

Why do we have so many different feelings, like love, pride, fear, and sadness?  All such feelings are evolved "omens" of our reproductive success that amplify the consequences of physical and social events that have some bearing on our gene survival. (Johnston; Why We Feel, viii)

Consciousness, in the form of working memory, has become an important part of the way LeDoux thinks about emotions, especially feelings. (LeDoux; Synaptic Self, 199)

Cognition

Ability to solve spatial problems efficiently is special, apart from straight logical or linguistic ability. (Gardner; Frames of Mind, 175)

One reason human cognition is so powerful is because we have language in our brains, which exponentially increases the ability to categorize information. (LeDoux; Synaptic Self, 177)

The emergence of cognitive capacities underlying language changed the way the brain works, making it possible for human brains to think and experience events in ways that other brains cannot. (LeDoux; Synaptic Self, 198)

Multiple Intelligences

Humans have great variety in their mental capabilities involving multiple intelligences; a few examples: (1) rapid, vivid conceptualization; (2) spatial visualization of geometrical objects; (3) mathematical, logical, analytical reasoning; (4) facility with mental arithmetic; (5) facility with language; (6) poetic creativity; (7) musical creativity; (8) artistic creativity; (9) expansive memory; etc. Theory of multiple intelligences was developed in 1983 by Dr. Howard Gardner, professor of education at Harvard University.

Motivation

 

 Movement control

Movement is nearly always the functional result of wake-time brain activity.  Movement is facilitated in the brain and nervous system by a hierarchy of modular functionality I call FAPs, but known by a number of names.

Voluntary movement requires the coordinated activity of all complements of the motor system including the motor cortex, basal ganglia, thalamus, midbrain, cerebellum, and spinal cord.

Startle Response

 

Modularity of Brain

Consciousness is mediated by widespread neural activity in many of the modular areas of the brain. Consciousness is an emergent property of the cortical activity that mediates a particular momentary thought, and since thoughts are fleeting from moment to moment, the subset of neural activity for thoughts changes on a momentary basis. The dynamic core of consciousness neural activity is focused in the thalamocortical system (thalamus and cortex reentrant circuits) but also includes working memory (frontal cortex with its subdivisions), emotional functionality of the limbic system, basal ganglia, cerebellum and other subcortical areas controlling movement, and the modulator areas of the brain stem.

 

 

 

A very significant paper on consciousness – Giulio Tononi and Gerald Edelman, in my opinion, authored a very significant paper on the scientific principles of consciousness.  However, it can seem very arcane, so I have rendered my paraphrase version which should provide the gist of their thought in a form much more readable and understandable.

 

 

 

Link to — Consciousness Subject Outline

Core Consciousness Recursive Functionality