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

Introduction to Consciousness

Consciousness is an emergent property of a biological neural network. Human brains have evolved over hundreds of millions of years from pre-human animals that have been successful in their struggle for survival. Each of us has a brain that is a result of the genetics of our ancestors together with the unique neurological development, both prenatally and postnatally, our brains have experienced in the environment. The intricate mechanisms in our synapses are the result of billions of years of molecular and cellular evolution. Our consciousness and our uniqueness as an individual person are stored in the functionality of more than 100 trillion synapses in our brain.

Consciousness not precisely defined

The term consciousness is not precisely defined, nor should it be in the current state of the science. We should not nitpick words and definitions in current descriptions relating to consciousness. If we get the gist of an idea being alluded to, that should be sufficient at the present time.

Human-type Consciousness founded upon Core Consciousness

Each of us has human-type consciousness, a huge expansion of the core consciousness usually associated with mammals such as dogs. I discuss core consciousness and human-type consciousness in separate sections.

Consciousness: ‘convolution’ of a current mental image with 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. Edelman uses the term ‘remembered present’ to express this idea. ‘Remembered’ conveys the notion of an accumulated store of individualized synaptic functionality representing the self. ‘Present’ conveys the notion of a current mental image, which can result either from sensory input data, or from a [reconstruction] of some past memory, or from some imagined thought. Working memory in the prefrontal cortex is likely to invoke neuronal network activity in other brain areas to synchronize into cyclical thalamocortical activity comprising the dynamic core. The images generated by fMRI studies give some indication of the brain activity that may include the dynamic core involved in various tasks.

Sense of Self

A person's individuality and personality are stored in the functionality pattern of many billions of synapses whose connectivity is determined by genetics and the environment in which the brain develops. Only a small subset of the brain’s 10¹⁵ possible synapses actively represents a person's sense of self. The synaptic pattern representing the sense of self is established over a lifetime of experience, with the detailed connectivity changing dynamically as a person experiences the environment. Keep in mind that the no specific set of neurons is required for the sense of self. Only the pattern of synaptic connectivity is preserved; individual neurons representing this connectivity pattern can vary.

Consciousness requires the neuronal representation of the self (Antonio Damasio).

Mental Image

Thalamocortical activity, supported by subcortical activity, mediates a neural representation of a worldly object or concept, either perceived or imagined. This neural representation is called a “mental image.” This momentary ‘mental image’ representing a thought is ‘convolved with’ the neural representation of ‘the self’ to yield core consciousness.

Gestalts in Neuronal Assemblies

Mental images are likely to be formed from gestalts of neuronal assemblies in the neural network. I enjoy experiencing my brain forming gestalts as I watch cloud formations in the sky when fracto-cumulus clouds break up into cloud-free fair weather. I have fun visualizing lambs, puppies, old men with beards, etc.

Complex mental images are likely to be formed from hierarchies of gestalts. I believe the brain forms gestalts comprised of assemblies of neurons recursively linked via synapses.

Perception

Our waketime daily lives are a continuous sequence of perceptions. In my understanding, perceptions are comprised of hierarchies of gestalts. Non-conscious background neural activity includes thousands of gestalts comprised of independently circulating neural signals. As perceptions are formed, appropriate hierarchies of these gestalts are recruited by synchronous phase-locking of 40-Hz activity into a subnetwork of the ‘dynamic core.’ As we all know, perceptions (thoughts) change on the basis of about half a second or less.

Bayesian Inference and Recursion

Without getting too technical, let me just alert you that much of the brain's neuronal activity can be interpreted as an implementation of the statistical technique of Bayesian inference with recursion. If you are inclined to have an interest in these topics, you may be interested when I mention them in further discussions.

Consciousness mediated by the Dynamic Core

My current hypothesis is that consciousness is mediated by a dynamic core (Gerald Edelman) of thalamocortical activity, which is ever changing on the basis of about 10 ms. Neurons comprising the dynamic core are ever changing. A particular thought at one instant can be comprised of a connected network of some hundreds of millions of neurons. If thoughts change and moments later return to the same thought, the individual neurons representing the thought will likely be slightly different. Thus the network comprising a particular thought need not require a precisely determined network of neurons. Individual neurons will sometimes (often fleetingly) participate in the dynamic core, but most often will not be a part of the dynamic core. Individual neurons comprising the dynamic core can be reused and connected differently 10 ms later as the dynamic core changes to mediate a different thought. The size of the dynamic core and the number of neurons involved can change dramatically as the intensity of thought varies from reverie to intense cogitation. Each instantaneous dynamic core of consciousness is likely to involve some neurons in the prefrontal cortex constituting working memory.

Most scholars emphasize how the collective Gestalt-like traits of the brain and its networks are critical to understanding consciousness. (Koch; Quest for Consciousness, 311)

Minimal dynamic core required for consciousness

The minimal dynamic core required for consciousness is currently unknown, but may become more clearly understood in the future decades. Uncertain consciousness states such as Persistent Vegetative State (PVS) continually present a challenge for the clinical medical community.

Modularity of brain anatomy and functions

The brain is modular in a number of ways. Evolution has produced a distinct anatomical modularity in the brainstem, subcortical structures, and cortex. All of these structures have intricate anatomical connectivity and functionality. Here are some of the ways the brain's modularity can be considered:

Evolutionary and anatomical modularity of brain -- Brain Stem, Limbic System, Cortex -- approximately corresponding to reptiles, mammals, and humans in the evolutionary sequence.

Four lobes of cortex -- frontal, parietal, occipital, temporal.

Approximately 50 Brodmann areas of cortex.

Functional areas of cortex -- Boca, Wernicke, visual hierarchy, auditory, somatosensory, motor, hippocampus, prefrontal, cingulate, etc.

Neocortex has six fairly distinct levels.

Paleocortex such as hippocampus has three levels.

Cortex has modular columns extending through the six levels.

Fortunately, the brain's overall functionality can be considered in terms of three topological networks working closely together

Three Topological Networks of the Brain

The brain's neural network can be considered in terms of three topological networks, closely interworking together. The thalamocortical system forms the fundamental biological mechanism of consciousness, supported by other functionality. A set of parallel, unidirectional neural pathways link the cortex to a set of its appendages, each with a special structure -- the cerebellum, the basal ganglia, and the hippocampus. Fan-out meshworks of diffusely projecting neuromodulatory neurons emanate from brain stem and midbrain nuclei. These 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.

Thalamocortical system

The thalamocortical system consists of continuously-ongoing, reentrant neural signals between nuclei in the thalamus and neurons in all modular areas of the cortex. In general, neurons are never idle. Neurons fire at about 5 Hz in the quiescent state and at rates of 100 Hz or more in the active state. A subset of thalamocortical activity comprises the dynamic core of consciousness. The magnitude of the dynamic core varies greatly with the intensity of thought.

 The thalamocortical system mediating the dynamic core becomes active early in embryonic life and continues to be active until death or until trauma states such as brain death.

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. Cerebellum is concerned with the coordination and synchrony of motion, although it is also involved in aspects of thought and language. Basal ganglia are involved in the planning and execution of complex motor and cognitive acts. Hippocampuses, which are evolutionarily ancient structures deep inside the temporal lobes, are involved in the process whereby short-term memory gets transferred to long-term memory, and also spatial memory.

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. A number of amine chemicals are associated with states of arousal. Four of them are: (1) serotonin, (2) acetylcholine, (3) dopamine, (4) norepinephrine.

Neuronal Network

Human brains have billions of neurons that together make trillions of synaptic connections among one another. 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.

Neurons and Synapses

Neurons communicate information via neurotransmitters in synapses. A neuron’s thousands of dendritic synapses receive pulse-like input from other neurons. Whenever a large group of spikes arrives nearly simultaneously, a neuron will generate an action potential, which is transmitted down its axon. This near simultaneous arrival of input spikes creates pulse-like behavior.

Neurotransmitters

Neurotransmitter molecules diffusing across synaptic space between neurons mediate the transmission of information in the neural network. Neurotransmitters mediating the rapid flow of information are released from pre-synaptic terminals of one neuron and diffused in a millisecond or so to the post-synaptic receptor of another neuron. Modulatory neurotransmitters, operating in seconds, minutes or longer, often emanate from widely-projecting neurons clustered in sub-cortical ganglia.

Neuromodulatory Systems

Modulatory neural activity. Neurotransmitters.

Dendritic Trees and Stochastic Neuronal Behavior

Projection neurons typically have a dendritic tree with perhaps 10,000 synapses. Because neurons signals occur in the form of pulses of about 1 or 2 ms, a population of synaptic input signals on a neuron' s dendritic tree must combine in any given time interval of the few milliseconds to exceed the neuron’s threshold to cause the neuron to fire. The result is a stochastic firing behavior for an individual neuron. Groups of closely allied neurons tend to fire together resulting in a more deterministic behavior. The population-based functionality of neuronal groups means that specific individual neurons are not required, and the functionality of the neural network can survive the death of the few neurons. It also means that when synaptic patterns of memories are reactivated, a slightly different pattern of synapses will be involved for each memory activation.

Oscillation, Synchronization

Simultaneity of neuronal activity arising from intrinsic oscillatory electrical activity, resonance, and coherence are at the root of cognition. Simultaneity of neuronal activity is the most pervasive mode of operation of the brain. Neuronal groups that oscillate in phase, i.e. coherently, support simultaneity of activity.

Plasticity of Neural Connections

The configuration of the neural network is continuously in a state of flux via the plasticity of synaptic connections. The LTP (long-term potentiation) of Hebbian plasticity, which hypothesizes that ‘neurons that fire together wire together’, begins the network formation prenatally and continues with lifelong changes that modify the sensitivities of the brain’s 10¹⁵ synapses.

Memory -- Declarative, Procedural, Emotional, and Working Memory

Memory can be can be distinguished into several types, including declarative memory, procedural memory, emotional memory, and working memory. Edelman's idea of consciousness as ‘remembered present’ implies that distant-past (not via hippocampus) recall of declarative memory must be functional, as exemplified in the case of epilepsy patient H.M. Procedural memory is [probably] not required for consciousness.

Attention

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.

Human interaction with our environment involves a fluid integration of externally driven perceptual information that demands attention based on stimulus salience or novelty (bottom-up processes) and internally driven, goal-directed decisions concerning external stimuli or stored representations (top-down modulation).

Fear – Pleasure

Release of dopamine onto the nucleus accumbens appears to underlie all reward feelings. The dopaminergic projection from the ventral tegmental area (VTA) to the nucleus accumbens is a key feature of the pleasure circuitry.

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.

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.

 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.

Cognition

 

Motivation

As I view it, motivation to action arises from a range of neural signals ranging from (1) fear of a perceived threat to (2) groping for an expected pleasure. Joseph Ledoux states that interactions between the amygdala and nucleus accumbens contribute to motivation.

Motivational circuitry of the brain includes the prefrontal cortex, basolateral amygdala, and ventral pallidum. The dopaminergic projection from the ventral tegmen­tal area (VTA) to the nucleus accumbens is a key feature of the circuitry.

The motivational circuitry of the brain connects the prefrontal cortex decision process to the premotor cortex, which uses its FAPs along with FAPs stored in the basal ganglia and cerebellum to plan movement, followed by the motor cortex, which invokes FAPs in the brain stem and spinal cord to produce movement.

Movement Control

Movement control is nearly always the functional result of wake-time brain activity. In the course of normal conversation, for example, the brain activity of listening to a friend and composing your own thoughts is then followed by the muscular movements of vocalization of speech, facial gestures, and gesticulations of arm and body movements.

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, including gestures, synergy, schemas, motor programs, stereotypical patterns of movement, etc.

FAPs are most probably implemented at the level of the basal ganglia and put into context by the reentry of the basal ganglia output into the ever-cycling thalamocortical system.

In addition to voluntary movement, a person can experience involuntary movement in response to a startle reaction.  For example, a visual startle pathway goes via the subcortical structure of the superior colliculus to invoke motor FAPs of muscular body movement.

Friendly Conversation

Friendly conversation is a brain activity that involves much of the brain's functionality of consciousness. Visual and auditory senses provide input data for the language functionality. Cognition and emotion provide links to autobiographical memory and, via a neuronal process of Bayesian statistical inference, a continuous stream of new perceptions. Premotor cortex, basal ganglia, and cerebellum provide motor planning for all of the non-conscious movements and FAPs of voice, gestures, and emotional reactions. Motor cortex invokes FAPs in the brain stem and spinal cord to produce movement for vocal speech along with gestures and facial expressions.

Sleep and dreaming -- Memory Consolidation – Creativity

Experts hypothesize that memories are consolidated during sleep and dreaming. Dreaming is an altered state of consciousness, akin to those induced by psychedelic drugs in waking.

Complexity, Self-Organization, Emergence

Complex systems involve nonlinear interactions between a large number of simple elements. Self-organization reflects matter's incessant attempts to organize itself into ever more complex structures, even in the face of the incessant forces of dissolution of the second law of thermodynamics. Emergence reflects the incessant urge of complex systems to organize themselves into patterns.

Language and Consciousness

Language is probably not required for consciousness. (Zeman; Consciousness, 285)

 

 

Further discussion -- Covington Theory of Consciousness