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

Synopsis of my Understanding of Consciousness

 

· Consciousness is an emergent property of a biological network of neurons resulting from billions of years of evolution.

· The objective of the scientific study of consciousness is to understand the biological basis of consciousness, sometimes called the neural correlate of consciousness (NCC).

· Control of movement is the ultimate result of neurological activity. (1) Cognitive activity for prediction, and (2) cognitive, memory and emotional activity for value judgments and decisions comprise the brain contributions to movement control.

· Consciousness serves to assist animals in their struggle for survival in a competitive environment. The brain serves as a reality emulator for prediction and planning.

· Consciousness is the moment-by-moment convolution of a neural subnetwork representing a perception within the activated subnetwork context of synaptically (etched/encrusted/ingrained/embedded/inscribed/imprinted/embossed) memory comprising ‘the self.’ Edelman terms this convolution of present mental image with lifelong memory the “Remembered Present.” Input from the senses is not required for consciousness; an imagined image  or a restored memory image can serve as the image convolved with lifelong memory.

· The brain's evolution over millions of years has resulted in a three-level modularity of (1) brainstem structures, (2) limbic system structures, and (3) neocortex and attendant subcortical structures. The brainstem functions to provide gross stability and unconscious support for neural operations. The limbic system provides evolution-engraved quick responses for external encounters. The neocortex provides culturally-refined responses that constrain the extremes of the limbic system.

· A person' s individuality as a person is represented in the neurons and synapses, thus forming the molecular signature, or "the self," of the person.

· The self is the totality of what an organism is physically, biologically, psychologically, socially, and culturally. (LeDoux; Synaptic Self, 31)

· Although the self is comprised of the nervous system’s entire ensemble of synapses whose efficacies are the legacy of genetic endowment together with life experiences encrusted in synaptic patterns, the sense of self arises from neural activity pattern in a portion of the network. A small and dynamically changing portion of the neural activity becomes conscious at any moment as the dynamic core.

· Your handwritten signature is the legal manifestation of your Self.

· Consciousness is mediated by a “dynamic core” of ever-changing neural activity in the thalamocortical system, reentrantly circulating within and between the thalamus and cortex, and perhaps including other structures, on a millisecond-by-millisecond basis. Consciousness arises as an emergent property of this neuronal network activity.

· Consciousness is supported by unconscious processes, including stereotype movements referred to by several related ad hoc names and definitions, including Central Pattern Generators (CPGs) and Fixed Action Patterns (FAPs) of movement: Innate FAPs of infant sucking, crying, sneeze, hiccups. Learned CPGs of walking, riding bicycle, finger movements of violin, piano, keyboard typing; Emotional FAPs, facial grimace, laugh. FAPs of vocal movements in speech. An infant learning to talk is a process of developing FAPs for speech. FAPs are thought to originate in the basal ganglia and associated neural circuitry.

· It is useful to distinguish two kinds of consciousness: (1) human-type conscious and (2) core consciousness.

· Human-type consciousness includes a sense of time from the distant past to the remote future. The ability to conceive ideas and manipulate ideas for planning of future movements and action is a major distinguishing feature of human-type consciousness. The brain is a reality emulator for planning action. Human-type consciousness also has the capability for a rich language. Human-type consciousness is founded on and includes core consciousness.

· Core consciousness has a sense of awareness of the present, which is based on a sense of self. The sense of self is based on the proto-self, the unconscious functions of such things as the hypothalamus and autonomic nervous system. Through the senses of vision, hearing, touch, taste, smell, core consciousness provides an awareness of the present world.  Cognition and emotion provide basis for motivation for action. Innate and learned FAPs support movement control dictated by motivation.

· The dynamic core of consciousness is dependent on activity in a subset of thalamocortical loops together with activity in a subset of the cortex itself, along with a few other possible areas. No specific neurons or loops within the areas are required. The size and spatial distribution of the dynamic core can vary widely with the intensity of momentary thoughts. Neurons and synapses comprising the dynamic core are used and reused in varying arrangements on a basis of about 10 milliseconds as thoughts change. The minimal neural correlate of consciousness is currently unknown but may become more clearly defined in future decades.

· Functionality of the dynamic core is best understood as a dynamic network of gestalts composed of assemblies of neurons. Many gestalts of various sizes are dynamically recruited into a hierarchical assembly mediated by instantaneously active synapses.  This momentary consciousness gestalt varies in time from tens to a few hundred milliseconds.  The consciousness gestalt varies in size from many tiny gestalts during reverie to a large gestalt embracing many smaller gestalts during ponderous thought.

· Patterns of neural signal traces in the dendritic trees of neurons, dynamically connected momentarily by efficacious synapses, sculptured by genetics and experience, mediate neural network activity, an ever-changing subset of which forms the dynamic core of consciousness.

· Consciousness is supported by areas in the brain stem and by the hypothalamus. Damage to certain of these areas leads to loss of consciousness or death. Sleep is a natural loss of consciousness controlled by these areas. General anesthetics influence these areas. Coma is caused by lack of function of certain of these areas. Vegetative state or “brain death” is the result of the residual function of these areas with no activity in the thalamocortical loops or cortex.

· The brain has modular anatomy and functionality. Evolution has formed the brainstem area, the limbic area, and the cortex. Neocortex is anatomically organized as six layers with cortical columns extending through the layers. Language for most humans is centered in the left hemisphere in Broca's area and Wernicke's area.

· The hypothalamus has many small subregions whose functions are to regulate hunger, thirst, temperature, sexual behavior, and similar body operations.

· Emotions are among the very oldest of our brain properties.

· Amygdala is the part of the limbic system most specifically involved with emotional experience.

· Sensory processing and interpretation is concentrated in the occipital, parietal and temporal lobes, while higher cognitive functions are more dominant in the frontal lobes. Vision, which has been more intensively studied than the other senses, has more than 30 functional areas identified. Visual processing in occipital cortex separates into the "where" pathway in parietal cortex and the "what" pathway in temporal cortex.

· Memory is a central component of the brain mechanisms that lead to consciousness. Memory is not simply recall or readout of information coded in synapses, but rather involves a regeneration of the original episode, semantics or procedure in terms of synaptic changes created by the original experience. The biological mechanisms of short-term and long-term memory continue to be intensively researched. The mechanism of long-term potentiation (LTP) alluded to by Donald O. Hebb has provided much insight. Memory can be mediated by circulating neural signals in the prefrontal cortex and association cortices; or by widespread modification in the brain’s synapses, including modifications in ion concentrations, ion channels, neurotransmitters or their receptors; or by structural modifications in dendrites, spines, or receptors. The combinatorics and relational associations of a million billion (10¹⁵) synapses provides an essentially limitless state-space of mental images.

· Plasticity of Synapses Mediates Memory. Biochemical changes in the synapses mediate memory in the relative near-term, whereas gene expression and protein changes in synapses and dendritic tree structures are consolidated over time for hippocampus-independent long-term memory. Neural signals activate a widespread but sparse  memory trace that most closely conforms to a synaptic efficacy pattern established by prior neural activity.

· Hippocampuses, which are evolutionarily ancient structures deep inside the temporal lobes, are involved in the memory consolidation process whereby biochemical synaptic efficacies of short-term memory traces in cortex dendritic tree synapses become gene-expressed, protein-inscribed synaptic efficacies of long-term memory.

·  Short-term memory gets consolidated into long-term memory.

· The hippocampus is not required for consciousness (classical patient HM), although it is required to form new declarative memories. It seems clear that procedural memory operates unconsciously, and hence does not require the hippocampus. The distinctive mechanisms of working memory, declarative memory (episodic and semantic), and procedural memory together with the effects of time duration and memory consolidation continue to be intensively researched.

· 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 iteratively 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 iterative neural activity generates a band of gamma (~40-Hz) oscillations in the normal waking state. The converged state of the dynamic core can change as individual thoughts change on an approximate 100 ms basis. 

· Simultaneity of neuronal activity arising from intrinsic oscillatory electrical activity, resonance, and coherence are at the root of cognition. (Llinás; I of the Vortex, 12)

· The term ‘synchronization’ should be interpreted broadly to mean ‘coherence of neuronal assemblies’ at the group level, not necessarily synchronized individual neuronal firing.

· Simultaneous processing of vast numbers of autonomous local circuits leads to gamma oscillations at the higher frequencies detected in EEG. Reentrant neural activity in more widespread neural circuits leads to lower frequency oscillations in the power spectrum.

· Neural network activity with its ubiquitous recurrent and reentrant circuitry generates electrical signals that can be detected on the scalp (Electroencephalogram EEG) and by invasive probes into the brain.  The spectral frequencies of these neural signals have a power law characteristic, displaying an inverse linear relationship on a log-log plot.  This kind of relationship is called "pink noise."

· The brain remains continuously active from an early time in the prenatal embryo until a time of accidental trauma, disease, stroke or death when the neurons and synapses no longer function. When the neurobiological basis of the dynamic core ceases to function, consciousness ceases.

· At the very end, as death takes hold, everything stops for us as we know it.  Consciousness departs. (Horstman; Healthy Aging Brain, 197)

 

 

 

 

Link to — Introduction to Consciousness

Link to — Consciousness Subject Outline

Further discussion -- Covington Theory of Consciousness