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Scientific Understanding of Consciousness |
Consciousness and Neural Network Architecture
My current hypothesis is that the neural network’s dynamic core of consciousness requires sparse but widespread activity patterns in portions of working memory, the thalamocortical loops, and the limbic system for ongoing successive intervals of a few hundred milliseconds. A person' s individuality as a person is represented by the brain’s entire ensemble of neurons and synapses, thus comprising the molecular signature, or "the Self," of the person. A person’s sense of self is mediated by certain activated subsets of the Self. The brain's neural network is connected by synapses with synaptic efficacies established by genetics and continuously modified by ongoing experience. A sensory input pattern propagates into the brain's established synaptic efficacies pattern, activating a pattern of synaptic efficacies closely conforming to the sensory input pattern.
The neural network likely implements reentry and recursion as nested hierarchies of recursive loops . As a simplistic pedagogical example, we can consider the visual sensory cortex operating on perhaps a ~20 ms recursive cycle, the multimodal association cortex on perhaps a ~50 ms cycle, and the frontal cortex, with back projections to the posterior cortical areas, operating on a >1 second recursive cycle. The network hierarchy is a fractal network hierarchy characterized by the complexity property of 1/f distribution of "pink noise." This distribution can be detected in the power spectrum of the EEG. The Perception-Action Cycle (Joaquín Fuster) and the Convergence-Divergence Zones (Antonio Damasio) likely can provide the framework for the nested hierarchies and recursive loops. Computer Simulation (e.g. Edmund Rolls) of the neural network likely can provide much insight into network circuitry, which provides functionality and, concomidantly, the electrical pink noise of the EEG. 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.
The neural network is in a state of constant flux via the plasticity of synaptic connections. 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. The memory function of synapses in the neural network provides an essential aspect of consciousness. There are many local short-term memory circuits in the brain. Rehearsal and biochemical modification of synapses mediates the short-term memory function. Consolidation to long-term memory continues persistently, especially for emotionally tagged memories that are frequently and continually rehearsed. An individual neuron can be a part of many memory patterns. The ~10,000 synapses of the dendritic tree of a projection neuron would have a vastly different activity configuration for each of the many memory patterns in which it participates.
Link to — Basal Ganglia diagram
Link to — Cerebellum diagram
Known by a number of names, but in future decades likely to converge on generally accepted terminology, perhaps parcellated into subtypes with special nuances.
Link to — Fear - - - - Pleasure
Link to — Limbic System pathways The cognitive brain of the cortex and the emotional brain are tightly entwined, providing control for movement and behavior. Emotion is the more ancient function, existing in well developed form in primitive mammals whose cortex is much less well developed than humans. Emotion and thinking contribute to the ‘value system’ enunciated by Edelman as a basis for decision making in humans. Both the emotional brain and the cognitive brain have aspects of unconscious as well as conscious functionality. The hypothalamus is the focus of much of the emotional action in the limbic system and the cortical areas. The hypothalamus tightly regulates bodily responses and influences modulator neurotransmitters that widely spray the frontal cortex neurons to influence attention and decision making. The hypothalamus is tightly entwined with the sense of self. Two especially important components of the limbic system not emphasized in early anatomical accounts are the orbital and medial prefrontal cortex and the amygdala. These two telencephalic regions, together with related structures in the thalamus, hypothalamus and ventral striatum, are especially important in the experience and expression of emotion.
Link to — Allan Hobson’s AIM diagrams |