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Scientific Understanding of Consciousness |
Samples of Reference Books ParaphrasesAn enormous amount of our activity is control automatically on the basis of environmental cues, existing habits and schemata, supplemented when necessary by automatic conflict resolution processes. (Baddeley; Working Memory, 344) The interference of two oscillators beating at slightly different frequencies and acting on the same neurons can systematically affect spike timing. Spikes of a place cell shift systematically relative to the phase of the ongoing theta oscillation. This phenomenon is called "phase precession." (Buzsáki; Rhythms of the Brain, 314) The phase precession demonstration was the first convincing example of a long suspected temporal "code," and it has remained the most compelling evidence in support of the critical role of oscillations in brain function. (Buzsáki; Rhythms of the Brain, 315) Functional connections within the feedforward CA3 -- CA1 system and the CA3 excitatory recurrent system is able to maintain self-organized activity, with the emergence of theta like oscillation. The buildup of excitation and inhibition in the CA3 region also gives rise to a transient gamma oscillation, associated with the increased gamma-cycle-locked oscillation of basket and chandelier cells. (Buzsáki; Rhythms of the Brain, 324) About 148,000 neurons beneath a square millimeter of cortical surface; organized into minicolumns of about 100 neurons each, which are sometimes organized into macrocolumns of about 300 minicolumns. (Calvin; Neil's Brain, 92) A 'concept' is a memory object that contains only a small sensory component, because it is the result of neuronal activity in association areas such as the frontal lobe (where multiple sensory or motor modalities are mixed) or in a large number of areas in different regions of the brain. (Changeux; Neuronal Man, 138) When nothing much is happening, a neuron usually sends spikes down its axon at a background rate between 1 and 5 Hz. When a neuron becomes excited, because it receives many excitatory signals, its firing rate increases to 50-100 Hz or more. For short intervals, a neuron's firing rate may reach 500 Hz. (Crick; Astonishing Hypothesis, 92) Hypothalamus, brain stem and the limbic system intervene in body regulation and in all neural processes on which mind phenomena are based (perception, learning, recall, emotion, feeling, reasoning, creativity). (Damasio; Descartes' Error, 123) Core consciousness is created in pulses, each pulse triggered by an object we interact with or that we recall. Each new object triggers the process of changing the proto-self. Proto-self modified by the first object becomes the inaugural proto-self for the new object. Continuity of consciousness is based on the steady generation of consciousness pulses, which correspond to the endless processing of myriad objects, whose interaction, actual or recalled, constantly modifies the proto-self. (Damasio; Feeling of What Happens, 176) Noradrenaline belongs to a family of catecholamines; it is synthesized from dopamine in the brain. Noradrenergic projections from the locus ceruleus in the mammalian brain. (diagram) (Dudai; Memory from A to Z, 178) Fornix is a great track with more than a million fibers. It is the main efferent pathway from the hippocampus and circles around under the corpus callosum to end in the septal nuclei, the hypothalamus, and the mammalliary bodies. (Eccles; Evolution of Brain, 98) Primary consciousness is achieved by the reentry of a value-category memory to current ongoing perceptual categorizations that are carried out simultaneously in many modalities. Primary consciousness is limited to the remembered present. Primary consciousness is necessary for the emergence of higher-order consciousness, and it continues to operate in animals capable of higher-order consciousness. (Edelman; Bright Air, 149) Global mappings are dynamic metastable patterns of activity involving mapped classification couples and nonmapped regions. Global mappings involve large parts of the brain and various combinations of local maps for different modalities. Global mappings involve both spatial and temporal relations. (Edelman; Remembered Present, 143) Conscious experience is associated with the activity of populations of neurons that are widely distributed in the thalamocortical system. The distributed groups of neurons must engage in strong and rapid reentrant interactions. (Edelman; Universe of Consciousness, 62) Mutual reentrant interactions, for a brief time, link various neuronal groups in each map to those of others to form a functioning circuit. Neurons that yield such circuits fire more or less in phase with each other, or synchronously. (Edelman; Wider than the Sky, 44) Majority of musical capacities, including the central capacity of sensitivity to pitch, are localized in most normal individuals in the right hemisphere. Injuries in the left hemisphere, which cause devastating difficulties in natural language, generally leave musical abilities relatively unimpaired. (Gardner; Frames of Mind, 118) Can computers be programmed to have the consciousness? The answer is NO! Consciousness depends on affective experience (i.e. the experience of one's own emotional patterns). True affects and their near infinite variations can only arise from living biological systems and their developmental processes. (Greenspan; First Idea, 292) Basal ganglia: EXTERNAL view; (caudate + putamen + nucleus accumbens + globus pallidus + substantia nigra + subthalamic nucleus); striatum (caudate + putamen + nucleus accumbens); corpus striatum (striatum + globus pallidus) (Hirsch; Neuroanatomy, 162) Thalamocortical system - In its activated state, information is rapidly and efficiently processed. Information can be either online data from the real world or data about the real world that are stored in the brain. The world, the self, and the body are re-represented in the network activation of the thalamocortical system. Consciousness at any instant is simply the integrated product of the information represented in the activated thalamocortical networks at that instant. That includes sense of self; awareness of body; and awareness of the world, be it real or fictive. (Hobson; Consciousness, 141) Most neurocognitivists believe that conscious experience arises in the forebrain with participation of widely distributed but interconnected circuits in the neocortex and in subcortical centers like the basal ganglia and limbic structures. Most neurocognitivists believe that the distributed and interconnected cortical circuits that are the physical substrate of conscious experience need to be synchronously activated, probably by the widely distributed thalamocortical system. Most neurocognitivists believe that the source of activation of the thalamocortical system and the distributed forebrain circuits underlying consciousness is the brainstem reticular formation, and especially its pontine-mesencephalic and diencephalic components, which regulate the cortex via its interaction with the thalamocortical system. (Hobson; Dream Drug Store, 176) Dramatic change in neuromodulation distinguishes REM sleep from waking. Brain stem cells containing the neuromodulators norepinephrine and serotonin change their outputs when animals go to sleep. Serotonin and noradrenaline cells that modulate the brain during waking reduce their output by half during non-REM sleep and shut off completely during REM sleep. Serotonin and noradrenaline implicated in awake state functions (attention, memory, reflective thought) that are lost in dreaming. Neuromodulatory neurons: (1) relatively few and relatively small, (2) highly localized to a few brain stem nuclei, (3) they are pacemaker cells; rhythmical and spontaneous, (4) fire at relatively low rates, metronome-like, (5) project their fine, multiply branching processes all over the brain and spinal cord. (Hobson; Dreaming, 63) When does consciousness begin? We all spend a very significant amount of time in a very REM-like state before we were born. Embryologists can see eye movements in fetuses only twenty weeks old. In the womb, brain circuits are laid out and tested by an automatic process that arises as soon as the networks of nerve cells are first formed. This self-organization is a property of all complex systems to create order out of chaos. At some point in early life, the brain network has enough images and thoughts to have conscious awareness. Add a few more and it has enough to be aware that it is aware. Once we have self-reflective awareness, we are fully conscious. (Hobson; Dreaming as Delirium, 141-2) Pulses throughout the CNS are pretty much the same size; amplitude carries little information beyond the presence or absence of a pulse. If enough pulses arrive at the surface of a neuron during a short interval of time, the neuron fires, propagating a new pulse down its own axon. The time it takes the body of a neuron to integrate incoming information is long compared with the time it takes a pulse to propagate between neurons. This time for processing of input information by each neuron sets the rate at which a network of neurons can function. The efficiency of neurotransmitter pulses in a synapse depends on the past history of pulses crossing the synapse. An unrelated metaphor - exercise can improve muscle efficiency; disuse can decrease it. Can think of synapses as weighted according to past experience. (Holland; Emergence, 85) The dopamine pathway to the nucleus accumbens is closely associated with the control of motor behavior and is correlated with hedonic tone that is a fundamental aspect of all feeling states. Specific portions of the limbic system project to different areas of the cingulate gyrus, allowing different patterns of limbic activity to generate qualitatively different emotional feelings and bias cognitive processes. (Johnston; Why We Feel, 119) Surface EEG shows typical patterns of activity that can be correlated with various stages of sleep and wakefulness. Normal human EEG shows activity over a range of 1-30 Hz with amplitudes in the range of 20-100 μV. Alpha waves (8-13 Hz) of moderate amplitude are typical of relaxed wakefulness and are most prominent over parietal and occipital sites. Lower-amplitude beta activity (13-30 Hz) is more prominent in frontal areas and over other regions during intense mental activity. Alerting a relaxed person results in the desynchronization of the EEG, with a reduction in alpha activity and an increase in beta. Theta waves (4-7 Hz) and delta waves (0.5-4 Hz) are normal during drowsiness and earliest slow wave sleep. (Kandel; Principles of Neural Science, 916) Jacob and Monod inferred what we now know to be a fact: that even in a complex organism like a human being, almost every gene of the genome is present in every cell of the body. Every cell has in its nucleus all of the chromosomes of the organism. In each cell type, only some of those genes are turned on, or expressed, all of the other genes are shut off or repressed. Genes are switched on and off as needed to achieve optimal functioning of the cell. Some genes are repressed for most of the lifetime of the organism; Other genes, such as those involved in the production of energy, are always expressed because the proteins they encode are essential for survival. Distinguish between effector genes and regulatory genes. Effector genes encode effector proteins such as enzymes and ion channels, which mediate specific cellular functions. Regulatory genes encode regulatory proteins, which switch the effector genes one and off. (Kandel; Search of Memory, 257) Access to concrete knowledge of higher hierarchical status requires structures in anteriorly placed temporal cortices, whereas access to concrete knowledge of lower complexity only requires posterior occipital cortices. Knowledge that can be accessed from the brain's neural network is not stored as an "image". Rather, the neural assemblies with their hierarchical convergence zones can provide network activity that may reenact the original explicit representation. Cells in high-order cortices forming the hierarchy of convergence zones are critical for the neural process of memory reenactment, but they are neither the "sole basis for" nor the "explicit site of" that neural process. There is no single basis or site for such a process. Each memory reenactment can utilize slightly different neural assemblies. (Damasio; Convergence Zone, 68) Working memory, composed of a central executive and several slave modalities, such as the visual buffer or scratchpad for visual information and. the phonological loop for language. Central executive of working memory controls access to the phonological loop, visual buffer, temporary storage for other modalities, via a sort of attentional selection process. Attention and working.memory are closely intertwined, making it difficult to cleanly separate them. The more working memory is taxed, the less effective attention is at disregarding distractors. (Koch; Quest for Consciousness, 196-7) Arousal occurs in any novel stimulus and not just to emotional stimuli. A novel but insignificant stimulus elicits a temporary state of arousal that dissipates almost immediately. Arousal is prolonged in the presence of emotional stimuli. Arousal elicited by a novel stimulus does not require the amygdala. (LeDoux; Emotional Brain, 290) Monoamines are a class of modulators that include substances such as serotonin, dopamine, epinephrine, and norepinephrine. Cells that produce monoamines are found in only a few areas, mostly in the brain stem. Monoamines achieve their effects by facilitating or inhibiting the actions of glutamate or GABA. Many drugs used in the treatment of psychiatric disorders work by altering monoamines. Prozac prevents the removal of serotonin from the synaptic space. Amines are targets of recreational drugs: cocaine and amphetamine affect norepinephrine and dopamine levels, while LSD acts on serotonin receptors. (LeDoux; Synaptic Self, 58) Looping circuits that center on the hypothalamus regulate the activities of glands and smooth muscle through the autonomic nervous system and the pitutiary complex. - (illustration) (Llinás; Biology of the Brain, 34) The 40-Hz oscillation is a candidate mechanism to produce temporal conjunction of rhythmic activity over a large ensemble of neurons. Thalamic input from the cortex is far larger than from the peripheral sensory systems. This suggests that thalamocortical iterative activity is a main mechanism of brain function. The thalamocortical system, by its hublike organization, allows radial communication of the thalamic nuclei with all aspects of the cortex. These cortical regions include the sensory, motor, and associational areas. These areas subserve a feedforward/feedback, reverberating flow of information. (Llinás; I of the Vortex, 124-6) Two aspects of neuron signals in the brain: (1) rate or mean frequency of firing, (2) fine temporal signal structure, which is evaluated in terms of correlations among sets of cells. If, during a time interval, the signals on a set of neurons are significantly correlated, the set is interpreted as being bound during that interval. There is experimental evidence for the existence in the nervous system of temporal signal structure of appropriate nature to encode binding by temporal synchrony. (von der Malsburg; Binding Problem, 137) Looping circuits that center on the hypothalamus regulate the activities of glands and smooth muscle through the autonomic nervous system and the pitutiary complex. - (illustration) Llinás; (Workings of the Brain, 34) Prefrontal regions are involved in the retrieval and monitoring of relational information, parietal regions are involved in the maintenance of relational structures (i.e., the explicit dimensions over which the relations are defined), and temporal regions are involved in the formation of bindings between related items. Information processing capacity of the central executive is limited in the complexity of the relational structures that it can process. (Halford; Relational Processing, 263) Cortical areas related to attention are reciprocally interconnected not only with each other but also with the inferior temporal and orbitofrontal cortex. This arrangement provides an anatomical substrate for parallel processing of information. Only the parietal, cingulate, and frontal areas appear to be critical for the organization of directed attention. (Webster; Neuroanatomy of Visual Attention, 28) 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. Pathway to the cortex arises primarily in the internal globus pallidus and reaches the motor cortex after a relay in the ventral anterior- and ventral lateral-nuclei of the dorsal thalamus. These thalamic nuclei project directly to motor areas of the cortex, thus completing a vast loop that originates in multiple cortical areas and terminates (after relays in the basal ganglia and thalamus) back in the motor areas of the frontal lobe. Axons from substantia nigra pars reticulata synapse on upper motor neurons in the superior colliculus that command eye movements, without an intervening relay in the thalamus. Because efferent cells of both the globus pallidus and substantia nigra pars reticulata are GABAergic, the main output of the basal ganglia is inhibitory. In contrast to the quiescent medium spiny neurons, the neurons in both these output zones have high levels of spontaneous activity that tend to prevent unwanted movements by tonically inhibiting cells in the superior colliculus and thalamus. (Purves; Neuroscience, 423) According to the master loop hypothesis the neural substrate of consciousness consists of large-scale electrophysiological or bioelectrical activity patterns that are enormously complex (probably involving millions of neurons and billions of synapses). The master loop networks are characterized by an architecture of recurrent connectivity. That special architecture supports closed loops of coherent bioelectrical activity. The loops extend "horizontally" across the cortex (like the feedback sweep in the ventral visual stream) and also "vertically" between the cortex and the thalamus ("specific" and "nonspecific" thalamocortical loops). (Revonsuo; Inner Presence, 319) Two coupled networks, one in the inferior temporal visual cortex for perceptual functions, and another in the prefrontal cortex for maintaining the short-term memory during intervening stimuli, provide a precise model of the interaction of perceptual and short-term memory systems. (Rolls & Deco; Noisy Brain, 94) Orbitofrontal cortex has a key role in representing primary reinforcers, and learning and rapidly changing associations between stimuli and primary reinforcers, and thus is important in many types of emotional and motivational behavior. (Rolls; Memory, Attention, and Decision-Making, 183) Another short-term memory system is human auditory-verbal short-term memory, which appears to be implemented in the left hemisphere as a junction between the temporal, parietal, and occipital lobes. (Rolls & Treves; Neural Networks, 247) Recall of a memory occurs best in associative networks when the input key to the memory is nearest to the original input pattern of activity that was stored. (Rolls; Emotion Explained, 195) The CA3 part of the hippocampus may operate as a single associative memory capable of linking together almost arbitrary co-occurrences of inputs, including inputs about emotional state that reach the entorhinal cortex from the amygdala. (Rolls; Emotion Explained, 195) To the extent that noradrenergic neurons are involved in memory, it is likely they would have a modulatory role on cell excitability, which would influence the extent to which voltage-dependent NMDA receptors are activated, and thus the likelihood that information carried on specific afferents would be stored. (Rolls; Brain and Emotion, 143) Consciousness (common sense definition) - refers to those states of sentience and awareness that typically begin when we awake from a dreamless sleep and continue until we go to sleep again, or fall into a coma or die or otherwise become "unconscious". (Searle; Mystery of Consciousness, 5) Rhythmic activity can be generated by two main mechanisms: intrinsic membrane properties and synaptic circuits. Intrinsic membrane properties were first found in pacemaker neurons in central pattern generator circuits controlling breathing, walking, and other highly stereotyped behaviors in invertebrates. Many types of neurons in the vertebrate central nervous system possess complex and highly nonlinear ionic conductances that allowed these cells to respond to inputs by oscillating at various frequencies. High frequency oscillations (40-60 Hz) of a large proportion of the neuronal population in a given area appear to be a common occurrence in awake, behaving animals. (Shepherd; Synaptic Organization of the Brain, 30) Basal ganglia participate in a variety of non-motor functions, including functions of the limbic system and cognitive functions. Outputs of the basal ganglia go to all areas of the frontal cortex, placing the basal ganglia in a position to influence a wide variety of behaviors. Basal ganglia have been implicated in a variety of non-motor disorders, including depression, obsessive-compulsive disorder, attention deficit hyperactivity disorder, and schizophrenia. Intrinsic circuitry is the same for cognitive and motor parts of the basal ganglia. (Squire; Fundamental Neuroscience, 834) Learning feelings of like or dislike requires the amygdala; learning habits requires the neostriatum; learning a discrete motor response to a conditioned stimulus requires the cerebellum. Declarative memory depends on the convergence of input from distributed cortical sites into the medial temporal lobe and ultimately into the hippocampus, and the convergence of this input with other activity that identifies the time and place of the event. Convergence of input from distributed cortical sites establishes a flexible representation such that the experience is remembered as part of a previous episode. (Squire; Memory & Brain, 212) Frontal cortex and sensory cortices work together as a neuronal system to perceive information and then hold it in in working memory for temporary use. Frontal cortex receives sensory information from upstream cortical areas and then -- depending on attention, motivation, and overall direction of behavior -- provide feedback to some subset of these areas, directing them to hold information in mind for impending action, for comprehension and planning, or possibly for integration into long-term memory. Cortical visual areas and some of their connections to major pathways from area V1. Processing stream for analyzing the visual form and quality of objects follows a ventral route into the temporal lobe. Processing stream for analyzing object location follows the dorsal root into the parietal lobe. (diagram) (Squire & Kandel; Memory, 87) Self-organization -- 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 (Waldrop; Complexity, 102) Fifteen or more distinctive aggregates of neurons, known as nuclei, can be discerned within the thalamus. All cortical regions communicate with the thalamus; it also receives important input from the regions of the brainstem that regulates wakefulness and arousal. Thalamus is well placed to regulate alertness generally and to focus selective attention. (Zeman; Consciousness, 59) A number of computer models of the basal ganglia have converged on the same core idea: the architecture of the basal ganglia are particularly well suited to support "action selection" -- that is, to implicitly weigh all available options for what to do next and to choose the best one. Actions that can be selected by the basal ganglia range from simple motor behaviors, to manipulation of information in memory, such as multiplying numbers in your head. Circuits that link parts of the basal ganglia to motor cortical areas are structurally identical to those linking other parts of the basal ganglia to the regions of the prefrontal cortex that are used for cognitive processes. (Frank; “Learning and the Basal Ganglia,” Cerebrum 2008, 154)
Link to — Consciousness Subject OutlineFurther discussion — Covington Theory of Consciousness |