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

Parapharse Highlights — Joseph LeDoux

Amygdala

Amygdala: centerpiece of the defense system. Amygdala determines whether danger is present and, if so, initiates bodily responses that were designed by evolution to deal with danger. (LeDoux; Synaptic Self, 8)

The Self

The Self is created and maintained by arrangements of synaptic connections. (LeDoux; Synaptic Self, 12)

Many important aspects of human social behavior, including decision-making as well as the way we react to members of racial and ethnic groups, are mediated unconsciously. (LeDoux; Synaptic Self, 27)

Our life's experiences contribute to who we are; implicit and explicit memory storage constitute key mechanisms through which the self is formed and maintained. (LeDoux; Synaptic Self, 28)

Self-preservation is a universal motive, independent of whether an organism is aware that it is working toward this goal. A cockroach can scamper away when a human foot approaches without being explicitly aware of danger. Bacteria can detect and move away from harmful molecules in its chemical world. (LeDoux; Synaptic Self, 29)

Modulator Neurotransmitters

Consider three classes of modulators: peptides, amines, and hormones. Each can have excitatory or inhibitory effects, depending on the specifics of their participation in functional circuits. (LeDoux; Synaptic Self, 57)

"Jogger's high" is said to be an opiate effect. (LeDoux; Synaptic Self, 58)

Monoamines are a class of modulators that include substances such as serotonin, dopamine, epinephrine, and norepinephrine. (LeDoux; Synaptic Self, 58)

Prozac prevents the removal of serotonin from the synaptic space. (LeDoux; Synaptic Self, 58)

Amines are targets of recreational drugs: cocaine and amphetamine affect norepinephrine and dopamine levels, while LSD acts on serotonin receptors. (LeDoux; Synaptic Self, 58)

Hormones are a class of modulators released from body organs such as the adrenal, pituitary, or sex glands. (LeDoux; Synaptic Self, 59)

Gap junctions, synchronizing hippocampal GABA cells. (LeDoux; Synaptic Self, 61)

Amygdala connected to sensory processing systems and to motor control regions - (diagram) (LeDoux; Synaptic Self, 62)

Synapses are ultimately the key to the brain's many functions, and thus to the self. (LeDoux; Synaptic Self, 64)

In humans, the vast majority of neurons are made in the months just prior to birth. At peak production, about 250k neurons are generated per minute. (LeDoux; Synaptic Self, 67)

Homeotic genes make proteins that control the placement of cells, providing boundaries that guide and restrict cell movement. (LeDoux; Synaptic Self, 68)

Cell type is not rigidly dictated by genes and is strongly influenced by the environment. (LeDoux; Synaptic Self, 68)

Cells have to migrate out from their segregated place to reach their final destinations in the growing brain. (LeDoux; Synaptic Self, 68)

Development of the cortex involves the building of scaffolds or chemical trails that migrating cells follow. (LeDoux; Synaptic Self, 69)

Neurons reach their destinations, sprout axons, find their way to their targets, then form synapses. Their pathfinding depends on growth cones. (LeDoux; Synaptic Self, 70)

Genes dictate that we will all have a human kind of brain with roughly the same kinds of circuits, but random individual differences will exist, and the connectivity of the circuits, selected by synaptic activity, will shape the individual brain. (LeDoux; Synaptic Self, 74)

The greatest number of synapses are present at around 24 months of age. (LeDoux; Synaptic Self, 74)

Activity only prevents the elimination of synapses -- "use it or lose it." (LeDoux; Synaptic Self, 75)

Donald Hebb, 1949, 'Cells that fire together wire together' (LeDoux; Synaptic Self, 79)

Noam Chomsky; natural language is unique to humans; a universal grammar encoded in the human genome; certain psychological capacities are innate. (LeDoux; Synaptic Self, 83)

Special times for learning - critical or sensitive periods - narrow time span in early life - learn a second language after puberty. (LeDoux; Synaptic Self, 94)

Learning is a lifelong process - early years are crucial - foundation for subsequent learning - extensive plasticity in early life -- synapses do not stop changing. (LeDoux; Synaptic Self, 96)

Declarative memory - medial temporal lobe, hippocampus, parahippocampal (rhinal) areas. (LeDoux; Synaptic Self, 102)

Hippocampus receives inputs from several convergence zones in the rhinal region; it can be thought of as a superconvergence zone. (LeDoux; Synaptic Self, 105)

Old memories are the result of accumulations of synaptic changes in the cortex. (LeDoux; Synaptic Self, 107)

Amygdala contains a dozen or so distinct divisions or areas; relatively few are important for fear conditioning. (LeDoux; Synaptic Self, 121)

Lateral nucleus of amygdala is the input zone, receiving information from the various senses. (LeDoux; Synaptic Self, 121)

Central nucleus of the amygdala is the output zone, connections with networks that control body physiology. (LeDoux; Synaptic Self, 122)

Low road and high road to fear - (diagram) (LeDoux; Synaptic Self, 123)

Emotional arousal makes any memory stronger. (LeDoux; Synaptic Self, 133)

Hebbian plasticity (LeDoux; Synaptic Self, 136)

John Eccles - synaptic transmission, memory involves synapses. (LeDoux; Synaptic Self, 137)

Habituation -- repeated stimulus leads to weaker response. (LeDoux; Synaptic Self, 138)

Long Term Potentiation (LTP), 1973, changes in the efficiency of synaptic transmission, memory (LeDoux; Synaptic Self, 139)

Classical conditioning as Hebbian plasticity - (diagram) (LeDoux; Synaptic Self, 160)

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)

All mammals have frontal cortex, but for most, its main job is movement control. (LeDoux; Synaptic Self, 179)

Prefrontal cortex is a convergence zone; receives connections from various specialized regions (visual, auditory, etc.); receives connections from hippocampus and other cortical areas involved in long-term explicit memory; retrieve stored information. (LeDoux; Synaptic Self, 180)

Prefrontal cortex sends connections to areas involved in movement control (frontal cortex and subcortical regions), allowing executive decisions to be converted into voluntary actions. (LeDoux; Synaptic Self, 180)

Pathways of visual processing in the cortex. Two broad aspects: (1) "what" and (2) "where". (LeDoux; Synaptic Self, 181)

Auditory working memory involves auditory processing streams and prefrontal cortex. (similar to the visual system) Specialized sensory processing systems and prefrontal cortex may be generally applicable to many systems. (LeDoux; Synaptic Self, 182)

A central aspect of this executive function is decision-making. (LeDoux; Synaptic Self, 185)

Temporary storage is carried out by domain-specific regions in the prefrontal cortex. (LeDoux; Synaptic Self, 187)

Executive function seams to be spread out across multiple regions of the frontal cortex. Lateral prefrontal cortex (working memory) and anterior cingulate cortex are anatomically connected, and both receive inputs from various specialized sensory systems. (LeDoux; Synaptic Self, 187)

Prefrontal cortex, like other areas of the neocortex, has six layers. Middle layers tend to receive inputs from the other regions, while the deeper layers tend to send outputs to the other regions. (LeDoux; Synaptic Self, 188)

Connections within the prefrontal cortex, both within and between layers, are far more numerous than the connections coming in from other areas, such as sensory processing areas. (LeDoux; Synaptic Self, 188)

Mutual excitations mediated by the internal connections enable input signals from the outside to be amplified and kept active, and may well contribute to the sustained activity that has been observed during delay periods. (LeDoux; Synaptic Self, 188)

Gap junctions, synchronizing hippocampal GABA cells. (LeDoux; Synaptic Self, 61)

Amygdala connected to sensory processing systems and to motor control regions - (diagram) (LeDoux; Synaptic Self, 62)

Rate at which a cell fires spontaneously is a function of certain electrical and chemical characteristics of the cell. (LeDoux; Synaptic Self, 64)

Synapses are ultimately the key to the brain's many functions, and thus to the self. (LeDoux; Synaptic Self, 64)

In humans, the vast majority of neurons are made in the months just prior to birth. At peak production, about 250k neurons are generated per minute. (LeDoux; Synaptic Self, 67)

Homeotic genes make proteins that control the placement of cells, providing boundaries that guide and restrict cell movement. (LeDoux; Synaptic Self, 68)

Autism might be due to a mutation of homeotic genes that leads to faulty brain construction and connections. (LeDoux; Synaptic Self, 68)

Homeotic genes have been preserved through many levels of evolutionary history. (LeDoux; Synaptic Self, 68)

Cell type is not rigidly dictated by genes and is strongly influenced by the environment. (LeDoux; Synaptic Self, 68)

Cells have to migrate out from their segregated place to reach their final destinations in the growing brain. (LeDoux; Synaptic Self, 68)

Development of the cortex involves the building of scaffolds or chemical trails that migrating cells follow. (LeDoux; Synaptic Self, 69)

Glial cells are guided by local chemical cues, made by genes and their by-products, that serve a molecular signposts, creating barriers that restrict movement and providing adhesive surfaces. (LeDoux; Synaptic Self, 69)

Neurons reach their destinations, sprout axons, find their way to their targets, then form synapses. Their pathfinding depends on growth cones. (LeDoux; Synaptic Self, 70)

Between 50 and 70 percent of all genes in the human body are in the brain. (LeDoux; Synaptic Self, 72)

Neural activity, both intrinsic prenatal and environmental stimulated postnatal, selects from the initial set of intrinsically established synaptic connections to form the mature neural network. (LeDoux; Synaptic Self, 72)

The "self" is not constructed, it is selected from preexisting possibilities. (LeDoux; Synaptic Self, 74)

The greatest number of synapses are present at around 24 months of age. (LeDoux; Synaptic Self, 74)

Activity only prevents the elimination of synapses -- "use it or lose it." (LeDoux; Synaptic Self, 75)

Activity does not produce wholesale rewiring of the brain, instead it makes relatively minor adjustments that make individual brains different. (LeDoux; Synaptic Self, 78)

Donald Hebb, 1949, 'Cells that fire together wire together' (LeDoux; Synaptic Self, 79)

Noam Chomsky; natural language is unique to humans; a universal grammar encoded in the human genome; certain psychological capacities are innate. (LeDoux; Synaptic Self, 83)

Subcortical circuits are more likely to be hardwired than cortical ones. (LeDoux; Synaptic Self, 89)

Special times for learning - critical or sensitive periods - narrow time span in early life - learn a second language after puberty. (LeDoux; Synaptic Self, 94)

Learning is a lifelong process - early years are crucial - foundation for subsequent learning - extensive plasticity in early life -- synapses do not stop changing. (LeDoux; Synaptic Self, 96)

Declarative memory - medial temporal lobe, hippocampus, parahippocampal (rhinal) areas. (LeDoux; Synaptic Self, 102)

Hippocampus receives inputs from several convergence zones in the rhinal region; it can be thought of as a superconvergence zone. (LeDoux; Synaptic Self, 105)

Electroconvulsive therapy (ECT) for depression, a procedure that often produces memory disturbances as a side effect. (LeDoux; Synaptic Self, 106)

Tend to remember recently learned things better than older ones. (LeDoux; Synaptic Self, 106)

Old memories are the result of accumulations of synaptic changes in the cortex. (LeDoux; Synaptic Self, 107)

Sensory information comes into the hippocampus from the neocortex via parahippocampal areas. Memories are established in the neocortex via reverse connections. (LeDoux; Synaptic Self, 111)

Hippocampus is involved in both the semantic and episodic aspects of declarative memory. (LeDoux; Synaptic Self, 115)

Amygdala contains a dozen or so distinct divisions or areas; relatively few are important for fear conditioning. (LeDoux; Synaptic Self, 121)

Lateral nucleus of amygdala is the input zone, receiving information from the various senses. (LeDoux; Synaptic Self, 121)

Central nucleus of the amygdala is the output zone, connections with networks that control body physiology. (LeDoux; Synaptic Self, 122)

Low road and high road to fear - (diagram) (LeDoux; Synaptic Self, 123)

Lateral nucleus of amygdala is a key site of plasticity during fear learning. (LeDoux; Synaptic Self, 124)

Emotional arousal makes any memory stronger. (LeDoux; Synaptic Self, 133)

Memories are distributed across many brain systems and many are not available to you consciously. (LeDoux; Synaptic Self, 133)

Hebbian plasticity (LeDoux; Synaptic Self, 136)

John Eccles - synaptic transmission, memory involves synapses. (LeDoux; Synaptic Self, 137)

Habituation -- repeated stimulus leads to weaker response. (LeDoux; Synaptic Self, 138)

Long Term Potentiation (LTP), 1973, changes in the efficiency of synaptic transmission, memory (LeDoux; Synaptic Self, 139)

Classical conditioning as Hebbian plasticity - (diagram) (LeDoux; Synaptic Self, 160)

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)

All mammals have frontal cortex, but for most, its main job is movement control. (LeDoux; Synaptic Self, 179)

Pathways of visual processing in the cortex. Two broad aspects: (1) "what" and (2) "where". (LeDoux; Synaptic Self, 181)

"What" pathway is involved in object recognition. (LeDoux; Synaptic Self, 181)

"Where" pathway is involved in figuring out the spatial location of that object relative to other stimuli in the outside world. (LeDoux; Synaptic Self, 181)

A central aspect of this executive function is decision-making. (LeDoux; Synaptic Self, 185)

Temporary storage is carried out by domain-specific regions in the prefrontal cortex. (LeDoux; Synaptic Self, 187)

Prefrontal cortex receives a rich supply of axons containing dopamine. (LeDoux; Synaptic Self, 189)

Dopamine cell bodies are located in the ventral tegmental area of the brain stem. Axons of these cells branch extensively into the forebrain where the terminals release dopamine. (LeDoux; Synaptic Self, 189)

Dopamine participates in working memory by biasing cells to mainly respond to strong inputs and thereby focusing attention on active current goals and away from distracting stimuli. (LeDoux; Synaptic Self, 189)

Dopamine cells in the brain stem modulate all aspects of the circuitry in the prefrontal cortex, enhancing or facilitating the excitation. (LeDoux; Synaptic Self, 190)

The stuff we are conscious of is the stuff working memory is working on. (LeDoux; Synaptic Self, 191)

Neural synchrony - coordinated firing of populations of neurons; (1) enhanced activation of post-synaptic cells, (2) coordination within local areas across widespread regions. (LeDoux; Synaptic Self, 194)

Postsynaptic cells are more strongly activated when they receive synchronous inputs from presynaptic cells. (LeDoux; Synaptic Self, 194)

Neurons that fire together in widespread brain regions are temporarily bound together. This coherence of firing, when combined in just the right way across the brain, facilitates the representation in working memory. (LeDoux; Synaptic Self, 194)

Working memory theory of consciousness - coherence of firing, when combined in just the right way across the brain, facilitates the representation in working memory of momentarily relevant information from diverse regions. (LeDoux; Synaptic Self, 194)

Domain-specific temporary storage may allow an awareness of significant stimuli, like the sight of a predator, the pain of being injured, the taste of food, or the joy of sex. (LeDoux; Synaptic Self, 196)

Brain stem arousal systems underlie vigilance. (LeDoux; Synaptic Self, 196)

Human prefrontal cortex has an important advantage over the prefrontal cortex of nonhuman primates -- processing module specialized for language. (LeDoux; Synaptic Self, 197)

In Joseph LeDoux's opinion, structuring of cognition around language confers on the human brain its unique qualities. (LeDoux; Synaptic Self, 197)

Working memory is not the function of one region but a complex interconnected network in the prefrontal cortex. (LeDoux; Synaptic Self, 198)

Working memory region -- lateral prefrontal cortex, medial prefrontal cortex (especially the anterior cingulate region), and the ventral prefrontal cortex (especially the orbital region). (LeDoux; Synaptic Self, 198)

Interpretive system in the left hemisphere gives rise to the unique properties of human consciousness. (LeDoux; Synaptic Self, 198)

No generally accepted criteria for stipulating which areas of the brain belong to the limbic system. (LeDoux; Synaptic Self, 211)

Emotions involve relatively primitive circuits that are conserved throughout mammalian evolution. (LeDoux; Synaptic Self, 212)

Amygdala is at the intersection of the input and output systems of fear. (LeDoux; Synaptic Self, 213)

Amygdala contains a dozen or so distinct divisions or areas. (LeDoux; Synaptic Self, 214)

Amygdala interacts with the medial prefrontal cortex (anterior cingulate and orbital regions). (LeDoux; Synaptic Self, 217)

Prefrontal cortex and amygdala are reciprocally related. (LeDoux; Synaptic Self, 217)

Amygdala connections with hippocampus strengthen the consolidation of explicit memories. (LeDoux; Synaptic Self, 222)

Attention and working memory are closely related. (LeDoux; Synaptic Self, 228)

Much of who we are is defined by our emotions. (LeDoux; Synaptic Self, 234)

Reticular formation in the brain stem, a region involved in arousal, alertness, and vigilance. (LeDoux; Synaptic Self, 244)

Dopamine neurons in the ventral tegmental area lead to release of dopamine in many parts of the forebrain. Nucleus accumbens is particularly germane to reward and motivation. (LeDoux; Synaptic Self, 246)

Motivation circuits include the hippocampus by way of its connections with the amygdala and accumbens. (LeDoux; Synaptic Self, 251)

Anterior cingulate cortex receives inputs from the dopamine cells in the tegmentum, as well as from the basal amygdala, ventral pallidum, and hippocampus. It sends outputs to the accumbens and to the motor cortex. (LeDoux; Synaptic Self, 252)

Much of what humans do is influenced by processes that percolate along outside of awareness. Consciousness is important, but so are the underlying cognitive, emotional, and motivational processes that work unconsciously. (LeDoux; Synaptic Self, 259)

Indian doctors discovered in the 1930s that Rauwolfia could reduce high blood pressure. (LeDoux; Synaptic Self, 265)

Selective Serotonin Reuptake Inhibitors (SSRIs) selectively enhance the availability of serotonin. - Prozac - side effects caused by enhancing norepinephrine are eliminated. (LeDoux; Synaptic Self, 275)

Synaptic connections are adjusted by neural activity. When these changes occur during early life they are said to involve developmental plasticity; when they occur later they are considered learning. (LeDoux; Synaptic Self, 307)

Modulatory neurotransmitters have a prolonged action compared with fast transmitters like glutamate or GABA .(LeDoux; Synaptic Self, 313)

The ability of working memory to use the outcome of processing to regulate what we attend to is a typical top-down or executive function. (LeDoux; Synaptic Self, 316)

Once emotions occur, they become powerful motivators of future behaviors. (LeDoux; Emotional Brain, 19)

We do not consciously plan the grammatical structure of the sentences we utter. (LeDoux; Emotional Brain, 31)

Much of mental life occurs outside of conscious awareness. (LeDoux; Emotional Brain, 33)

Language comprehension, Wernicke area. (LeDoux; Emotional Brain, 77)

Speech syntax, Broca area. (LeDoux; Emotional Brain, 77)

Papez circuit theory, takeoff point for limbic system theory. (LeDoux; Emotional Brain, 90)

Importance of the hypothalamus in emotional expression; importance of the cerebral cortex in emotional experience. (LeDoux; Emotional Brain, 92)

Neocortex lacks significant connections with the hypothalamus; evolutionarily older areas of the medial cortex (rhinencephalon) are intimately connected with the hypothalamus. (LeDoux; Emotional Brain, 92)

Forebrain, according to MacLean (1970), had gone through three stages of evolution: (1) reptilian, (2) paleomammalian, (3) neomammalian. (LeDoux; Emotional Brain, 98)

Hypothalamus is connected to all levels of the nervous system, including the neocortex. (LeDoux; Emotional Brain, 100)

Breathing is controlled in the medulla oblongata, that utility station down in the subbasement of the brain. (LeDoux; Emotional Brain, 105)

Human species seems to be endowed with natural language. (LeDoux; Emotional Brain, 106)

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

Pride, shame, gratitude might be uniquely human emotions. (LeDoux; Emotional Brain, 114)

All vertebrates have a hindbrain, midbrain, and forebrain; all the basic structures and major neural pathways in all animals. (LeDoux; Emotional Brain, 123)

Basic building blocks of emotions are neural systems that mediate behavioral interactions with the environment, particularly behaviors that take care of fundamental problems of survival. (LeDoux; Emotional Brain, 125)

Feelings can only occur when a survival system is present in a brain that also has the capacity for consciousness. (LeDoux; Emotional Brain, 125)

Capacity to have feelings is directly tied to the capacity to be consciously aware of one's self and the relations of oneself to the rest of the world. (LeDoux; Emotional Brain, 125)

Although a neuron usually has only one axon, it branches extensively, allowing many other neurons to be influenced. (LeDoux; Emotional Brain, 139)

Fear conditioning is quick and very long lasting; there is little forgetting with conditioned fear. (LeDoux; Emotional Brain, 145)

Fear conditioning is an evolutionarily old solution to the problem of acquiring and storing information. (LeDoux; Emotional Brain, 147)

Auditory cortex is composed of a number of regions and subregions. (LeDoux; Emotional Brain, 153)

Pathway that can transmit information directly to the amygdala from the thalamus; elicit fear responses without the aid of the cortex. (LeDoux; Emotional Brain, 158)

Amygdala function established eons ago, at least since dinosaurs ruled the earth, maintained through diverse branches of evolutionally development. (LeDoux; Emotional Brain, 174)

Memory is not mediated by any particular neural system but instead is diffusely distributed in the brain. (LeDoux; Emotional Brain, 182)

What goes into your short-term memory is what can go into your long-term memory. (LeDoux; Emotional Brain, 185)

Formation of long-term memories involves the temporal lobe; short-term memories involve other brain systems. (LeDoux; Emotional Brain, 185)

Working memory -- temporary storage mechanism that allows several pieces of information to be held in mind at the same time and compared, contrasted, and otherwise interrelated. (LeDoux; Emotional Brain, 270)

Executive functions take care of overall coordination of the activities of working memory. (LeDoux; Emotional Brain, 271)

Consciousness is the awareness of what is in working memory. (LeDoux; Emotional Brain, 278)

Prefrontal areas may not store anything but instead just control the activity of other regions, allowing activity in some areas to rise above the threshold for consciousness and inhibiting the activity of others. (LeDoux; Emotional Brain, 278)

Projections of the amygdala to the cortex are considerably greater than the projections from the cortex to the amygdala. (LeDoux; Emotional Brain, 284)

Orbital cortex may be especially involved in working memories about rewards and punishments. (LeDoux; Emotional Brain, 285)

The amygdala receives inputs from the latest stages of cortical processing within the sensory systems, but projects back to all stages of cortical processing, even the earliest. (LeDoux; Emotional Brain, 286)

EEG is slow and rhythmic when the cortex is not aroused; fast and out of sync during arousal. (LeDoux; Emotional Brain, 287)

Aroused cells go from a state in which they fire at a very slow rate and more or less in synchrony to a state in which they are generally out of sync, but with some cells being driven especially strongly by incoming stimuli. (LeDoux; Emotional Brain, 287)

A number of different systems contribute to arousal; four are located in the brainstem. Neurotransmitters: (1) acetylcholine (Ach), (2) noradrenaline, (3) dopamine, (4) serotonin. (LeDoux; Emotional Brain, 288)

Arousal elicited by a novel stimulus does not require the amygdala. (LeDoux; Emotional Brain, 290)

‘Gut feelings' -- entire pattern of somatic and visceral feedback from the body. (LeDoux; Emotional Brain, 293)

We can daydream while doing other things; go back and forth between daydream and the other activities. (LeDoux; Emotional Brain, 300)

Consciousness is not the prerequisite to nor the same thing as the capacity to think and reason. An animal can solve lots of problems without being overtly conscious of what it is doing and why it is doing it. (LeDoux; Emotional Brain, 302)

Return to — Experts

Link to — Reference Book Paraphrases

Link to — Consciousness Subject Outline