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

Amygdala

Amygdala is the part of the limbic system most specifically involved with emotional experience. (Kandel; Principles of Neural Science, 988)

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)

Amygdala is concerned with the implicit memory of the appropriate cues that signal emotions expressed by faces. (Kandel; Principles of Neural Science, 989)

Amygdala receives input directly from the major sensory systems. (Kandel; Principles of Neural Science, 331)

Amygdala is an important interface between visual and auditory emotionally competent stimuli and the triggering of emotions, in particular, though not exclusively, fear and anger. (Damasio; Looking for Spinoza, 60)

Emotional memories are not stored in the amygdala directly but are stored in the cingulate and parahippocampal cortices, with which the amygdala is interconnected. (Kandel; Principles of Neural Science, 992)

Through its projections to the brainstem, the amygdala can modulate somatic and visceral components of the peripheral nervous system and thus orchestrate the body's response to a particular situation. (Kandel; Principles of Neural Science, 331)

As a central player in your emotional life, your insula  sends signals to and receives signals from  other emotional centers in your brain including the amygdala, the autonomic nervous system (powered by the hypothalamus), and the orbitofrontal cortex, which is involved in nuanced emotional judgments. (Ramachandran; Tell-Tale Brain, 98)

Since the amygdala receives input from the inferior temporal cortex and has strong connections to the autonomic nervous system, it can mediate emotional responses to complex visual stimuli. (Kandel; Principles of Neural Science, 989)

Low Road and High Road response to Danger

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

Two pathways of stimuli to the amygdala can be seen as a low road and a high road of responses to danger. (Ratey; User's Guide to Brain, 234)

Path straight through the thalamic projection to the amygdala (the low road) is rough and crude but fast. (Ratey; User's Guide to Brain, 234)

Pathway using the cortex (the high road) gives a more accurate assessment and can be expected to lead to a more considered response, but it takes longer. (Ratey; User's Guide to Brain, 234)

 

Amygdala a Complex Structure

Amygdala is a complex structure, consisting of about 10 distinct nuclei. (Kandel; Principles of Neural Science, 990)

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

Amygdala in animals has yielded important new information, most notably in the work of Joseph Ledoux. (Damasio; Looking for Spinoza, 60)

Amygdala Regions

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

Lateral nucleus has connections with most of the other amygdala regions. (LeDoux; Synaptic Self, 121)

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

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

Amygdala, (Pinel; Anatomy of Human Brain, 123, 125, 194)

 

Research study — Amygdala Circuitry Controlling Anxiety

 

A research study has shown that the Amygdala to Nucleus Accumbens Pathway is both necessary and sufficient to promote the expression of motivated behavioral responding.

 

Connections

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

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

Information flow to the Amygdala, (diagram) (LeDoux; Synaptic Self, 207)

Amygdala receives massive projections from the visual and auditory temporal lobe cortex. (Rolls & Treves; Neural Networks, 146)

Amygdala receives inputs from the inferior temporal visual cortex, but not from earlier stages of cortical visual information processing. (Rolls & Treves; Neural Networks, 146)

The amygdala also receives inputs that are potentially about primary reinforcers, for example taste inputs (from the secondary taste cortex, via connections from the orbitofrontal cortex to the amygdala). (Rolls & Treves; Neural Networks, 146)

Two major bundles of fibers connect the amygdala with other areas of the brain: the stria terminalis and the ventral amygdalofugal pathway. The centromedial amygdala projects through the stria terminalis primarily to the hypothalamus and through the ventral amygdalofugal tract to the brain stem, where it can influence hormonal and somatomotor aspects of behavior and emotional states (eg, eating, drinking & sex). Projections from the lateral and central amygdala go to the lateral hypothalamus through the ventral amygdalofugal pathway. The basolateral amygdala has direct connections with many cerebral areas, allowing it to receive and modulate sensory and polysensory processing. The strongest connections are with the insular cortex, orbital cortex and the medial wall of the frontal lobe. These connections (like cortical pyramidal connections) use glutamate and/or aspartate as the neurotransmitter. Like the cerebrum, the basolateral nuclei project to the striatum (caudate nucleus, putamen and nucleus accumbens of the basal ganglia) and receives direct cholinergic (ie, acetylcholine neurotransmitter) input from the basal nucleus of Meynert. The basolateral group also projects to the mediodorsal thalamus (which projects to the prefrontal cortex). (http://www.benbest.net/science/anatmind/anatmd9.html)

Within the amygdala itself, connections primarily begin in the basolateral division and terminate in the centromedial division. Projections in the opposite direction are much weaker. It is the lateral nucleus that receives most of the sensory information arriving at the amygdala from the cerebrum. The lateral nucleus receives highly processed visual (recognition) information from the TE region of the temporal cortex. This information is projected into the magnocellular basal nucleus of the amygdala, which returns projections to every level of the visual information-processing hierarchy of the temporal and occipital cortex. Recordings of individual neurons in the amygdala have found neurons that respond specifically to auditory, taste, smell or somatosensory as well as visual stimuli, but the visual neurons are the most plentiful. Some amygdala neurons respond primarily to faces. (http://www.benbest.net/science/anatmind/anatmd9.html)

 

Research study — Amygdalar and Hippocampal substrates of Anxious Temperament

 

 

Link to — Limbic System

Link to — Fear ---- Pleasure

Further discussion -- Covington Theory of Consciousness