Limbic System: Amygdala

Patients were shown slides of green, blue, yellow, or red colors. After some colors, a loud and frightening horn blast was sounded. Autonomic responses were recorded (via GSR recordings) to determine learning

Amygdala patients did not become conditioned to colors followed by the loud horn. But when asked how many colors were presented and which were followed by the horn, their recall was correct. That is, they had *explicit* memory about the events. Hippocampal patients showed learning and conditioning to the colors followed by the horn, but could not recall which they were. That is, they had *implicit* memory about the events. Patients with both types of lesions showed no conditioning and had no explicit memory about which colors were followed by the horn.

Amygdala & connection to cortical structures

Connection to cortical structures is through the ventral amygdalofugal pathway

Control of Emotional Reaction and Conditioning by Executive Control (Prefrontal Cortex)

Normal viewing erotic films (vs neutral films) produced activation in right amygdala (A), right anterior temporal pole (B) & hypothalamus (C). Suppression of emotion/feelings elicited by erotic films eliminated those activations (D, E, F).

Severe and disruptive movement disorders also arise from dysfunctions in the striatum in conjunction with subthalamic nuclei

Parkinson's disease Dystonia (slow twisting movements and abnormal postures) Ballism (large amplitude movements of proximal limbs)

Emotional learning: pathways

Pathways from the thalamus to the amygdala are particularly important Output pathways from the central nucleus of the amygdala make extensive connections with the brain stem for emotional responses and extensive connections with cortical areas through the nucleus basalis. Cholinergic projections from the nucleus basalis to the cortex are thought to arouse the cortex.

The amygdala receives and processes many different sensory inputs. Like the hippocampus it combines external and internal stimuli

These are integrated with somatosensory and visceral inputs—this is where you get your "gut reaction"

Amygdala receives inputs from

all senses as well as visceral inputs

Drugs of abuse

also tap into the brain reward circuitry where dopamine plays a major role (e.g., research has shown that addictive drugs increase extracellular dopamine levels in the nucleus accumbens, and those that do not are not addictive).

Learning and memory in hippocampus vs. amygdala

amygdala is involved in a kind of primitive emotional memory, one that is likely preserved by evolution declarative memory is mediated by the hippocampus and the cortex lesions of the hippocampus have little effect on fear conditioning except in discriminating environmental stimuli

Medial nucleus outputs connect to

anterior olfactory nucleus and some areas of the temporal lobe cortex (green)

Suppression condition

associated with activation peaks in BA 10 of the right lateral prefrontal cortex (LPFC) and BA 32 of the right rostral-ventral anterior cingulate cortex (ACC). (The ACC along with the insula are often associated with conflict resolution.) These results show that a neural circuit involving the prefrontal cortex can cognitively modulate emotional responses generated at a subcortical level.

Central nucleus of the amygdala produces:

autonomic components of emotion (e.g., changes in heart rate, blood pressure, and respiration) via pathways to the lateral hypothalamus and brain stem conscious perception of emotion via the ventral amygdalofugal output pathway to the anterior cingulate cortex and orbitofrontal cortex

Huntington's disease

autosomal dominant degeneration of the ventral striatum, with the caudate nucleus being more affected than the putamen

Lesion of auditory cortex pathway

basic fear conditioning is unaltered, but auditory discrimination is altered. In the discrimination procedure one sound is paired with shock and another sound is not paired with shock. These lesioned animals had to rely solely on the thalamus and amygdala for learning and so they could not learn to discriminate; apparently the two stimuli were indistinguishable. Therefore, the cortex is not needed for simple fear conditioning; instead it allows us to recognize an object by sight or sound— to interpret the environment. Thus, pathways from the sensory thalamus provide only a crude perception of the world

Panic attack

brief spontaneously recurrent episodes of terror that generate a sense of impending disaster without a clearly identifiable cause. PET scans have shown an increase in blood flow to the parahippocampal gyri (cortex overlying the amygdala) with panic attacks beginning with the *right* parahippocampal gyrus. Similar but attenuated blood flow increases occurs during anxiety attacks.

Amygdala inputs and output (afferents and efferents)

bundled together with communication being bidirectional in pathways

Urbach- Wiethe disease

calcium is deposited in the amygdala If this disease occurs early in life, then these patients with complete bilateral amygdala lesions cannot discriminate emotion in facial expressions, but their ability to identify faces remains.

Pathways from the cortex

can provide more detailed and more accurate representations of the environment, they are slower because they have multiple neural links

Destructive lesions such as ablation of the amygdala

cause tameness in animals, and a placid calmness in humans, characterized as a atness of affect can occur as a result of Urbach- Wiethe disease

Stimulation of the amygdala

causes intense emotion such as aggression or fear. One form of stimulation arises from "irritative lesions" as a result of temporal lobe epilepsy.

Basolateral nucleus outputs

connect directly to the hippocampus, entorhinal cortex, and the dorsomedial nucleus of the thalamus. also connect to ventral and frontal brain areas via the ventral amygdalofugal pathway ---- ventral striatum ---- orbital-frontal cortex ---- prefrontal cortex ---- anterior cingulate cortex

Central nucleus outputs

connect to: --- the ventral-medial and lateral nuclei of the hypothalamus & septal area via the stria terminalis ---- direct connections to hypothalamus and brain stem (red)

Pathways from the sensory thalamus

crude perception of the world, but involve only one neural link --> fast quick reaction to potential danger. The thalamus—amygdala pathway provides us with quick reactions and may also prepare the amygdala to receive more highly processed information coming back from the cortex

Kluver-Bucy syndrome

entire temporal lobes of monkeys were removed (bitemporal lesions of medial temporal lobe) Flatness of affect is one of the symptoms just lesions of the amygdala were shown to be primarily responsible for flatness of affect This work led to the psychosurgical technique of prefrontal lobotomies to control violent aggression of schizophrenic patients.

Irritative lesions

excite the area and amplify its function In its most extreme form, irritative lesions produced by temporal lobe epilepsy can cause a panic attack

Postcommissural branch of stria terminalis

goes to the hypothalamus, like the fornix unlike the fornix, the stria terminalis projects to feeding centers of the hypothalamus (lateral and ventral-medial nuclei)

Precommissural branch of stria terminalis

goes to the septal area, like the fornix

Link between prefrontal cortex, septal area, hypothalamus, and amygdala likely gives us our

gut feelings, those subjective feelings, about what is good and what is bad

Fear Conditioning: Example of the Role of the Amygdala in Learning

usually conducted with auditory stimuli --- neutral stimulus electric shock --- unconditioned stimulus w UC response ---- rat freezes and BP and HR increase, gets twitchy, startles easily auditory stimuli becomes conditioned stimulus (get a conditioned response to it)

Anterior cingulate cortex

where the cingulate cortex makes connections with many neocortical areas as well as looping back to connect to the hippocampus and amygdala primarily through the entorhinal cortex.

Amygdala associates

sensory, somatosensory, and visceral responses with feelings (emotional reactions) of pleasure (good ) and revulsion/danger (bad).

Stria terminalis

similar in form, function, and location as the fornix for the hippocampal pathway has precommissural and postcommissural branches in relation to the anterior commissure like the fornix the stria terminalis connects only to subcortical structures Like the fornix, some fibers enter anterior commissure, cross to the contralateral amygdala

Olfactory sensory information comes from

the olfactory bulb

Auditory, visual and somatosensory information comes from

the temporal and anterior cingulate cortices

Visceral inputs to the amygdala are relayed from the

hypothalamus, septal area, orbital cortex, and parabrachial nucleus.

Thalamus also passes the information to the cortex so that

more careful (and slower) judgments can be made about the real potential danger. (arrow to visual cortex and then to amygdala)

Amgydala - location

more interior to the uncus abuts the anterior of the hippocampus

Ventral amygdalofugal pathway is a link whereby....

motivation and drives, through the limbic system, can determine associative learning. That is, associating rewards and punishers with the responses that produce these consequences.

Anatomical area for face recognition and memory

multimodal association area of the inferotemporal cortex. emotion in one area (amygdala) is linked with perception in another area (inferotemporal cortex) to create an intense emotionally charged memory

Ventral striatum

nucleus accumbens septi (nucleus that reclines on the septum; often shortened to nucleus accumbens), putamen, and caudate important in learning and memory when considered in combination with the Globus pallidus forms the Basal ganglia, an area where learning can be translated into responses.

Major outputs of the amygdala

originate from three nuclei: Central, Medial, and Basolateral

Last brain area to fully develop

prefrontal cortex perhaps explaining why teenagers often have emotional control issues Such developmental differences are echoed by evolutionary comparisons, where the greatest differences across primate brains is found in the degree of development of the prefrontal cortex.