Limbic System Flashcards
Le Grande Lobe Limbique
- Described by Broca
- Cortical areas forming a rim around the diencephalon on the medial surface of the brain
- Cingulate cotex, parahippocampal gyrus, olfactory cortex
- Originally though to have primary role in olfaction
Papez Circuit
- James Papez hypothesized the limbic system is involved in emotions
- Components: Hippocampus connected to mammilary bodies (hypothalamus), mammilary bodies connected to the anterior nucleus of the thalamus, anterior nucleus connected to the cingulate cortex, cingulate cortex back to the hypothalamus
- KEY missing part: amygdala
Klucy-Buver Experiment
- Removal of temporal lobes of aggressive monkey
- Became docile, over ate, ate inappropriate things, hyperoral, hypersexual
Modern limbic system primary components
-Amygdala, anterior and mid-cingulate cortex, mediodorsal nucleus of thalamus, prefrontal cortex
Anterior cingulate cortex
- Store emotional/valenced information and recode the amygdala
- Involved in AFFECT
- Stores long-term emotional memory
- Operates through ANS projections to the nucleus of the solitary tract and dorsal motor nucleus of vagus
Mid cingulate cortex
- Select responses (mental or motor), predict outcomes and resolve ambiguity, improvise new behaviors for new problems
- Involved in motivated behavior and response selection
- Anterior part activated during fear
- Operates through spinal projections to the skeletomotor system
- Projections to the striatum, red nucleus, pontine nuclei, and CN nuclei for somatomotor driving of Alpha motor neurons
Amygdala
-Invests sensory experience with emotional significance (valence), most prominently in fear
Hypothalamus
-Autonomic/hormonal control
Periaqueductal gray
- Coordinate behaviors, autonomic/skeletal
- Surrounds aqueduct in the midbrain between 3rd and 4th ventricle
- Stimulating different parts produce different classes of behavior
- Ventral area: rest and digest, dorsal: fight or flight
- Has none of its own memory
Autonomic nervous system
-Skeletal motor output and memory enhancement
Locus Coeruleus
- Coordinates responses and enhances storage of emotional memories, helps to remember responses
- Critical for fight or flight response
- Located in pons
- Extensive projections throughout the cortex, especially the limbic parts
- Driven by input from the amygdala and limbic cortex
- Releases norepi that is critical for storage of emotionally valenced memories
Dorsal Raphe Nucleus
-Helps to regulate mood, produces serotonin
Two types of emotion
- Primary: fear, surprise. Reflexive emotions linked with autonomic reflexes (amygdala, hypothalamus, PAG)
- Secondary: conscious emotions (cortical limbic structures and hippocampus)
Basal-lateral nucleus of amygdala
- Input: thalamus, sensory, entorihinal, and association cortex
- Output: cortex and striatum
Central nucleus of amygdala
- Input: brainstem, sensory and prefrontal cortex
- Output: brainstem and hypothalamus
- Connects to basal lateral to mediate fear response
Urbach-Weithe Disease
- Loss of amygdalas due to calcification (hippocampus left intact)
- Example patient SM could not recognize fear
Inputs to the amygdala
- MGN
- Auditory cortex
- Thalamus
- Receives primary and sensory input from all modalities
- Direct input from thalamus critical to the role of the amygdala in fear response
Primary emotion (fear) response steps
- Fear evoking stimulus (visual)
- Stimulus perceived
- Input goes directly from LGN to the amygdala, activating fear response (activates cortex and output pathways)
- Expression of fear somatically and viscerally through ANS activation
- Memory of event encoded in the amygdala and cortex
- Memory enhanced by presence of norepi for the LC
Sham rage
- Lesion to the hypothalamus/PAG can produce a rage without external control (primary emotion)
- Activation of the lateral hypothalamus is the cause
- So losing the descending control to PAG can be dangerous
PAG projections
-Regulates projections to the nucleus of the solitary tract, dorsal motor nucleus of vagus, intermediolateral nucleus–activates ANS during emotional events
HPAA Axis
- Amygdala and limbic cortex and NE from LC cause paraventricular hypothalamic nucleus (PVN) to secrete cortisol releasing hormone (CRH) into portal veins.
- CRH evokes release of ACTH from pituitary, then evokes release of cortisol from adrenal cortex
Effects of the release of cortisol by adrenal cortex
- Binds to glucocorticoid receptors
- Increases glucose levels and metabolism
- Increases AA metabolism
- Increases fat breakdown
- Increases memory (amyg, insula, acc)
Reciprocal projections from amygdala to ACC
-Helps form the conclusion that the ACC is mainly involved in emotion and may be vulnerable to emotional diseases
Different regions of cingulate activation with memory of emotional events
- Fear: anterior MCC
- Sadness: ventral ACC
- Happiness: rostral ACC
Electrical stimulation of MCC results
- Complex motor outputs that are emotionally relevant
- Ex: lip puckering, finger kneading
Site of emotional facial awareness and expression
- Anterior cingulate cortex, called the facial region
- Projects to the facial motor nucleus
- Allows us to read each others emotions, also explains why we “wear our emotions on our sleeves”
Points at which the LC intercedes in limbic systems to coordinate motor outputs
- NTS/paraventricular nucleus in the thalamus mediates heart responses from ACC/central amyg
- PAG: NE selects fight or flight
- PVN drives HPA axis: NE, ACTH, Cortisol
- Enhances amygdala processing and memory
Disorders of the limbic system
- Conduct disorders, sociopathies, mood disorders, neuropsychiatric disorders
- Most prevent are depression and anxiety
Evidence of limbic involvement in depression
- Increased amygdala volume in depressed patients
- Reduced glucose metabolism in ACC in major depression
- Decreased ACC volume in patients with major depression
Depression and 5HT in limbic system
- Serotonin produced in raphe nucleus, near PAG
- 5HT is an important modulator of mood through limbic pathways
- Determines tonic activity of the system
Deep brain stimulation
- Targets the ACC
- Can be used to treat depression
- Long lasting effects
