Week 3 - Limbic Systems Flashcards
what is “Le Grade Lobe Limbique”?
the initial components of the limbic lobe for emotions
-cortical area forming rim around diencephalon on medial surface of brain (cingulate cortex, parahippocampal gyrus, olfactory cortex)
what did the Papez circuit hypothesize?
hippocampus is connected to mammillary bodies (hypothalamus) to the anterior nucleus of the thalamus to the cingulate cortex to the hippocampus (and neocortex)
-proven via rabies spread synaptically
does NOT include amygdala
what is the Kluever-Bucy experiment?
removing temporal lobes of aggressive monkeys caused them to become docile, over-eat, eat inappropriate things, hyperoral, hypersexual
-originally agreed with Papez, but then disproved b/c could recapitulate symptoms by removing/damaging amygdala
what are the limbic system and downstream targets known today?
- anterior and mid-cingulate cortex (ACC and MCC)
- amygdala
- hypothalamus
- periaqueductal gray (PAG) matter
- autonomic nervous system
- dorsal raphe nucleus (DRN; serotonin) and locus coeruleus (LC; norepinephrine)
what does the anterior cingulate cortex do?
- store emotional/valenced (emotional weight)information
- recode amygdala (so no primary fear response)
what does the mid-cingulate cortex do?
- select responses (mental or motor)
- predict outcomes and resolve ambiguity
- improvise new behaviors for new problems
what does the amygdala do?
- invests sensory experience with emotional significance (valence)
- most prominently involved in fear
what does the hypothalamus do?
autonomic/hormonal control
what does the periaqueductal gray do?
coordinate autonomic/skeletal behaviors
-surrounds aqueduct in midbrain between 3rd and 4th ventricles
what does the autonomic nervous system do?
skeletal motor output and memory enhancement
what does the locus coeruleus do?
- coordinates responses for fight/flight
- enhances storage of emotional memories
what does the dorsal raphe nucleus do?
regulate mood
what is “emotion”, and the difference between primary and secondary emotions? what are brain structures involved?
emotion = weighting (valencing) object and events with positive or negative responses
primary = reflexive emotions (implicit, don’t need to think about it); linked with autonomic reflexes
- fear is most well-studied
- amygdala, hypothalamus, PAG
secondary = conscious emotions; object and context-dependent
-cortical limbic structures
what mediates the fear response in the amygdala?
the basal-lateral nucleus connects to the central nucleus
what happened to SM, the patient with Urbach-Wiethe disease?
loss of amygdalas bilaterally (due to calcification), but hippocampus intact
- inability to experience fear or recognize fear in faces
- -excessive risk taking, odd relations and financial decisions
- no motor or sensory defects; no intelligence, memory, or language deficits
why would the fear response be intact if the connection between the auditory cortex and amygdala was cut?
amygdala gets input from both auditory cortex (which gets it from medial geniculate nucleus), and directly from MGN
-since the thalamic message has no cortical processing, thus dominating initial primary response to fear
steps in how amygdala is involved in fear perceptions, ANS responses, and memory
- fear-invoking stimulus from any sensory modality (visual, auditory, touch, etc.)
- stimulus is perceived
- input goes directly from LGN to amygdala (and visual cortex), activating fear response
- activates both cortex and output pathways - expression of fear somatic and viscerally (fight or flight response)
- memory gets encoded in amygdala and cortex
- memory is dramatically enhanced in presence of NE for LC
what does electrical stimulation of PAG (or hypothalamic nuclei that project to it) do? how are responses organized? does it have memory?
evoke complex and fully integrated behaviors
- stimulating different parts of PAG makes different classes of behaviors
- responses are organized by PAG projections into different parts of ANS and skeletomotor systems to produce fully coordinated outputs
- PAG has no memory, since it’s controlled by higher brain regions