Limbic Flashcards
Overview of limbic anatomy
Cortical - hippocampus - "limbic lobe" surround - insula, parahippocampal (= piriform/olfactory + entorhinal), orbital and medial frontal, subcallosal, cingulate Subcortical - olfactory bulb - hypothalamus - amygdala - septal nucleus - thalamus (anterior, dorsomedial) Proximity! ex parahippocampal piriform cortex right next to amygdala, hippocampus, hypothalamus
Overview of limbic function
Self-preservation and sex
Thinking (cortex) -> emotional content (memory, sensory -> limbic cortex) -> autonomic, endocrine, behavioral output (subcortical)
- arousal/fear
- motivation, behavior
- emotional memory
Closely tied to olfaction, other sensory
Output is tied through medial forebrain bundle (hypothalamus, septal nuclei, midbrain reticular and PAG)
Limbic cortex
Emotional meaning, value, how should I react?
- personality! ex Phineas Gage
Prefrontal cortex (orbital, medial)
Cingulate
Insular
Parahippocampal
Prefrontal cortex
Judgment/insight, mood, motivation, emotional context
- dorsolateral - executive (attention, abstract, planning)
- orbital/medial - personality (mood, behavior/tact)
- targetted by EtOH
- R lesion -> apathy, L lesion -> euphoria
Connectivity - all reciprocal
- cingulum -> cingulate cortex
- sup longitudinal/arcuate fasciculus -> post cortex
- uncinate fasciculus -> ant temporal, amygdala
- septal nuclei
- dorsomedial nucleus of thalamus
- medial forebrain bundle -> hypothalamus
Greatest amount of postnatal dev’t = susceptible through childhood
Depression
Cortical patterns (MRI)
- overactive ant cingulate, subcallosal
- underactive dorsolateral (executive fx)
- underactive post cingulate
- cerebellum, hippocampus, amygdala, basal ganglia, thalamus
Effects reversed/normalized by SSRI or placebo
Pain perception
Chronic - ant cingulate overactive (similar to depression)
Sensitivity determined by cortical amplitude (primary somatosensory and ant cingulate), thalamus is same
Insular cortex
Interoception -
- internal/visceral input (ex visceral pain in IBS)
- emotional responses, meaning (disgust, fear, happy)
- esp anterior portion, connects to amygdala
-> autonomic output
Important in addition (environmental cues)
Olfactory pathways
Receptor cells -cribriform plate> glomerulus -> mitral cells -> tract
- anterior perforated substance
- amygdala (medial uncus)
- piriform cortex (rostral uncus)
Both ant perforated and piriform -> mediodorsal thalamus -> orbitofrontal cortex
Amygdala -> stria terminalis -> ventromedial thalamus (emotional response)
Septal region
Between lateral ventricles (ant horn), dorsal to ant commissure
Neuro-endocrine:
- GnRH -> median eminence -> repro fx
- cholinergic -> hippocampus -> memory
- lesions -> septal rage (over-reactivity)
Connections
- reciprocal: hippocampus, amydala, hypothal/pre-optic
- efferent only: mammillary body, median eminence
Amygdala function
Central coordination of emotional stimuli and response
- > behavior, emotional, autonomic
- feeding, drinking, sex, maternal, etc
- input - looking at fearful face
Stress (b/l lesions = Kluver-Bucy - no stress response)
Conditioned responses (ex PTSD)
- learn to pair stimuli with stress
Stimulation -> arousal, rage
Amygdala connectivity
Located in ant temporal (uncus)
Almost all reciprocal
- olfactory tract - direct, only afferent
- brainstem
- input mostly solitary
- output -> autonomic: solitary, central gray, parabrachial, dorsal vagus, pregang SNS in IML)
- limbic cortex (orbitofrontal, cingulate/mesial temporal)
- sensory and association cortex
- septal nuclei
- hypothalamus
- stria terminalis, ventral amygdalofugal
- hippocampus, parahippocampal
- thalamus - MD and sensory -> limbic cortex
Ex: auditory via primary auditory, association and MGN of thalamus - modulated by frontal lobe (basis for CBT)
Hippocampus
Focus for learning, memory
- spatial/mapping
- explicit/declarative memory (with medial temporal, entorhinal)
- establishment of new memories (vs storage in association cortex of frontal, P-T-O)
- long-term potentiation via Ca and NMDA glutamate
- retrieval of memories
- vs implicit (procedural, priming, habits, autonomic)
- other areas important (ex EtOH -> Korsakoffs -> MD, mamillary)
Glucocorticoid regulation (highest concentration of receptors)
Structure of hippocampus
3-layered allocortex
Regions
- dentate gyrus - granule cells
- Cornu Ammonis -> 4 curved CA fields with pyramidal cells
- subiculum - blends into entorhinal cortex
Input
- diffuse cortex (association, limbic, amydala) -> entorhinal -> perforant pathway
- septal, hypothalamus -> fornix
Output
CA and subiculum -> entorhinal
Dentate granule -> CA3 pyramidal -> CA1 -> fornix
-> post-commissural -> mammillary. ant thalamus
-> pre-commissural -> septal, preoptic (hypothal), ventral striatum, neocortex (orbital, subcallosal)
Ventral striatal system
Habituation, rewards - not through hippocampus
- anticipation (inc activity after conditioned stimulus) -> decreases if reward missing
- all addictive substances affect directly or indirectly
Amygdala, hippocampus, limbic cortex
-> ventral striatum/nucleus accumbens
(+ DA from ventral tegmental -> D3)
-> ventral pallidum -> dorsomedial thalamus
Schizophrenia
Disrupted balance of cortical vs limbic dopamine
- less DA -> mesocortical -> prefrontal -> negative sx
- more DA -> mesolimbic -> limbic -> positive sx
Increased activity in many areas (ex basal ganglia)
