Lecture 16: Limbic System

limbic system

set of interconnected forebrain structures which play key role in mediating certain aspects of behavior/drives, memory and emotion

hypothalamus

serves executive role in regulation of emotional responses

James Lange Theory

the theory that a person expresses emotion first and then has an emotional experience that correlates with the expression

Cannon-Bard Theory

the theory that a person has an emotional experience and then expresses that emotion

telencephalon

gray matter structure made up of the limbic cortex, hippocampus, amygdala, and septal nuclei

diencephalon

gray matter structures made up of the thalamus and hypothalamus

limbic connections

connections throughout the limbic system of white matter

cingulate gyrus

parahippocampal gyrus

hippocampus

forms floor of interior horn of lateral ventricle and folds into medial surface of temporal lobe; lays down and consolidates new memories

fornix

major efferent pathway of hippocampus which forms a C shape

hippocampus proper

subiculum

dentate gyrus

hippocampal afferent connections

parahippocampal (entorhinal) cortex → septal nuclei → fornix → amygdala

hippocampal efferent connections

hypothalamus (especially mammillary bodies) via fornix; parahippocampal cortex → septal nuclei via fornix; amygdala, and anterior thalamus

explicit (declarative) memories

things that are clear cut details (ex: mom’s birthday, periodic table of elements), from medial temporal lobe

implicit (non-declarative) memories

knowledge of skills or how to do things (ex: baking, sewing) from basal ganglia, cerebellum, neocortex, and amygdala

amnesia

loss of memory

anterograde amnesia

lost capacity for consolidating short-term memories into long term memories; cannot form new memories

retrograde amnesia

loss of memory prior to injury/accident

Korsakoff’s psychosis

damage to mammillary bodies or DM thalamus; patients cannot form new memories or recall events; confabulations 

confabulations

making up an answer to something they don’t remember

amygdala

almond shaped collection of nuclei within anterior temporal lobe

medial amygdala

used mostly by animals to assess food/mate/danger; in humans, greatest connection to olfactory system

basolateral amygdala

more important for humans, extensive connections with cortex; formulation response to sensations, expression of emotions, and associations with memories

central amygdala

interacts with hypothalamus; important for autonomic and emotional responses

major afferent connections of amygdala

hypothalamus & septal nuclei via stria terminalis; thalamus (DM) & hypothalamus via VAP; olfactory bulb

stria terminalis

big connecting fiber bundle of amygdala

major efferent connections of amygdala

hypothalamus & septal nuclei via stria terminalis; thalamus (DM), hypothalamus, ventral striatum, and brainstem via VAP

amygdala function

determines appropriate emotional responses, helps effect autonomic responses and behavioral reactions, important for attachment of emotional significance to various stimuli (9/11), mediates anxiety and formation of fearful associations

bilateral amygdala destruction

experiences lose emotional significance, inability to response appropriately to social cues, loss of fear, decreased aggression, placid emotions

Kluver-Bucy Syndrome

bilateral damage to temporal lobe, loss of amygdala, some of hippocampus and parahippocampal gyrus; general characteristics of increased inappropriate sexual behavior, increase oral behavior, loss of fear/flattened emotions, indiscriminate dietary behavior

septal nuceli

located medial to anterior horns of lateral ventricle; may be a part of pleasure reward circuitry, role in memory, and social behavior and expression of fear

major afferent connections of septal nuclei

hippocampus via fornix; amygdala via stria terminalis

major efferent connections of septal nuclei

hippocampus via fornix, amygdala via stria terminalis, and hypothalamus and midbrain via MFB

septal nuclei lesion

violent aggression provoked by innocuous stimuli “Sham Rage”

Paul Broca

identified limbic system

James Papez

originated ideas about limbic system and hippocampal function; suggested that compex set of interconnections between hippocampus and other limbic structures constituted anatomical circuit for emotion and memory

Papez circuit

hippocampus → fornix → mammillary bodies → mammillothalamic tract → anterior nucleus of thalamus → cingulate gyrus → cingulum → parahippocampal cortex → hippocampus