9. Limbic System Flashcards
what aspects of human behavior are associated with the
limbic system?
- emotions
- learning
- memory
reward:
define
positive reinforcer; something for which we will work to approach and contact
punisher:
define
negative reinforcer; something we will work to avoid
emotion:
define
state elicited by rewards or punishers
motivation:
define
state in which reward is being sought OR punisher is being avoided
feelings:
define
conscious awareness of emotional state
mood:
define
predominant emotional state over time
primary reinforcer:
define
a reinforcer that an animal is born needing such as food, water, shelter.
secondary reinforcer:
define
or conditioned, reinforcers are stimuli, objects, or events that become reinforcing based on their association with a primary reinforcer
positive primary reinforcers
(examples)
- light touch,
- food,
- water
all are unconditioned reinforcers
positive secondary reinforcer
a secondary reward because she learned the associations with the image/person and makes him a secondary reinforcer
(example given was a picture of her grandfather)
negative primary reinforcers
those that threaten our survival;
e.g. pain and hunger
negative secondary reinforcer
something you may associate w/ pain and threat to survival;
such as warfare
emotions are produced by…
delivery, omission, or termination of a reward or punisher
2 critical anatomical structures for emotions, learning, and memory?
where are these found?
- amygdala (sl more anterior) & hippocampus
- can be seen on medial surface of temporal lobe (you can’t see them on external surface of the brain)
parahippocampal gyrus:
define and fxn
- grey matter cortical region of the brain surrounding hippocampus
- part of the limbic system
- fxn: important role in memory encoding and retrieval
cortical association areas involved in memory
- temporal
- parietal
- cingulate
- olfactory
- prefrontal
procedural (implicit) memory:
define and assoc. anatomical structures
- habits, skills, sensorimotor adaptations
- cerebellum and neostriatum –> brainstem and spinal motor outlets
emotional memory:
define and assoc. anatomical structures
- conditioned preferences or aversions; memory modulation
- amygdala –> hypothalamus, autonomic, & hormonal inputs
declarative (explicit) memory:
define and assoc. anatomical structures
- episodic and semantic;
- conscious recollection of facts, flexible expression
- new learning
- spatial memory
- parahippocampal region <–> hippocampus
working memory:
define and assoc. anatomical structures
- brief memory, capacity 7-10, e.g. reading phone # and punching it into a phone
- prefrontal cortex –> prefrontal (lateral aspect)
what aspect of memory takes place in hippocampus?
memory consolidation:
processes whereby initially labile memories become “permanent”
case of H.M.
procedure and outcomes
- suffered from epilepsy
- surgery to both medial and temporal lobes
- lost ability to take short term memories and consolidate them to long term memory; but could still retain previous memories
what aspects of HM’s memory remained in tact?
- could still retain previous memories
- *IMPLICIT MEMORY (non-declarative) remained largely in tact:
- can learn motor skills (e.g. mirror drawing)
- simple learning
- short-term memory okay (time-dependent)
knocking out hippocampus or related structures –>
has what effect?
causes anterograde amnesia
CC: anterograde amnesia
define
- loss of semantic memory (and loss of ability to form new memories)
- knowledge of:
- facts
- people
- objects
- new word meaning
location and processing of long term memory
- resides in higher-order association areas of cerebral cortex
- processed by hippocampus (encodes the memories and sends them off to be stored; associations in the cerebral cortex)
Papez circuit:
define
circuit is involved in learning and memory;
◦ damage to this circuit –> memory problems
CC: Korsakoff syndrome
- Results from alcohol abuse, thiamine deficiency
- (nutrient deficiency secondary to alcoholism)
- Sxs: memory loss due to destruction of mammillary bodies or thalamus
Intracranial self-stimulation in rodents
- implant electrode in live rodent brain
- link electrode stimulation w/ lever pressing
- If electrical stimulation of brain region is rewarding, the rodent will press the lever vigorously –> may even ignore food/ other survival instincts
This indicates that the electrical current is an extremely rewarding sensation
reward circuit: encoding
- all rewards are encoded the same way –>
- rewarding stimuli –> causes release of NT dopamine in nucleus accumbens
- hippocampus lays down memories of pleasurable sensation
- amygdala creates a conditioned response to rewarding stimuli
reward circuit and addictive drugs
- addictive drugs hijack the reward circuit
- by flooding the nucleus accumbens w/ dopamine
mesocorticolimbic dopamine system:
define and components
- aka mesolimbic system, the reward system
- connects the ventral tegmental area (VTA) in the midbrain, –> to the ventral striatum of the basal ganglia in the forebrain.
- (The ventral striatum includes the nucleus accumbens and the olfactory tubercle)
where is the nucleus accumbens found?
important connections?
- found in the ventral striatum
- reciprocal connections w/ orbitofrontal cortex and anterior cingulate cortex
- part of mesolimbic dopamine circuit
ventral tegmental area:
define and location
- origin of the dopaminergic cell bodies of the mesolimbic system
- may be involved in drug and natural reward circuitry of the brain
- important role in: cognition, motivation, orgasm, & intense emotions relating to love, as well as several psychiatric disorders.
- neurons in the VTA project to multiple areas of the brain: prefrontal cortex, caudal brainstem, etc.
- location: VTA is close to midline in floor of the midbrain
amygdala:
function & structure
- emotions and behavioral expressions
- contains multiple different nuclei:
- basolateral nucleus (input to amygdala)
- central nucleus (outputs from amygdala)
fast route and slow route of input to amygdala
- fast route: is from thalamus –> directly to basolateral nucleus of amygdala
- long route: is from the thalmus –> *sensory and association cortex* –> then to basolat. nucl of amygdala
flow of info w/in the amygdala
input to basolateral nucleus of amygdala –> central nucleus of amygdala
four different output pathways from amygdala,
and respective functions
From central nucleus of amygdala –>
- prefrontal, cingulate cortex: decision making
- hypothalamus: autonomic & endocrine response
- PAG: pain modulation, defensive behavior
- LC (NE), Raphe (5-HT), VTA (DA): attention, sensory perception
function of amygdala circuit & example:
prefrontal, cingulate cortex
- decision making
- e.g. behavioral response to remove yourself from the situation
function of amygdala circuit & example:
hypothalamus
- autonomic & endocrine response
- (e.g. inc HR & inc CRH–>ACTH–>cortical response)
function of amygdala circuit & example:
periaqueductal gray
- (PAG): pain modulation, defensive behavior
- e.g. due to adrenaline; one’s own pain is modulated to be able to mobilize in stressful situations
function of amygdala circuit & example:
Locus ceruleus (NE), Raphe (5-HT), VTA (DA)
- attention, sensory perception
e. g. attention is focused on emotional stimulus/senses may tune into the stimulus to better pay attention
primary sensory stimuli:
general pathway organization
DRTC (A/O)
- detection
- relay
- thalamus
- cortex
- amygdala OR orbitofrontal cortex
taste receptor:
pathway
- taste receptor (detection)
- nucleus of solitary tract (relay)
- ventroposteromedial (VPM) (thalamus)
- fronto-parietal operculum insula (cortex)
- amydgala or orbitofrontal cortex
touch (primary sensory stimuli):
pathway
- touch (A-delta, C fibers) (detection)
- Dorsal horn and spinal n. nuclei (relay)
- ventral posteromedial nucleus or ventral posterolateral nucleus (VPM & VPL) of thalamus
- Somatosensory cortex (of cortex)
- amygdala or orbitofrontal cortex
olfactory (primary sensory stimuli):
pathway
- olfactory neurons (detection)
- olfactory bulb (relay)
- medial temporal lobe cortex (cortex)
key inputs to the learning centers?
- visual and auditory cortex unimodal association cortex
- primary reinforcers
key center(s) for learning associations?
key center(s) for explicit memory?
- amygdala & orbitofrontal for learning associations
- hippocampus for explicit memory
outputs from learning centers?
- autonomic and endocrine
- implicit actions (basal ganglia, emotional memory, conditioning)
- explicit actions, language systems
function of amygdala w/ regards to emotional experiences
- determines which stimuli are responded to
- how overt responses to stimuli are organized
- internal responses of the body’s organs
damage to amygdala results in:
- inability to recognize facial expressions (esp. fear)
- generalized reduction in fear responses (can be dangerous)
- inability to recognize the emotional content of speech
which brain structure lights up on functional imaging studies if looking at a
fearful facial expression?
a healthy amygdala should light up bilaterally upon seeing an expression of fear
where do conditioned responses occur?
- amygdala –> hypothalamus and periaqueductal gray (PAG)
- conditioned responses to rewards/punishers; automatic and unconscious
where does memory modulation occur?
- amygdala –> hippocampus
- declarative memory of emotional situations; conscious memories of situations with emotional content
where are unconscious/automatic responses found?
where are conscious memories of situations w/ emotional content found?
- unconscious/automatic: hypothalamus & periaqueductal grey
- conscious emotional memory: hippocampus
based on MRI studies, which type of image has the strongest MRI stimulation of amygdala?
- frightening images stimulate most activity of amygdala
- *memory for the dangerous dog was much stronger than for the pleasant image
- there is little to no response to a neutral stimulus
association center for emotion?
what is the output?
- amygdala associates the image with an emotion (e.g. fear or behavior)
- output is via the hypothalamus and frontal lobes
which region relates image to the environment?
what is its output?
-
hippocampus relates image to the environment, context, and modifies behavior
- Places the information in context; (e.g. rattling, triangular head of a snake) and relating the emotional stimulus to the context
- Freeze –> contextualize –> then frontal cortex helps w/ decision-making (fight or flight)
- output is through frontal lobes
