5/28- Limbic System Flashcards
What is the most common type of epilepsy?
Medial temporal lobe seizure
Flowchart outlining fit of limbic system into the rest of the brain?
Input from:
- Cerebral cortex (sensory)
- Reticular formation
Outputs to:
- Cerebral cortex (association and motor)
- Hypothalamus
Basically tells you what’s most important with everything coming into the brain
Where is the limbic system (broadly)?
Top/middle of prefrontal brain
Major limbic system components and their functions (one word/phrase)?
Prefrontal cortex: conscience
Basal forebrain: relay system (like thalamus for rest of nervous system)
Hippocampus: memory center
Amygdala: emotions/fear
Large connections between limbic system components (what they are and what they connect)?
Uncinate fasciculus: medial and temporal lobes
Cingulate fasiculus: temporal and frontal lobes (via cingulate gyrus)
Medial forebrain bundle: many connections to hypothalamus
What is the prefrontal cortex (PFC)- characteristics/job?
Connects to what via what?
- Large relative size in humans compared to other primates/mammals
- Emotional parts: orbitofrontal and ventromedial cortex (dorsolateral is more rational thought)
- “Conscience”- powerful inhibition of lower hypothalamic-mediated aggression (superego)
- Connected via the uncinate fasciculus to medial temporal structures
Ex) Prefrontal lobotomy effects
Ex) Phineas Gage
Why was the prefrontal lobotomy performed? Effects?
- Wide variety of conditions from schizophrenia to chronic pain syndromes
(“Ice-pick lobotomy” also became popular through orbitofrontal cortex)
- Resulted in emotionally-stunted individuals; couldn’t express emotion
(Replaced by anti-psychotic medications)
What happened to Phineas Gage?
- Knocked out his orbitofrontal cortex with a tamping rod through his cheek/eye
- Remained conscious, but significant change in personality
- Became rude, very disinhibited, couldn’t hold a job (not inhibiting lower functions of hypothalamus)
Nuclei in basal forebrain?
- Nucleus accumbens
- Substantia innominata (involves basal nucleus of Meynert)
- Septal area (near septum pallucidum)
- Diagonal band of Broca
More posterior nuclei in basal forebrain?
- Septal area continued
- Stria terminalis and bed nuclei
- Diagonal band of Broca (now separated by anterior commissure)
Septal area connects most to what?
Septal area has many hippocampal connections
Afferent fibers: from hippocampus to medial/lateral septal areas
Efferent fibers: to diagonal band of Broca to hippocampus and back
Other septal area connections?
- To prefrontal cortex
Via medial forebrain bundle:
- To hypothalamus
- To mammillary bodies
- To medial thalamus
Function of septal area?
- Relay station between hippocampus and hypothalamus
- Modulates function of both of these
- Electrical stimulation modulates aggressive behavior and elicits drinking behavior
- Lesions cause “septal rage” (uninhibited lower structures/hypothalamus)
Nucleus accumbens connections?
Afferent: receives large dopaminergic projection from ventrotegmental area (VTA) in the mesolimbic pathway
Efferent:
- Projections back to VTA
- Substantia innominata
- Substantia nigra
Functions of nucleus accumbens?
- Integrates sequencing of motor responses associated with emotion and rewards
- Implicated in addiction (e.g. cocaine induces release of dopamine into this region)
– e.g. mice would hit reward level over food, reproduction, etc…
Where is the hippocampal formation located?
Temporal lobe
Three divisions of the hippocampal formation?
- Subicular cortex/subiculum
- Hippocampus (CA regions, esp CA3 and CA1)- Archicortex
- Dentate gyrus (mossy fiber cells as opposed to pyramidal)
Two basic pathways in hippocampus
Both enter via entorrhinal cortex:
- Perforant pathway- through subiculum to dentate gyrus (projections back to CA 3 and 1 and back out entorrhinal path)
- Alvear pathway- forms fornix going to other regions of limbic system and cortex
What are the Schaffer collaterals?
Connection between CA3 and CA1 region; underly memory
What process sets memory storage?
Long term potentiation (e.g. CA3 input to CA1 neuron)
- Brief high frequency stimulation results in strong and long term potention of an otherwise weak signal
- Input without tetanus will not receive LTP
Biochemical process at play in long term potentiation (LTP)?
- Strong depolarization removes Mg2+ ion block of the NMDA receptor
- Glutamate binds and allows Ca to enter the post-synaptic neuron
- Ca acts as a 2nd messenger to activate kinases which can potentiate existing AMPA receptors and recruit new AMPA receptors to the synapse
What is the Papez Circuit?
- Efferent projections from hippocampus through fornix to post-commissural fornix down to mammillary bodies
- Mamillary bodies send projections through mammillothalamic tract to anterior nucleus of thalamus
- Ant. nucleus of thalamus sends projections to cingulate gyrus
- Then from cingulate gyrus back through entorrhinal cortex back to hippocampus
Mnemonic: “He Man Ate a Cat”
Efferent projections of the amygdala?
- Corticomedial group to the medial hypothalamus via stria terminalis (directly or via bed nuclei)
- Basolateral group to the lateral hypothalamus (and also PAG, and prefrontal cortex) via ventral amygdalofugal path
What controls conditioned fear?
2 different pathways?
The amygdala
- Direct route: through thalamus (never appears through conscious mind)
- Indirect route: through cortex (through occipital cortex through associated cortices back to amygdala)
Medial temporal lobe seizure symptoms (categorized by component of limbic system)?
Amygdala:
- Fear
- Bad smell
Hippocampus:
- Deja vu (familiarity in unfamiliar place)
- Jamais vu (unfamiliarity in familiar place)
- Amnesia
Basal forebrain nuclei:
- Increased heart rate (via hypothalamic connections)
- Increased blood pressure (via hypothalamic connections)
- Altered consciousness
- Laughing (hypothalamus)
- Spitting
Prefrontal cortex:
- Automatic behaviors (lip smacking, picking…)
- Post-ictal confusion/psychosis
