limbic system

limbic function

lower level cognitive functions: homeostasis, emotions, memory, reward, olfactory recognition

limbic structures

diencephalon: hypothalamus, mammillary bodies, fornix

corpus callosum: cingulate gyrus, orbitofrontal cortex

thalamic nuclei, nucleus accumbens, insula, olfactory system, hippocampus, amygdala

archicortex

3 layers: molecular, pyramidal, polymorphic

hippocampus + olf cortex

thalamic nuclei

from limbic → cortex: emotions, memory, arousal, sleep

anterior (papez circuit) + medial dorsal + midline nuclei (paraventricular, paratenial, reuniens, rhomboid) + intralaminar complex (central medial nucleus)

diencephalon

hypothalamus: amygdala input, release oxytocin/vasopressin/GH/DA

mammillary bodies: hypo relay → thalamus (memories)

fornix: white matter pathway from posterior temporal lobe → superior temporal lobe → medial thalamus → mamm. bodies → hippocampus

olf system?

hippocampus structures

6 subregions: subiculum (laterally) + 4 Ammon’s horn (CA1-CA4) + dentate gyrus (medial) + parahippocampal gyrus (bonus)

3 layers (molecular + pyramidal/granule + polymorphic) communicate via perforant/alvear/mossy/schaffer collateral pathways

input @ cortex/septal areas/contralateral hippocampus via commisural fibers

output @ association areas/diencephalon/septal areas via fornix (add emotion/context)

hippocampus functions

left (verbal/declarative memory) VS. right (spatial memory) → bilateral ablation → anterograde amnesia

LTP: glutamate release (AMPA/NMDA), adds more receptors to synapse

• NMDA: removes Mg+ block → Ca+ entry → stronger synapse

amygdala

socioemotional meaning of sensory information, startle reflex

central nucleus: CeA, fight/flight, pro/anti nociception, reward/punishment memory learning, unconscious memory

medial nucleus: MeA, social/innate behavior regulation, chemosensory processing

basolateral amy: BA, fear conditioning/extinction, phobia creator

limbic pathology

depression, schizophrenia, PTSD: memory loss, emotional instability, behavior changes

limbic encephalitis: inflammatory, paraneoplastic syndrome (lung/breast cancers), seizures

damage: hippocampus (amnesia), amygdala (emotion), mamm/hypo (memory/behavior), cingulate gyrus (emotion/cognition)

wernicke-korsakoff syndrome

chronic alcoholism → mammillary body hypotrophy → amnesiac symptoms

acute phase: confusion, nystagmus/diplopia, ataxia, memory degradation

chronic phase: anterograde amnesia, confabulation, apathy, ataxia