23B: Limbic Flashcards
Where is the limbic lobe?
-surrounds the lateral ventriccles
What are the parts of the limbic lobe?
cingulate gyrus
subcallosal gyrus
parahippocampal gyrus
hippocampal formation
What is the main function of the limbic lobe?
emotion (amygdala especially) and cognition (more hippocampus)
What are the roles of the amygaloid nuclei?
important for regulating emotions and autonomic function, as well as olfaction
Where are the amygdaloid nuclei located?
anterior temporal lobe, just anterior to the hippocampal formation (basically at the level of the anterior termination of the inferior horn of the lateral ventricle)
Amygdala- note that it is composed of several nuclei, not all of which are functionally related
What are the three main groups of amygdaloid nuclei?
-Corticomedial (Co: the olfactory part)
Central (C: the principle output nucleus; striatum-like in structure; important for autonomic control)
Basolateral: (the principle input nucleus; associated with neocortex and thalamus; B= basal; L= lateral)
What does the corticomedial amygdaloid nuclei group include?
anterior, medial, and cortical nuclei
What does the central amygdaloid nuclei group include?
has a close relationship with the striatum
What is the main cell type in the central amygdaloid nucleus?
medium spiny GABAergic neurons with a high density of dopamine containing axons
What does the basolateral amygdaloid nuclei group include?
basal, lateral, and accessory basal nuclei (this is the largest, best differentiated nucleus in the human body)
What are the main neurons in the basolateral amygdaloid nuclei group?
pyramidal cells (glutamatergic), similar to neocortex and hippocampus
What is the major input into the corticomedial nucleus?
mainly from the olfactory bulb (this is aka the olfactory amygdala)
also from the parabrachial nucleus (a taste processing nucleus), and the medial dorsal (MD) and ventromedial (VM) thalamus
What is the major output from the corticomedial nucleus?
hypothalamus via the stria terminalis and back to the olfactory bulb
What is the major input into the central nucleus?
basolateral nuclei of the amygdala and from the hypothalamus
What is the major output from the central nucleus?
to the brain stem nuclei and hypothalamus (regulate autonomic systems), and
the striatum and midline (non-specific) thalamic nuclei (effects on arousal)
What is the major input into the basolateral nucleus?
input from many areas of association cortex (including highly processed sensory info)
olfactory cortex
thalamus
hippocampal formation
septal area
What is the major output from the basolateral nucleus?
mainly to the central nucleus of the amygdala
some to the hypothalamus
many areas of the cortex (prefrontal)
thalamus (especially dorsomedian, DM)
reward circuits in the nucleus accumbens and striatum
How does the basolateral amygdala project to the hippocampal formation?
entorhinal cortex (ERC) and subiculum
What is the main function of the central amygdaloid nucleus?
autonomic control (e.g. blood pressure, heart rate), arousal, and subjective experience
Again, the amygdala is considered crucial for regulating what emotions?
emotional and social behavior (different responses seen in different animals)
How do bilateral amygdala lesions present in animals (monkeys)?
- hypersexual
- tame
- lack of fear to predators
- feeding disorders (if the basolateral is lesioned, the animals have hyperphagia; if the central nucleus is lesioned, they have hypophagia and starve)
- hyperorality (put things in their mouth)
Bilateral loss of the anterior temporal lobe is called what?
Kluver-Bucy syndrome (rare)
How does Kluver-Bucy syndrome present?
pts are hypersexual,
overly oral,
tame,
exhibit hyperphagia,
are hyperactive, and
express psychic blindness (they dont recognize the emotional content of facial expressions)
What is Urbech-Wiethe disease?
This disease results in clacification of neural tissue (can be the amygdaloid nuclei) resulting in the patient being bad at recognizing faces expressing FEAR (this inhibits one’s to act appropriately toward others)
Note that the amygdala, especially the _______ nuclei is thought to control fear response
basolateral
The basolateral nuclei is also important for:
the emotional component of learning and memories
Where is the hippocampal formation found?
within the temporal lobe, posterior and inferior to the amygdala (telencephalon)
close to the inferior horn of the lateral ventricle (the formation is medial and superior to the ventricle)
What is the alveus?
the collected axons of the hippocampal pyramidal cells
The collected axons of the hippocampal pyramidal cells, aka the alveus, collect and form ________
the fimbria, which turn becomes the fornix
Much of the gray matter in the parahippocampal gyrus is what?
the entorhinal cortex (mesocortex), with characteristic deep white matter and superficial grey matter
What are the main components of the hippocampal formation?
subiculum
the CA fields (CA1-4) (considered the hippocampus proper)
dentate gyrus
What are the two major input pathways of the hippocampal formation?
the ‘perforant’ pathway’ from the lateral entorhinal cortex
‘alvear’ pathway from the medial entorhinal cortex
note the fine cell bodies of the granular cells that are in the dentate gyrus
Golgi-filled neuron types in each part of the hippocampal formation. Note the fornix at the bottom of the picture
What are the principle cells in the entorhinal cortex (ERC)?
pyramidal cells (glutamergic, excitatory)
What are the principle cells in the subiculum and CA (“Cornus Ammoni”) fields?
pyramidal cells (glutamatergic, excitatory)- note the numerous dendritic spines (primary site of excitatory inputs)
Below: Golgi stain on left; photomicrograph of fluorescence filled cell to show spines and apical dendrites on right)
What are the principle cells in the dentate gyrus?
small granule cells (glutamatergic, excitatory)
The _______ are considered the hippocampus proper
CA fields
coronal section of the hippocampus
The cellular distributions of all of the hippocampal formation subregions are highly laminar and regular. Describe the CA fields and subiculum
they are considered to be 3 layered allocortex (with molecular, pyramidal, and polymorphic layers).
The molecular layer is cell poor, the pyramidal cell layer contains the cell bodies of the principle, pyramidal neurons, and the polymorphic layer contains many cell types (mainly interneurons)
Describe the dentate gyrus composition
also 3-layer (molecular, granular, and polymorphic)- note the granular difference (no pyramidal cells)
What is the main input into the dentate gyrus?
from the entorhinal cortex
What is the main output from the dentate gyrus?
to CA3
Describe the trisynaptic circuit
1) Main input to the hippocampal formation is an excitatory (glutamatergic) projection from the entorhinal cortex to granule cells in the dentate gyrus (perforant path)
2) Granule cells in the dentate gyrus project (excitatory, glutamatergic) to CA3 pyramidal cells via mossy fibers
3) CA3 pyramidal cells project (excitatory, glutamatergic) to CA1 pyramidal cells via Shaeffer collaterals
What is the Alvear path?
alternative to the trisynaptic circuit, in which the ERC projects directly to CA1
What is another source of input into CA fields?
CA1 and CA3 both receive inputs and project to the septal nuclei and the contalateral hippocampus (via commissural fibers)
All areas involved in the trisynaptic circuit receive modulatory input from where?
brain stem nuclei containing nor, serotonin, and ACh
Almost all inputs to the hippocampal formation come via where?
the entorhinal cortex
Almost all output from the hippocampal formation goes where?
the subiculum (which projects widely throughout the cortex)
The hippocampus receives highly processed info about most our existence. How?
the entorhinal cortex receives inputs from widespread areas of cortex, thalamus, and brainstem
Hippocampal pyramidal cells (especially CA1) are highly susceptible to many insults, including:
As in the neocortex, the less numerous _____________ play an important role in downregulating excitability in the hippocampus
GABAergic inhibitory interneurons
The hippocampal formation is very important for certain forms of learning and memory. What kinds in particular?
spatial learning and spatial memories (possibly via “place cells”, whose activity is related to positioning and orientation in relation to the external environment)
What is declarative memory?
available to the conscious mind and the materal can generally be encoded in language. The hippocampal formation is essential for the formation of declarative memories
What is implicit memory?
not available to the conscious mind. Note that there are several types of implicit memories, such as priming, muscular conditioning, emotional memory, and procedural memory (aka riding a bike, playing an instrument, complex motor action, etc.)
What is priming?
a process whereby subjects show improved performance on tasks for which they have been subconsciously prepared.
The ______ and ______ are crucial for implicit memory formation
basal ganglia and cerebellum
The ________ is essential for the emotional content of memories
basolateral amygdala
Where are most long-term memories stored?
neocortex, although the hippocampus may be necessary for recall (projections from the subiculum to widespread areas of cortex may be the substrate for distribution and storage of long-term memories)
In addition to the hippocampal formation, damage to what other structures results in memory deficits?
midline thalamic and hypothalamic structures (e.g. mammillary bodies, also fornix)
