limbic Flashcards
basal forebrain structures
Nucleus Basalis of Meynert: cholinergic neurons that project to the entire cortex. Play a role in attention, memory, and learning.
Septal Nuclei: Often referred to as the “pleasure center.” Just in front of anterior commissure.
Nucleus of the diagonal band: connects the 2.
Thalamus and the limbic system
Anterior nucleus projects to the cingulate gyrus and is responsible for learning and memory.
Dorsomedial nucleus are emotions and involve the amygdala, ventral basal ganglia, hypothalamus
What is the fornix
Fornix is the main output tract of the hippocampus
info travels from crura of fornix > body of fornix > columns of fornix > precommisural fornix to septal nuclei.
Post commisurals go to mamillary bodies
From there the mammilary bodies project to the anterior thalamic nuclei via the mammillothalamic tract.
Orbitofrontal and Medial Prefrontal cortexes
responsible for decision making, emotional regulation, complex social interactions.
The source of personality.
Lesion will cause either heightened affect or lack of emotion
Processing emotions > choose correct behavioral responses.
Determine to act in response to a threat, a complex social interaction, an emotion.
It also governs ethics, moral judgements, behavioral inhibitions, personality
Elaborate how emotions can trigger action.
If sensory stimuli are emotionally salient, emotional systems are activated and activate centers in the brainstem reticular formation and hypothalamus.
This can activate somatic motor, autonomic nerves and pituitary gland.
Skeletal muscle (freeze), smooth or cardiac muscle (rise in BP), endocrine gland (stress hormones).
*ponto-medullary RF centers coordinate cranial nerve outputs (like facial expressions, laughing, crying, gagging, chewing, vomiting, sneezing), small lesions can produce uncontrolled laughing, crying, hiccuping.
What would be presented on a face with a lesion in the pathway from forebrain and hypothalamus.
When a patient undergoes an involuntary smile response, the ipsilateral upper and lower face will not have emotional expression.
This is despite the corticobulbar being intact.
The amygdala has 12 nuclei and is divided into what 3 nuclear groups
Medial nuclei - olfactory (direct or indirect from piriform complex) and autonomic functions
Basolateral nuclei - received direct sensory input from the thalamus and sensory cortices
>projects to basal forebrain (attention) and frontal association cortex (behavior), upper connections are behavioral responses focusing attention.
Central nucleus - output nuclei, they project to hypothalamus (endocrine responses in blood stream) and brain stem. (signals to muscles in face and limbs, autonomic signals)
-lower connections are important for visceral and autonomic responses which include arousal.
medial forebrain bundle
It is the main projection from the limbic system and hypothalamus to the brain stem.
Fear conditioning in the amygdala and synaptic plasticity
Auditory pathways reach the medial geniculate nucleus > auditory cortex + or directly from MGN) + also other sensory input (like pain) + NOREPINEPHRINE FROM THE LOCUS COERULEUS (wow) which intensifies the learning> amydala > outputs to circuits that influence somatomotor and autonomic activity.
Synaptic Plasticity (Implicit Learning) Synaptic strength in the amygdala increased in response to tones. NMDA receptor antagonist block this effect.
Kluver-Bucy syndrome
causes Herpes simplex encephalitis,
bilateral temporal lobe surgery,
CNS degenerative disorder - alzheimers disease or Pick’s disease
bilateral damage to the temporal lobes (loss of amygdala)
Loss of emotional responses to sensory stimuli, such as threats
from other animals.
Fearlessness (snakes).
Loss of rage, and aggression, especially towards humans.
Overattention to sensory stimuli (especially mouth—putting
many objects in the mouth).
Hyperphagia (excessive eating) Hyperactivity
Hypersexuality
Amygdala and prefrontal cortex in PTSD
hyperactivation of amydala
hypoactivation of prefrontal cortex during fear conditioning trials
-prefrontal cortex helps to extinguish emotional memories
What is the BG limbic loop
- Anterior cingulate, orbital frontal cortex, amygdala.
- Amygdala, hippocampus, orbitofrontal, anterior cingulate, temporal cortex
- basically assigning value to experience, pleasant vs aversive - Ventral striatum (aka n. accumbuns)
- influences values - 5 - mesolimbic pathway (the reward pathway), dopamine from VTA project to nucleus accumbens, fire when an experience is rewarding. Reinforces the direct loop “im motivated to do it again”
- inhibits ventral pallidum, substantia nigra, pars reticulata
- inhibits Mediodorsal nucleus
This can form habits
What parts of the brain are responsible for
Working memory
Recent memory
Long-term memory
Working: dorsolateral prefrontal cortex
Recent: medial temporal cortex/diencephalon
Long-term: medial temporal and specific cortical regions. (but once memories are in the cortex they are stored there and don’t need medial temporal anymore.
Hippocampal connections
Entorhinal cortex > granule cells in dentate gyrus send mossy fibers to pyramidal cells in hippocampus CA3 these send Schaffer collateral to pyramidal cells in CA1 (major output of the hippocampal formation).
CA1 Hippocampal neurons exhibit long-term potentiation.
After receiving repeated inputs, they respond more to those inputs. (EPSPs get bigger).
alzheimers and memory loss
Symptoms include forgetfulness, anterograde and retrograde amnesia, cognitive impairment, disorientation and abnormal behavior.
Caused by degeneration of hippocampal and parahippocampal neurons, and a loss of cholinergic cells in basal forebrain nuclei (which project to cerebral cortex.)
