Limbic System & Alzheimer’s disease Flashcards
What are the limbic functions of the olfactory cortex, hippocampal formation, amygdala and hypothalamus?
Olfactory cortex- Olfaction
Hippocampal formation- Memory
Amygdala- Emotions and behaviour
Hypothalamus- Homeostasis; autonomic and neuroendocrine control
What is orbitofrontal cortex function?
Orbitofrontal cortex associated with social behavior (Case of Phineas Gage). Prefrontal lobotomy resulted inappropriate behavior and the lowering of moral standards as seen in Phineas Gage
What is anterior part of insula function?
Anterior part of insula involves in olfaction, vomiting, nausea and disgust.
What is entorhinal cortex function?
Entorhinal cortex lies in the anterior portion of the parahippocampal gyrus and plays a critical role in memory (gateways to the hippocampus). It is also part of the olfactory cortex.
What is subcallosal part of the cingulate gyrus function?
The subcallosal part of the cingulate gyrus is associated with sadness and depression.
What is anterior part of the cingulate gyrus function?
The anterior part of the cingulate gyrus contains an inhibitory control center (second thoughts).
What are the 6 key functions of the amygdala?
- Emotional Processing: The amygdala is a major processing center for emotions. It is involved in all types of emotional response (both ‘positive’ and ‘negative’), however, it is particularly important in situations that elicit anxiety, fear or rage.
- Connecting Emotions to Memories: The amygdala connects our emotions to memories and learning. For example, when we encounter emotionally charged situations, the amygdala helps encode memories associated with those events.
- Automatic Danger Detection: It automatically detects potential threats. It processes and integrates sensory, cognitive and other information to determine what is dangerous. If we encounter similar situations later, the amygdala triggers fear or related emotions and appropriate autonomic responses (‘fight or flight’ reaction).
- Implicit Memory: It handles implicit (unconscious,no verbal) memory, allowing us to perform certain tasks without consciously recalling how we learned them. This becomes more prominent during emotionally charged situations (fear conditioning) which is associated with anxiety and post-traumatic stress disorder (PTSD).
- Social Communication: The amygdala is involved in understanding social cues and interpreting intentions from speech or actions or emotional facial expressions. This is disturbed in autism.
- Parenting and Caregiving: It influences emotions related to parenting and caregiving.
What are the functions of the 3 groups of the nuclei of the amygdala?
Basolateral group; receives information from the visual and auditory association areas of the cortex.
Corticomedial group mainly receives sensory afferent from the olfactory bulb.
Central nucleus: elicits emotional responses by projecting to the hypothalamus and autonomic nuclei of the brain stem
What are the inputs and outputs to the amygdala? HINT: 1 input, 2 outputs
- Input from Sensory Areas: The amygdala receives input from sensory cortices such as visual, auditory, and somatosensory areas.
- Output to Hypothalamus and Brainstem:
The amygdala influences our emotional reactions, including fear and aggression. Therefore, It communicates with the hypothalamus ( via stria terminalis, regulating autonomic functions) and the brain stem to regulate autonomic and behavioral responses.
- Output to Hippocampus:
The emotional significance are remembered through connection between amygdala and the hippocampus.
Describe voluntary facial paresis and emotional facial paresis
The voluntary facial paresis occurs due to damage of descending pathways from the motor cortex (e.g., stroke). The patients have difficulty in voluntarily contraction of the muscles in response to command , however they produce symmetrical involuntary facial movements when they laugh, frown, or cry in response to emotional stimuli. In such patients, pathways from limbic cortex remain intact to activate facial movements in response to stimuli with emotional significance.
The emotional facial paresis (another neurological injury) demonstrates the opposite set of impairments, i.e., individuals are able to produce symmetrical pyramidal smiles, but fail to display spontaneous emotional expressions involving the facial musculature contralateral to the lesion (asymmetrical emotional smiles).
What are the 3 parts of the hippocampus?
Dentate gyrus
Hippocampus proper (Ammon horn)
Subiculum
What is the fornix?
It is a white, cord-like structure that sweeps up to the midline and forms an arch below the corpus callosum and terminates in the mamillary bodies (of the hypothalamus) in the floor of the third ventricle. The fornix originates from the hippocampus as the fimbria of the fornix which leaves the hippocampus and becomes the crus of the fornix. As the two crura converge toward the midline, they exchange fibres, forming the hippocampal commissure. Each crus then continues forward as the body of the fornix. The body passes forward beneath the corpus callosum and arches downward as the column of the fornix.
What is the Papez circuit?
The hippocampus is the initial centre of papez circuit. Fornix is a major part of the circuit, which connects the hippocampus to the mamillary body of hypothalamus. The mamillary bodies project in turn to the anterior thalamic nucleus (via mamillothalamic tract) which then project axons to the cingulate gyrus. The information reach to the entorhinal cortex via the cingulum bundle which then pass to the hippocampus, thus completing the Papez circuit.
When particular items of information are important to remember, the hippocampus emits the signals over and over in Papez circuit until they are stored permanently in the cerebral cortex for long-term memory.
What are the symptoms of Kluver-Bucy syndrome? How is it caused?
Fail to show normal fear of anxiety: The animals become fearless, and they do not respond to threats, to social gestures by other animals, or to objects they would normally flee from or attack.
Hypersexuality: Male animals become hypersexual and are impressively indiscriminate in their choice of sex partners (the same gender, different species).
Compulsive attentiveness and hyperorality: The animals show an excessive degree of attention to all sensory stimuli. They respond to every object within sight or reach by sniffing it and examining it orally.
Caused by bilateral lesions of the amygdala and temporal lobe
Where are neuropathological findings found in people with autism?
Neuropathological findings are observed mostly in the limbic system, frontal cortex, and cerebellum. Microscopically, neurons in the entorhinal area, hippocampus, & amygdala are abnormally small and relatively more densely packed.
