L1 - Memory systems Flashcards
What main areas make up the limbic system of the brain?
- Hippocampus (main bit)
- Amygdala
- Mamillary bodies of the Hypothalamus
- Cortical ares (congulate gyrus, olfactory cortex..)
What is the function of the limbic system?
Regulation of emotion and memory formation
5 F’s: Feeding, forgetting (memory), fighting, family, fornication
What anatomical region is the ‘core area’ of the limbic system?
Medial temporal lobe (MTL)
This is key in memory formation
What makes up the medial temporal lobe?
Hippocampal formation and its adjacent cortical areas…
Hippocampal formation subregions:
- Cornu ammonis (CA1-CA3)
- Dentate gyrus
- Subiculum
Adjacent/connected cortical areas:
- Entorhinal cortex
- Perirhinal cortex
- Parahippocampal gyrus
What are the 2 hypothesisisisises about memory formation at the MTL?
Hypothesis 1:
- MTL plays role in immediate storage of incoming information
- MTL serves as temporary storage (buffer)
- Ultimate storage of memories in cortex
Hypothesis 2:
- MTL (hippocampal formation specifically) serves for long-term storage of memories
- Cortical areas are more for helping memorising stuff
Which MTL hypothesis for memory storage is thought to be correct?
Hypothesis 1 (MTL is temporary and cortex is ultimate storage)
Data supports that the MTL temporarily stores incoming info, consolidates it and then yeets some of it to the cortical areas for proper storage
What are the 2 types of long term memory?
Declarative (explicit) & Non-declerative (implicit)
Declarative = further split into Semantic & Episodic
Non-declarative = Priming, Habits/skills, implicit emotions
What is meant by Declarative memory?
Declarative (explicit) long term memory
Divided into Semantic (facts) and Episodic (events)
Semantic (facts) = remembering a fact about something without the experience of learning that fact (ie we know strawberries are fruit but dont remember the time when we first found that out)
Episodic (events) = eg remembering weddings, first time you fell in love etc
What is meant by Non-declarative long term memory?
Implicit memory
Habits, skills (how to ride a bike (but not the first time riding a bike))
Priming (idk what this means)
Implicit emotions
What type of memory formation/access is particularly affected in neurodegenerative diseases like alzheimers?
Episodic (events) memory
(Type of Declarative/explicit long term memory)
What are the two major pathways for afferent/efferents into and out of the Hippocampus?
Fornix (connects to Mamillary bodies, thalamus, basal forebrain)
Entorhinal cortex (connects to cortical areas)
Give the basic characteristics of cognitive decline seen in alzheimers
progressive decline in mental function, memory and acquired intellectual skills (orientation, abstract thinking, judgement)
Leads to progressive cognitive decline; sensory and motor skills are generally not affected
What memories are most/least affected in alzheimers?
Contrast this to other forms of dementia
Recent memory is most affected - with childhood memories relatively preserved
In Semantic FTD (fronto-temp) - where the temporal lobe is affected most - the opposite is seen where recent memory is alright but childhood memory is affected most
What are the two main histopathological features of alzheimers?
Which is found intracellularly and which is found extracellularly?
(note these are end-stage pathologies and not causative of alzheimers (i think))
Beta-amyloid plaques (ßA) - often called senile plaques
Tau tangles - described as neurofibriallary tangles
Beta amyloid plaques are EXTRACELLULAR
Tau tangles are INTRACELLULAR (until neurone dies)
Macroscopically - what are the main pathological features of a brain of someone with alzheimers?
Enlarged ventricles
Inflammation (not macroscopic but shut up)
Atrophy (esp cortical)
What diseases are Beta-amyloid plaques associated with?
Only Alzheimers disease (AD)
What diseases are Tau tangles associated with?
AD
FTD
(fronto-temporal dementia)
What diseases is A-synuclein associated with?
Parkinson’s disease (PD)
Lewy-body dementia (DLB)
What diseases is TDP-43 associated with?
Amyotrophic lateral sclerosis (ALS)
Nobody reallhy knows what causes alzheimers to happen - but there are certain causative genes (EOA) and certain risk factor genes
What process do the causative genetic mutations affect?
They affect the metabolism of APP (amyloid precursor protein)
However - Beta-amyloid plaques are not the cause of alzheimers
There are a bunch of risk factor genes shown in the photo attached
What is the cholinergic hypothesis of Alzheimers?
The hypothesis suggests that a dysfunction* of acetylcholine containing neurons in the brain contributes substantially to the cognitive decline observed in those with advanced age and Alzheimer’s disease (AD)
*Dysfunction caused by reduced levels of ChAT
This is the only symptomatic target for treatment of alzheimers
The cholinergic hypothesis involves which area of the brain?
Nucleus basalis of Meynert
Cholinergic neurones project from here to 90% of cortical brain
Aside from genetics - what are other risk factors for Alzheimers
- Stroke, heart disease, obesity, diabetes
- Smoking
- Depression
- Sleep disorders
- Poor diet / vitamin deficiency
- Metal exposure (lead, alumin, mercury etc)
How is Alzheimer’s staged?
Post-mortem via Braak staging - which looks at Tau pathology
There is the newer ABC staging - but I dont think this is that good
What specifically is the single biggest:
a) Risk factor for AD
b) Genetic risk factor for AD
a) Age is the biggest risk factor
b) ApoE 4 isoform is the biggest genetic RF - although genetic AD is rare
