This document has a 1st class level answer for Neurobiology question.
Question: critically discuss how clinical cases of amnesia and experimental studies have aided our understanding of learning and memory processes.
Question: critically discuss how clinical cases of amnesia and experimental studies have
aided our understanding of learning and memory processes.
Amnesia is a condition in which there is an issue recalling memory or the inability to form
new long-term memory. Memory is split into two categories, explicit and implicit memory.
Implicit memory refers to automatic memory such as habits or learned motor skills (i.e
cycling, walking etc). Amnesia however, specifically affects the explicit memory functions.
Explicit memory refers to the conscious retrieval of leaned facts or previous stored
experiences. Explicit memory formation is broken down into to four stages and each stage
involves different parts of the brain. The first stage is the encoding phase which occurs at
the pre-frontal cortex. This is where an experience is initially sensed and processed. The
information is then projected to the hippocampus where the second stage of consolidation
occurs. Consolidation is when short-term memory is converted to long-term memory
through Long-term potentiation which is a form of synaptic plasticity which works to
strengthen neuronal connections. The third stage of explicit memory formation is the
storage and retention of the newly formed memory into the cerebral cortex from the
hippocampus. The fourth and final stage is the retrieval of the specific information, this
involves the repetition of the first three stages which further strengthens the efficacy of
synaptic connections through long term potentiation.
Amnesia is a condition that can affect any of the four stages of explicit memory formation.
Amnesia can be grouped into to two categories, retrograde and anterograde amnesia. Both
types of amnesia are responsible for affecting different stages of explicit memory formation
and therefore, have differing effects on memory. Anterograde amnesia is the inability to
form new long term memories through recent experiences. This kind of amnesia often arises
due to defects and issues in the encoding or consolidation stages. Often a result of trauma
to the prefrontal cortex or hippocampus. Conversely, retrograde amnesia refers to the
inability to recall previous memory and experiences. This type of amnesia is a result of
issues in the storage or retrieval stages of explicit memory formation. This type of amnesia
is often seen due to damage to the cerebral cortex.
Amnesia can result due to acute or chronic conditions. Acute causes include traumatic head
injury or infections. However, chronic causes of amnesia include neurodegenerative
diseases (i.e Parkinsons, hutingtons) or brain tumours.
Memory formation and consolidation (short term to long term memory) is thought to be
controlled in the hippocampus. The hippocampus is an important brain structure that is
located one each hemisphere. The hippocampus is also crucial in spatial learning of the
environment. The hippocampus consists of several cell bodies that send signals and
information between each other via a loop circuit. These structures include the dentate
gyrus, which receives initial signals from the entorhinal cortex via the perforant pathway.
The dentate gyrus then projects its axons (mossy fibre) to the CA3 neurones which then
relays the signal to the CA1 neurones. It is in this the Shaffer collateral- CA1 synapse where
strengthening of neuronal connections via LTP is visualised. The CA1 the sends this
information to the subiculum which then loops the signal back to the entorhinal cortex. It is
in this loop in which form the basis of memory consolidation.
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