Learning and Memory (Karius)

Question 1

• known as implicit memory, non-declarative memory, and reflexive memory
• skills and habits that have been used so much they are automatic
• anatomic substrates: cerebellum (motor skills) and nucleus accumbens (non-motor)

Answer 1

procedural memory

Question 2

• known as explicit memory
• conscious recognition/recollection of learned facts and experiences
• subdivided into two forms: episodic (memory of events) and semantic (memory of words, language, and rules)

Answer 2

declarative memory

Question 3

What are the types of memory based on duration?

Answer 3

• short-term: seconds to hours
• long-term: years
• working: recalling a fact/memory for use, may be subset of short-term memory

(neural mechanism for each of these is different)

Question 4

• alterations in the CNs based on use
• required for production of memory and learning
• may be synpatic function that is altered
• may be changes in physical structure of neurons (more synapses or new branches to new cells)

Answer 4

plasticity

Question 5

What are the components of plasticity that lead to changes in synaptic functioning and changes in structure of neurons?

Answer 5

• changes in synaptic functioning: post-tetanic potentiation and long-term potentiation (LTP)
• changes in structure of neurons: gain/loss of synapses, structural changes in dendrites, structural changes in some of neuron

Question 6

• brief, high frequency discharge of presynaptic neuron that produces an increase in NT release that lasts ~60 sec
• increases probability of APs in post-synaptic cell
• example: remembering a phone number long enough to write it down

Answer 6

post-tetanic potentiation

Question 7

Describe the mechanism of post-tetanic potentiation:

Answer 7

• high level of stimulation allows more Ca2+ to enter the terminal that can be “dealt” with
• this causes elevated levels of NT release (short enough that extra Ca2+ does not damage cell)
• with more Ca2+, more vesicles can fuse to cell membrane, leading to greater NT release, and greater probability of APs in post-synaptic cell

Question 8

• a series of changes in the pre- and post-synaptic neurons of a synapse which leads to increased response to the released NT
• usually follows a strong stimulation
• model is based on EAA NT, however other NTs can induce this event as well
• event has to last more than 30-60 min
• more Ca2+ in post-synaptic neuron vs PTP where Ca2+ increased in pre-synaptic neuron

Answer 8

long-term potentiation (LTP)

Question 9

Describe the mechanism of long-term potentiation:

Answer 9

(occurring in post-synaptic cell)

• NT (EAA) released which binds to non-NMDA receptor, allowing Na+ to flow into cell and cause depolarization
• depolarization is enough for Mg2+ to unblock NMDA receptor (which EAA is also bound to), allowing Ca2+ to flow into cell
• Ca2+ binds to calmodulin > increases adenylyl cyclase/cAMP > phosphorylation of AMPA receptor (non-NMDA) > increase Na+ influx in response to EAA (more depolarization = more probability of APs)
• ALSO, Ca2+ binds to calcineurin > activates nitric oxide synthase > produces NO > (in pre-synaptic cell) increases cGMP and NT release
• ALSO, (unrelated to above process but still a/w LTP), gene transcription related to increased CREB (physical changes in neurons)

Question 10

What are the underlying mechanisms that lead to changes in structure of neurons in terms of plasticity?

Answer 10

• a/w gene transcription related to increased CREB
• in both pre- and post-synaptic cells
• proteins include: NT synthetic enzymes, NT receptors, proteins required for growth/synapse formation

Question 11

Components of plasticity (PTP, LTP, and structural changes) summary:

Answer 11

• post-tetanic potentiation: increased activity increases amnt of Ca2+ in pre-synapetic terminal which increases NT release; very short (~60 sec)
• long-term potentiation: changes in both pre- and post-synaptic responses to NT release, so same NT release creates larger response (NMDA receptors); lasts for hours
• CREB: changes in synapse structure (permanent) and creation of new synapses via protein synthesis (can block learning/memory formation by blocking protein synthesis)

Question 12

What are the steps to declarative (explicit) memory?

Answer 12

1. encoding: attending to new info (focus, attention), linking it to previous memories, emotion is important component
2. storage of info: retention of info over time (short-term mem limited due to cognitive load, long-term mem is theorectically unlimited); anatomical substrates (hippocampus, parahippocampal cortex, prefrontal cortex), physiological substrate (LTP, allows use to store info), and interconnections to neocortex and amygdala via nucleus basalis of Meynert (cholingeric projection, target of Alzheimer’s dz); temporary storehouse for memory
3. consolidation: process of making memory permanent; involves physical changes in synaptic structure; anatomical substrates (hippocampus, temporal lobes for factual info, Papez circuit), physiological substrates (LTP as starting point, continued activation through Papez, creates new synapses in associated regions of the brain); long-term mems are stored in the area of the cortex related to modality of individual components of that mem
4. retrieval: recalling/using the mem; bringing it into working mem; can be modified/lost at this point; components of memory are pulled from neocortex > sent to parahippocampal regions > sent to hippocampus for reconstruction > info travels back through parahippo to cortex > then sent through working memory

Question 13

Describe the process of consolidation as it relates to declarative (explicit) memory:

Answer 13

• consolidation is the process of making a memory, which involves physical changes in synaptic structure
• requires: hippocampus, temporal lobes (factual info), and Papez circuit
• Papez circuit: hippocampus (stores short-term mems) > hypothalamus/mammillary bodies (physical response to mem/event) > anterior thalamus (sensory info) > cingulate cortex (emotion) > hippocampus
• the memory is repeatedly sent through Papez circuit, inducing LTP and neuronal plasticity (repeated activation), eventually limbic system is not required to access the mem
• long-term mems are stored in area of cortex related to modality of individual components (i.e. one memory could be stored in multiple parts of the brain depending on modality, creates an issue for retrieval)

Question 14

Describe the process of retrieval as it relates to declarative (explicit) memory:

Answer 14

• recalling/using memory, bringing it into working memory, can be modified/lost at this point
• requires: neocortex (pieces), parahippocampal regions, hippocampus (reconstructing mem)
• info related to each component of mem is sent from neocortex > parahippocampal regions > hippocampus where mem is reconstructed > back through PH to cortex (PH important for prolonging life of cortical trace of mem)
• working memory used for retrieving memories via 3-component model: central executive (prefrontal cortex, determines needed memory), phonological loop (Broca’s and Wernicke’s areas, words/rules), visuospatial loop (occipital cortex, visual mems)

Question 15

What is the importance of spatial memory in terms of long-term memory formation?

Answer 15

• spatial map that serves as an anchor for reconstruction of memory
• detailed memory of space is stored in hippocampus, using special pyramidal cells in CA1 known as place cells
• place cells: neurons that are active only at specific places (one type esp strongly activated if you receive reward at that place); receive inputs from grid cells (in entorhinal cortex that create a triangular/hexagonal grid map of place you are in), head direction cells (which direction was your head pointing to see/explore area), and border neurons (fire when near a border)