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What is memory and how is it?11.1 Memory can be explicit or implicit and short-term or long-term: Insights from amnesic patients11.2 Hypothesis I: Memory is stored as strengths of synaptic connections in neural circuits11.3 Hypothesis II: Learning modifies the strengths of synaptic connectionsHow is synaptic plasticity achieved?11.4 Long-term potential (LTP) of synaptic efficacy can be induced by high-frequency stimulation11.5 LTP at hippocampal CA3 → CA1 synapse exhibits input specificity, cooperativity and associativity11.6 The NMDA receptor is a coincidence detector for LTP induction11.7 Recruitment of AMPA receptors to the postsynaptic surface is a major mechanism of LTP expression11.8 CaMKII auto-phosphorylation creates a molecular memory that links LTP induction and expression11.9 Long-term depression weakens synaptic efficacy11.10 Spike-timing-dependent plasticity can adjust synaptic efficacy bidirectionally 11.11 Homeostatic synaptic plasticity adjusts overall synaptic strengths according to overall activity levels11.12 Postsynaptic cells can produce retrograde messengers to regulate neurotransmitter release by their presynaptic partners11.13 Long-lasting changes of connections strengths involve formation of new synapsesWhat is the relationship between learning and synaptic plasticity?11.14 Animals exhibit many forms of learning11.15 Habituation and sensitization in Aplysia are mediated by changes in synaptic strength11.16 Both short-term and long-term memory in Aplysia engage cAMP signaling11.17 Olfactory conditioning in Drosophila requires cAMP signaling11.18 Modifications of the mushroom body synaptic weight matrix underlie Drosophila olfactory conditioning11.19 In rodents, spatial learning and memory require the hippocampus11.20 Many manipulations that alter hippocampal LTP also alter spatial memory11.21 From correlation to causation: the synaptic weight matrix hypothesis revisitedWhere does learning occur, and where is memory stored in the nervous system?11.22 The neocortex contributes to long-term storage of explicit memory11.23 The amygdala plays a central role in fear conditioning11.24 Dopamine plays a key role in reward-based learning11.25 Earlier experience can leave behind long-lasting memory traces to facilitate later learningSummary
What is memory and how is it?
11.1 Memory can be explicit or implicit and short-term or long-term: Insights from amnesic patients
Memory categories:
- Explicit memory (declarative memory 陈述性记忆): memory requiring conscious recall, such as memories of names, facts, and events. When we say memory in daily life, we are usually referring to explicit memory.
- Implicit memory (nondeclarative or procedural memory 程序性记忆): memory in which previous experience aids in performance of a task without conscious recall.
Memory process:
- Acquisition: the initial formation of a memory as a consequence of experience and learning
- Retrieval: the recall of a memory
- Storage: the step in between acquisition and retrieval, during which memory is held somewhere in the nervous system
- Consolidation: newly acquired memory is stabilized for long-term use, one-time event following initial memory formation
- Reconsolidation: when same memory is reactivated for retrieval
HM病人保留先前的explicit memory，但是不能形成新的记忆，可以与人交谈（working memory），可以完成镜子画画任务（implicit memory）
→ Hippocampus:
- An important region of the medial temporal lobe essential for acquisition of new explicit memories.
- But nor for long-term storage or retrieval
- Working memory and implicit memory do not require hippocampal function
11.2 Hypothesis I: Memory is stored as strengths of synaptic connections in neural circuits
KEY QUESTION: What is the cellular basis of memory storage?
A leading hypothesis: Memory is stored as strengths of synaptic connections in neural circuits.
Synaptic weight matrix: https://youtu.be/yoF1KnmKl08?si=dV1sDsFKNF3oi4_z
Circuit organization of the hippocampus
内嗅皮层 → 海马
- 内嗅皮层 superfcial layers 的神经元伸出轴突组成 perforant path ，与 DG 的 granule cells 形成突触连接；
- DG granule cells 的轴突形成 mossy fibers 与 CA3 锥体神经元的树突形成突触连接；
- CA3椎体神经元的轴突形成 Schafer collaterals 与 CA1 锥体神经元的树突形成突触连接
- CA1树突也接受来自内嗅皮层perforant path的直接输入
These connections can provide a huge capacity for memory acquisition and storage.
11.3 Hypothesis II: Learning modifies the strengths of synaptic connections
KEY QUESTION: How to alter such weights based on experience
A leading hypothesis: Using the term synaptic plasticity to describe changes in the strengths of synaptic connections in response to experience and neuronal activity.
Hebb‘s rule and its extensions: When the firing of a presynaptic neuron repeatedly participates in causing a postsynaptic neuron to fire, their synaptic connection is strengthened; conversely, when the fring of a presynaptic neuron repeatedly fails to elicit fring of a postsynaptic neuron, their synaptic connection is weakened
Learning:
- Supervised: the output of a circuit is compared with a desired target output, and synaptic weights are modifed to minimize discrepancies. Example: Cerebellar gain adjustment of the vestibular-ocular refex.
- Unsupervised: synaptic weight changes result from experience without specifc instructions.
- Reinforcement based: olfactory learning in fruit fies and reward-based learning in mammals
Other plastic changes: modulating the expression level and subcellular distribution of ion channels (NaV at AIS); degree of axon myelination
研究方法：
- top-down: deconstructs complex pehnomena to reveal the underlying mechanism.
- bottom-up: start with more basic, smaller-scale phenomena and explore how they related to higher-level event.
