M&C Exam 2

Medial Temporal Lobe (MTL)

• Regions: The medial temporal lobe consists of several key structures:

  • Hippocampus: A crucial area for memory formation and consolidation.

  • Parahippocampal gyrus: Involved in processing spatial information and memory.

  • Entorhinal cortex: Acts as a relay between the hippocampus and neocortex, playing a role in memory encoding and retrieval.

  • Perirhinal cortex: Involved in object recognition and memory.

Hippocampus (HC)

• Regions: The hippocampus can be broken down into several areas:

  • Cornu Ammonis (CA) regions: CA1, CA2, CA3, and CA4, which are involved in different aspects of memory processing.

  • Dentate gyrus: Key in the formation of new memories.

  • Subiculum: Acts as a major output structure of the hippocampus.

Hippocampus Regional Specialization of Function

• CA1: Critical for the retrieval of memory.

• CA3: Important for the encoding of episodic memories and has a role in pattern separation (distinguishing similar memories).

• Dentate Gyrus: Plays a role in the encoding of new information and contributes to pattern separation.

• Subiculum: Involved in output to other brain regions, affecting memory storage and retrieval.

Medial Temporal Lobe (MTL) Regional Specialization of Function

• Parahippocampal gyrus: Involved in spatial memory and the recognition of scenes.

• Entorhinal cortex: Critical for the initial stages of memory encoding and linking information to long-term memory.

• Perirhinal cortex: Associated with object recognition and object memory.

Encoding

• Factors that Aid Encoding:

  • Attention, emotional arousal, sleep, rehearsal, and elaborative processing (connecting new information to prior knowledge).

• Things Bad for Encoding:

  • Stress, distractions, sleep deprivation, lack of attention, and lack of meaningful association to prior knowledge.

• How the Brain Supports Encoding:

  • The hippocampus is crucial for forming new memories. The entorhinal cortex and parahippocampal gyrus assist in organizing and encoding sensory information into meaningful memories.

Memory Consolidation

Memory consolidation is the process through which newly acquired information becomes stable and long-term memory. This process occurs in two main stages: synaptic consolidation and systems consolidation.

1. Synaptic Consolidation

Synaptic consolidation refers to the initial phase of memory stabilization, which occurs at the level of the synapses (connections between neurons). It typically takes place within the first few hours after learning or experiencing something new. During this phase, changes in the strength and structure of synapses take place. This is largely driven by biochemical processes, such as long-term potentiation (LTP), which enhances synaptic transmission and makes it easier for neurons to fire together, reinforcing the neural circuit involved in the memory.

• Duration: Minutes to hours

• Processes involved: Involves protein synthesis and changes in the synaptic structure.

• Key Mechanism: Long-term potentiation (LTP)

2. Systems Consolidation

Systems consolidation occurs over a longer period (days, weeks, months, or even years) and involves the reorganization of memories across different brain regions. Initially, newly learned memories rely heavily on the hippocampus, but over time, the cortical areas of the brain (especially the neocortex) take over the storage and retrieval of these memories. This transition reduces the dependence on the hippocampus as memories become more stable and resistant to disruption.

• Duration: Long-term (weeks to years)

• Involved Brain Structures: Initially hippocampus, later neocortex

• Key Mechanism: Reorganization and transfer of memories from the hippocampus to cortical regions

Reconsolidation

Reconsolidation is the process through which previously consolidated memories become labile (able to be modified) again when retrieved. When a memory is recalled, it enters a "fragile" state, making it susceptible to changes, distortions, or updates before it is "re-stabilized" or reconsolidated. This allows the brain to incorporate new information or adjust memories based on current contexts or experiences.

• Key Aspect: Memory becomes flexible upon recall and can be altered.

• Duration: Typically short (from minutes to hours after recall).

• Implication: This process is important for memory updating, but it also means that memories are not fixed and can be influenced by new information or events.

False Memory

• Why Memory is a Constructive Process:

  • Memory is reconstructed each time we retrieve it. Our brain fills in gaps with plausible information, leading to errors or false memories.

• Brain Areas Related to Memory Errors and Confabulation:

  • The prefrontal cortex (involved in decision-making and memory retrieval), hippocampus, and parietal cortex (involved in the sense of self and context) are implicated in memory errors and false memories.

• Research Experiment on False Memories:

  • The Deese-Roediger-McDermott (DRM) paradigm is a classic experiment where participants are shown a list of related words (e.g., “bed,” “pillow,” “dream”) and later falsely recall a word (e.g., “sleep”) that was not in the list.

• Why Memory Errors Are Costs of Adaptive Processes:

  • Our memory system is designed for efficiency, and we fill in gaps to avoid cognitive overload. While this can lead to errors, it also helps us to make reasonable decisions based on past experiences. Constructive memory is advantageous when it allows for flexibility and generalization from prior experiences.

Storage

• LTP (Long-Term Potentiation):

  • LTP is the strengthening of synapses based on recent patterns of activity. It is crucial for learning and memory consolidation, especially in areas like the hippocampus.

• Where Are Declarative Memories Stored in the Brain?:

  • Declarative memories (facts and events) are stored across multiple brain areas, with the hippocampus playing a key role in initial consolidation. Over time, memories are transferred to cortical regions for long-term storage.

• Necessary for Long-Term Memory Formation:

  • The hippocampus is essential for the initial encoding and consolidation of long-term memories. Also, sleepplays a vital role in memory consolidation.

• Structural Plasticity:

  • Structural plasticity refers to the brain's ability to form new synaptic connections or even generate new neurons (neurogenesis), particularly in areas like the hippocampus.

Retrieval

• Recall vs Recognition:

  • Recall: Retrieving information without cues (e.g., essay questions).

  • Recognition: Identifying information from a list or set of options (e.g., multiple-choice questions).

• Relationship Between Context and Mood and Retrieval:

  • Context (environment) and mood can serve as cues that improve retrieval, a phenomenon known as context-dependent memory and mood-congruent memory.

• Retrieval’s Effects on Memory:

  • Retrieval can strengthen memories (via retrieval-induced forgetting) or lead to errors (e.g., through retrieval-induced errors).

• How the Brain Supports Retrieval:

  • The hippocampus is involved in the retrieval process, helping to access stored information. The prefrontal cortex supports strategies for searching memory, while the parietal cortex is involved in the retrieval of spatial and contextual information.

Episodic Memory

• What is Episodic Memory?:

  • Episodic memory is the ability to recall personal experiences and specific events, including the time and place they occurred.

• Why Do Young Children Not Have Fully Developed Episodic Memory?:

  • Young children have underdeveloped prefrontal cortices and hippocampi, which are essential for episodic memory encoding and retrieval. Their ability to form detailed, autobiographical memories improves as these brain regions mature.

• Brain Areas Supporting Episodic Memory Encoding and Retrieval:

  • The hippocampus and prefrontal cortex are critical in episodic memory encoding and retrieval, along with the parietal cortex for context and sensory processing.

Semantic Memory

• What are Semantic Networks?:

  1. Semantic networks are models of knowledge representation where concepts are interconnected in a web of associations.

• Two Explanations for How the Brain Represents Semantic Knowledge:

  1. Distributed Representation: Semantic information is spread across multiple brain regions, with areas like the anterior temporal lobe playing a key role in integrating information.

  2. Hub-and-Spoke Model: The anterior temporal lobe serves as a hub for semantic memory, interacting with other brain regions (spokes) that handle sensory and motor information.

Semantics and Patients

• Distributed Accounts of Conceptualization:

  • This theory posits that semantic knowledge is represented across a network of brain regions, including sensory, motor, and abstract conceptual areas.

• Evidence that the Anterior Temporal Lobe Serves as a Hub for Semantic Cognition:

  • Studies of patients with damage to the anterior temporal lobe show deficits in semantic knowledge across various domains, supporting the idea that this area integrates semantic information.

Autobiographical Memory (AM)

• How AM Has Both Semantic and Episodic Components:

  • AM includes personal memories (episodic) as well as general knowledge about oneself (semantic). The two types of memory are interrelated and support one another in forming a coherent self-narrative.

• What is HSAM (Highly Superior Autobiographical Memory)?:

  • HSAM is a rare condition where individuals can recall nearly every detail of their personal past with high precision.

• Does AM Have a Sensory Component?:

  • Yes, autobiographical memory often involves sensory details, such as sights, sounds, and smells, which help make the memories more vivid and emotionally rich.

• How Does the Brain Support AM?:

  • The hippocampus, prefrontal cortex, and posterior cingulate cortex are involved in encoding, retrieving, and processing autobiographical memories.

Autobiographical Memory Anatomy

• Hippocampus: Links sensory and motor information to create coherent, context-rich memories.

• Frontal Lobes: Responsible for organizing memory search, controlling retrieval, and inhibiting irrelevant memories.

• Posterior Cortex: Involved in storing sensory details, especially those linked to specific autobiographical events.

Interactions Between Memory Systems in Complex Human Activities

• Different memory systems (e.g., episodic, semantic, procedural) work together in complex activities like problem-solving, decision-making, and social interactions. The integration of different types of memories helps create a comprehensive understanding of the world and allows adaptive behaviors.