Bio psych2 5

Lecture Overview

• Course: Biological Psychology 2

• Lecture Focus: The Neuroscience of Memory Processes

• Instructor: Dr. Richárd Reichardt

Understanding Memory

The Engram

• Definition: The engram refers to the physical manifestations of memory in the brain.

• Related Concepts: Long-Term Potentiation (LTP) signifies a lasting enhancement in signal transmission between two neurons, while Neural Replay refers to the reactivation of memory through neural firing patterns.

The Substrate of Memory

• Historical View: Early beliefs proposed that memories were housed in an immaterial soul, compared metaphorically to notes being inscribed on a wax tablet by Aristotle.

• Modern Understanding: The brain is recognized as the physical substrate of memories, with memory formation relying on associations between impressions.

Memory Formation and the Engram

Richard Semon's Contributions

• Psycho-physiological Parallelism: Semon suggested that psychological experiences correspond directly to changes in the nervous system, introducing the concept of the mneme (memory representation) and the mnemic trace (engram) which can be revived by stimuli related to the original experience.

The Distributed Engram

• Research by Karl S. Lashley:

  • Experiment: Lashley trained rats to navigate mazes and excised their cerebral cortex to study memory impairments.

  • Findings: Memory degradation increased with more tissue removal, but the specific area removed was inconsequential, implying memories might not reside in one isolated location.

Neural Mechanisms of Memory

Hebb’s Rule

• Donald O. Hebb's Insights: Advocated that memory formation is due to changes in synaptic weights, a concept now acknowledged as Hebbian learning, wherein multiple coactive neurons strengthen their connection through associatively learned experiences.

Habituation and Sensitization

• Eric Kandel's Research: Examined simple non-associative learning, revealing changes in membrane potential in response to presynaptic signals that characterize the two processes of habituation (decreased response) and sensitization (increased response).

The Hippocampus and Memory

Role in Long-Term Memory (LTM)

• Case Study: The classic case of HM revealed crucial insights into the function of the hippocampus in encoding long-term declarative memories, distinguishing them from procedural memories.

Morris Water Maze

• Experimental Setup: This task involves placing rats in opaque water to find a hidden platform, demonstrating that normal rats can learn to navigate while those with hippocampal damage struggle to do so, indicating the hippocampus's essential role in forming complex memory traces.

Long-Term Potentiation (LTP)

Studies and Findings

• Bliss and Lømo's Work: Their studies on rabbit hippocampus pinpointed LTP as a significant synaptic enhancement where persistent changes in synaptic strength occur, lasting for extended periods post-stimulation.

Molecular Mechanisms of LTP

• Receptors Involved: Both NMDA and AMPA receptors facilitate LTP. In normal conditions, only AMPA receptors transmit signals, but robust depolarization activates NMDA receptors, leading to subsequent intracellular signaling and synaptic enhancements.

• Classic Study Implications: Research indicates that removing the NMDA receptor gene results in impaired memory performance, affirming its critical role in LTP induction.

Memory Reactivation and Consolidation

Place Cells in the Hippocampus

• Functional Significance: Place cells provide a neural map, activating as animals traverse their environment, and are crucial for memory consolidation through reactivation during sleep.

Sleep and Memory Consolidation

• Reactivation Patterns: Studies show that activity of place cells corresponds with sharp-wave ripples during sleep, promoting communication between the hippocampus and cortex.

• Active System Consolidation Hypothesis: The model posits coordinated patterns of hippocampal and cortical activity during sleep facilitate memory consolidation.

Synaptic Homeostasis and Creativity

• Synaptic Strength Adjustments: The reduction in synaptic strength during sleep is theorized to enhance memory consolidation through systematic processes.

• Memory and Creativity: Sleep may also foster innovative thinking through mechanisms like unitization and abstraction, resulting in novel ideas during dreams.

Closing Thoughts

• Next Lecture Preview: The following class will cover the interplay between emotions and memory.