1. What Is Memory?

Memory is the brain’s ability to encode, store, and retrieve information. It underpins learning, decision-making, and identity.

Key Processes:

  • Encoding: Transforming sensory input into a form that can be stored.
  • Storage: Maintaining encoded information over time.
  • Retrieval: Accessing stored information when needed.

2. Types of Memory

Type Duration Capacity Example
Sensory Memory Milliseconds Unlimited Visual afterimage
Short-Term Memory Seconds to minutes 7±2 items Remembering a phone #
Working Memory Seconds to minutes Manipulation Mental math
Long-Term Memory Days to lifetime Unlimited Childhood memories

3. Brain Regions Involved

  • Hippocampus: Consolidation of new memories; spatial memory.
  • Amygdala: Emotional memory; fear conditioning.
  • Prefrontal Cortex: Working memory; executive functions.
  • Cerebellum: Procedural memory (skills).
  • Basal Ganglia: Habit formation.

Brain Regions


4. Molecular Basis of Memory

  • Synaptic Plasticity: Changes in synaptic strength, especially Long-Term Potentiation (LTP).
  • Neurotransmitters: Glutamate (main excitatory), GABA (inhibitory), acetylcholine (attention).
  • Protein Synthesis: Required for long-term memory formation.

Diagram:
Synaptic Plasticity


5. Memory Formation Stages

  1. Acquisition: Initial learning.
  2. Consolidation: Stabilization of memory trace.
  3. Recall: Retrieval of stored information.
  4. Reconsolidation: Memories can be updated or modified upon retrieval.

6. Recent Breakthroughs (2020+)

  • Engram Cells: Identification of specific neurons (“engrams”) that store discrete memories.
    Reference: Roy, D.S. et al. (2022). “Memory retrieval by activating engram cells in the hippocampus.”
  • Optogenetics: Light-based control of neurons allows activation or suppression of memories in animal models.
  • Sleep & Memory: Deep sleep (slow-wave) shown to be critical for memory consolidation.
  • AI-Assisted Imaging: Machine learning reveals new patterns in memory-related brain activity.

Recent Study:

Roy, D.S., Muralidhar, S., Smith, L.M., Tonegawa, S. (2022). “Silent memory engrams as the basis for retrograde amnesia.” Proceedings of the National Academy of Sciences, 119(9): e2114643119.
Link to study


7. Memory Disorders

  • Alzheimer’s Disease: Progressive loss of neurons, especially in hippocampus.
  • Amnesia: Loss of memory due to injury or disease.
  • PTSD: Persistent, intrusive emotional memories.
  • Anterograde Amnesia: Inability to form new memories.

8. Surprising Facts

  1. Memories Can Be Erased and Rewritten: Activation or inhibition of engram cells can delete or restore memories in mice.
  2. False Memories Are Common: The brain reconstructs memories, often introducing errors or fabrications.
  3. Memory Capacity Is Vast: The human brain is estimated to store up to 2.5 petabytes of information.

9. Memory Trick

Chunking:
Break information into smaller, meaningful groups (chunks). For example, memorize a phone number as 123-456-7890 instead of 1234567890.


10. Most Surprising Aspect

Memories Are Not Static:
Every time a memory is retrieved, it becomes malleable and can be altered before being stored again. This process, reconsolidation, means that our memories are constantly being edited, not just replayed.


11. Concept Diagram

Memory Systems


12. The Great Barrier Reef Fact

The largest living structure on Earth is the Great Barrier Reef, visible from space.


13. References

  • Roy, D.S., Muralidhar, S., Smith, L.M., Tonegawa, S. (2022). “Silent memory engrams as the basis for retrograde amnesia.” PNAS, 119(9): e2114643119.
  • Nature News: Optogenetics and Memory

End of Study Notes