• Learning and memory

• 1e11 neurons
• 1e3 synapses/neuron
• 1e14 synapses or 1.25e13 bytes
• 1e9 gigabyte, 1e12 terabyte, 1e15 petabyte

http://www.scientificamerican.com/article.cfm?id=what-is-the-memory-capacity

• Learning
  • ?
• Memory
  • ?

• Learned?
• Remembered?

• Learning
  • Change in perception, thought, behavior, emotion over time
• Memory
  • Information derived from past experience that influences current behavior

• Stored in sequences of binary digits (bits): {0,1}
• Stored by address: "011000" stored in "1110000"
• Single characters, images, sounds, data stored as sequences of bits.
• Volatile vs. non-volatile

• Changes in patterns of neural activity
• Changes in patterns of connectivity
  • New synapses
  • Changes in synaptic strength (+/-)

When an axon of cell A is near enough to excite cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficacy, as on of the cells firing B, is increased. (Hebb, 1949, p. 62)

Neurons that fire together wire together. (Lowell & Singer, 1992, p. 211).

• Coincidence detector
  • Sending cell has released NT
  • Receiving cell is/has been recently active
• Chemically-gated
  • Ligand- (glutamate + glycine co-factor) gated
• Voltage-gated
  • Mg++ ion 'plug' removed under depolarization

• Associate (link)
  • Concept A -> Concept B
  • Neuron A -> Neuron B

• Trump
• Duck
• Draper

• Increase in synaptic strength based on recent activity.
• But how to learn/remember "causal chains"?
  • e.g., lightning THEN thunder
  • unusual food THEN indigestion

• A before B: strengthen A->B
• A after B: weaken A->B
• Neural Plasticity
  • Lasting changes in neural firing, connectivity
• NMDA receptor molecular mechanism for implementing LTP and spike-timing-dependent plasticity

• Ca++ entry triggers biochemical cascade
• Existing (AMPA) glutamate receptors made to stay open longer
• New AMPA Glu receptors synthesized, inserted into postsynaptic membrane

• Memory of what?
  • Facts/events/places vs. skills
• Memory of when?
  • Immediate vs. distant past
• Memory for how long?
  • Seconds vs. years

• Learning and memory involve changes in neural firing, circuitry
• Hebbian learning a type of associative learning
• NMDA receptor as coincidence detector
  • Molecular basis of one form of long-term potentiation (LTP)
• Different types of information stored in different brain systems

• Intractable/untreatable epilepsy
• Bilateral resection of medial temporal lobe (1953)
• Epilepsy now treatable
• But, memory impaired
• Lived until 2008

• Acquired loss of memory
• ≠ normal forgetting
• Note: computers don't forget

• Retrograde amnesia
  • Can’t remember 10 yrs before operation
  • Distant past better than more recent
• Severe, global anterograde amnesia
  • Impaired learning of new facts, events, people
• But, skills (mirror learning) intact

• Retrograde ('backwards' in time)
  • Damage to information acquired pre-injury
  • Temporally graded
• Anterograde ('forward' in time)
  • Damage to information acquired/experienced post-injury

Every day is alone in itself, whatever enjoyment I’ve had, and whatever sorrow I’ve had…Right now, I’m wondering, have I done or said anything amiss? You see at this moment, everything looks clear to me, but what happened just before? That’s what worries me. It’s like waking from a dream. I just don’t remember.

• Disease
  • Alzheimer’s, herpes virus
• Korsakoff’s syndrome
  • Result of severe alcoholism
  • Impairs medial thalamus & mammillary bodies

• Fencing accident
• Damage to medial thalamus
• Anterograde + graded retrograde amnesia
• Are thalamus & medial temporal region connected?

• Skill-learning
• Mirror-reading, writing
• Short-term memory
• “Cognitive” skills
• Priming

• Long-term memory for facts, events, people
• ≠ Short-term memory
• ≠ Long-term memory for “skills”
• Separate memory systems in the brain?

• Alzheimer's disease
• The hippocampus, memory