Lecture 18: Learning and Memory 2

Question 1

Engram

Answer 1

The neural representation of memories

Question 2

Karl Lashley ( 1890-1958)

Answer 2

• First researcher of brain mechanisms of learning and memory
• Examined learning in rats following transactions (cuts of axons) and lesions (removal of brain matter) of different cortical regions
• Cortical transactions failed to block learning
• Cortical lesions slight learning impairments, and location did not really matter
• Larger lesions led to more impairment
  “this series of experiments has yielded a good bit of information about what and where the memory trace is not”

Question 3

Equipotentiality of Memory in the Cortex

Answer 3

All areas of the cortex are equally involved in memory

Question 3

Patient H.M.

Answer 3

• Suffered from epilepsy in the hippocampus as a child
• Doctors removed the hippocampus and adjacent structures on both hemispheres
• Epilepsy largely relieved
• Lost the ability to form new episodic memory
• Anterograde amnesia
• Also suffered temporally graded (just before the removal of the hippocampus) retrograde amnesia
• Could learn skilled movements

Question 3

Mass Action

Answer 3

Ability to form memories depends only on the mass of brain matter

Question 4

Synaptic Plasticity Hypothesis

Answer 4

Experience can leave a memory trace by causing long-lasting changes in synaptic connections

Question 4

Long-Term Potentiation (LTP)

Answer 4

• A potential mechanism for experience-dependent synaptic plasticity
• Repetitive high-frequency (intense stimulation of a presynaptic neuron induces a long-term increase of the synapse with the postsynaptic neuron

Question 4

Glutamate binding to AMPA receptors

Answer 4

• Glutamate bings to AMPA causing a sodium channel to open
• Results in depolarization (EPSP) in the postsynaptic cell

Question 4

Trisynaptic Circuit of the Hippocampus

Answer 4

1. Information about experience arrives into the hippocampus from the entorhinal cortex to the dentate gyrus through the performant pathway (LPP/MPP)
2. info gets through mossy fibers (MF) to CA3 pyramidal cells
3. Through schaefer collaterals (SF) info reaches CA1 pyramidal cells

Question 4

Hebbian Plasticity (Learning)

Answer 4

If cell A persistently and repeatedly excited cell B, the efficacy of the synapse between them will increase

Question 5

Glutamate binding to NMDA receptors

Answer 5

• Opens a calcium channel
• Molecule of magnesium blocks Ca2+ from entering
• Strong and consistent depolarization in AMPA causes Mg2+ to leave
• Ca2+ causes more AMPA to be produced via genes and more transport via second messenger cascades