Chapter 9 Memory Failures

Question 1

Patient H.M.

Answer 1

• developed epilepsy as a child, unable to be dependent in 20s
• neuroscience experimental surgery
• believed source of epilepsy was in medial temporal lobe and cut this part of the brain out
• treated the epilepsy but had unexpected consequences: amnesia
• memories are formed in medial temporal lobe
• could not learn new memories but could remember things before the surgery
• could remember things for up to 20 minutes
• could not make new long-term declarative memories
• mirror tracing task abilities= procedural memory was intact

Question 2

Retrograde Amnesia

Answer 2

• inability to remember memories before damage
• graded/limited retrograde amnesia; don’t remember things right before an accident
• H.M. could not remember much until 3 years before the surgery
• H.M. doesn’t have complete retrograde amnesia means the medial temporal lobe is NOT the permanent storage unit of long-term memories
• may be stored there for a little but not forever

Question 3

Anterograde Amnesia

Answer 3

• inability to form memories after the damage

- graded/limited anterograde amnesia; wisdom teeth removal

Question 4

Major Structures of Medial Temporal Lobe

Answer 4

1. perirhinal cortex
2. entorhinal cortex
   - damage to just this area can also develop anterograde amnesia
   - inputs to the hippocampus go through the entorhinal cortex so this may be the reason
3. Amygdala
   - not important for declarative long-term memories
4. Hippocampus
   - very important
   - damage limited to the hippocampus creates severe anterograde amnesia for declarative memory

Question 5

MRI scans of H.M’s brain

Answer 5

• areas that weren’t supposed to be in tact were actually intact
• could explain JFK phenomenon

Question 6

Delayed Nonmatch-to-Sample Task

Answer 6

• Monkeys chose the stimulus that was already seen in fact they are supposed to chose the novel stimulus
• Monkey has to remember what was seen before so it doesn’t pick it up
• For short delays monkeys can do this without the hippocampus
• for longer delays monkeys could not do this without the hippocampus

Question 7

Place Cell Video

Answer 7

• CA1 regions of the hippocampus
• fire in response to particular location in an environment
• depends on landmarks within a space
• the hippocampus is creating and storing a cognitive map of our environment and these cells are a part of that

Question 8

Morris Water Maze & Spatial Learning

Answer 8

• hidden platform mice must find
• can the mouse do this without a hippocampus?
• depends on whether you start the mouse from the same location every time or from a variable location
• variable location you need the cognitive map from the hippocampus
• same location its procedural memory which is independent of the hippocampus
• lesioning the hippocampus prevents rodents from learning how to find the platform from a variable start position

Question 9

Mammillary Bodies

Answer 9

• very sensitive to thymine deficiency
• poor diet and severe alcoholism
• the neurons respond
• results in seizures
• doses of thymine can stop it, but the damage is usually already done

Question 10

Korsakoff’s Syndrome

Answer 10

• symptoms similar to hippocampal damage
• severe anterograde amnesia
• graded retrograde amnesia
• confabulation

Question 11

Hippocampus and mammillary bodies

Answer 11

• memories can’t be permanently stored in declarative long-term memory because H.M. can still remember some older memories
• must be stored somewhere in the neocortex
• when people damage areas of the neocortex, memories in general seem to be a little fuzzier, harder to retrieve
• memories stored throughout a network in the neocortex rather than a specific location in the neocortex
• damaging any area of the brain is not going to completely wipe out memories

Question 12

Amygdala pathways and fear conditioning

Answer 12

• central nucleus
  
  • triggers fear responses; heart rate, stress
• patient S.M. missing amygdala; does not have fear; gets into trouble because she doesn’t learn to fear things that are dangerous
  1. conditioned stimulus pathway
  
  • does not automatically go to the central nucleus
  • change in the amygdala in the way the amygdala respond
• causes the central nucleus to respond
  2. Unconditioned stimulus pathway
  
  • automatically goes to central nucleus

Question 13

Advantage of studying Sea Slugs

Answer 13

• Eric Candel
• the simplicity of the sea slug’s nervous system
• you can study a specific neuron in one sea slug and find that exact neuron and connections in other sea slugs

Question 14

Sea Slug Anatomy

Answer 14

• Gills
  
  • Gill withdrawal reflex
• Siphon
  
  • Blow water out that if filtered through the gills
• Mantle shelf
• Siphon and gill sensitization
  
  • to habituate flick the siphon rather than the tail

Question 15

Mechanism of Sea Slug Habituation

Answer 15

• reflex arc
• neuron fires when the siphon is touched and excites the neuron that causes the muscles to contract and pull in the gills
• the touch neuron fires and the motor neuron fires less and less after habituation
• the synapse between the touch neuron and motor neuron changes in that less calcium enters this button in response to each action potential
• memories can be stored by changing the information/strength at the synapse

Question 16

Hebb’s Law

Answer 16

• fire = active at the same time
• wire = synaptic connection is strengthened
• as we learn a language we start to associate words with concepts
• Neuron A responds to hearing the word cat and Neuron B responds when you think of the concept/image of cat and vice versa

Question 17

Long-Term Potentiation

Answer 17

• hippocampus and entorhinal cortex
• entorhinal cortex sends axons through the preforant path and synapse onto granule cells in the dentate gyrus
• stuck recording in the dentate gyrus
• test pulse stimulates it a little and got an excitatory response
• then high frequency stimulation of the perforant path and causing granule cells to fire like crazy; fire together wire together

Question 18

AMPA and NMDA receptors

Answer 18

• AMPA
• glutamate depolarizes postsynaptic neuron, sodium flows in, neuron is excited
• NMDA
• glutamate also binds to them, but they get clogged a lot
• magnesium tends to get jammed in the receptor and is positive so it wants to go in the cell, it doesn’t fit, and nothing can go into the NMDA receptor

Question 19

Getting rid of magnesium in NMDA receptors

Answer 19

• you have to depolarize the postsynaptic membrane so the positive magnesium does not want to go in
• you need glutamate to depolarize the post synaptic membrane and then calcium can enter through the NMDA receptors
• the pre synaptic and post synaptic neuron must be firing for NMDA to fire
• NMDA triggers LTP
• if NMDA is blocked there is no LTP

Question 20

Synaptogensis

Answer 20

• starting out with a small amount of connection and creating more active sites and synapses
• have a potentiated response in the post neuron
• you need lasting potential for long-term memories
• you can also get rid of synaptic connections to weaken the strength
• children have more connection than adults that get pruned away as you get older and learn
• only save connections that make the system work best and getting rid of the ones that aren’t necessary