Memory and cognition

Question 1

Outline the role of the limbic system in learning and memory

Answer 1

• The limbic system gives events emotional significance, which is essential to memory
  
  • The limbic system represents the “old cortex” but has important connections with the “neo cortex” in particular, the frontal lobes which allows us to make sense of situations through learning
  • The limbic system is responsible for thirst, hunger, sex and emotive behaviours and is driven by seeking reward and avoiding punishment
  • Electrical stimulation of certain areas of the limbic system in conscious patients cause intense feelings of wellbeing, euphoria and sexual arousal (these are the reward areas)
  • Electrical stimulation of other areas of the limbic system cause elicit terror, anger or pain (these are the punishment areas)
  • Reward and punishment are essential to aspects of learning as they cause the “affective components” of sensory experiences
  • Motivation to learn comes from gaining a reward (passing exams) or avoiding punishment (resitting exams)
  • Reward and punishment drives almost every conscious thing that we do
  • Experiences that are neither rewarding or punishing (insignificant experiences) are barley remembered

Question 2

What are the areas of the limbic system?

Answer 2

• The limbic system consists of 4 distinct areas

• The hypothalamus: Associated with ANS responses
• The hippocampus: involved in learning and memory
• The Cingulate gyrus: plays a role in emotion
• The amygdala: associated with emotion and memory

Question 3

Outline the differences between short-term and long-term memory

Answer 3

• New memories are formed by the hippocampus
• If there is bilateral damage to the hippocampus then you won’t be able to form new memories and so will not have a good short term memory
• This does not affect the memories already formed which are stored in the cortex and are found by the thalamus

Question 4

What is immediate or sensory memory?

Answer 4

• A few seconds
• It describe the ability to hold experiences in the mind for a few seconds
• Based on different sensory modalities
• Visual memories (<1s) decay faster than auditory memories (<4s)

Question 5

What is short term memory?

Answer 5

• seconds- hours
• Often referred to as working memory
• The brain’s post-it note
• Used for short term tasks such as dialling a phone number, mental arithmetic and reading a sentence
• Associated with reverberated circuits (they need to be constantly refreshed)
• Each synapse in a reverberating circuit is excitatory and hence a brief excitatory stimulus at A will cause a long lasting neuronal activity at B as the reverberating circuit neurons continues to excite
• If deemed significant eventually this reverberation circuit results in consolidation of the memory in the long term memory storage
• If it is deemed insignificant then the reverberation fades and no consolidation occurs

Question 6

What is intermediate-long term memory?

Answer 6

• Hours to weeks
• What you did last weekend
• Associated with the chemical adaption at the presynaptic terminal
• Increasing calcium entry to the presynaptic terminals, increase neurotransmitter release

Question 7

What is long term memory?

Answer 7

• Can be life long
• Where you grew up and your childhood friends
• Long term memory involves structural changes at the synapses
- Increase on neurotransmitter release sites on presynaptic membrane
- Increase the number of neurotransmitter vesicles stored and released
- Increase in the number of presynaptic terminals
• At the same time increased amplitude in graded membrane potential in the post-synaptic cell in observed (Long term potentiation)
• Declarative or explicit memory
- Abstract memory of events (episodic memory)
- Words, rules and language (semantics memory)
• Procedural/ reflexive/ implicit memory
- Acquired through slow repetition
- Motor memory for acquired motor skills such as playing tennis
- Rules based learning such as in the UK drive on the left
- Thinking about these skills often impairs performance
- Is based mainly in the cerebellum
- Is independent of the hippocampus

Question 8

What is retrograde amnesia?

Answer 8

• Can’t remember events leading up to the injury
• Recall of events that happened a long time ago is fine (they are better rehearsed and more deeply ingrained)
• Retrograde amnesia often presents with antegrade amnesia but if only the thalamus is damaged (and the hippocampus is OK) then only retrograde amnesia is seen

Question 9

What is anterograde amnesia

Answer 9

• Can’t form new memories
• Depending on the extent of the injury it can be short lived or long term
• Destruction of the hippocampus results in the permanent inability to form new memories

Question 10

What are the mechanisms involved in consolidating short term memories into long term memories?

Answer 10

• Short term memory is converted to long term memory through consolidation
• Consolidation involves strengthening of synaptic connections through repetition
• A similar process occurs in the cerebellum during motor learning
• During the consolidation process memory simply exists as electrical activity and is vulnerable to being wiped out
• Your brain naturally gives attention to events that it deems significant
• New memories are “coded” and then stored in the sensory and association areas of the cortex
• Coding results in new memories being stored beside older memories that it deems similar
• If the memory is considered useful then the frontal cortex “gates” the so called papez circuit
• Reverberating activity then continues between the Papez circuit, the frontal cortex, the sensory and association areas until the consolidation process is complete

Question 11

Why is sleep important for the memory process?

Answer 11

• Consolidation requires attention and thus learning is more difficult when you are tiered
• REM sleep is significant for memory
- Subjects deprived of REM sleep show significant impairment of memory consolidation for complex cognitive tasks
- Dreaming may enable memory consolidation (reinforces week circuits)