Memory and cognition

Question 1

What is cognition?

Answer 1

The integration of all sensory information to make sense of a situation. Requires the ability to learn and remember.

Question 2

What is neuronal plasticity?

Answer 2

The ability of central neurons to adapt their neuronal connections after we learn something.

Question 3

What is most of the brain made of?

Answer 3

Association areas which integrate information from multiple sources.

Question 4

Where are memories formed?

Answer 4

In the limbic system (part of the old cortex but has important connections with the neo/new cortex, especially temporal and frontal lobes).

Question 5

What are the 4 parts of the limbic system?

Answer 5

Most primitive part of the cortex:

• hypothalamus
• hippocampus (memory)
• cingulate girus
• amygdala

Question 6

What is the limbic system responsible for?

Answer 6

• Instinctive behavior - drives for sex, thirst, hunger etc

- Emotive behavior - driven by seeking reward or avoiding punhshment

Question 7

What happens if certain areas of the limbic system are stimulated in conscious individuals?

Answer 7

• Reward areas: intense feelings of well-being, euphoria and sexual arousal
• Punishment areas: terror, anger or pain

Question 8

What are the affective components of sensory experiences?

Answer 8

Reward and punishment are central aspects to learning - motivation to learn comes from gaining a reward (passing an exam) or avoidance of punishment (resitting an exam). This drives everything we do.

Memory recall depends on the significance of an event.

Question 9

What is habituation?

Answer 9

Experiences that are neither rewarding or punishing, and are therefore barely remembered.

Question 10

Where does all sensory information go before going to different limbic system structures?

Answer 10

Via the hippocampus.

Question 11

Which structure is central to learning and the formation of new memories?

Answer 11

Hippocampus.

Question 12

What happens in people with bilateral hippocampal damage?

Answer 12

• Have an immediate sensory memory seconds in length
• Intact long-term memory from before the damage, but unable to form new long-term memories
• Reflexive motor skills remain intact

(Clive Wearing - HSV infection caused bilateral hippocampal destruction)

Question 13

What are the 4 stages of memory?

Answer 13

1) Immediate/sensory memory: holding experiences in the mind for a few seconds (visual memories decay fastest, auditory slowest)
2) Short-term memory: seconds to hours; working memory eg dialling a phone number; associated with reverberating circuits
3) Immediate long-term memory: hours to weeks eg what you did last weekend; associated with chemical adaptations at the presynaptic terminal
4) Long-term memory: hours to a lifetime eg where you grew up and childhood friends; associated with structural changes in synaptic connections

Question 14

Describe reverberating circuits.

Answer 14

Short-term memory is a chemical phenomenon that depends on maintained excitation from reverberating circuits - need to be constantly refreshed:

• Each synapse in a reverberating circuit is excitatory –> brief excitatory stimulus at A causes long lasting neuronal activity in B –> reverberating circuit neurons continue to excite all neurons in the pathway
• This keeps a short-term memory alive

Question 15

What happens if a short-term memory is deemed significant/insignificant?

Answer 15

• significant: reverberation results in consolidation of the memory to long-term memory
• insignificant: reverberation fades and so no consolidation occurs

Question 16

What happens when the refreshing effect of reverberation is interrupted?

Answer 16

Loss of memory –> amnesia. Typically seen following head injury or cerebrovascular events.

Question 17

What is anterograde amnesia?

Answer 17

Inability to recall events following an injury - can be short-lived or permanent (Clive Wearing - destruction of the hippocampus whoch results in a permanent inability to form new memories).

–> Anterograde After

Question 18

What is retrograde amnesia?

Answer 18

Inability to remember events before an injury. Recall of events a long-time ago is usually unaffected (better rehearsed and more deeply ingrained).

Question 19

What happens if only the thalamus is damaged?

Answer 19

Only retrograde amnesia, suggesting that the thalamus is required for searching out existing memory bank.

Question 20

What chemical changes in pre-synaptic neurons occur in immediate long-term memory?

Answer 20

Increasing Ca+ entry to presynaptic terminals increases neurotransmitter release and therefore strengthens the synapse.

Question 21

Which structural changes at synapses does long-term memory involve?

Answer 21

1) Increase in neurotransmitter release sites on presynaptic membrane
2) Increase in the number of neurotransmitter vesicles stored and released
3) Increase in number of presynaptic terminals

Question 22

Define long-term potentiation.

Answer 22

A greater change in graded membrane potential in the post synaptic cell (EPSP) which strengthens the synapse in long-term memory. Forms the basis of learning and memory.

Question 23

What are the 2 main types of long-term memory?

Answer 23

1) Declarative/explicit memory: abstract memory for events (episodic memory), and for words, rules and language (sematic memory) - mainly based in the hippocampus.
2) Procedural/reflexive/implicit memory: acquired slowly through repetition; motor memory for acquired motor skills such as playing tennis and rule based learning (driving). Based in the cerebellum and is independent of the hippocampus.

Question 24

How is short-term memory converted to long-term memory?

Answer 24

Through consolidation - improves selective strengthening of synaptic connections through repetition (this is why you need to keep challenging the brain when studying). This process takes time - if interrupted by anaesthesia or electrical convulsion then these memories are lost.

Question 25

Where are memories stored?

Answer 25

In the sensory and association areas of the cortex - similar memories are stored together (which is why you sometimes see things that don’t exist in certain images).

Question 26

What is the Papez circuit?

Answer 26

This is a circuit gated by the frontal cortex if it finds an experience useful:

1) Sensory input to sensory and association areas
2) Frontal cortex assesses the significance with limbic system punishment and reward areas
3) Papez circuit: cingulate gyrus, hippocampus, mamillary body, anterior thalamus
4) Significant?
5) Written into the LTM
6) ‘Gating’ of the Papez circuit
7) Still significant?
8) Keep writing into LTM

Question 27

What happens ti different components of a memory?

Answer 27

They are laid down in different parts of the cortex - this is why recall of a memory can be evoked by multiple associations eg smell, sight etc.

Question 28

Why are smells powerful at evoking long-term memories?

Answer 28

Olfactory stimuli go from the olfactory tract, through the amygdala and hippocampus to the prefrontal cortex where they are acknowledged –> this is why smells are powerful in evoking LTM’s.

Question 29

What is Korsakoff’s syndrome?

Answer 29

Chronic alcoholism - vitamin B1 deficiency which leads to damage of limbic system structures. Ability to consolidate memory is impaired.

Question 30

Why is there impairment of memory in Alzheimer’s disease?

Answer 30

Severe loss of cholinergic neurons throughout the brain, including the hippocampus.

• Anti-cholinesterases can be used and show some improvement, but underlying degeneration continues.
• Unknown cause.

Question 31

Why is REM sleep important for memory?

Answer 31

Dreaming may enable memory consolidation and reinforcement of weak circuits.

• Patients with Korsakoff’s syndrome or Alzheimer’s have greatly reduced REM sleep (as cholinergic neurons are responsible for REM.

Question 32

What is the purpose of dreaming?

Answer 32

To tidy up memory stores so that the same information can be packaged up more compactly. Dreaming may also help us to forget memories that are no longer useful.