Brain Mechanisms of Memory Flashcards
How can your memory be better than a computer’s?
Much more flexible aand works in special ways which help you remember useful information.
Why is memory important? (6)
- Learning from experience shapes thought and behaviour in an adaptive way
- Attention is driven by memory
- Memory underpins conscious and unconscious decisions
- Culture and society
- Central to personal identity
- Language
Who is Clive Wearing?
- Conductor and musicologist who developed dense amnesia
- Using his STM, he can retain about 20 seconds
What parts of Clive Wearing’s memory were in tact?
- He can still read and learn to play new pieces of music
- He can still remember his wife as he met her before the brain injury
- Not all LTM is damaged
What happened to Henry Molaison (HM)?
- Performed bilateral medial temporal lobectomy to remove both his hippocampi
- Epilepsy cured but unexpected consequences for memory
Where is the hippocampus?
Embedded deep inside the temporal lobes
What parts of HM’s brain were removed?
Virtually all anterior hippocampus and surrounding cortex removed, plus amygdala.
Some posterior hippocampus remains
What is anterograde amnesia?
condition in which a person is unable to create new memories after an amnesia-inducing event
What is retrograde amnesia?
amnesia where you can’t recall memories that were formed before the event that caused the amnesia
What is temporal gradient?
a pattern of retrograde amnesia characterized by greater loss of memory for events from the recent past (i.e., close to the onset of the amnesia) than for events from the remote past.
What memory loss did HM show?
- Unable to learn new things
- Temporal Gradient
What does HM show via the temporal gradient?
That the hippocampus is crucial for new learning but not for storing older memories.
What type of amnesia usually shows a temporal gradient?
Retrograde amnesia
What other causes are there of amnesia other than surgical lesions?
- Anoxia
- Head injury
- Herpes simplex encephalitis
- Korsakoff’s syndrome
- Alzheimer’s disease
Why can Anoxia cause amnesia?
Hippocampal neurones have a high metabolic rate and so require lots of oxygen.
How does information get from the hippocampus to the cortex?
The major outputs from the hippocampus go to the fornix.
The mammillary bodies are a gateway from the fornix to the thalamus.
The thalamus feeds back to the cortex.
What types of memory are conscious and what parts are unconscious?
Episodic and Semantic = Conscious memory
Procedural = Unconscious
How does Herpes Simplex Encephalitis cause amnesia?
Herpes simplex virus spreads from face along cranial or olfactory nerves to the brain.
How is verbal learning impaired in amnesia?
- Paired-associate learning is tested
Patients with dense amnesia like HM and Ep do not remember studying any words and so cannot attempt this task
How is visual learning impaired in amnesia?
- Rey Figure Copy task
- If they are asked to recall the picture again after 15 minutes, they don’t have the ability to recall it with any level of detail at all.
How is STM preserved in amnesia?
- Normal ability to hold on to info actively for a few seconds
- Patients are only impaired when asked to retain the information for later.
How is Semantic Information preserved in amnsesia?
- Normal retention of factual knowledge
- Normal performance on tests such as providing definitions, naming pictures, understanding sentences
Explain preserved implicit memory in terms of classical conditioning.
Claparede 1911 shook hands with a patient while he pricked her and the patient later refused to shake his hand despite no recollection with the doctor.
Explain preserved implicit memory in terms of motor learning.
Brenda Milner did a mirror drawing task with HM to test his procedural memory.
- HM gets extremely good at the task each time he does it despite having no recollection of having done it before
Explain preserved implicit memory in terms of priming.
- Patients studied a word, then were presented with the begging of the word and asked to finish it.
- Patients did the same, if not better than the controls
What type of memory seems to be impaired in hippocampal damage?
- Episodic
What evidence is there for preserved implicit memory in amnesia?
- Classical Conditioning
- Motor learning
- Priming studies
What does the study of amnesia show us about the hippocampus?
Hippocampus is crucial for the conscious retrieval of an experience.
What does a slice through the hippocampus look like?
Onion rings
What does hippocampus mean?
Seahorse
What structures are within the hippocampus?
- Dentate gyrus
- Subiculum
- CA1
- CA3
What is the role of the dentate gyrus?
- Major input structure of the hippocampus
- Projects to the CA3 field
Where in the hippocampus is the dentate gyrus located?
Towards the middle
How are the CA3 and CA1 fields related?
They have very dense connections between them
What role are the CA1 and CA3 fields thought to play?
The synapses between CA1 and CA3 are supposed to play a critical role in long term memory
Where does CA1 project information to?
The subiculum
What is the role of the subiculum?
Major output structure of the hippocampus projecting to lots of other parts of the brain
Where is the entorhinal cortex?
- Adjacent to the hippocampus
- Gateway between hippocampus and cortex
Where is the entorhinal cortex?
- Adjacent to the hippocampus
- Gateway between hippocampus and cortex
What types of cortex supply the entorhinal cortex?
- Perirhinal cortex
- Parahippocampal cortex
What is the role of the perirhinal cortex?
Important for object recognition
What is the role of the parahippocampal cortex?
Spatial layout coding
What are polymodal association areas?
Represent information across lots of different modalities of info
What are unimodel association areas?
Processing of sensory inputs or motor functions, so they represent only one modality of info
Where does the posterior of the hippocampus receive most of its input?
From parahippocampal cortex: spatial memory
Where does the anterior of the hippocampus receive most of its input from?
- Amygdala and perirhinal cortex: emotional memories and familiarity/salience
Why is the hippocampus ideal for associative learning?
It contains multiple nested feedback loops
What is long-term potentiation?
there are physical changes at the synapse that make it more likely after you formed a memory that all the other parts of the memory will be associated with one part of it
What are cell assemblies?
Memories are stored in connections between neurons
What is the idea that ‘cells that fire together, wire together’
The idea that when two cells fire at the same time, a stronger connection is formed between them
Is glutamate excitatory or inhibitory?
Excitatory
What happens during long-term potentiation?
- Release of some glutamate by pre-synaptic neuron, Na+ channels open briefly
- Release of lots of glutamate, ion channels in post-synaptic cells open for longer, large influx of Na+ ions
- This strengthens communication at this particular synapse
What evidence is there for LTP?
- LTP in rabbit hippocampus
What is EPSP?
Excitatory postsynaptic potential
What are the two types of glutamate receptors?
AMPA
NMDA
When do NMDA receptors open?
When the neuron depolarises, then lets calcium in as well as sodium
What is the role of AMPA receptors?
Do the legwork in terms of opening channels in response to glutamate.