What is the difference between episodic memory and familiarity?
Episodic:
- What, when, where
- Long-term, declarative memory
- Hippocampus and medial temporal cortex
Familiarity:
- Feeling of recognition without necessarily remembering when or where
- Automatic, implicit form of recognition
- Relies on different neural mechanisms compared to episodic memory, and is associated with regions like perirhinal cortex
Which structures are involved in encoding of familiarity? And evidence
- Familiarity: A form of memory stored in and around the entorhinal cortex
- Activity shown in familiarity was measured at encoding, not retrieval
- Stronger activity = Higher familiarity
- Evidence can be found in the memory retrieval task where they measured brain activity during encoding
- fMRI activations correlated with confidence ratings, can be seen in the entorhinal cortex
- Focus on confidence judgment!!
Which structures are involved in encoding of episodic memory? And evidence
- Posterior Hippocampus and Posterior Parahippocampal Cortex/Fusiform Gyrus
- Both areas showed large activity the prev day when the next day, recollection was accurate
- Both showed low activity when the next day, the recollection was poor
MTL and Retrieval of Familiarity
- Hippocampus (both right and left) plays a role in source retrieval but not in familiarity retrieval
- Correct recollection = Higher change in fMRI
- Correct rejection = Lower change in fMRI
- Not much change in fMRI between correct familiarity and miss
Where are episodic memories stored? And evidence
Memories are stored in higher order sensory areas
- More activity during encoding than retrieval, and storage
- These memories are actually stored in the cortex that originally encodes the information (word paired with sound = encoded in auditory cortex = stored in auditory cortex)
- Hippocampus simply helps find the information and retrieve it when needed
Exp:
1. Shown a word which was either paired with a picture or a sound, while inside an fMRI scanner
2. Delay of one day
3. Asked whether a word was paired with a picture or a sound, while inside an fMRI scanner
What is the role of the frontal cortex in memory storage and retrieval?
Two theories for this
- Left frontal cortex: Episodic encoding and semantic retrieval
- Right frontal cortex: Episodic retrieval
- Evidence is from studies comparing cases of cognitive deficits
OR
- Left FC: Verbal material/memory
- Right FC: Object and place material/memory
- Evidence is from fMRI activations (encoding) showing left FC for words, right FC for faces, and both FCs for nameable objects
How are memories stored? Seamless/dispersed?
- When we have an episodic memory, it all comes together as one holistic thing -> Supports argument for seamless
- The storage of a memory is related to where is what encoded -> Supports argument for dispersed
- Explicit memory is stored in many different places, whereby working memory helps link these fragments
- Lesions, fMRI and PET studies argue for category-specific encoding and storage of memory
*Exp:
1. Ps went in a scanner and were shown words of animals or of tools and had to memorise it
2. Animals encoded in visual domain; Tools encoded in areas that are involved when in use
Apperceptive agnosia
Person can verbally identify an object but cannot visually replicate it
Associative agnosia
Person can visually replicate an object but cannot verbally identify it (can’t assign meaning to the image/object)
Learning at the neuronal level
- Neurons communicate through axons and synapses
- Learning is the strengthening or weakening of this connection
- Learning happens in the form of synaptic plasticity, which can be LTP or LTD
What is Long Term Potentiation (LTP)?
Learning (or the strengthening) of connections between our neurons
What is Long Term Depression (LTD)?
Unlearning (or the weakening) of connections between our neurons
Hippocampus and Place cells
Exp:
- Place cells found in mice and rats originally; Recorded in the hippocampus
- Would record that neuron while the mouse is simply exploring their environment (i.e. an open arena)
- As the mouse runs about, when it reaches a certain place, the hippocampal place cell will fire more action potentials (train of electrical activity)
Place Cells:
- It is a way of telling us where we are in the environment
- Place cells encode space over time; They have a fairly stable place preference
NMDA activity disruption in CA1:
- No NMDA = No LTP in the hippocampus = No spatial learning
