Remembering the Brain Flashcards
What are the characteristics of sensory memory?
- milliseconds to seconds time course
- high capacity
- no conscious awareness
What are the characteristics of Short-term and working memory?
- seconds to minutes time course
- limited capacity
- has conscious awareness
What are the characteristics of Long-term non-declarative memory?
- minutes to years time course
- high capacity
- no conscious awareness
What are the characteristics of Long-term declarative memory?
- minutes to years time course
- high capacity
- has conscious awareness
Examples of Nondeclarative (implicit) memory.
- Procedural memory
- Perceptual representation system (perceptual priming)
- Classical conditioning
- Nonassociative learning (habituation, sensitisation)
Brain regions responsible for episodic memory and semantic memory.
Medial temporal lobe
Middle Diencephalon
Neocortex
Regions responsible for Procedural memory.
Basial ganglia
Skeletal muscle
Brain regions responsible for perceptual representation system.
Perceptual and association neocortex
Brain regions responsible for Classical conditioning
Cerebellum
Responsible for Non-associative learning.
Reflex pathway
What is the function-structure relationship in memory.
- function and structure do not match exactly
- A structure can participate in multiple functions
- Any function may rely on multiple structures
What are the 3 definitions of Episodic Memory?
- Mental time travel: emphasis on re-experience
- Links: emphasis on relational memory
- Time and Place: emphasis on context
Structures that make up the MTL
- Hippocampus
- Entorhinal cortex,
- Parahippocampal gyrus (rhinal sulcus, perirhinal cortex, parahippocampal cortex).
Structures/divisions of the hippocampus
○ Dentate gyrus
○ Cornu Ammonis (CA) subfields (CA1, CA2, CA3, CA4)
○ Subiculum
How does information flow through the hippocampus?
- Info enters through Entorhinal Cortex
- projects to the Dentate Gyrus through the Perforant pathway.
- to CA3 through mossy fibre pathway
- projects to CA1
- projects to subiculum (output region)
Brain regions responsible for Declarative memory
- medial temporal lobe
- middle diencephalon
- neocortex
What is the role of the hippocampus in the MTL
- The hippocampus transfers the memory back to the cortex for long-term memory storage.
○ Memory consolidation
Describe the Information flow within the MTL.
- info initially collected through the perirhinal and parahippocampal cortices.
- → entorhinal cortex → different subregions of the hippocampus.
A large network of connections both within and among the subregions of the MTL cortical regions perform extensive information processing
Describe the The “Extended MTL” System.
- MTL structures are critical for memory function but they do not work in isolation.
- They work together with other brain regions, including the thalamus and the medial prefrontal cortex (extended MTL)
○ These brain region send and receive information from the MTL.
Define Retrograde Amnesia
Memory Impairment for information acquired prior to the cause of amnesia (brain damage)
Define Anterograde Amnesia
Memory impairment for events that occurred after brain damage.
Define Global Amnesia
Retrograde + Anterograde amnesia
What did H.M. suffer from after Medial Temporal Lobectomy?
○ Minor retrograde amnesia (for events within the 2 years preceding the surgery)
○ Profound anterograde amnesia: could not form long-term memories for events after surgery
○ Problems were limited to declarative/explicit memory
What did H.M. Mirror Drawing task show?
- Implicit memory intact – explicit impaired
- could learn task even though he couldn’t remember doing the task.
- MTL is critical for making new memories and retrieving old
Describe the aims and uses of the Subsequent Memory Paradigm.
- Evaluates encoding-phase activity leading to successful (versus unsuccessful memory)
- Records neural responses whilst Ps are engaged at encoding a series of words.
- Later memory of seeing the words is tested.
- compare responses between remembered and forgotten trials
What did Wagner et al. (1998): Remembered vs Forgotten stimuli study find?
- Brain activity at encoding predicts which items are later going to be recognized and which will be forgotten.
- Activity in the left ventrolateral PFC (a) and the left MTL (b) was predictive of later remembered versus forgotten stimuli
Define Familiarity.
- sense of memory that a stimulus has been encountered before
- Not recognising any information
Define Recollection
Memory for the context or other associative information about a previous encounter with a stimulus
Which brain areas of the MTL support the different aspects of familiarity & recollection?
Eichenbaum et al. (2007)
- Perirhinal cortex processes item representations (important for familiarity)
- Parahippocampal cortex is assumed to process “context” (including scene perception)
- Hippocampus binds items in context (important for recollection) - binder for relational memories
What did Ranganath et al. (2004) look at?
- Used subsequent memory paradigm to explore which brain region at encoding may differentiate between later familiar from later recollected stimuli.
- At encoding the Ps were presented with words as asked make a decision
- Ps engaged in 2 types of memory tasks
- Items categorised as recollected or familiar.
What did Ranganath et al. (2004) find?
- Familiarity-based recognition was predicted by activation in the Perirhinal cortex.
- Recollection-based recognition was predicted by activation in the hippocampus and the parahippocampus
What did Ranganath et al. (2004) conclude?
The study supported the differential contribution of the hippocampus and the perirhinal cortex in supporting recollection and familiarity respectively
What is the role of the hippocampus in Familiarity and Recognition?
- Hippocampus = recollection-based recognition (but not familiarity) independently of the type of stimulus
What is the role of the MTL (- Hippocampus) in Familiarity and recognition?
The rest of the MTL = familiarity-based recognition with a degree of material-specialisation
What roles do the Regions of the MTL play in familiarity?
- Perirhinal cortex supported familiarity for objects
- Entorhinal cortex supported familiarity for objects and faces
- Parahippocampal cortex responded to familiarity for objects and scenes.
- Amygdala supported familiarity for faces in this study
What do Alzheimer’s Patients tell us about the functional specialisation within the MTL?
- first structures affected in Alzheimer’s is entorhinal cortex and the hippocampus.
- first stages of the disease, people have difficulty with recall and with spatial memory
- can assume that familiarity memory can assist these patients in recognising familiar faces and places.
Describe synaptic consolidation.
- structural changes in the synaptic connections between neurons
- hours to days to complete
Describe system consolidation.
- Gradual shift of memory from hippocampus to the cortex
- slow process
What are the 2 theories of consolidation (related to hippocampal function)?
○ Standard consolidation theory → Temporary role of hippocampus (in storing remote memories)
○ Multiple trace theory → Permanent role of the hippocampus (in storing remote memories)
Define Ribots Law.
- observation that memories from early life tend to be preserved in amnesia.
- Memory loss following brain damage has a temporal gradient
- Explanation is that remote memories have undergone systems consolidation – they do not rely upon the MTL anymore, but are cortex-dependent
What did patient PZ show?
- had temporal gradient in amnesia.
- Unable to learn new paired associates - anterograde Amnesia
Describe the Standard Consolidation Model.
- Initially, hippocampus plays an active role in ‘binding’ the activity of disparate cortical ‘modules’
- Over time, the hippocampus plays less of a role
○ This happens due to memory reactivation. - the more we retrieve a memory the cortical areas become stabilised and refined.
What is semantic dementia?
What is Alzheimer’s disease?
- SD: Semantic dementia - progressive damage to anterior temporal lobes (cortex)
- AD: Alzheimer’s disease – progressive damage to hippocampus and related structures
What is the difference in the temporal gradient in Alzheimer’s and semantic dementia?
- SD patients can remember recent but not old events because memories not yet completely dependent on cortex – yet to be transferred out of hippocampus
- AD patients can access remote memories followed the temporal gradient dictated by Ribot’s law.
○ More recent memories were effected more than remote memories.
Describe the Multiple Trace Theory.
Nadel and Moscovitch (1997,1998)
- Hippocampus never stops having an important role in episodic memory recall
- Older memories have been reactivated many times over the years = have more traces.
- Each reactivation creates new traces in the MTL and in other neocortical structures
- To the extent that damage is not global, older memories are more likely to be remembered as they have multiple traces.
What did Gilboa et al. (2004): fMRI study of remote personal memories find about the hippocampus?
○ Hippocampus activated for both recent and remote memories
○ Hippocampal activation was related to the richness of re-experiencing (vividness) rather than the age of the memory per se
What 2 studies show the role of the hippocampus and spatial memory?
Morris water maze test
- rats find platform
London Taxi Drivers study
- More time as a taxi driver the larger the hippocampus.
Describe Place Cells
Neurons mapping locations within a 2D environment. Each neuron represents one location (i.e., its place field).
Describe Grid Cells
Neurons in entorhinal cortex (EC) mapping multiple locations in 2-dimensional environments
Describe Boundary/Border Cells.
Neurons in EC activating when the animal is near the borders of the environment.
Neuroimaging work has suggested that during retrieval of a list of study items, the hippocampus is most active for what?
It is most active for items that are correctly recollected as old items
Under the standard consolidation theory, the involvement of the hippocampus in accessing memories is best described as what?
Temporary
