Chapter 6: Other Declarative Memory Approaches Flashcards
What are the limitations of studying amnesia?
lesion-deficit approach: tells us what behaviors impaired following damage to a certain structure
however, this approach doesn’t necessarily tell us much about normal memory processes: intact brain memory processes
Can we study memory processes in intact humans and animals?
recording during memory processes
lesion studies don’t show us how brain structures support intact memory
What is positron emission tomography (PET)?
involves internalization and detection of radioactive substances
What is functional magnetic resonance imaging (fMRI)?
involves measuring the “relaxation” of endogenous molecules in the brain
What do PET scans and fMRI have in common?
both indirectly measure differences in blood flow and oxygen consumption of the brain
correlated with increases in neural activity
What are the advantages of PET scans and fMRI?
non-invasive (humans)
whole brain monitoring (global changes)
What are the disadvantages of PET scans and fMRI?
indirect
lack of precise spatial and temporal specificity
require well constructed “control” baseline tasks that can be used to measure differences
What are the difficulties for memory imaging?
hippocampal activation can appear even when no explicit learning is taking place
example: word lists, even only reading a word list activates the HPC
activation of NPC during both: encoding, retrieval - associations
however, careful controls allow for imaging areas involved in memory processes per se
How are verbal and non-verbal memory lateralized?
bilateral MTL damage induces global amnesia: across all modalities of stimuli and stimuli classes; auditory, visual, verbal, non-verbal, spatial, non-spatial
imaging studies reveal increased activation of: left MTL for verbal stimuli (words), right MTL for non-verbal stimuli objects
What are the associations between stimuli processed by the MTL?
associative condition: would this person be likely to live in this house or would they be a visitor?
non associative condition: is this person male or female? is this an exterior or interior shot of this house?
more MTL activation in associative memory (a form of deep coding, remember association better, better memory)
MTL critical for learning associations/relations between items: not processing them separately, influential, using previous knowledge
How was MTL activation measured during conscious recall in a fMRI?
subjects attended to two lists of words before fMRI
2 different instructions:
- perceptual encoding (vocal qualities); speaker male or female?
- conceptual encoding (word meanings): living or non living thing?
tested for recall of both word lists during scan
results: subjects better at recalling conceptual list (anything they encoded deeply)
more MTL activation for words of this list
consciously recalling conceptually (or semantically) encoded words (i.e., declarative memory) requires activation of MTL
When is the MTL region activated?
new, complex material is presented
new associations or relations among separate items are encoded
information is consciously recalled
MTL: encoded and retrieves new declarative memories; precisely what is lost in amnesia
What are unit recording techniques?
action potential activity of single or multiple neurons in behaving animals
direct measure of neuronal activation
What are the advantages of unit recording techniques?
direct measure
high degree of temporal, spatial resolution
millisecond time scale, precise brain areas
What are the disadvantages of unit recording techniques?
invasive
upper limit to how many cells and how many areas can be recorded from
not a global measure
How do the recordings of HPC neurons in freely moving rats show?
cellular activity is well-correlated with a variety of stimuli and behavioral events (often combinations)
“place cells”
What are hippocampal “place cells”?
cells that fire in a particular location
What are the properties of place cells?
- location specific
- develop fast; last for months
- same cell can represent different places in different environments
- not topographic in brain
- absolute activity depends on what the rat is doing at the time
- activity of cells correlates to animal’s spatial behavior in a particular environment
Is the hippocampus a cognitive map?
subtle changes in the immediate environment change the firing properties of place cells (like introducing a new object)
many place cells only fire if the rat is doing something specific at a particular spatial location (e.g., approaching, leaving)
many hippocampal neurons respond to non-spatial stimuli, or to specific combinations of spatial and non-spatial stimuli
What is the evidence for the notion that place cells may be “episodic cells”?
look like they’re coding for more than just space, encoding a combination of space and context
alternating T-maze: have to remember what they did last time and turn the other way
overlapping place fields dependent on trial & choice (i.e. whether rat will make a right or left turn)
linear track and directionality: get place field to predict the way the animal will turn, even if it is a mistake
How do hippocampal cells respond to diverse stimuli?
cup of sand (with reward on non-match trials) moved around; pick the odor that doesn’t match the last one, odor-guided DNMS task
non-match odor trial: rat rewarded for digging
matching odor trial, no reward: rat turns away
hippocampal cell response correlated with combinations of multiple task events: location of cup, the odor, whether the odor was a match, etc.
hippocampus does not just encode space
How does the MTL & HPC encodes both declarative memories (both episodic and semantic)?
HPC links conscious “events” and “facts” in an associative network
hippocampal neurons encode complex events
cells might be activated in sequence to represent an episode
repeated or similar events are linked via synaptic plasticity (LTP?)
the HPC as “memory space”: creating a space for episodes to be strung together, consisting of networks of linked neurons
How does the MTL encode episodic and semantic memory?
specific networks of hippocampal cells encode all the relevant stimuli (spatial, non-spatial), task parameters (left versus right). motivation (food, escape), of an episode
also: cells that fire on both trial types highlight similarities between episodes
independent relations between items held in memory can themselves be linked to create non-explicit associations
the hippocampus as an overlapping memory space
