Week 12 Lecture 12 - the remembering brain 2 Flashcards
What is working memory (WM)?
- better encapsulates idea that the info currently in the mind is manipulated
- the active manipulation of information within a STM store in the service of high cognitive functions
What does WM underlie?
the successful execution of complex behaviour, regardless of the cognitive domain or domains that are being engaged
What happens when working memory fails?
our ability to carry out many activities of daily life also fails
What is Baddeley’s (2000) Model of Working Memory?
see summary sheet
Separate STM stores and an executive system for manipulating & controlling info within the stores
What Functional Imaging evidence for the dissociation between Verbal and Visuospatial STM is there?
What theory of WM does this support?
PET study by Smith et al (1996)
Conditions:
* Short-term retention of either letters (verbal STM) or location of markers (visual STM)
Distinct brain regions are active in the two WM tasks
* Verbal STM – Left hemisphere
* Visuospatial STM – Right hemisphere
Supports Baddeley’s model of WM
According to the Baddeley model of WM, what does the phonological loop contain?
a phonological store component (i.e., verbal STM) and a rehearsal mechanism
What evidence is there that the phonological loop has 2 separate components?
Paulesu et al. (1993) PET study while participants performed tasks engaging:
- a) Short-term memory for letters (both store and rehearsal components) or
- b) while taking rhyming judgments of letter (rehearsal system only)
- Phonological store –> left supramarginal gyrus
- Rehearsal system –> Brodmann’s area 44 (Broca’s area)
- Ranganath et al., (2004) explored visual WM maintenance and long-term associative retrieval
What was found?
Activity within category-selective regions of inferior temporal cortex reflected the type of information that was actively maintained during both the associative memory and working memory tasks.
- Maintaining single object in STM involves activating ventral stream representations
- These regions are functionally connected to frontal and parietal regions during the delay period
How are delayed response tasks used to assess WM in animals?
Delayed-response task measures working memory in monkey
- The animal must continue to retain the location of the unseen food during the delay period (working memory)
- Prefrontal lesions affect their ability in performing this task
How are delayed response tasks used to assess associative memory in animals?
- Food is paired with a visual cue (plus sign)
- The task measures the animal’s ability to retain long-term rules
- No need for the animal to retain visuospatial information during the delay period (as in the working memory task)
- PFC damage disrupts a but not b
What is response like in PFC neurons in monkeys (WM - delayed response tasks)?
- Prefrontal neurons differential respond to different stages of the experiment (cue – delay – response)
- Neurons active during the delay period provide a neural correlate for keeping a representation active after a triggering stimulus is not longer active
- They remain active only if the animal needs to use the information for a forthcoming action
- If the task conditions change, the same neurons become responsive to a new set of stimuli
How might WM be an interaction between PFC and posterior cortex?
- Prefrontal cortex activation reflects a
representation of task goal - Working memory relies on the interaction between PFC and other parts of the brain that contain perceptual and long-term knowledge relevant to a goal
What does Petrides’ Theory of Working Memory assume?
assumes division of PFC into at least two separate processes – maintenance and manipulation
What evidence is there for Petrides’ Theory of Working Memory?
- Patients with PFC damage impaired at self-ordered pointing task
- PET study showed that short-term retention of spatial information =
ventrolateral PFC, but retention + update new locations = dorsolateral PFC
What is the strongest evidence that the STM and LTM are separate?
Neuropsychological (patients) and
behavioural (primacy and recency effects)
Who was patient HM?
- Inability to make new memories (i.e., cannot transfer new information into LTM)
- But intact short-term memory
Who was patient KF?
- Left parieto-occipital damage
- Normal LTM, good long-term learning (word lists, paired associates)
- Small STM span (low digit span)
What do patient HM and KF provide evidence for?
Evidence of separation between STM and LTM
What is the thinking behind unitary models of WM/STM?
- Working memory is just the temporary
activation of long-term memories - How capacity limitations are explained?
- More items active in WM –> More interference there is
Give an example of a unitary model of WM/STM
Cowan’s WM model (Cowan, 2001)
- similar to Baddeley’s formulation but does not necessitate separate stores for STM
- Instead central executive/attention is responsible for selecting and activate
LTM representations to bring them into “Focus of Attention”
What evidence is there for unitary models of WM/ STM?
- Cognitive neuroscience evidence consistent with the idea that WM entails temporary activity in parts of the brain involved in long-term storage
- Baddeley: studies of this kind support the idea that working memory and long-term memory are not completely distinct
How is the PFC involved in LTM?
- Responsible for maintenance and active control of information represented in LTM systems
- PFC functions are also prevalent in purely LTM tasks (encoding and
retrieval)
What evidence is there that suggests the PFC is involved in memory encoding?
*Lateralised responses in PFC at encoding depend on the type of materials
* Encoding of words or semantic materials (e.g., objects that can be verbalised) involve the left PFC
* Encoding of spatial information or faces (as in Kelley et al., 1998 study) involve the right PFC
Long et al., 2010 considered the PFC subsequent memory effect for clustered recall
What was found?
- Dorsolateral prefrontal cortex (DLPFC) activation was predictive of subsequent semantic clustering.
- Ventrolateral prefrontal cortex (VLPFC) activation was predictive of subsequent recall, whether clustered or non-clustered
What processes does the PFC aid in in terms of retrieval?
aid in the organisation, selection, monitoring, and evaluation of processing that occurs at retrieval
Fletcher and Henson (2001):
Evaluation of what has been retrieved from LTM = monitoring – in DLPFC
What was found?
- Activity in this region increases with increased demands (or increased need for monitoring retrieval)
- E.g., free recall, recall (vs recognition), low confidence judgments increased DLPFC activity
- PFC damage results in more severe impairment during free recall as compared to recognition
How is the PFC involved in free recall?
see summary sheet
How is the PFC involved in source monitoring?
- Related to recall and recollection that stresses the ability to attribute retrieved
memories to their original context - The PFC is involved as placing an event in context requires active evaluation process before we are able to access the origin of the memory
