Neural Mechanisms of WM Flashcards
What is WM
acts to bridge temp gaps between perception + action
Iconic Memory - sperling
- can briefly attain lots of visual info but it fades very quickly
- ability to remember a string of letters drops As increases durations
WM- Baddeley Muiti-component model
- multiple ways to store info on a ST basis
- visual stored in visuo-spatial sketchpad
- Auditory stored in phonological loop
- central executive = memory integration
WM Tests
- Digit span
- corsi block = experimenter taps blocks in certain order + asks ppts to copy
- Macaque model - delay saccade (eye movement) task
- Rat Model T Maze
- spatial /verbal span forwards/backwards
Frontal lobe lesion - Penfield + Evans
- ppts with frontal lobe lesions struggled with everyday tasks
- linked damage to WM deficits
frontal lobe lesions -Shallice + Burgess - 2 task impairement
- frontal lobe lesion patients impaired on both tasks
- six element test: 6 tasks ( route + math problems) in 15 mins
- Multiple Errand test: shopping for several items when constrained by rules
Prefrontal cortex + WM - Goldman + Rosvold - Delayed response task - monkeys
- Delayed Response Task
- made PFC lesion in monkeys
- Trained to perform a task where they had to remember which well the food was in
- Blind goes up + asked to indicate where food was located after a delay
- monkey with lesions impaired in ability to remember location across delay
Memory cell in PFC - Fuster + Alexander and Miller - Delayed response task
- Fuster+ Alexander - Delayed Response Task
- cells holding onto memory during delay fire
- shows PFC involved in maintaining WM items
- Miller et al > delay activity maintains items in Visual working memory when distracter items are shown
- neurons show preference for certain stimuli + fire harder when present
Delay activity in PFC - Sakai et al - study
- Delay activity in Visual WM in human fMRI
- learned Spatial sequence , distractor task then memory test
- Results: delay activity in PFC is higher than baseline activity for correct trials
Recency judgement + PFC
- Recency Judgement = which was shown most recently
- PFC is critical for maintaining temporal organisation of WM
- lesions impair recency judgement relative to control + struggle to accurately maintain order of info in WM
Functional segregation with PFC memory systems -Sakai
- memory span task : verbal or spatial info remembered in forward (maintenance) or reverse direction (manipulation)
- verbal task increased BOLD (Blood Oxygen Level Dependent ) activity in dorsal PFC
- spatial task - ventral PFC
Delay activity in Visual cortex + Distractors - Miller et al - Temporal lobe + PFC
- Temporal lobe: delay activity is abolished by distracting stimuli
- PFC: delay activity is robust to distracting stimuli
challenging delay activity theory
- Maintain items in WM in a silent state
Fuster - Random gaps in persistent delay activity
- Not all PFC cells show persistent activity
Waxing + waning of PFC delay activity
- Brain activity when dual task starts drops off rapidly
- continuous activity isn’t always necessary for successful WM
metabolic cost of persistent firing
more efficient for brain to encode info differently so it can preserve energy
Bridging activity gaps in silent state - stokes et al - neuron communication
- Neural state can be described as different levels : activity pattern (neuronal firing) , functional connectivity ( neuronal communication)
- can construct memory through remembering conversation between neurons
- Neurons have lower threshold (fire less AP) in functional connectivity level
WM in a silent State- stokes et al - cued target detection task
- cued target detection task
- 0-3 non target ( neutral or distractor) distractors then cued target
- Neurons in PFC don’t show continuous firing pattern during delay but monkeys still able to perform task
- High firing when Stimuli present , during delay return to baseline
- Neural stimulus acting as boosting activity
WM as a dynamic process
- Info held in WM changes over time
- During encoding task-relevant Stimuli are represented as highly dynamic activity
- Maintenance is a stable, low energy State
- retrieval brings it back to an active state of task relevant neurons
Interaction between WM+ attention
- Attention as a gate keeper inter WM
- Attention can select which items go into WM + which to prioritise
- WM as an Attentional template
- wM holds attentional template
- WM content biases attention
Attentional selection into WM- Sperling - letter study
- WM has limited capacity
- Partial report task: Cue shown after letter array telling pprs which letters to report
- Vigel et al - attended items can be selectively stored in WM
Attentional selection Within WM - Murray et al - retro cue + trials
- Attention works within WM to improve performance
- All WM items decay over time
- Retro cue slows down decay
- WM can be modulated during maintenance
- long trial - cue reduces comp among other items
- short trial- cue enables remembering of a forgotten item
WM automatically biases attention - Soto et al - dual task
- Dual Task : store cue item, find target in search array, report if item is same as cue
- Attention in search task is auto drawn to WM contents
- poor performance in search for a target not in WM
Anatomy behind cog control- 2 systems + goals
- set of psychological processes that enable US to use our perceptions + knowledge to bias actions + thoughts
- cog control is necessary to meet goals
- Develop a plan that uses personal experiences
- monitor action to stay on target + attain goals
- 2 prefrontal control systems : lateral PFC , orbitofrontal cortex + frontal pole supporting goal-oriented beh medial FC for guiding + monitoring ben
cog control deficits
- Frontal lobe lesions
- patient May persist in a response even once being told its incorrect (preservation beh)
- patient may be apathetic, distractible, impulsive, unable to Plan or make decisions
lesions + cog control deficits
- Shallice + Burgess -> + took 3 patients with frontal lobe lesions to a shopping centre + assigned each a list
- obtaining all the items was a real problem
- 1 failed as store didn’t have favourite brand, 1 wandered outside + 1 failed to pay for an item
Drug addiction + cog control
- Goldstein + Volkow
- one model of drug addiction suggests disruption of PFC underlies characteristic of inability to stop destructive ben
Goal-oriented Beh
- Based or assessment of expected reward + knowledge
- Action-outcome relationship
- Habitual actions = actions no longer under control of reward but is stimulus driven
PFC is necessary for WM- monkey study
- in spatial memory test 0 monkeys observe food in 1 well + curtain lowered after delay must choose correct well
- Demands monkey to continue to retain location of unseen food
- monkeys with PFC lesions do poorly
LPFC + WM
- LPFC actively reflects representation of task goal
- functional image studies support this: delayed -response tasK found BOLD response in LPFC began to rise during encoding + response maintained across delay
LP+C is critical for WM sustains representation of task goal
Organisational principles of PFC
.- Anterior-posterior gradient across PFC follows a hierarchy : simple WM tasks limited to posterior regions + challenging tastes extend anterior
- Demonstrates how o goal-riented ben can require integration of multiple pieces of info
WM representations in PFC
- cells in PFC maintain WM - through sustained firing
- Miller-> some cells maintained memory specificity After distracting items indicating potential distracter-resistant wM
WM basis for preparatory attention
- WM important for maintaining relevant info determining focus of attention
- Desimone + Duncan -> WM representations could Constitute top-down bias
- Soto et al found WM representations are sufficient for biasing visual processing
Dynamic Population coding
- Info content peaks during most dynamic phase of trajectory
- Dynamic changes in population coding could reflect remapping from cue representation to anticipated target representation
- stimulus processing is associated with complex spatiotemporal trajectory
- Buonomano + Maas argue complex population dynamics could result from evolution of state- dependent processing that is determined by cascading interaction between past + current input
- Hidden states can be used to maintain info in WM
