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Cognition & Emotion II > Neuronal Working Memory Mechanisms > Flashcards

Neuronal Working Memory Mechanisms Flashcards

1
Q

SUMMARY I

A
  • neuronal mechanisms of WM
  • “standard model” of role of prefrontal cortex (PFC) in WM:
    1) info stored in PFC
    2) PFC organised according to type of info stored
    3) WM for objects VS locations
  • evidence against standard model:
    1) PFC organised according to type of processing NOT info type (manipulation VS maintenance)
    2) no info about stored items in PFC
    3) role of PFC in WM = attentional
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2
Q

FUSTER (1974): PROCEDURE

A
  • monkey neurophysiology studies suggest role for prefrontal cortex (PFC) in WM
  • monkeys see piece of food on tray; shutter comes down -> tray closes
  • when shutter opens, monkey has to remember where food = located
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3
Q

FUSTER (1974): RESULTS

A
  • single neuron recording from PFC showed elevated neuronal firing during delay period (ie. when shutter is down)
  • interpreted as showing that neurons in PFC hold representation of to-be-remembered stimulus (ie. food location)
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4
Q

GOLDMAN-RAKIC (1987)

A
  • proposed standard model of WM
  • suggests that this PFC activity reflects neuronal instantiation of Baddeley’s WM storage buffers containing template (ie. temporary representation) of info maintained during delay
  • became dominant view of PFC role in WM for some time
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5
Q

FUNAHASHI ET AL. (1989): PROCEDURE

A
  • evidence from monkey neurophysiology
  • oculomotor delayed response task
  • monkeys saw cue on left/right of fixation; had to maintain eye gaze at centre for 3s then make eye movement (saccade) in cue direction
  • had to hold cue direction in memory for 3s
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6
Q

FUNAHASHI ET AL. (1989): RESULTS

A
  • found that single neurons in PFC showed direction-specific firing during delay period of task (between cue/response)
  • this particular neuron fired strongly to locations in upper left quadrant
  • interpreted as showing direct neurophysiological correlate of WM template aka. temporary representation of spatial location indicated by cue
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7
Q

PETRIDES & MILNER (1982): PROCEDURE

A
  • further evidence for standard model from human neuropsychology studies
  • administered self-ordered task to patients w/frontal lobe lesions
  • patients had to touch 1 pic; would then be given next sheet where they’d have to touch a dif pic etc. until they go through 12 sheets & touch all 12 pics
  • aka. task requires them to remember from 1 sheet to next which images they’ve touched
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8
Q

PETRIDES & MILNER (1982): RESULTS

A
  • patients w/frontal lobe lesions were disproportionately impaired on self-ordered task; indicates that patients had deficit w/WM
  • interpreted this as evidence that PFC holds representation of to-be-remembered info over short periods of time of WM task
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9
Q

WHAT VS WHERE IN WM

A
  • 1 of key tenants in standard model = 2 visuospatial WM types:
    1) objects system
    2) spatial locations
  • appealing idea as extended what we already know about visual object recognition into PFC
  • aka. idea that 2 visual streams (1 for locating, other for identifying) extends into PFC & enables remembering info over short time periods
  • evidence came predominantly from monkey neurophysiology studies
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10
Q

WILSON ET AL. (1993): PROCEDURE

A
  • majority evidence for ventral/dorsal dissociation in PFC for objects VS spatial WM came from monkey neurophysiology
  • monkeys trained to perform oculomotor delayed response task
  • saw cue instructing them to make eye movement in particular direction then had to remember info before making response
  • key change = pattern cues (pattern appeared in screen centre instructing eye movement) in addition to standard spatial cues (cue in actual location)
  • so response in both trial types = same BUT info type to be remembered differed
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11
Q

WILSON ET AL. (1993): RESULTS

A
  • neuron in inferior ventral PFC showed higher activation to patterns BUT lower activation to spatial cues
  • neuron in upper dorsal PFC shows higher activation to spatial cues BUT lower activation to patterns
  • each neuron preferred particular pattern/direction
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12
Q

COURTNEY ET AL. (1996): PROCEDURE

A
  • supporting evidence from fMRI for ventral/dorsal what VS where distinction in WM
  • pps required to remember identity/location of 3 faces & to say if test stimulus matched any identities/locations
  • activation for object WM task seen in ventral PFC
  • activation for spatial WM task seen in dorsal PFC
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13
Q

RAO ET AL. (1997): PROCEDURE

A
  • evidence AGAINST standard model aka. PFC doesn’t store representations of stored stimuli
  • task required monkey to remember object & 1st make eye movement to correct object; then make eye movement to correct location
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14
Q

RAO ET AL. (1997): RESULTS

A
  • single neurons in PFC can encode both location/object as well as its identity
  • suggests flexible adaptation of responses in PFC
  • aka. neurons can adapt to represent whatever info is task relevant
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15
Q

NEUROPSYCHOLOGICAL EVIDENCE FOR PFC ROLE IN WM

A
  • self-ordered pic task requires processes including:
    1) storage of previously touched item
    2) suppression of previously touched item
    3) selective attention to novel item
    4) planning/strategy use
    5) sustained attention
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16
Q

WM x PFC: POSSIBLE CONFOUNDS

A
  • activation in dorsal PFC = spatial WM
  • activation in dorsal PFC = object WM
  • possible confound = processing type aka. pps may use strategies (ie. chunking) to help performance for spatial task
  • requires manipulation of stored info in WM
17
Q

WM x PFC: CONCLUSIONS

A
  • evidence doesn’t seem to support idea of dorsal/ventral distinction for storing locations/objects in WM
  • maybe PFC = organised according to processing type > stored info type
18
Q

D’ESPOSITO ET AL. (1999): PROCEDURE

A
  • fMRI evidence to support idea that PFC = organised according to processing type carried out > stimulus type maintained
  • asked pps to perform WM task; had to either:
    1) maintain info in WM by simply holding letter string in memory then judging if probe letter = part of memory set
    2) (manipulation condition) rearrange letters into alphabetical order & judge if probe letter = in specific location in letter sting post rearranging
19
Q

D’ESPOSITO ET AL. (1999): RESULTS

A
  • found activation in both dorsal/ventral PFC during delay period of WM task
  • BUT dorsal PFC activation = greater during delay period of manipulation trials > during delay period of maintenance trials
  • suggests that PFC = organised according to processing type (dorsal = manipulation; ventral = maintenance) > stimulus maintained type (spatial VS nonspatial)
20
Q

HUMAN x MONKEY STUDY CONVERGENCE

A
  • both suggest that standard model = incorrect
  • aka. PFC isn’t organised according to stimulus type held in WM
  • PFC may be organised according to processing type (dorsal = manipulation; ventral = maintenance)
  • PFC may not even hold representations of stimuli held in WM (where is it stored? what’s its real role?)
21
Q

MULTIVOXEL PATTERN ANALYSIS (MVPA): FMRI DATA

A
  • used to try and answer where in the brain WM info is stored
  • traditional fMRI = smooth data so groups of individual vowels are treated as clusters; useful way to reveal where in the brain a particular process is happening
  • BUT risks missing important info that might be contained in individual vowel responses
22
Q

MULTIVOXEL PATTERN ANALYSIS (MVPA)

A
  • takes advantage of fine-grained patterns of activation in brain
  • uses machine learning techniques to teach algorithm about neural activation pattern associated w/particular stimuli
  • so algorithm = able to “decode” what pp is looking at simply by viewing brain activity pattern
23
Q

LINDEN ET AL. (2012): PROCEDURE

A
  • pps performed task requiring them to hold several objects in WM
  • each trial required pps to decide if single object = part of memory test
  • 4 object categories: faces/bodies/flowers/scenes
  • trained pattern classifier to learn activation patterns for each category
  • tested ability of pattern classifier to predict which category pps were holding in WM in each trial
24
Q

LINDEN ET AL. (2012): RESULTS

A
  • regions holding category related info = exclusively in posterior brain region aka. visual processing regions (ie. FFA/other ventral visual stream regions activated when object categories present to pps)
  • implication = same regions enabling processing object when seen w/eyes also involved in storing temporary representations of said objects in WM
  • PFC doesn’t hold temporary representations of WM info; so what is its role?
25
Q

RIGGALL & POSTLE (2012): PROCEDURE

A
  • also looked into where dif info types are represented in brain during WM
  • scanned pps performing WM task; had to memorise moving dot array; cued during delay period to remember direction OR speed of dots
  • then shown probe (match/mismatch)
  • when cue appeared pps had to follow rule (attend to speed OR direction) while holding specific stimulus in WM (particular speed/direction)
26
Q

RIGGALL & POSTLE (2012): RESULTS

A
  • could decode which direction/how fast dots were moving BUT only from visual cortex/temporal cortex; PFC provided no info about this
  • task instructions could be decoded from PFC/parietal regions
  • consistent w/Linden (2012); stimulus specific info = stored in posterior sensory specific cortex
  • BUT info about task rules = stored in frontal/parietal cortex
27
Q

HIGO ET AL. (2011): PROCEDURE

A
  • provided direct evidence for idea that PFC performs attentional role in WM
  • pps held 2 objects in WM; subsequently cued either to:
    1) maintain both (non-selective attention condition)
    2) maintain 1 (selective attention condition)
  • finally asked to decide if any objects in array matched objects they were holding
28
Q

HIGO ET AL. (2011): RESULTS

A
  • activation in inferior PFC = greater for selective attention > non-selective
  • implication = PFC performs attentional function by prioritising processing of item in WM that is most relevant to current task
  • activation in PFC directly modulated activation in posterior regions; suggests that PFC biases activation in sensory-specific regions during WM in same way as during attention to external stimuli
  • aka. (at least in this task) WM involved process of directing attention to specific items held in WM
29
Q

DISTRIBUTED NEURAL ARCHITECTURE OF WM

A
  • WM model where:
    1) lower level visual regions maintain temporary representations of items held in WM (templates)
    2) PFC/parietal regions hold representation of task rules for manipulating info (central executive)
30
Q

SUMMARY II

A
  • PFC neurons show sustained activity during delay period of WM tasks
  • BUT activity doesn’t reflect WM item storage
  • representations of stored items = maintained in sensory-specific cortex
  • PFC seems to play role in processing stimuli held in WM; role may involve enhancing attention to internal representations of task relevant stimuli in WM & manipulating this info

Cognition & Emotion II (15 decks)

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