Imaging of Episodic Memory PFC Subregions

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UNIV OF PENNSYLVANIA HEALTH SYSTEM

• Imaging of Episodic MemoryPFC Subregions

J. Daniel Ragland, Ph.D.
Department of Psychiatry, Brain Behavior
Laboratory
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Student Recommendations

• Monkey vs. Human PFCSemendeferi K, Lu A,
  Schenker N, Damasio H. Nature Neuroscience, 2002
  5(3), 272-6
• HERA
• Nyberg L, et al, Proceedings of the National
  Academy of Sciences, 1996 3(2), 135-148

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Todays Lecture

• PFC subregions
• PFC connectivity
• Methodological issues
• Introduction to Classroom Discussion

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Frontal Lobe Anatomy
Boundaries posterior central sulcus inferior
Sylvian fissure (lateral fissure) medial/inferior
corpus callosum
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Frontal Lobe Anatomy
1. Superior frontal gyrus 2. Superior frontal
sulcus 3. Central sulcus 4. Precentral gyrus 5.
Postcentral gyrus 6. Supramarginal gyrus 7.
Angular gyrus 8. Postcentral sulcus 9.
Parieto-occipital sulcus 10. Superior parietal
lobule 11. Intraparietal sulcus 12. Precentral
sulcus 13. Middle frontal gyrus 14. Inferior
frontal sulcus 15. Inferior frontal gyrus 16.
Anterior ascending ramus of lateral sulcus 17.
Transverse temporal gyrus 18. Anterior horizontal
ramus of lateral sulcus 19. Superior temporal
gyrus 20. Superior temporal sulcus 21. Middle
temporal gyrus 22. Orbitofrontal gyrus 23.
Inferior temporal sulcus 24. Inferior temporal
gyrus 25. Preoccipital notch 26. Posterior branch
of lateral sulcus 27. Triangular part of inferior
frontal gyrus 28. Opercular part of inferior
frontal gyrus
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Cytoarchitecture

• Cell structure (and function) varies within a
  gyrus
• Imaging interested in divisions based on exam of
  neural tissue
• Brodmanns maps of cytoarchitectonic
  fields(Brodmann, 1909 1925)

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Frontal Lobe Anatomy

• Major Subdivisions
• Precentral Gyrus (PCG, primary)
• - Area 4 (motor cortex)
• Premotor Cortex (PMC) (secondary)
• - Area 6 (PMC, lateral)
• - Area 6 (SMC, medial)
• - Area 8 (FEF, lateral)

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Frontal Lobe Anatomy

• Major Subdivisions
• Prefrontal (PFC) (tertiary/association)
• - Dorsolateral Areas 9,46
• - Ventrolateral Areas 44,45,47
• - Orbitofrontal Areas 10,11
• - Anterior Area 8, 10
• - Medial Area 11, 25, 32
• Anterior Cingulate
• - Areas 24, 32, 33

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PFC Subdivisions
Dorsolateral - DLPFC (9,46)
Ventrolateral - VLPFC (44,45,47)
Anterior - APFC (8,10)
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Frontal Lobe Connections

• PMC (4) to spinal motor neurons - Fine hand,
  finger, arm, leg, facial movements
• Premotor Areas (6, 8) to spinal motor neurons
• - Programming Motor Engrams (fluid
  movements/action)
• Prefrontal Cortex (9, 10, 11, 44, 45, 46, 47) to
  rest of brain
• Reciprocal Connections
• - DLPFC, NAC, HI and Posterior Parietal Lobe
• OPFC and Temporal Lobe/Amygdala
• Efferent Connections - from Association Cortex
  (all lobes)
• Convergence of Higher Order Processes

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Hemispheric Specificity

• HERA Model- Left PFC (mostly VLPFC) -
  semantic retrieval and novel episodic
  encoding- Right PFC (mostly APFC) - episodic
  retrieval

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Regional Specificity

• Beyond HERA- Left IPFC (44,45) - episodic
  semantic word retrieval- Left IPFC (10,47) -
  word retrieval based on meaning- Right APFC
  (10) - episodic retrieval, not material
  specific- Right IPFC (45,47) - episodic
  retrieval of faces only

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Working Memory PFC Specificity

• Process Specificity (Petrides, 1994)- VLPFC and
  information maintenance- DLPFC and information
  manipulation
• Material/Domain Specificity (Goldman-Rakic, 1987)
  - Left VLPFC and verbal maintenance- Right
  VLPFC and spatial maintenance - No clear what
  vs. where distinction- No clear verbal vs.
  non-verbal laterality

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LTM PFC Encoding Specificity

• Encoding Success (Wagner et al., 1998)- left
  posterior VLPFC during encoding of words
  successfully retrieved confidently-
  relationships also found with left DLPFC
• Levels-of-Processing (Craik Lockhart, 1972)-
  left anterior VLPFC and semantic vs. perceptual
  encoding

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LTM PFC Encoding Specificity

• Organization of Information (Baddeley et al.,
  1984)- left DLPFC and increased organization
• Selection Demands (Thompson-Schill, 1997)-
  similarity judgment based on feature (hi) or
  global (low) e.g., tooth goes with tongue
  or bone - left DLPFC increases when response
  selection demands increase, not just semantic
  retrieval
• Controlled Processing (Wagner et al., 2001)-
  manipulated target number and associative
  strength with equal selection demands (e.g.
  candle-flame vs candle-halo)- all conditions
  activated posterior and dorsal LIPC- posterior
  LIPC (44,6) sensitive to number of targets-
  anterior LIPC (47,45) sensitive to associative
  strength- not dependent upon load (number of
  targets) or selection demand

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LTM PFC Retrieval Specificity

• Episodic Retrieval vs Encoding- right APFC
  consistently found, variable effects of retrieval
  success- stronger for explicit paradigms when
  memories are weak and hard to retrieve- not
  limited to APFC or right hemisphere
• Source Monitoring- left APFC and DLPFC
• Remember/Know- right DLPFC

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Caveats Design Issues

• Selection of Reference Determines Results- use
  of active versus passive reference-
  assumption of pure insertion (Friston, 1996)
• Individual Anatomy Does Not Always Match Brodmann
  Areas and Talairach Coordinates- problem of
  standard space
• Task Demands Rarely Orthogonal- e.g., working
  memory during encoding
• Statistical Threshold Somewhat Arbitrary- Lack
  of Significance does not equal lack of activity

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Caveats Individual Variability

• Differences in Neuroanatomy- may produce variant
  regional activations between studies
• Differences in Cognitive Ability- variability in
  intellectual level- variability in research
  exposure- variability in strategy usage
• Problems Exacerbated by Small Samples

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Recommendations

• Search for Convergence- across analyses within a
  study- across studies- need for replication
• Acknowledge Limitations- in sample
  characteristics- in task design
• Greater Study of Normal Variability

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Classroom Discussion

• Nyberg (1998)- Review of Episodic Memory
  Imaging Studies
• Fletcher Henson (2001)- Ventrolateral,
  dorsolateral anterior subregions
• Monday - presentation and discussion of fMRI
  network analyses