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Last Lecture

Last Lecture. The Wernicke-Geschwind Model of Reading Category-specific semantic deficts and the representation of meaning Introduction to the Frontal Lobes. This Lecture. Frontal Lobe Anatomy Inhibition and voluntary control A model task: working memory . Announcements. FINAL EXAM:

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Last Lecture

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  1. Last Lecture • The Wernicke-Geschwind Model of Reading • Category-specific semantic deficts and the representation of meaning • Introduction to the Frontal Lobes

  2. This Lecture • Frontal Lobe Anatomy • Inhibition and voluntary control • A model task: working memory

  3. Announcements FINAL EXAM: • 182 Dennison • Wednesday, 4/19 • 4:00 pm - 6:00 pm. • Please contact us immediately if this poses a conflict.

  4. Prefrontal cortex • ~ 1/3 of cortical surface • Most recently evolved • Well developed only in primates • the advent of the human species: "age of the frontal lobe" • develops late in ontogeny • differentiation through age 1 • maturation through age 6

  5. Connectivity of Prefrontal regions • input from association cortex(occipital, parietal, temporal & olfactory areas) • convergence of higher-orderinputfrom all modalities. • reciprocal connections:prefrontal processing modulates perceptual processing. • LIMBIC connections(memory/emotion) • Input to premotor areas- controls/programs behavior.

  6. Premotor & Motor Areas • Premotor areas (6) - input from prefrontal regions and parietal association areas (5,7). • Area 4: primary motor cortex • input from premotor area (6) and area 44 • sends output to spinal cord, and other motor structures (basal ganglia) • Frontal network controls voluntary, planned actions.

  7. Frontal Release signs Re-emergence of "primitive" reflexes following frontal damage. • grasp reflex: forceful grasping of an object that contacts palm or sole of foot. • sucking reflex: elicited by touching the lip • groping reflex: involuntary following with hand /eyes of moving object • stimulus capture: utilization behavior The frontal lobes normally inhibit stimulus-bound reflexes.

  8. Mediate voluntary control of behavior... ANTI-saccade task • saccade AWAY from an eccentric target • patients w/ prefrontal damage including FEF (Area 8): • reflexive saccades to the target. • Cannot correct error and make anti-saccades • e.g., left lesion patients impaired on right anti-saccades +

  9. Poor performance on Anti-saccade task • Why more reflexive saccades? • Superior colliculus- control rapids, stimulus-driven eye movements. • Disinhibited by frontal lobe damage, "releasing" reflexive glances • Why were Anti saccades impaired? • Difficulty forming representation of goal to control voluntary behavior.

  10. Model task to study frontal lobe function: Delayed Response Task • Correct response requires keeping baited well in mind. • Monkeys and humans w/lesions of LPFC fail these tasks. • Infants younger than 12 months also fail versions of these tasks.

  11. Delayed Saccade Task (Goldman-Rakic) • Single unit recordings from principal sulcus (Brodmann's 46). TASK: • Cue one of 8 locations • 3 sec. delay • fixation removed signaling GO • Saccades to remembered location

  12. Cognitive Role of area 46 • Delay activity -- location specific • Delay activity reduced when monkeys made errors. • Lesions of 46 impair performance on this task. Interpretation: • Neural activity corresponds to mental representation of a GOAL • The goal is maintained "on-line" available for use. • This is working memory.

  13. Without goal representation... Behavior is determined by • reflex • habit • past-reward (perseveration) • immediate stimulus conditions Rather than by intentions that integrate the relevant current spatial and temporal context.

  14. Frontal Lobes and Working memory... A system for maintaining and manipulating information to perform complex cognitive activities (Baddeley, 1992).

  15. EXECUTIVE visuo- spatial sketch pad phono- logical loop Working Memory • on-line store • short-term retention (approx. 10 sec) • executive processes • rehearsal processes • material specific buffers • verbal (phonological loop) left hem. • spatial (visuo-spatial sketchpad) right hem.

  16. Executive Functions of Prefrontal Cortex Aleksandr Luria (1966) Programming, regulating, monitoring Smith & Jonides (1999) Attention/inhibition, task management, contextual coding, planning, monitoring

  17. Verbal WM Tasks • M R • • K D Verbal 500 msec m Memory 500 msec 3000 msec 1500 msec • M M • Verbal M M • 3200 msec Control m 500 msec 300 msec 1500 msec

  18. Spatial WM Tasks + + + Spatial 500 msec + Memory 500 msec 3000 msec 1500 msec + + Spatial + 3300 msec + Control 500 msec 200 msec 1500 msec

  19. Regions of Significant Activation Verbal Spatial

  20. Hypothesized Working Memory Circuitry • Frontal sites control rehearsal and manipulation of stored information. • Parietal sites control the storage of this information. Anterior Posterior

  21. Aging and Working Memory Synapses in LPFC • WM - contributes broadly to higher cognition. • WM declines w/age. • PFC atrophies w/ age. • How does the neural substrate of WM change w/age? Birth 1 yr 60 100 (after Huttenlocher, 1979)

  22. VERBAL-Recognition Errors 10 8 6 Errors( %) 4 2 0 Young Seniors Performance Results • Seniors made more Verbal errors than Young(p = 0.02) • Senior and Young groups had equal Spatial accuracies (p = 0.6) SPATIAL-Recognition Errors 10 9 8 7 6 5 Errors (%) 4 3 2 1 0 Young Seniors

  23. Regions of Activation(Reuter-Lorenz et al., 2000)

  24. *** 2.0 2.0 LH RH LH RH *** 1.8 1.8 *** 1.6 1.6 *** 1.4 1.4 *** 1.2 1.2 1.0 1.0 Percent Activation Change 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0.0 0.0 Younger Older Younger Older -0.2 -0.2 Neuroimaging Results (verbal) Anterior Regions Posterior Regions (* = p < .05 ** = p ≤ .02 *** = p < .005)

  25. LH RH LH RH Neuroimaging Results Spatial Anterior ROIs Posterior ROIs 2.0 2.0 1.8 1.8 1.6 1.6 1.4 1.4 1.2 1.2 *** 1.0 1.0 ** Percent Activation Change ** ** ** 0.8 0.8 ** ** 0.6 0.6 0.4 0.4 0.2 0.2 0.0 0.0 Younger Older Younger Older -0.2 -0.2 (* = p < .05 ** = p ≤ .02 *** = p < .005)

  26. Aging and Working Memory: Summary • Neural substrate for WM is affected by aging. • Selectivity: Frontal circuitry more vulnerable. • Decreased lateralization. • Compensatory? • Recruitment as a “neural strategy” to cope with age-related loss of neural efficiency.

  27. Long Term Memory and its Dysfunction • Memory: the ability to retain & recollect the contents of our experience • typically multimodal • rich in associations • Expanding the definition to include... the ability to acquire new skills & demonstrate improved performance as a result of experience.

  28. Human Amnesia • Anterograde: Inability to acquire NEW memories. • Retrograde: Inability to recollect OLD memories.

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