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

FINAL EXAM:

  • 182 Dennison
  • Wednesday, 4/19
  • 4:00 pm - 6:00 pm.
  • Please contact us immediately if this poses a conflict.
prefrontal cortex
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
connectivity of prefrontal regions
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.
premotor motor areas
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.
frontal release signs
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.

mediate voluntary control of behavior
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

+

poor performance on anti saccade task
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.
model task to study frontal lobe function
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.
delayed saccade task goldman rakic
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
cognitive role of area 46
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.
without goal representation
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.

frontal lobes and working memory
Frontal Lobes and Working memory...

A system for maintaining and manipulating information to perform complex cognitive activities (Baddeley, 1992).

working memory

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.
executive functions of prefrontal cortex
Executive Functions of Prefrontal Cortex

Aleksandr Luria (1966)

Programming, regulating, monitoring

Smith & Jonides (1999)

Attention/inhibition, task management, contextual coding, planning, monitoring

verbal wm tasks
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

spatial wm tasks
Spatial WM Tasks

+

+

+

Spatial

500 msec

+

Memory

500 msec

3000 msec

1500 msec

+

+

Spatial

+

3300 msec

+

Control

500 msec

200 msec

1500 msec

hypothesized working memory circuitry
Hypothesized Working Memory Circuitry
  • Frontal sites control rehearsal and manipulation of stored information.
  • Parietal sites control the storage of this information.

Anterior

Posterior

aging and working memory
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)

performance results

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

neuroimaging results verbal

***

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)

neuroimaging results spatial

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)

aging and working memory summary
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.
long term memory and its dysfunction
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.
human amnesia
Human Amnesia
  • Anterograde: Inability to acquire NEW memories.
  • Retrograde: Inability to recollect OLD memories.