Last Lecture - PowerPoint PPT Presentation

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

• Frontal Lobe Anatomy
• Inhibition and voluntary control
• A model task: working memory

FINAL EXAM:

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

• ~ 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

• 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 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.

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.

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

+

• 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.

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.

• 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

• 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.

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.

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

EXECUTIVE

visuo-

spatial

sketch pad

phono-

logical

loop

• 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.

Aleksandr Luria (1966)

Programming, regulating, monitoring

Smith & Jonides (1999)

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

•

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

500 msec

+

Memory

500 msec

3000 msec

1500 msec

+

+

Spatial

+

3300 msec

+

Control

500 msec

200 msec

1500 msec

Verbal

Spatial

• Frontal sites control rehearsal and manipulation of stored information.
• Parietal sites control the storage of this information.

Anterior

Posterior

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)

VERBAL-Recognition Errors

10

8

6

Errors( %)

4

2

0

Young

Seniors

• 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

***

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

Anterior Regions

Posterior Regions

(* = p < .05 ** = p ≤ .02 *** = p < .005)

LH

RH

LH

RH

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)

• 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.

• 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.

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