Last Lecture

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
• 400 pm - 600 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-order input from 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
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
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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
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
Neuroimaging Results (verbal)
Anterior Regions
Posterior Regions
( p lt .05 p .02 p lt .005)
25
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 lt .05 p .02 p lt .005)
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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.