Title: Last Lecture
1Last Lecture
- The Wernicke-Geschwind Model of Reading
- Category-specific semantic deficts and the
representation of meaning - Introduction to the Frontal Lobes
2This Lecture
- Frontal Lobe Anatomy
- Inhibition and voluntary control
- A model task working memory
3Announcements
- FINAL EXAM
- 182 Dennison
- Wednesday, 4/19
- 400 pm - 600 pm.
- Please contact us immediately if this poses a
conflict.
4Prefrontal 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
5Connectivity 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.
6Premotor 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.
7Frontal 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.
8Mediate 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
9Poor 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.
10Model 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.
11Delayed 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
12Cognitive 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.
13Without 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.
14Frontal Lobes and Working memory...
- A system for maintaining and manipulating
information to perform complex cognitive
activities (Baddeley, 1992).
15Working 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.
16Executive Functions of Prefrontal Cortex
- Aleksandr Luria (1966)
- Programming, regulating, monitoring
- Smith Jonides (1999)
- Attention/inhibition, task management, contextual
coding, planning, monitoring
17Verbal 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
18Spatial WM Tasks
Spatial
500 msec
Memory
500 msec
3000 msec
1500 msec
Spatial
3300 msec
Control
500 msec
200 msec
1500 msec
19Regions of Significant Activation
Verbal
Spatial
20Hypothesized Working Memory Circuitry
- Frontal sites control rehearsal and manipulation
of stored information. - Parietal sites control the storage of this
information.
Anterior
Posterior
21Aging 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)
22Performance 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)
24Neuroimaging Results (verbal)
Anterior Regions
Posterior Regions
( p lt .05 p .02 p lt .005)
25Neuroimaging 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)
26Aging 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.
27Long 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.
28Human Amnesia
- Anterograde Inability to acquire NEW memories.
- Retrograde Inability to recollect OLD memories.