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Category-specific semantic deficts and Category-specific semantic deficts and the representation of meaningthe representation of meaning

Introduction to the Frontal LobesIntroduction to the Frontal Lobes

This LectureThis Lecture

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

AnnouncementsAnnouncements

FINAL EXAM:FINAL EXAM: 182 Dennison 182 Dennison Wednesday, 4/19 Wednesday, 4/19 4:00 pm - 6:00 pm.4:00 pm - 6:00 pm.

Please contact us immediately if Please contact us immediately if this poses a conflict.this poses a conflict.

Prefrontal cortex Prefrontal cortex

~ 1/3 of cortical surface~ 1/3 of cortical surface Most recently evolvedMost recently evolved Well developed only in Well developed only in

primates primates the advent of the human the advent of the human

species: "age of the frontal species: "age of the frontal lobe"lobe"

develops late in ontogenydevelops late in ontogeny differentiation through age 1 differentiation through age 1 maturation through age 6maturation through age 6

Connectivity of Prefrontal regions Connectivity of Prefrontal regions

input from association input from association cortexcortex (occipital, parietal, (occipital, parietal, temporal & olfactory areas)temporal & olfactory areas)

convergence of higher-convergence of higher-orderorder inputinput from all modalities.from all modalities.

reciprocal connections:reciprocal connections: prefrontal processing modulates prefrontal processing modulates perceptual processing.perceptual processing.

LIMBIC connectionsLIMBIC connections (memory/emotion)(memory/emotion)

Input to premotor areasInput to premotor areas - - controls/programs behavior.controls/programs behavior.

Premotor & Motor Areas

Premotor areas (6) - input Premotor areas (6) - input from prefrontal regions and from prefrontal regions and parietal association areas parietal association areas (5,7).(5,7).

Area 4: primary motor cortexArea 4: primary motor cortex

input from premotor area (6) input from premotor area (6) and area 44and area 44

sends output to spinal cord, sends output to spinal cord, and other motor structures and other motor structures (basal ganglia)(basal ganglia)

Frontal network controls Frontal network controls voluntary, planned actions.voluntary, planned actions.

Frontal Release signsFrontal Release signs

Re-emergence of "primitive" reflexes following Re-emergence of "primitive" reflexes following frontal damage.frontal damage.

grasp reflex:grasp reflex: forceful grasping of an object that forceful grasping of an object that contacts palm or sole of foot.contacts palm or sole of foot.

sucking reflex:sucking reflex: elicited by touching the lip elicited by touching the lip groping reflex:groping reflex: involuntary following with hand involuntary following with hand

/eyes of moving object/eyes of moving object stimulus capture:stimulus capture: utilization behavior utilization behavior

The frontal lobes normally inhibit stimulus-The frontal lobes normally inhibit stimulus-bound reflexes.bound reflexes.

Mediate voluntary control of behavior...Mediate voluntary control of behavior...

ANTI-saccade taskANTI-saccade task saccade AWAY from an saccade AWAY from an

eccentric targeteccentric target patients w/ prefrontal damage patients w/ prefrontal damage

including FEF (Area 8):including FEF (Area 8): reflexive saccades to the target.reflexive saccades to the target. Cannot correct error and make Cannot correct error and make

anti-saccadesanti-saccades e.g., left lesion patients impaired e.g., left lesion patients impaired

on right anti-saccadeson right anti-saccades

+

Poor performance on Anti-saccade taskPoor performance on Anti-saccade task

Why more reflexive saccadesWhy more reflexive saccades?? Superior colliculus- control rapids, stimulus-driven Superior colliculus- control rapids, stimulus-driven

eye movements.eye movements. Disinhibited by frontal lobe damage, "releasing" Disinhibited by frontal lobe damage, "releasing"

reflexive glancesreflexive glances

Why were Anti saccades impaired?Why were Anti saccades impaired? Difficulty forming representation of goal to control Difficulty forming representation of goal to control

voluntary behavior.voluntary behavior.

Model task to study frontal lobe function:Model task to study frontal lobe function:

Delayed Response TaskDelayed Response Task Correct response requires Correct response requires

keeping baited well in mindkeeping baited well in mind.. Monkeys and humans Monkeys and humans

w/lesions of LPFC fail these w/lesions of LPFC fail these tasks.tasks.

Infants younger than 12 Infants younger than 12 months also fail versions of months also fail versions of these tasks.these tasks.

Delayed Saccade Task (Goldman-Rakic)Delayed Saccade Task (Goldman-Rakic)

Single unit Single unit recordings from recordings from principal sulcus principal sulcus (Brodmann's 46).(Brodmann's 46).

TASK:TASK: Cue one of 8 locationsCue one of 8 locations 3 sec. delay3 sec. delay fixation removed fixation removed

signaling GOsignaling GO Saccades to Saccades to

remembered locationremembered location

Cognitive Role of area 46Cognitive Role of area 46

Delay activity -- Delay activity -- location specificlocation specific Delay activity reduced when Delay activity reduced when

monkeys made errors.monkeys made errors. Lesions of 46 impair performance Lesions of 46 impair performance

on this task.on this task.

Interpretation:Interpretation: Neural activity corresponds to Neural activity corresponds to

mental representation of a GOAL mental representation of a GOAL The goal is maintained "on-line" The goal is maintained "on-line"

available for use. available for use. This is working memory.This is working memory.

Without goal representation...Without goal representation...

Behavior is determined byBehavior is determined by reflexreflex habithabit past-reward (perseveration)past-reward (perseveration) immediate stimulus conditionsimmediate stimulus conditions

Rather than by intentions that Rather than by intentions that integrate the relevant current integrate the relevant current spatial and temporal context.spatial and temporal context.

Frontal Lobes and Working memory... Frontal Lobes and Working memory...

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

Working Memory

on-line storeon-line store short-term retention short-term retention

(approx. 10 sec)(approx. 10 sec) executive processesexecutive processes rehearsal processesrehearsal processes material specific buffersmaterial specific buffers

verbal verbal (phonological (phonological loop) left hem.loop) left hem.

spatialspatial (visuo-spatial (visuo-spatial sketchpad) right hem.sketchpad) right hem.

EXECUTIVE

phono-logical loop

visuo-spatialsketch pad

Executive Functions of Executive Functions of Prefrontal CortexPrefrontal CortexExecutive Functions of Executive Functions of Prefrontal CortexPrefrontal Cortex

Aleksandr Luria (1966)Aleksandr Luria (1966)

Programming, regulating, Programming, regulating, monitoringmonitoring

Smith & Jonides (1999)Smith & Jonides (1999)

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

Verbal WM TasksVerbal WM Tasks

•M

M

M

M

•

500 msec500 msec500 msec500 msec

3000 msec3000 msec1500 msec1500 msec

•

3200 msec3200 msec500 msec500 msec

300 msec300 msec

1500 msec1500 msec

VerbalVerbal MemoryMemory

Verbal Verbal ControlControl

••

m•

M

K

R

D

m

Spatial WM TasksSpatial WM Tasks

+

500 500 msecmsec 500 500

msecmsec 3000 3000 msecmsec 1500 1500

msecmsec

+

3300 msec3300 msec500 msec500 msec

200 msec200 msec1500 msec1500 msec

Spatial Spatial MemoryMemory

Spatial Spatial ControlControl

++

+

++

+

Regions of Significant ActivationRegions of Significant Activation

Hypothesized Working Hypothesized Working Memory CircuitryMemory Circuitry

Frontal sites Frontal sites control rehearsal control rehearsal and manipulation and manipulation of stored of stored information.information.

Parietal sites Parietal sites control the storage control the storage of this information.of this information.

Anterior Posterior

Aging and Working MemoryAging and Working Memory

WMWM - - contributes contributes broadly to higher broadly to higher cognition.cognition.

WM declines w/age.WM declines w/age. PFC atrophies w/ PFC atrophies w/

age.age. How does the How does the

neural substrate of neural substrate of WM change w/age?WM change w/age?

Birth 1 yr 60 100

Synapses in LPFCSynapses in LPFC

(after Huttenlocher, 1979)

SeniorsSeniors made made more more Verbal errors than Verbal errors than YoungYoung (p = 0.02)(p = 0.02)

SeniorSenior and and YoungYoung groups had groups had equalequal Spatial accuracies Spatial accuracies (p = (p = 0.6)0.6)

Performance Results Performance Results

SPATIAL-Recognition Errors

0

1

2

3

4

5

6

7

8

9

10

Young Seniors

Err

ors

(%)

VERBAL-Recognition Errors

0

2

4

6

8

10

Young Seniors

Err

ors(

%)

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

Neuroimaging Results Neuroimaging Results (verbal)(verbal)

Anterior RegionsAnterior Regions Posterior RegionsPosterior Regions

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

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

YoungerYounger OlderOlder

*** ***

RHLH

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

YoungerYounger OlderOlder

***

***

***RHLH

Per

cen

t A

ctiv

atio

n C

han

ge

Per

cen

t A

ctiv

atio

n C

han

ge

Neuroimaging Results Neuroimaging Results SpatialSpatial

Anterior ROIsAnterior ROIs Posterior ROIsPosterior ROIs

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

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

YoungerYounger OlderOlder

***

**

****

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

YoungerYounger OlderOlder

** ****

RHLH RHLH

Per

cen

t A

ctiv

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Per

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Aging and Working Memory: Aging and Working Memory: SummarySummary

Neural substrate for WM is affected by Neural substrate for WM is affected by aging.aging.

Selectivity: Frontal circuitry more Selectivity: Frontal circuitry more vulnerable.vulnerable.

Decreased lateralization.Decreased lateralization. Compensatory? Compensatory?

Recruitment as a “neural strategy” Recruitment as a “neural strategy” to cope with age-related loss of neural to cope with age-related loss of neural efficiency.efficiency.

Long Term Memory and its Dysfunction

Memory: the ability to retain & recollect the contents Memory: the ability to retain & recollect the contents of our experienceof our experience

typically multimodaltypically multimodal rich in associationsrich in associations

Expanding the definition to include... the ability to Expanding the definition to include... the ability to acquire new skills & demonstrate improved acquire new skills & demonstrate improved performance as a result of experience.performance as a result of experience.

Human Amnesia

Anterograde: Anterograde: Inability to acquire NEW memories.Inability to acquire NEW memories. RetrogradeRetrograde: Inability to recollect OLD memories.: Inability to recollect OLD memories.