Transcript Divisions of the Frontal Cortex

Frontal Cortex
Frontal Lobes
• Traditionally considered to be the seat of
intelligence.
• This is probably because:
– The frontal cortex is the most recent to evolve.
– Humans have particularly large frontal lobes
compared to other animals.
• The frontal cortex is the brain lobe least
amenable to quantitative testing.
Divisions of the Frontal Cortex
1.
2.
3.
4.
Motor cortex
Premotor cortex
Prefrontal cortex
Orbitofrontal & Ventromedial prefrontal
cortex
5. Anterior cingulate gyrus
6. Broca’s area
Divisions of the Frontal Cortex
Primary Motor Cortex
Motor cortex
1. Primary level of motor control
2. Direct connections with the cranial nerves and
spinal motor neurons
3. Focal lesions result in a loss of voluntary motor
control over a specific area of the body
4. Chronic deficits of fine motor control
5. Reduction of the speed and strength of limb
movements
Penfield & Graziano
Premotor Cortex
Premotor cortex
1. Secondary level of motor control
2. Influences motor movements through
connections to subcortical centers (e.g.,
basal ganglia & thalamus).
3. Deficits are subtle because subcortical
centers still exert some control over
movements.
Premotor Cortex II
4. Damage impairs the integration of
separate movements into fluid sequences
of action.
5. Reflex changes:
a. “Counter-pull”
b. Involuntary grasp reflex
c. Clumsy, rapid, short steps
Prefrontal Cortex
Working memory
• Refers to the capacity to keep track of and update
information at the moment
• E.g., 7 + - 2
• Patricia Goldman-Rakic
• ODR paradigm (oculomotor delayed-response)
• Electrodes record activity from monkey neurons
during the task.
• Different neurons respond to different task
characteristics.
Regional Specialization:
1. Superior prefrontal
convexity (dorsal)—
spatial location
2. Inferior prefrontal
convexity (ventral)—
objects, faces
Impaired Response Inhibition
• Stroop
Purple
Red
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Yellow
Orange
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Brown
Blue
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Yellow
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Orange
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Red
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Yellow
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Orange
Red
Purple
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Purple
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Green
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Yellow
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Purple
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Orange
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Brown
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Green
Perseveration
• Carrie’s timing task with frontals
Shifting Difficulty
• Reduced fluency
– Generate animals beginning with “C”
• Difficulty generating hypotheses and
flexibly shifting to new task demands
Wisconsin Card Sort Task
(WCST)
Test Cards
Wisconsin Card Sorting Task
(WCST)
Alternating &
Sequencing Deficits
***VIDEO: Pick’s Disease
Alternating &
Sequencing Deficits
1. Motor
2. Planning & organizing tasks
3. Developing strategies for learning
new tasks
Frontal Eye Fields
Exploratory Eye
Movement Deficits
Other Dorsolateral Deficits
1. Pseudo-depression
2. Perceptual deficits
3. Corollary discharge
Mirror Neurons:
Characteristic Firing Properties
of Inferior DLPFC
•
•
•
•
(Fadiga et al., 2000)
Motor
Visual
Somatosensory
Body-part centered
“Mirror” Property
of Human DLPFC
(Iacoboni et al., 1999)
Orbitofrontal &
Ventromedial Prefrontal Cortex
Phineas
Gage
The Case of Phineas Gage
An explosion projected a tamping rod through his left cheek.
Miraculously, he recovered and had “normal intellegence”.
Months later, however, Gage began to have startling changes in
personality and in mood.
He became extravagant and anti-social, a fullmouth and a liar
with bad manners, and could no longer hold a job or plan his
future.
He was quick to anger and often got into fights.
"The equilibrium between his intellectual faculties and animal
propensities seems to have been destroyed.” - Harlow
This is hypothesized to occur as
a result of impoverished social
learning as a result of failure to
make appropriate mappings
between events and their
outcomes.
Personality Changes
1. Lack of concern for the future
•
•
Consistently poor decision-making
Impulsiveness
2. Failure to obey rules
3. Lack of social graces
4. Disposed to imitation
Personality Changes II
1. Mild euphoria
2. Silliness & facetiousness
3. Pseudo-depression
4. Irritability
Orbitofrontal Cortex
Decision-Making
Reinforcement Value
of Sensory Stimuli
Empathy
Orbitofrontal Cortex
1. Secondary odor & taste cortices
2. Deficits in perceiving auditory or visual
emotional cues
– Can be Modality Specific
3. Cells respond to the rewarding or aversive nature
of stimuli
– Primary reinforcers
– Learned (secondary) Reinforcers
–Cells respond better to real than to 2-D faces
–Cells respond preferentially to specific faces
–Cells change their response to objects when reward associations change
Anterior Cingulate
Anterior Cingulate
Bilateral lesions produce:
1. Akinetic mutism—inability to initiate speech
2. Minimal movement
3. Incontinence
4. No emotional display to pain
5. Profound apathy
6. Indifference
• ***Striatum Pict – Sagittal?
5 Frontal-Subcortical Circuits
1.
2.
3.
4.
5.
Motor
Oculomotor
Dorsolateral prefrontal
Lateral orbitofrontal
Anterior cingulate
Frontal-Subcortical Circuits II
Frontal lobe 
Striatum (caudate, putamen, ventral striatum) 
Globus pallidus & Substantia nigra 
Specific thalamic nuclei 
Frontal lobe
Summary I
Motor cortex
1. Loss of voluntary control over a specific body area
2. Deficits of fine motor control
3. Reduction of strength & speed
Premotor cortex
1. Impairs the integration of sequences into fluid actions
2. Reflex changes (i.e., grasp reflex)
Summary II
Prefrontal cortex
1. Working memory problems
(superior—where; inferior—what)
2.
3.
4.
5.
Difficulty generating new items or hypotheses
Lack of inhibition
Perseveration
Difficulty planning sequences or organizing
strategies
6. Eye movement deficits
Summary III
Orbitofrontal &
Ventromedial prefrontal cortex
1.
2.
3.
4.
Personality & emotional changes
Disregard for rules
Imitation
No IQ or dorsolateral problems
Anterior cingulate
1. Problems with initiating movements
2. Apathy
3. No emotional response to pain