Transcript 2-2

The Prefrontal Cortex – An Update:
Time Is of the Essence
(Joaquin M. Fuster, 2001)
Action-Perception-Learning Cycles
2012-09-13
Chun, Hyo-sun
• The Prefrontal Cortex – An Update: Time
Is of the Essence
– Joaquin M. Fuster, 2001
• The cognit: A network model of cortical
representation
– Joaquin M. Fuster, 2006
Overview
Anatomy and Connections
Neuropsychology of the PFC
The PFC in the Cortical Cognitive Map
The PFC in the Cortical Dynamics of
Cognition
• Memory and Set, for the Two Sides of Time
• Cortical Mechanisms of Temporal
Integration
• Conclusions
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Anatomy and Connections
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Cerebral cortex
Prefrontal cortex
Three major regions of PFC
Development of PFC
Connections
Cerebral cortex
• Cerebral cortex is the out layer of the cerebrum
• It plays a key role in memory, attention, perceptual
awareness, thought, language, and consciousness
• It is organized in hierarchical manner
PFC: representation and
execution of actions
specific sensory and motor functions
sensory and motor areas
The prefrontal cortex (PFC)
• The PFC is the association cortex of the frontal lobe.
• The PFC constitutes the highest level of the cortical
hierarchy dedicated to the representation and
execution of actions
Frontal lobe
Three major regions of PFC
• orbital / medial / lateral
• orbital and medial: emotional behavior
• lateral: temporal organization of behavior, speech, and reasoning
• Two common errors:
– 1) to argue for one particular prefrontal function while
opposing or neglecting others that complement it
– 2) to localize any of them within a discrete portion of PFC
Development of PFC
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Phylogenetically, PFC is one of the latest cortices to develop, having
attained maximum relative growth in the human brain (Brodmann,
1912; Jerison, 1994)
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The PFC undergoes late development in the course of ontogeny.
(Flechsig, 1920; Conel, 1939; Huttenlocher, 1990; Huttenlocher and
Dabholkar, 1997)
Neuroimaging studies indicate that, in the human, prefrontal areas
do not attain full maturity until adolescence. (Chugani et al., 1987;
Paus et al., 1999; Sowell et al., 1999)
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Thus, these areas are critical for higher cognitive functions
Connections
• The functions of the PFC rely closely on its
connections with a vast array of other cerebral
structures.
– Brainstem, thalamus, basal ganglia, limbic system
• The profuse variety of connections of the PFC is
obviously related to the variety of the information it
integrates.
• Those connections presumably constitute the structural
frame of cognitive networks(Fuster, 1995)
• A cognit is one such network(Ref)
Summary:
Anatomy and Connections
• Cerebral cortex is organized in hierarchical manner
• The PFC is the association cortex of the frontal lobe.
• Three major regions of PFC: orbital / medial / lateral
– Orbital and medial region: emotional behavior
– Lateral region: temporal integration
• Phylogenetically and ontogenetically, PFC is one of the
latest part to develop.
– These areas are critical for higher cognitive functions
• The complex connections with other cerebral
structures are related to its function of integration
Neuropsychology of the PFC
• Lesions of orbital PFC
• Lesions of medial PFC
• Lesions of lateral PFC
Lesions of orbital PFC
• Phineas Gage
• Showed dramatic changes of personality (Damasio et
al., 1994; Fuster, 1997)
• Impulsive, disinhibited in a host of instinctual
behaviors, irritable, contentious,
and exhibit a severe disorder
of attention.
• Thus, major role of
orbital PFC is to control
emotional behavior
Lesions of medial PFC
• Loss of spontaneity and difficulty in the initiation of
movements and speech (Verfaellie and Heilman, 1987;
Cummings, 1993)
• Apathetic, disinterested in the environment, and unable to
concentrate their attention on behavioral or cognitive tasks.
• Neuroimaging of normal subjects shows marked activations
of the medial region in tasks that demand sustained effort
and concentrated attention (Posner et al., 1988; Raichle,
1994)
• Thus, the major role of
medial PFC is to maintain attention
Lesions of lateral PFC
• The inability to formulate and to carry out plans and sequences
of actions.
• The difficulty to consciously represent sequences of speech or
behavior, especially if they are novel or complex
• The difficulty to initiate sequences and to execute them in orderly
manner
• Thus, lateral PFC plays a crucial role in the organization and
execution of behavior, speech, and reasoning
Summary:
Neuropsychology of the PFC
• orbital PFC controls emotional behavior
• medial PFC helps to sustain attention
• lateral PFC plays a crucial role in the organization and
execution of behavior, speech, and reasoning
The PFC in the Cortical Cognitive Map
• The cortex of the human appears divided by the
Rolandic fissure into two major parts
– The cortex of the occipital, temporal, and parietal lobes
• Sensory functions - Perceptual memory
– The cortex of the frontal lobe
• Motor functions - Executive memory
Summary:
The PFC in the Cortical Cognitive Map
• Perceptual memory network
• Executive memory network
• These are organized hierarchically.
The PFC in the Cortical
Dynamics of Cognition
• Encoding and retrieving memory
• Temporal integration
Encoding and retrieving memory
• By functional imaging methods
– Encoding new memory activates the left
more than the right PFC
– Conversely, retrieving stored memory
activates the right more than the left PFC
• It is not clear that the asymmetric
activations are attributable to their
differential involvement in two cognitive
operations.
Temporal integration
Basal ganglia
Cerebellum
Lateral thalamus
PFC
Summary:
The PFC in the Cortical Dynamics of Cognition
• In fMRI studies,
– encoding new memory: left >> right PFC
– retrieving stored memory: left << right PFC
– but, not clear dissociation of the function.
• Routine sequences do not engage PFC
• Novel and complex sequences do engage PFC
Memory and Set,
for the Two Sides of Time
• Working memory: “memory for action”
• Preparatory set: “memory of the future”
Temporal integration
• Experiment
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(4)
Brief tone from overhead loudspeaker
10s delay
two colors simultaneously in two buttons
animal rewarded for choosing the color that matches the tone
• Results
– Firing frequency histograms of two cells
– Two separated stimulus are integrated
Cortical Mechanisms of
Temporal Integration
• The mechanisms of temporal integration and
the role of the PFC in them are still poorly
understood.
– How are the components of an executive cortical
network timely and selectively activated in the
execution of a goal-directed sequence of behavior?
– How is a cortical network maintained active in the
process of bridging temporally separated
components of the sequence?
Perception-action cycle
• The behavior of an organism is subject to a
continuous circular flow of information between itself
and its environment
Conclusion
• PFC: memory, planning, execution of
actions
– Orbital, medial: emotional behavior
– Lateral: temporal organization of behavior
• Perceptual memory and Executive memory
– Organized hierarchically
• Temporal integration
– Working memory, preparatory set
– Perception-action cycle
Q1
• Explain the general organization of cognitive
representations of the human cortex in Figure 3. Is it
hierarchically organized? What are the three major
regions of the prefrontal cortex (PFC) and what are
their functions?
Q1- answer
• Two memory network
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Anterior part(PFC) represents executive memory
Posterior part represents perceptual memory
Hierarchical, heterarchical
Interacts with each other
• Orbital / medial / lateral region
– Functions
• Orbital, Medial: emotional behavior
• Lateral: temporal organization of behavior
Q2
• How are the actions temporally sequenced or
integrated? Explain Figure 4. How does the cortex
process a novel and complex sequence?
Q2- answer
• Routine, automatic, or overlearned behavioral
sequences, however complex, do not engage the PFC
and may be entirely organized in subcortical structures
(basal ganglia, cerebellum, lateral thalamus, etc.)
• Sequences with cross-temporal contingencies, or with
ambiguities and uncertainties in their controlling
stimuli or in their motor acts, do engage the PFC.
Q3
• Explain Figure 7. What is the experimental paradigm?
What is the objective of the experiment? What is the
conclusion of the experimental results? How sound
and color are cross-temporally integrated in frontal
cortex?
Q3- answer
• What is the experimental paradigm?
• What is the objective of the experiment?
– To see the temporal integration in the PFC
• What is the conclusion of the experimental
results?
– Different kinds of temporally separated stimulus
integrated at lateral PFC
• How sound and color are cross-temporally
integrated in frontal cortex?
Q4
• Explain the cortical dynamics in the perception-action
cycle in Figure 10.
Q4- answer
• The behavior of an organism is subject to a
continuous circular flow of information between itself
and its environment
• Environmental stimuli are received and processed by
sensory structures; as a result of sensory processing,
actions are generated that cause certain changes in
the environment, which lead to new sensory input, and
so on.
• Working memory and preparatory set work together
toward their goals in every sphere of action, including
speech.
Q5-1
• Q5-1: Compare the modular models and
network models of the cortex. How do they view
the cortex differently? What can they explain
and what they cannot?
• Modular model
– A discrete area of the cortex has functions
– Most of these models have failed for lack of
conclusive evidence
• Network Model
– Cognitive representations consist of widely
distributed networks of cortical neurons
– Only large cortical lesions were observed to lead to
deficits in cognitive memory and function.
Q5-2
• What are the cognits? Explain the global
architecture of the brain in terms of the
cognits.
• The network model postulates the memory and
knowledge are represented by distributed, interactive,
and overlapping networks of neurons in association
cortex. Such networks are cognits.
• They constitute the basic units of memory or
knowledge. The association cortex of post-rolandic
region contains perceptual cognit, frontal-association
cortex contains executive cognit.
Q5-3
• Explain the main cognitive functions of
the brain in the following regions:
posterior and frontal cortex, parasensory
and premotor and prefrontal cortex?
• -> Question 1
Q5-4
• What brain connections are responsible
for the perception-action cycle in
sequential behavior, speech, and
reasoning?
• Connections between posterior and
frontal cortex
Q5-5
• What is a relation code? Why is it
important? How is it different from other
coding mechanisms known to be used in
the brain?
• the code of cortical representation is a
relational code
– Memories consist of networks made of
connections between more or less widely
dispersed neurons of the cortex of association