The Prefrontal Cortex – An Up-date: Time Is of the Essence

(Joaquin M. Fuster, 2001)Action-Perception-Learning Cycles

2012-09-13Chun, Hyo-sun

• The Prefrontal Cortex – An Update: Time Is of the Essence– Joaquin M. Fuster, 2001

• The cognit: A network model of corti-cal 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 Cogni-

tion• Memory and Set, for the Two Sides of Time• Cortical Mechanisms of Temporal Integra-

tion• Conclusions

Anatomy and Connec-tions

• 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, percep-

tual awareness, thought, language, and con-sciousness

• It is organized in hierarchical manner

sensory and motor areas

specific sensory and motor func-tions

PFC: representation and execution of actions

The prefrontal cortex (PFC)• The PFC is the association cortex of the frontal

lobe.• The PFC constitutes the highest level of the corti-

cal 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• Phylogenetically, PFC is one of the latest cortices to develop, having

attained maximum relative growth in the human brain (Brodmann, 1912; Jerison, 1994)

• 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)

• Thus, these areas are critical for higher cognitive functions

Connections• The functions of the PFC rely closely on its con-

nections with a vast array of other cerebral struc-tures.– 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 struc-tures 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 (Dama-

sio et al., 1994; Fuster, 1997)• Impulsive, disinhibited in a host of instinctual be-

haviors, irritable, contentious, and exhibit a severe disorder of attention.

• Thus, major role of orbital PFC is to controlemotional 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 activa-tions of the medial region in tasks that demand sus-tained effort and concentrated attention (Posner et al., 1988; Raichle, 1994)

• Thus, the major role ofmedial PFC is to maintain attention

Lesions of lateral PFC• The inability to formulate and to carry out plans and se-

quences 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 Cogni-tive 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 Dynam-ics 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 cogni-tive operations.

Temporal integration

Basal gangliaCerebellumLateral 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 ac-tion”

• Preparatory set: “memory of the fu-ture”

Temporal integration• Experiment

– (1) Brief tone from overhead loudspeaker– (2) 10s delay– (3) two colors simultaneously in two buttons– (4) 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 Tempo-ral 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 corti-

cal 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 con-

tinuous circular flow of information between itself and its environment

Conclusion• PFC: memory, planning, execution of ac-

tions– 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 rep-

resentations 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– 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 in-

tegrated? Explain Figure 4. How does the cortex process a novel and complex sequence?

Q2- answer• Routine, automatic, or overlearned behavioral se-

quences, 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 con-trolling stimuli or in their motor acts, do engage the PFC.

Q3• Explain Figure 7. What is the experimental para-

digm? What is the objective of the experiment? What is the conclusion of the experimental re-sults? 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 stimu-

lus 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 con-

tinuous circular flow of information between itself and its environment

• Environmental stimuli are received and processed by sensory structures; as a result of sensory pro-cessing, 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 to-gether toward their goals in every sphere of ac-tion, 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 ar-

chitecture of the brain in terms of the cog-nits.

• The network model postulates the memory and knowl-edge 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 knowl-edge. 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 pre-frontal cortex?

• -> Question 1

Q5-4• What brain connections are respon-

sible 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 impor-

tant? How is it different from other coding mechanisms known to be used in the brain?

• the code of cortical representation is a re-lational code– Memories consist of networks made of con-

nections between more or less widely dis-persed neurons of the cortex of association