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

This article provides an update on the prefrontal cortex, highlighting its anatomy, connections, and role in cognition. It discusses the development of the prefrontal cortex and its critical functions in memory, attention, behavior, and reasoning. The article also explores the neuropsychology of the prefrontal cortex and its relationship with other cerebral structures.

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

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  1. The Prefrontal Cortex – An Update: Time Is of the Essence (Joaquin M. Fuster, 2001) Action-Perception-Learning Cycles 2012-09-13 Chun, Hyo-sun

  2. 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

  3. 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

  4. Anatomy and Connections • Cerebral cortex • Prefrontal cortex • Three major regions of PFC • Development of PFC • Connections

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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)

  10. 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 • Phylogeneticallyand 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

  11. Neuropsychology of the PFC • Lesions of orbital PFC • Lesions of medial PFC • Lesions of lateral PFC

  12. 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 controlemotional behavior

  13. 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 ofmedial PFC is to maintain attention

  14. 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

  15. 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

  16. 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

  17. Summary:The PFC in the Cortical Cognitive Map • Perceptual memory network • Executive memory network • These are organized hierarchically.

  18. The PFC in the Cortical Dynamics of Cognition • Encoding and retrieving memory • Temporal integration

  19. 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.

  20. Temporal integration Basal ganglia Cerebellum Lateral thalamus PFC

  21. 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

  22. Memory and Set, for the Two Sides of Time • Working memory: “memory for action” • Preparatory set: “memory of the future”

  23. 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

  24. Results • Firing frequency histograms of two cells • Two separated stimulus are integrated

  25. 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?

  26. Perception-action cycle • The behavior of an organism is subject to a continuous circular flow of information between itself and its environment

  27. 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

  28. 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?

  29. 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

  30. Q2 • How are the actions temporally sequenced or integrated? Explain Figure 4. How does the cortex process a novel and complex sequence?

  31. 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.

  32. 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?

  33. 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?

  34. Q4 • Explain the cortical dynamics in the perception-action cycle in Figure 10.

  35. 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.

  36. 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.

  37. 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.

  38. 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

  39. Q5-4 • What brain connections are responsible for the perception-action cycle in sequential behavior, speech, and reasoning? • Connections between posterior and frontal cortex

  40. 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

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