Neural Foundations of Executive Function LISTENING

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Neural Foundations of Executive
FunctionLISTENING SPOKEN LANGUAGE
SYMPOSIUMSt. Louis, MO. July 2009

• Melody Harrison, Ph.D.
• Speech Hearing Sciences
• University of North Carolina at Chapel Hill

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• Eight Organizing Principles

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1. Interconnectivity of the Brain.

• All primary sensory and motor regions are
  connected through association and commissural
  and projection fibers.
• Association within the hemisphere
• Commissural between the hemispheres
• Projection among components of the CNS

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Association Fibers

• Association fibers are the most numerous and
  provide bi-directional communication among
  cortical areas within a hemisphere
• Short association fibers are U shaped arcuate
  fibers and usually connect two adjacent gyri.
• Long Association fibers connect cortical
  areas. The superior longitudinal fasciculus
  (arcuate fas) connects the frontal, (Broccas
  area), temporal (Wernickes area) and occipital
  lobes (visual processing).

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Arcuate Fasciculusconnects Broccas
Wernickes
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Superior Longitudinal Fasciculusor Arcuate
Fasciculus (2) fromhttp//brainmind.com/Brain
Atlas2.html
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Commissural Fibers

• Commissural fibers run horizontally and connect
  corresponding areas in the two hemispheres
• Most of the commissural fibers are found in the
  corpus callosum (3-4 hundred million fibers).
• The remainder are found in the anterior
  commissure.

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Corpus Callosum fromhttp//brainmind.com/BrainAt
las2.htm
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Projections Fibers Projection fibers are long
ascending and descending fibers. (7
Corticospinal Tract)
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2. Centrality of the Central Nervous System

• Almost everything is processed by one the
  nuclear elements of the thalamus the switchboard
  of the CNS.
• For example, information related to hearing does
  not proceed to the auditory cortex without being
  processed in the medial geniculate body of the
  thalamus

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Nuclei of the Thalamus
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3. Hierarchy of Neuraxial Organization

• Lower segment levels perform functions that are
  modified by the axial segments above i.e.
• The spinal cord produces reflexive responses
• The cerebellum interprets, integrates and
  regulates incoming signals to modulate intensity
  and rhythm of muscular response
• The cortex produces an integrated, complex motor,
  visceral, emotional, linguistic, and who knows
  what else.. response

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4. Laterality of Brain Organization

• The three most important aspects of brain
  organization are
• a. bilateral anatomical symmetry between the two
  hemispheres , connected by the corpus callosum
• b. unilateral functional differences. Hemispheres
  have equipotential but developmental diversity.
• c. contra-lateral sensorimotor control. All
  sensory motor fibers decussate (cross) the
  midline, usually in the caudal medulla, at the
  pyramids

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Physical Hemispheric Symmetry
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Pyramidal Decussation
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5. Structural and Functional SpecializationNeur
onal systems are functionally specialized so that
there are many different parallel and adjacent
pathways traveling in extremely close proximity.
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6. Topographical Organization Peripherally to
Centrally in Cortical Pathways

• Each peripherally located
• area in the body is discretely
• represented within the
• information carrying
• pathway and is projected to
• specific areas in the brain.
• The cochlea is an
• exquisite example.

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Homuculus
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• 7. Plasticity in the Brain
• Functional plasticity is the ability to
  reorganize and modify functions and adapt to
  internal and external changes
• 8. The Brain is Non-mythical
• Operations are straightforward and not governed
  by gender, personal characteristics, or culture.

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A Brief Structural Overview

• Surface Features
• Foldings and convolutions increase cortical area.
  
• Each ridge is called a gyrus.
• Each groove a sulcus.
•  If sulcus is particularly deep it is called a
  fissure.

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The Cerebral Lobes

• Each cerebral hemisphere
• is divided into four
• physically definable lobes,
• which can be seen in the
• undissected brain.
• The 5th lobe, the limbic
• lobe is actually composed
• of components of the brain
• and is not a distinctly
• separate physical entity

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The Limbic System (Lobe)
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The Human Brain
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Lobes of Other Brain

• Parietal associated with 3 functions
• The postcentral gyrus coincides with the primary
  somatosensory cortex. It is concerned with the
  initial cortical processing of tactile and
  proprioceptive (sense of position) information.
• Much of the inferior parietal lobe of one
  hemisphere (usually the left), together with
  portions of the temporal lobe, involved in the
  comprehension of language.
• The remainder is involved in aspects of spatial
  orientation and perception.

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Occipital Lobe

• The primary visual cortex is contained in the
  walls of the calcarine sulcus and bits of
  surrounding cortex.
• The remainder of the lobe is referred to as
  visual association cortex.

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Temporal Lobe

• The primary auditory cortex is a small area of
  the superior temporal gyrus
• The parahippocampal gyrus and hippocampus are
  part of the limbic system.
• The temporal lobe is involved in complex aspects
  of learning and memory.
• 2 and 3 overlap i.e., hippocampus involved in
  memory.
• Factoid part of the fusiform gyrus is very
  involved in
• recognition of faces.

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Frontal Lobe

• The primary motor cortex
• in the precentral gyrus. It is
• the site of initiation of all
• voluntary movements.
• The premotor area is the
• adjacent portions of the
• superior and middle frontal
• gyri and is also related to the
• initiation of voluntary
• movements.

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More Important Frontal Lobe Areas

• Brocas area is important in the production of
  written and spoken language and is located in the
  opercular and triangular parts of the inferior
  frontal gyrus of (usually) the left hemisphere.
• 4. The prefrontal cortex, a very large and
  confusingly named area which makes up the
  remainder of the frontal lobe. It is involved in
  such abstract concepts as personality, insight,
  motivation, initiation, organiozation, and
  foresight
•  

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The Prefrontal Cortex

• with apologies to
• Joaquin Fuster and John Nolte

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Rolands Fissure

• The cortex posterior to
• RF is primarily involved
• in perceptual memory.
• Executive memory is
• managed in the area
• anterior to the fissure.

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Misrepresentations of the PFC

• To argue for one prefrontal function while
  neglecting those that compliment or collaborate
  with it.
• To exclusively localize any function within a
  discrete portion of the prefrontal cortex.
• The functions of the PFC rely on its connections
  with a
• vast network of other cerebral structures. None
  of its
• cognitive functions can understood if taken out
  of the
• context of those connections.

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The connectivity between prefrontal cortex and
other brain regions.
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PFC Factoids

• It is the association cortex of the frontal lobe.
• It comprises almost one-third of the neocortex.
• Phylogenetically it is one of the latest cortices
  to develop.
• Ontology it displays late myelinization of nerve
  fibers and late completion of neural connections
• Maturity of the PFC in humans does not seem to
  occur until late adolescence. (imaging evidence)

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Three Major Regions of the Prefrontal Cortex

• The Orbital and Medial regions are involved in
  emotion
• The Lateral region provides the cognitive support
  to the temporal organization of speech, behavior,
  reasoning.
• Each of these areas is connected with itself and
  with the other two areas.
• There are also interhemispheric connections

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Connectivity of the Prefrontal Cortex

• TO REPEAT The functions of the PFC rely on
  connections with a vast network of other cerebral
  structures. None of its cognitive functions can
  understood if taken out of the context of those
  connections.
• It is connected with the
• Thalamus (mediodorsal area)
• Basal ganglia
• Limbic system
• Most connections are reciprocal.

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Connectivity of the Prefrontal Cortex

• These connections provide information to the PFC
  about
• Internal level of arousal
• Drives and motivations
• The visceral concomitants of emotion
• The motivational aspects of sensory stimuli

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Neuropsychological Aspects

• What we know about the integrative functions of
  the
• Prefrontal cortex is based primarily on
  neuropsychological
• studies of humans.
• There are studies related to the three general
  areas of the prefrontal lobe
• Orbital
• Medial/cingulate gyrus
• Lateral

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The first and most famous case was that of
Phineas Gage.
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Damage to the Orbital Area

• Lesions of the orbital area create dramatic
  personality changes including
• Impulsivity gtgthigh risk behaviors run-ins with
  the law
• Disinhibited instinctual behaviors
• Tendency towards coarse humor
• Disregard for social and moral behavior
• Severe disorder of attention

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Damage to the Orbital Area

• This disorder of attention is characterized by an
  inability to maintain focus on a task in the
  presence of a distraction.
• Thus, one primary role of this part of the PFC is
  to suppress reactivity to competing stimuli.

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Medial Area Prefrontal Cortex

• The medial area includes the anterior cingulate
  gyrus and the medial gyrus. (34)
• Seems to also be involved in attention, emotion,
  and initiation of activity.

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Medial Area Prefrontal Cortex

• In healthy brains of individuals who display
  normal attentional behaviors, imaging studies
  (PET fMRI) show the anterior cingulate gyrus is
  very active when the individual is engaged in
  tasks that demand sustained effort and focused
  attention.
• The medial cingulate area of the prefrontal
  cortex is refered to as the anterior attentional
  system.

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Medial Area Prefrontal Cortex

• Damage in this area of the prefrontal cortex
  manifests itself as
• Loss of spontaneity
• Difficulty initiating movement
• Bilateral lesions can cause akinetic mutism
• Speaking and other movements are inhibited
• Apathetic
• Disinterested in the surrounding environment
• Unable to focus on behavioral or cognitive tasks

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Lateral Area Prefrontal Cortex

• Damage in this area create the most
  characteristic deficits from frontal lobe damage.
• Inability to formulate and carry out plans and
  sequences of actions
• Includes the ability to construct and execute
  written and spoken language (Luria, 1966, 1970)
• Difficulty to consciously represent sequences of
  speech or behavior
• Difficulty initiating and executing them in an
  orderly manner especially if they are novel or
  complex.

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Lateral Area Prefrontal Cortex

• This set of difficulties has been called the
  dysexecutive syndrome.
• It is usually accompanied by a severe attention
  disorder to the point of loss of supervisory
  attentional control.
• The lateral PFC plays a crucial role in the
  organization and execution of reasoning
  speech/language and novel or complex behaviors.

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Cognition and the Lateral PFC

• Imaging studies have demonstrated that
• Overlearned or routine behaviors do not require
  the involvement of the prefrontal cortices.
• Novel or complex behavior and language do
  activate this area of the brain.
• In language or other complex or novel behavior,
  temporal integration is key to temporal order.
• Choice and timing of acts such as these are
  contingent upon
• a plan of action
• goals
• any acts which precede or follow

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Hierarchy of Lateral PFC Function
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References

• Barbas, H. (2000). Connections underlying the
  synthesis of cognition, memory and emotion in
  primate prefrontal cortices. Brain research
  bulletin, 52, 319-330,
• Fuster, J. (2001).The prefrontal cortex-An
  update Time is of the essence. Neuron,30(2),
  319-333.
• Netter, F. (2006). Netters atlas of human
  anatomy 4th Edition. Saunders Elsevier
  Philadelphia, PA.
• Nolte, J. (2002 ). The human brain An
  introduction to functional anatomy 5th Edition.
  Mosby St.Louis, MO.
• Posner, M. Petersen, S. (1990) The attention
  system of the human brain. Annual Review of
  Neurocience, 13, 25-42.