Cognitive Neuroscience PSYC 768 Neuroscience 101

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Cognitive NeurosciencePSYC 768Neuroscience 101

• Raja Parasuraman

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OverviewFunctional NeuroanatomyNeurophysiology
Elements of Neurochemistry
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Early Views of the Brain

• Galen
• Vesalius (1542)
• Leonardo da Vinci

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Functional Neuroanatomy of Cognition
Stimulus
Response
Anatomical subdivisions
Carving the mind at its joints
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Nervous System Organization
Peripheral (PNS)
Somatic (SNS)
Autonomic (ANS)
Spinal Cord
Forebrain
Midbrain
Hindbrain
Cortex
Cortical Areas
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Major Brain Structures
Forebrain
Midbrain and Hindbrain
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The Brain is a 3-D Structure

• Forebrain
• (Neommamalian brain)

II. Midbrain (Paleomammalian brain)
III. Hindbrain (Reptilian brain)
II and III sometimes collectively known as the
brainstem
http//www9.biostr.washington.edu/da.html
(University of Washington Digital Anatomist
Project)
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The Triune Brain (Paul McLean)
Increasing Functional Complexity
Increasing Evolutionary Age
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Development and Evolution
paleomammalian
reptilian
neomammalian
Ontogeny recapitulates phylogeny
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The Hindbrain

• Medulla
• Life support functions
• Regulation of respiration, muscle tension, etc.
• If damaged
• death
• coma
• Pons
• Arousal and sleep (reticular formation)
• Consciousness
• If damaged
• coma
• sleep disorders

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The Hindbrain (contd.)

• Cerebellum
• Coordination of movements (under cortical
  control)
• Cognitive functions?
• If damaged
• Motor disorders

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The Midbrain

• Tectum
• Superior colliculus
• Eye movements
• Inferior colliculus
• Auditory orientation
• Tegmentum
• Reticular formation
• Arousal and sleep
• Substantia nigra
• Motor initiation
• If damaged
• Parkinsons disease

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The Forebrain

• Basal ganglia
• Monitoring of voluntary movements
• If damaged
• Motor disorders (Huntingdons disease)
• Thalamus
• Sensory relay center
• If damaged
• Attentional disorders

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The Limbic Lobe

• Cingulate gyrus
• Hypothalamus
• Amygdala
• Hippocampus
• Phylogenetically older than neocortex (allocortex
  and mesocortex)
• These structures are involved in various aspects
  of emotional behavior

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The 4 Major Cortical Lobes
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Brodmanns Areas (original)
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Brodmanns Areas (simplified functional)
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Cortical Areas

• Occipital Lobe
• Primary visual cortex (Striate cortex V1 Area
  17)
• Secondary visual areas (Extrastriate cortex V2
  Areas 18, 19)
• Demarcated from the parietal and temporal lobes
  by the parieto-occipital sulcus

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Cortical Areas

• Parietal Lobe
• Primary somatosensory cortex Postcentral gyrus
• Association areas play a role in attention and
  spatial processing
• Demarcated from the frontal lobe by the central
  sulcus (or Rolandic fissure)

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Cortical Areas

• Temporal Lobe
• Primary auditory cortex Superior temporal gyrus
  (A1 Areas 41, 42)
• Inferior temporal gyrus plays a role in visual
  object recognition
• Medial temporal lobe (hidden in this view) plays
  a role in memory formation
• Demarcated from the parietal lobe by the lateral
  sulcus (or Sylvian fissure)

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Cortical Areas

• Frontal Lobe
• Primary motor cortex Precentral gyrus (Motor
  strip Area 4)
• Homunculus in motor and somatosensory cortices

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Cortical Areas

• Frontal Lobe
• Primary motor cortex Precentral gyrus (Motor
  strip Area 4)
• Homunculus in motor and somatosensory cortices
• Prefrontal cortex plays a role in higher
  cognitive functions
• Dorsolateral prefrontal cortex
• Anterior cingulate and medial prefrontal cortex
• Orbitofrontal cortex

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Cortical Regions
http//www.med.harvard.edu/AANLIB/cases/caseNA/pb9
.htm (Harvard Brain Anatomy and Pathology Project)
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Cortex

• Outer layer (bark) of forebrain
• Approximately 3 mm thick and 2000 sq. cm in area
• About 20 billion neurons, plus 200 billion glial
  cells
• Convoluted cortex is folded on itself
• Gyrus (gyri) protuding surfaces or bulges
• Sulcus (sulci) grooves or enfolded regions
• Large sulci (fissures)
• Longitudinal
• Central (Rolandic)
• Lateral (Sylvian)
• Degree of convolution higher in primates, highest
  in humans

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Cortical Layers

• I Molecular layer mostly dendrites
• and long axons few cell bodies
• II External granular layer small pyramidal
  cells
• III Outer pyramidal layer medium and large
  pyramidal cells input from other cortical
  columns
• IV Internal granular layer mostly granule
  cells input layer from thalamus
• V Inner pyramidal layer large pyramidal cells
  motor output to spinal cord
• VI Multiform layer mostly spindle cells

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Cortical Columns (Vernon Mountcastle)

• Oriented perpendicular to the cortical surface
• 30-50 um diameter, spanning the 3 mm depth of the
  cortical layers
• Each column contains approximately 100 neurons
• Shape is quasi-hexagonal, because each cortical
  column is typically surrounded by six other
  columns
• Columns function as modules

A cortical column is a complex processing and
distributing unit that links a number of inputs
to a number of outputs via overlapping internal
processing chains" (Mountcastle, 1998).
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Modular Structure of Cortex
Functional Columns
I
II
III
IV
V
VI
Six Structural Layers
Basic Information Processing Unit?
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Neuronal Information Processing

• Neuron to neuron communication
• action potentials
• postsynaptic potentials
• Neurochemical innervation of cortex (subcortex)

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Neuronal Conduction

• Resting neuron membrane potential - 70 mV
• Active postsynaptic potential generated by input
  to neuron
• Passive current flow through neuron
• Depolarization (membrane potential ?)
• Hyperpolarization (membrane potential ?)
• Repolarization (return to resting membrane
  potential)

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Neuronal Conduction (contd.)

• If net potential at axon hillock gt threshold, ion
  channels open (active process), and action
  potential generated (exchange of Na and K ions)
• Na ions in Rising phase of AP
• K ions in Falling phase of AP
• AP duration approximately 1-2 ms (refractory
  period)

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Neuronal Conduction The Problem

• Action potential decays over length of axon due
  to resistance and capacitance
• Not a problem over short axonal distances (e.g.,
  retina) but is for long distances (e.g., spinal
  motor neurons)
• Resistance is reduced (and axonal speed
  increased)
• However fat motor neurons needed to reach distant
  muscles would exceed width of spinal cord

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The Solution Myelin and Saltatory Conduction

• Myelin (glial cell membrane) insulates axon and
  reduces resistance and increases speed of
  conduction
• AP regenerated at gaps in myelin (Nodes of
  Ranvier) where ion channels are found
• Saltatory conduction (jumps) represents a
  tradeoff between signal loss due to axonal length
  and speed

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Saltatory Conduction
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Myelin and Saltatory Conduction (contd.)

• Unmyelinated neurons are the fastest in the
  nervous system, but can only conduct over short
  distances
• Myelinated neurons are slower, but can conduct
  over longer distances ( 100 m/s)

Unmyelinated (no Nodes of Ranvier), fastest,
short distance
Myelinated (many nodes), slow, longer distance
Myelinated (few nodes), faster, shorter distance
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Synaptic Transmission

• Synapse Gap between axon of one neuron and
  dendrite (or cell body) of another cell
• presynaptic neuron
• postsynaptic neuron
• Synaptic transmission involves communication
  across the synapse from one neuron to another
• chemical
• electrical

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Synaptic Transmission (contd.)

• Chemical transmission involves
• voltage-gated Ca2 ion channels in the
  presynaptic neuron
• receptors (specialized ion channels) in the
  postsynaptic neuron

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Chronology of Events at Synapse

• Action potential arrives at axon terminal
• Vesicles containing neurotransmitter fuse with
  presynaptic membrane (with help of Ca2)
• Neurotransmitter released into synaptic cleft
  (gap)
• Neurotransmitter diffuses across cleft and binds
  with postsynaptic receptors

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Chronology of Events at Synapse (and beyond)

• Binding (lock and key) of NT and receptor results
  in postsynaptic potential (PSP)
• Depending on postsynaptic receptor, the PSPs can
  be excitatory or positive (EPSP) or inhibitory or
  negative (IPSP)
• Spatial and temporal summation of EPSPs and IPSPs
  at axon hillock leads to action potential, and so
  the process of neuronal communication continues
• Action potential On or off a digital signal
• PSPs Can have multiple values, positive or
  negative an analog signal

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Discovery of The First Neurotransmitter

• Acetylcholine (ACh)
• Discovered by Otto Loewi (1924)
• Vagus nerve stimulation of heart muscle
• Chemical stimulation of second heart
• Henry Dale showed that ACh is also involved at
  the neuromuscular junction
• Curare (as in poison darts) occupies receptor
  sites in muscles, hence preventing ACh to work
  and causing paralysis

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Routes to Paralysis and Intoxication
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We now understand the microstructure of
neurotransmitter receptors
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Classes of Neurotransmitters

• Acetylcholine
• Amino acids
• excitatory
• glutamate
• aspartate
• inhibitory
• gamma-aminobutyric acid (GABA)
• glycine
• taurine4
• Biogenic amines
• serotonin
• histamine
• catecholamines
• dopamine
• norepinephrine
• Neuropeptides
• Over 50 known

Underlined NTs have been linked to different
aspects of cognitive functioning
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Key Historical Figures
Sir Charles Sherrington 1857-1952
Sir Henry Dale 1875-1968
Otto Loewi 1873-1951
All Nobel Prize Winners
Eric Kandel 1934 - present
Sir John Eccles 1903-1997
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Internet Resources

• www.cogneurosociety.org (Cognitive Neuroscience
  Society)
• www.sfn.org (Society for Neuroscience)
• http//www.humanbrainmapping.org/ (Organization
  for Human Brain Mapping)
• http//www9.biostr.washington.edu/da.html
  (University of Washington Digital Anatomist
  Project)
• http//www.med.harvard.edu/AANLIB/home.html
  (Harvard Brain Anatomy and Pathology Project)
• http//www.univie.ac.at/anatomie2/plastinatedbrain
  /main.html (The Plastinated Brain)
• http//www-medlib.med.utah.edu/kw/sol/sss/subj2.ht
  ml University of Utah Medical School)