Memory and Cognition

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Memory and Cognition

• PSY 324
• Chapter 2 Cognition and the Brain
• Part I Microstructure of The Brain
• Dr. Ellen Campana
• Arizona State University

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A Brain

• Gray White Matter
• Solid tissue
• Made up of neurons
• Golgi showed by staining slices with dye
• Ramon y Cajal gave us the terms we still use today

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Neurons

• Similarities with other cells of the body
• Have a nucleus containing DNA
• Surrounded by a cell membrane
• Contain mitochondria and other organelles
• Do basic cell stuff (protein synthesis, energy
  production)
• Unique characteristics
• Do not reproduce
• Structure, function, chemicals (details to come)

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Structure of a Neuron
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Structure of a Neuron
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Varieties of neurons

• Function transmit information to other cells
• Sensory / Afferent neurons info TOWARD CNS
• Motor / Efferent neurons info AWAY from CNS
• Interneurons info to other neurons in the CNS

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Info Transmission Simple Story

• Neurons are transducers convert environmental
  energy to electrical energy (starting with
  receptors)
• Energy is propagated from the dendrites into the
  cell body.
• Energy is propagated to the end of the axon. Once
  energy goes above a threshold, it triggers the
  release of neurotransmitters into the synapse
• The neurotransmitters in the synapse trigger the
  same process (or a different one) in the next cell

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Synapses
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Synapses

• Action Potential reaches the end of the axon,
  triggering release of neurotransmitters

• Excitatory neurotransmitters increase firing rate
  in next neuron
• Inhibitory neurotransmitters decrease firing rate
  in next neuron
• NOTE Other neurotransmitters do other things
  (less well understood, less relevant to
  cognition, especially to models we will talk
  about)

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Method Single-Cell Recording

• It is possible to record activity of a single
  cell in a living organism
• Tiny wires (called microelectrodes) stuck into
  axon, and surrounding area.
• Measure charge difference inside/outside cell
• Can be attached to oscilloscope for data display
• Time is a factor
• De/Repolarization cycle 1/1000 S or 1 ms
• Activities of cognition take at least 100ms at
  that resolution action potentials show up as
  spikes
• Often most useful to talk about firing rate

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Method Single-Cell Recording

• Visit Pictures http//viperlib.york.ac.uk/ and
  enter in the search words single cell recording
• Pictures of actual neural spikes
• Video clip from Hubel Weisel
• Recordings from cat visual cortex. Sounds you
  hear are individual spikcs and the video is what
  the cat was seeing at the time
• they got the 1981 Nobel Prize in physiology and
  medicine for this work)
• Different types of cells (simple, complex).

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History of Single-Cell Recording

• Participants in experiments
• 1880s People injured by accident with exposed
  brains, also patients with epilepsy
• 1950s Fully anesthetized animals (cats,
  squirrels, monkeys, apes)
• 1980s Awake, active monkeys and apes
• Invasive, destructive procedure
• Data there is a cell in the animal that
  increases firing under conditions

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Value of Single-Cell Recording

• By itself, the data doesnt tell us much
• Can find cells that do almost anything
• The value of single-cell recording for
  understanding human cognition depends on
• Functional organization of the brain
• Consistencies of organization within species
• Meaningful mapping from animal models to
  organization of human brain
• Fortunately (for scientists), these do exist

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The End

• Next up
• Localization of Function
• Neural Coding / Representation