Temporal Integration Lecture 9

1
Temporal Integration(Lecture 9)

• Harry R. Erwin, PhD
• COMM2E
• University of Sunderland

2
Resources

• Shepherd, G., ed., 2004, The Synaptic
  Organization of the Brain, 5th edition, Oxford
  University Press.
• Nicholls et al.
• Kandel et al.
• Koch, 2004, Biophysics of Computation, OUP.
• Koch and Segev, 1998, Methods in Neuronal
  Modelling, 2nd edition, MIT Press.
• Bower and Beeman, 1998, The Book of Genesis,
  second edition, TELOS, ISBN 0-387-94938-0
• Rieke et al, 1999, Spikes Exploring the Neural
  Code, Bradford Books.
• Churchland and Sejnowski, 1994, The Computational
  Brain, Bradford Books.

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The Response of the Postsynaptic Potential

• See Chapter 6, of Bower and Beeman
• How do multiple synaptic inputs interact?

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Voltage Response

• The resting potential reflects the relative
  permeability of the channels to various ion types
  and the ionic concentration gradients
• To understand the effect of a current pulse,
  solve the network using Kirchoffs Law. The net
  current leaving the compartment should equal the
  current entering (the current pulse).

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Membrane Time Constant

• This reflects the resistance to current flow and
  the storage of ions on the lipid bilayer.
• ?m RmCm, ranging from 1 to 1000 msec.
• Rm varies from 1 to several hundred M?
• Cm is typically close to 1 ?F/cm2
• RmCm RMCM

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Response to Synaptic Activation

• The classical fast synapse results in a local
  conductance change, described by a smooth alpha
  function.
• This is reflected in the post-synaptic potential
  (PSP) change.
• You may have several kinds of synapses and
  receptors interacting.
• For example, long term potentiation involves NMDA
  receptors. These stay open longer than AMPA
  receptors and bind Glu much more strongly. This
  allows non-synaptic NMDA receptors to nucleate
  synapse formation.

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Types of Receptors

• Excitatory, resulting in EPSPs
• Inhibitory or hyperpolarizing, resulting in
  IPSPs.
• Shunting, resulting in decreased membrane
  resistance
• Facilitating, resulting in depolarization, but
  also shunting.

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Somatic Interaction
9
Conclusions

• These non-linear interactions may be more or less
  important.
• In any case, they allow the biological neuron to
  do much more than artificial neural networks can.
• The basal ganglia (next) contain neurons that
  have particularly short time constants,
  electrical synapses, and facilitating channels.
  What this means is unclear.