Bursting Neurons Lecture 10

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Bursting Neurons(Lecture 10)

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

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Resources

• 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.
• 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.
• Churchland and Sejnowski, 1994, The Computational
  Brain, Bradford Books.

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The Platonic neuron

• Consists of a soma, one or more dendrites, and an
  axon
• Any of these elements may be missing
• You can also have binary neurons where a dendrite
  is axon-like. These can signal bi- or
  unidirectionally

Apical Dendrite
Soma
Basal Dendrite
Axon and Axon Collateral
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More complex biologically relevant neurons

• Characterised by wide variation in firing
  patterns
• Often make use of active conductances in the
  dendritic tree, which serve to amplify PSPs
  generated there and send them over longer
  electrotonic distances.
• Many different ion channel types
• The HH model found in the squid is particularly
  simple, serving to conduct regular neural
  impulses rapidly.

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Physiological behaviour of the neuron

• Determined by the types of conductances found in
  its membranes and its topological structure.
• These experiments will address how periodic
  bursts of action potentials can be generated.
• This behaviour is found in molluscan pacemaker
  neurons and in the CA3 pyramidal neurons of the
  mammalian hippocampus.

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Molluscan neurons

• R3 beater neuron
• R15 regular burster
• L10 irregular burster
• (from Kandel via Bower and Beeman)

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Periodicity

• Often entirely endogenous to a neuron, persisting
  when the soma is isolated. These are termed
  pacemakers, responsible for controlling highly
  regular behaviour that is only moderately
  regulated.
• Other neurons generate a periodic signal in
  response to inputconditional bursters.
• In the cortex, dopamine and GABA seem to be able
  to turn this on and off.

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Control of periodicity

• Uses channels qualitatively similar to the Na
  and K channels in the HH model.
• Shape and firing patterns influenced by other
  channels and their interactions.
• Conductances for Ca and Cl- exist.
• Activation and inactivation is more complex than
  for the HH model.
• Voltage and ligand-sensitive channels are also
  important.
• Finally, time constants vary greatly

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Dance of the ions
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Ionic conductances

• Nominal resting potential of -40 mV
• Reaches 0 mV during the action potential
• The model molluscan neuron includes
• Fast Na currents
• Delayed K currents
• High-threshold Ca currents
• Slow inward B-current (Na/Ca)
• Calcium dependent K C-current
• Transient K A-current

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Details

• Fast Na currents, associated with AP generation.
  Do not inactivate for hyperpolarisation.
• Delayed K currents, associated with APs and
  repolarisation. Delayed rectifier current.
• High-threshold Ca currents, activated by APs.
  These channels trigger transmitter release.
• Slow inward B-current (Na/Ca). Produces a
  sustained depolarisation. Burst current.
  Creates the burst region.
• Calcium dependent K C-current. Produces a slow
  hyperpolarisation and an inward Ca current.
  Ends the burst. In mammals shifted lower (and
  called the T-current).
• Transient K A-current, maintaining
  hyperpolarisation and delaying the next AP in
  pacemaker neurons. Primitive.

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Adrift in parameter space

• Experiments are often insufficient to provide all
  the parameters needed.
• Approach
• Build a correct compartmental model
• Add passive membrane properties
• Incorporate active channels based on experimental
  evidence
• Search parameter space for solutions, taking
  advantage of the different time scales for
  subsystems.

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Research opportunities

• I have been funded by EPSRC for a large-scale
  computational model of the inferior colliculus, a
  part of the auditory system
• We have opportunities for MSc-level projects
  associated with elements of the modelling.
• This will involve work similar to that described
  here, and also with exploiting those results in
  robotics and linguistics applications.
• Interested?