Neural Networks B, SS06 1

UA Dr. Robert Legenstein, WiMAus Prashant Joshi, M.S.

Institute for Theoretical Computer Science
Technische Universität Graz
A-8010 Graz, Austria
{legi, joshi}

NACHNAME Vorname Matrikelnmr Teammitglieder

Exercise 8: The inhibitory rebound

NOTE: You can download this exercise in pdf or postscript(ps) format here.

In this exercise, you are going to analyze an important electrophysiological feature of neurons; the post-inhibitory rebound also called as the post hyperpolarising response. For this exercise you are going to use the NEURON simulator.


We shall try to observe the inhibitory rebound in rat subthalamic nucleus neurons. An important electrophysiological feature of subthalamic neurons is the post hyperpolarising response. When a neuron is hyperpolarised (e.g. by current injection or inhibitory synaptic input), at the end of the hyperpolarisation, a burst of activity is observed in subthalamic projection neurons. This response is mediated by a low threshold calcium selective ion channel, called the T-type calcium channel.

The code sthA.hoc availaible at: creates the soma for a subthalamic nucleus neuron. The code by default only contains the default Hodgkin and Huxley types of sodium and potassium ion selective channels, and the passive membrane properties. We would like to make our neuron much more electrophysiologically characteristic of subthalamic nucleus neurons. There are many channel types we would want to add, but for this exercise we will add only one new type, i.e. the T-type calcium channel.

Sadly this cannot be done with the programming language hoc that we have used to create the initial subthlamic neuron in sthA.hoc. Instead we have to learn the Model Description Language (NMODL) provided for defining additional distributed membrane mechanisms such as ion channels and calcium pumps and point processes such as synapses.

The URL, gives a tutorial that shows you how to use NMODL to create the T-type calcium channel that we intend to add to our model neuron. Follow this tutorial and create the T-type calcium channel, and add it as an additional membrane mechanism to your existing neuron model.


For all parts the stimulus to the neuron is of type IClamp with delay = 100, and dur = 50.

  1. Set the amplitude of the stimulus, amp = 0.05. Essentially this gives an excitatory stimulus to the neuron. Plot the membrane potential of the neuron for this stimulus.

  2. Set the amplitude of the stimulus, amp = - 0.05. This gives an inhibitory stimulus to the neuron. Plot the membrane potential of the neuron for this stimulus. You will see the phenomenon of inhibitory rebound. You know from material covered in lecture why it happens. Make an additional plot of the channel variables for the T-type channel (r, s, and d), and write a short explanation of this phenomenon.

  3. Now plot this phenomenon of inhibitory rebound for 10 different levels of inhibition (on the same plot, with different colors). You can do this by creating 10 neurons, and simulating them at the same time with 10 different levels of inhibition. Explain what you observe here.

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Neural Networks B, SS06 1

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Joshi Prashant 2006-05-30