CAAM/NEUR 415: EXAMINATION #2
April 24, 2006
1 Answer the following questions (total 26 points):
1. What are the two main assumptions made by the quantal model of synaptic release
about the release of neurotransmitter from the presynaptic terminal at a chemical
synapse? At a synapse in the central nervous system, would you expect the binomial
or the Poisson version of the model to better describe synaptic release? Briefly justify
your answer. (4 points)
2. Assume an AMPA synapse is activated in a neuron at rest (-70 mV) or at a de-
polarized membrane potential (40 mV above rest). Do you expect more current to
flow through the channel at rest or in the depolarized state? What about an NMDA
synapse? Briefly explain why. (3 points)
3. Explain what is meant by ”silent” inhibition. (2 points)
4. An optimally oriented, stationary oscillating sinusoidal grating is presented in the
receptive field of a simple and complex cell at various phases with respect to the
receptive field center. Briefly describe the two main differences expected between
their responses. (3 points)
5. Briefly explain how the spatial receptive field of a complex cell is obtained from that
of simple cells in Hubel and Wiesel’s model and why their idea is plausible. (2 points)
6. Why is the Fourier transform an important tool to describe the spatial receptive
fields of the visual neurons studied in class? (2 points)
7. Sketch the spatio-temporal (x, t) receptive field of a simple cell sensitive to motion
from left to right. Based on the sketch, briefly explain why the cell responds to one
direction of motion and not the other. (2 points)
8. Give two common measures of variability used to describe the spike trains of neurons.
Briefly explain the difference between the two. What is for each of these measures the
expected range of values that you expect from cortical neurons in vivo? (3 points)
9. Briefly explain in words how the Tsodyks-Markram model of synaptic release extends
the classical quantal model. How does in this model short term synaptic depression
affect the transformation between pre- and postsynaptic rate? (2 points)
10. Briefly explain how a temporal weighting function is obtained using reverse-correlation.
Give two assumptions that need to be satisfied by the stimulus and/or neuronal sys-
tem under consideration for the method to work. (3 points).
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