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Homework: Coding and Neurons 1. Name some of the parameters that one can extract from a neural spike train in order to test for a correlation with a given stimulus quality (like amplitude). #action potentials, rate, frequency, interspike interval, latency to first spike … 2. Can you describe (or draw) what a rasterplot looks like and why it is useful? Its shows when spikes occurred on each trial lined up by experimental time, for example beginning of a trial 3. What is an interspike-interval distribution? Shows how often an interval between two subsequent spikes occurred in a spike train 4. Let me know what was not clear and should be repeated again. Questions? 5. Look at the following spike trains depicting a neuron’s responses to tones of a) increasing frequency and b) increasing loudness. Find the spike train parameter(s) that vary with frequency and/or loudness and draw a response-curve. 2500 Hz 60dB 2000 Hz 50dB 1500 Hz 40dB 1000 Hz 30dB frequency Interspike interval 1500 Hz Tone (1000 ms) #action potentials rate Tone (1000 ms) f (Hz) f (Hz) 1. Describe the elements of the McCulloch Pitts neuron. How do they correspond to elements in real neurons? These neurons sum up their inputs and compare that sum to a threshold. 2. Which characteristics of real neurons are not taken into account in McCulloch Pitts neurons? Temporal summation, leak currents 3. Very briefly describe how the characteristics mentioned in (2) can be taken into account using integrate-and-fire or leaky integrate-and-fire neurons. Temporal summation, leak 4. Which characteristics of real neurons can you think of that leaky integrate-and-fire neurons do not model? Non-linearities in summation, refractory period 5. If one does not want to explicitly model action potential generation using Na+ and K+ channels, what is a good alternative? How is a refractory period modeled in that case? How can noise be introduced in these simulations? You reset the voltage to 0 after a spike, which creates a refractory period. Or you can even reset it to a negative valule. Noise can be added by making the threshold variable, introducing a noise to the input 6. Look at the diagrams below. Label them as McCulloch Pitts, integrate and fire or leaky integrate and fire. Explain. A. Input Firing thres hold LIF Output B. Input Firing thres hold IF Output C. Input Firing threshold McCulloch Pitts Output