Neuro730- lab exercise #3.

Each class member is to analyze an auditory nerve fiber's responses to sounds that cover the unit's response area.

See assignment table at end of document. You will need the IDs listed there to retrieve the data.

at the prompt: type DF N730L3. this defines the file that contains the 'raw data'. The data consists of the times of occurrence of discharges of auditory nerve fibers that were recorded with a micropipete in a chinchilla. The only information recorded was the time at which the action potential passed a criterion level set by the experimenter. The times are recorded to 1 microsec accuracy. These times represent a complete description of the ANFs response to the sounds.

Each unit has three separate items that are to be studied: a different unit is assigned to each student.

1. response area: the response of a unit to repeated presentations of a tone over the frequency-intensity plane has been called a response area. The 'area' is sampled for a specified range and in a specified increment for the two parameters, in this case frequency and level. Note: the term response area for the output is actually a misnomer and since the output is really a response surface, sometimes the graph is called a response map. This output will appear in the standard plot you will generate.

From this plot you can determine the ANF's CF, threshold, spontaneous rate, maximum discharge rate and it's Q₁₀. (Q₁₀ = CF/(bandwidth at 10 dB above threshold). These numbers are to be recorded in the Class summary description of lab3.

Try graphing the response to only one repetition of the stimulus. (hint: type tr 1 1 to analyze only the first trial. tr 3 4 to analyze trials 3 to 4, etc.). Comments?

Smooth the curves: type sm line n. This is a symmetric moving average filter (e.g., n=3 means y(i)=(x(i-1) + x(i) + x(i+l))/3: why is it a symmetric filter and what does that do for you?

What is the restriction on n?

Could you use this filter to smooth a signal in real time? If not, why not?

One of the commonly used analysis techniques is the IRC or isorate curve. This has an equivalency with the frequency threshold curve (FTC) for a unit. FTCs are often gathered using an adaptive up/down procedure to determine the threshold at each frequency. We will use the response area data.

you can specify the criteria for which the curve is determined (e.g. PER = 10).

This analysis usually works better when the data is smoothed ahead of time. Measure the slope of the IRC above and below CF (you need a hardcopy first & a log scale). Record these values.

Given the maximum discharge rate for the unit. what change in rate does the 10% criteria correspond to?

How many spikes in a 50ms tone pip would this correspond to?

List the points that determine the curve: (type dis irc) this data will be entered into a MATLAB file so that all the curves can be superimposed in a single plot (a population study).

Before leaving this topic consider the tradeoffs between using an FTC to obtain CF, TH, Q₁₀ and an isorate curve obtained from a response map. What are some of the tradeoffs?

2. Short-tone at CF: In order to study the statistics of the unit ( & obtain smooth appearing plots), the short tone is repeated 250Xs. The unit response can be studied using Poststimulus time histograms (PSTH), interval histograms (IH), cycle histograms (CH), latency dot display (LDD) and a variety of other techniques. Plot each of these and examine the outputs.

when should you 'believe' the phase value obtained from the calculation of vector strength that is provided in the cycle histogram?

3. Rate-level function. Another method of studying unit response is to determine how they respond as some parameter is varied- e.g., stimulus level which results in a rate-level function. You can plot spike rate vs level, the synchronization vs level, and latency versus level.

It would be interesting to combine all synchronization coefficients vs frequency curves in a single plot.

Each student: hand in (oct. 8) RA plot, IRC curve with slope calculation, pst, rate level curve.

Answer all the questions in this exercise.

The class is responsible for:

Summary graphs of unit thresholds, Q₁₀ , spontaneous rate, maximum discharge rate, slopes of the IRC curve. Make sure the curves are labeled adequately.

Auditory nerve fiber assignment.

* when no rate curve has been collected, it can be obtained from the response area. Given the CF of the unit. use the RR command to reset the frequencies being analyzed to CF only. RR X CF CF. xv 2. then plot the data as before.