Tutorial: Conditioning

What is the effect of conditioning one stimulation with another? - The technique of conditioning is widely used. In this example we'll use electrical stimulation to condition the stretch reflex. You can surely think of many other combinations - and much more advanced ones than this simplified example.

Conditioned Stretch Reflexes

The stretch reflex is under investigation, say we stretch the Soleus muscle and measure the reflex in the EMG from that muscle. EMGs from other muscles may be relevant as well, so is position and force / torque.

Just before we perturbate (rotate) the ankle joint to elicit the stretch reflex we'll apply electrical stimulation to the enervating nerve. The time interval from the electrical stimulation to the stretch onset is not fixed as we want to investigate the timing dependencies. It would also be appropriate to leave out the electrical stimulation occasionally in order to monitor if the unconditioned stretch reflex change during the experiment.

Building the Setup

This will use many of the features discussed in earlier lessons. Instead of referring back to these lessons, let's build the setup almost from scratch - starting out from the settings found in ttDefault.mat.

The final setup will be available from ttCondt0.mat.

Acquisition

The stretch reflex characteristics are discussed earlier. A total sweep length of 800 ms is appropriate and we'll choose 200 ms PreTrig to monitor activity just before the stretch.

A SampleRate of 2 kHz is reasonable for the measurement of EMG, whereas force and position may be sampled at 500 Hz - a factor of four lower than the EMG.

Analog Input

We'll measure EMG from four muscles along with both force and position. The six analog input channels are turned On and each is labeled according to the signal measured. All EMGs will be sampled at high sample rate, rectified and low-pass filtered. Force / torque and position are sampled at low sample rate and grouped as Kinematic.

In order to avoid saturation of the EMG amplifiers due to the electrical stimulation we may have to lower the gain of some channels. Don't forget to set the Gain or Sensitivity controls to reflect the actual settings of the EMG amplifiers and other sources.

All sources supply voltages in the range from -10 to +10 V.

Classification

We'll randomly vary the time interval from electrical stimulation to stretch onset. For Mr. Kick to control this interval via event timing set Sub (or Main) Classification to Stimulus Type. Choose Random for Stimulus Select. Let classification Act On Event Timing.

In order to achieve a good resolution we'll investigate the time interval in 15 steps, plus monitoring the unconditioned stretch reflex. For this we'll need 16 classes.

We can monitor the size of the stretch reflex online, e.g. by measuring the peak amplitude (Maximum) of the Soleus EMG from 40 to 140 ms after stretch onset. This is specified in the Y-Analysis section.

Trigger

We'll induce stretches and acquire reflexes at a regular interval, say approx. every five seconds. We'll choose Internal as the trig Mode/Source for Mr. Kick to control this. In order to avoid anticipation stretches should not be applied exactly every four seconds. By setting Refractory to 4.5 s and Max Interval to 5.5 s the interval between stretches will vary randomly ±0.5 s around a 5 s mean.

Event Timing

Data acquisition will be synchronized to the stretch - both controlled by event timer #0. To allow different timing of the electrical stimulation we'll trigger the stimulator via event timer #1. To monitor the unconditioned stretch reflex we'll turn event timer #1 off in one class, 0.00.

The range of the time interval will be from 200 ms before stretch onset to 20 ms after.

For those classes where electrical stimulation comes first we'll set a zero delay for event timer #1 (el. stim.), and delay event timer #0 (stretch) by the following amounts: 200, 150 , 120, 100, 80, 70, 60, 50, 40, 30, 20, 10, 0 ms (class 0.01 through 0.13).

For those classes where electrical stimulation comes last we'll set a zero delay for event timer #0 (stretch), and delay event timer #1 (el. stim.) by the following amounts: 10 and 20 ms (class 0.14 and 0.15).

Analog Output

We choose First AO Channel to control the stretch device setting Active to Primary. The Sensitivity is set to reflect the stretch device in use - let's assume the pedal will move 0.5 degree for each volt supplied to its controller.

In the D/A section check that the AO trig Source is synchronized to Timer 0 / AD and the Update Rate is reasonable, say 1 kHz.

Load the plug-in that should generate the analog output pattern: The AOPI Ramp-Hold-Ramp.vi. The Ramp-Hold-Ramp SetUp will pop up to allow you to specify the type of stretch you want. We'll go for a 4 degree stretch Amplitude with a Rise Time and Fall Time of 40 ms and a Hold Time of 460 ms (Duration 500 ms).