Experiment: Neuron Stimulation

Invertebrates

Grade 6+

Neural stimulation

We've learned how to record electrical signals from neurons — now let’s see if we can send signals to neurons! Specifically, we want to test if alternating electrical currents (like those from your smartphone’s earbuds) can stimulate a cockroach leg.

Background

In the late 1700s, Luigi Galvani discovered that applying electricity to frog nerves caused muscle twitches. This phenomenon—later called “Galvanism”—revealed that animal electricity (the body's own electrical signals) could interact with external electrical currents.

These experiments inspired Mary Shelley's classic novel Frankenstein, which imagined bringing an entire creature to life with a spark of electricity.

In modern neuroscience, we know that small pulses of electricity—called microstimulation—can excite neurons, causing them to fire signals that lead to muscle movement or perception changes. Medical devices like Deep Brain Stimulation (DBS) rely on these principles to treat conditions such as Parkinson’s disease. But what frequency works? We will find out.

Instead of using a electrical stimulator from a neuroscience lab, we will use one from your pocket! Have you ever wondered how your phone’s earbuds can send music signals?

Your headphones drive a small speaker by changing voltage at different frequencies. We can harness that same signal to stimulate the cockroach’s nervous system. Included with your Neuron SpikerBox is a special red headphone cable with clips. This will be used to send electricity to our prep.

Procedure

To conduct this experiment, begin by carefully preparing a cockroach leg and securing it with pins through the femur and coxa, ensuring that the tibia (front part of the leg) can move freely. Next, select a smartphone or music-playing device that either has a standard headphone jack or can accommodate an adapter if necessary. Connect the clips of Stimulation Cable to the pins in the cockroach leg.

Music Stimulation

Now we are ready for the experiment. Load up your favorite music app, and choose 2 songs for your experiment. One should be in the hip hop genre (our roaches prefer anything from the Beastie Boys album "Paul's Boutique") and another in classical music (such as Goldberg Variations by J.S. Bach). Start with a low volume (low current to the pins) and slowly start to increase the volume. Note down the song and at what volume you began to observe changes in the leg. Repeat a few times. Which of these two songs made the legs move more easily?

Tone Stimulation

To determine which frequencies stimulate neurons with the least current, we’ll use a setup similar to the music stimulation experiment, but instead of music, we’ll play pure tones. Download a tone generator app for your device (free apps work fine). Adjust the tone frequency to change the pulse width (longer pulses sound lower) and use the volume control to adjust amplitude (higher volume delivers more current).

Test tones at various frequencies (20, 50, 100, 200, 500, 1000, 2000, 5000 Hz) across four volume levels (25%, 50%, 75%, 100%). Record which tones cause spikes at the lowest volume to identify the most optimal frequency for stimulating nervous tissue.

Results & Analysis

Analyze your data to identify patterns in the cockroach leg’s response to stimulation.

For music stimulation, compare the volume levels at which each song caused visible leg movements. Did certain genres or tracks produce stronger or quicker responses than others?

For tone stimulation, chart the lowest volume settings that triggered a twitch at each tested frequency. Look for trends across the frequency spectrum. Are there particular frequencies that consistently require less volume to evoke movement?

Reflect on the relationship between frequency, volume, and leg response. Consider how changes in stimulation parameters might affect neural activation. Document any anomalies, such as inconsistent responses or delayed movements, and think about potential reasons for these variations.

Finally, consider external factors that might influence results, such as electrode placement or environmental conditions, and how they could shape the neural and muscular response.

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