Neural Stimulation

We’ve learned how to record spikes—now let’s try sending signals to neurons. Can the alternating current from a phone’s earbud output make a cockroach leg move?

Devices and Accessories

About the Experiment

What Will You Learn?

How external electrical currents can excite neurons.
How music signals differ from pure tones—and why that matters.
Why frequency and amplitude jointly determine stimulation thresholds.

Background

In the 1780s, Luigi Galvani showed that electricity makes frog legs twitch, launching the study of bioelectricity. Two centuries later, deep-brain stimulation treats Parkinson’s disease with the same idea: tiny currents trigger neural firing. Here you’ll swap a lab stimulator for a phone’s headphone output to explore which waveforms move a cockroach leg with the least current.

Experiment

Music Stimulation

Setup

Mount a cockroach leg so the tibia can move freely; insert two pins through femur and coxa.
Clip the red stimulation cable (included with the SpikerBox) to the pins, then plug the TRRS jack into your phone.

Test 1 – Play a hip-hop track (e.g. Paul’s Boutique, Beastie Boys). Start at low volume and raise it slowly. Note the volume where the leg twitches.

Test 2 – Repeat with a classical piece (e.g. Bach’s Goldberg Variations). Which genre moves the leg more easily?

Tone Stimulation

Pure-Tone Sweep

Install a free tone-generator app.
Test frequencies 20 Hz, 50 Hz, 100 Hz, 200 Hz, 500 Hz, 1 kHz, 2 kHz, 5 kHz.
For each tone, start at 25% volume and increase to 50%, 75%, and 100% until the leg twitches. Record the lowest volume that works.

Compare your threshold chart to discover the frequency that stimulates neurons with the least current.

Results & Analysis

Music – At what volume did each track evoke movement? Did rhythm-heavy hip-hop or steady classical patterns require less current?

Tones – Plot stimulation threshold (volume) versus frequency. Expect lower frequencies (longer pulses) to recruit neurons more readily than high-frequency tones.

Think about how pulse width, amplitude and electrode placement interact, and how the same principles scale up to medical devices like DBS.