Touch and Pressure: How Your Body Feels Different Forces

How does the brain tell a light tap from a firm press? By examining a cockroach leg, we can see how sensory neurons encode touch intensity through a process called rate coding.

Devices and Accessories2

About the Experiment

What Will You Discover?

How touch intensity changes neural firing rate.
The mechanics of rate coding in sensory neurons.
How tactile neurons package information for the brain.

Background

The sense of touch is vital for both humans and cockroaches. When you press harder on a touch-sensitive hair, the neuron does not increase spike size; instead it fires spikes more rapidly. This higher frequency tells the brain that the force has increased.

Experiment

Rate-Coding With Three Levels of Pressure
Setup
1. Prepare a cockroach leg on cork and insert two recording pins very close together for a clear single-neuron signal.
2. Locate a touch-sensitive hair that spikes when probed with a toothpick.
Procedure
1. Using the toothpick, apply three brief presses—light, medium, firm—each lasting about 0.5 s.
2. Watch the spikes in SpikeRecorder and note the firing rate for each press.
3. Repeat several trials, recording the first half-second of activity each time.

Analyzing Results

Count the spikes in the first half-second of each pressure level and plot them. You should see firing rate rise with force, illustrating that neurons encode intensity in rate, not spike size.