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Grade 6+ Grade 6+
Invertebrates Invertebrates

Experiment: Somatotopy

In this experiment, you’ll explore how touch neurons respond differently depending on the part of the body that’s stimulated. By carefully touching specific barbs on a cockroach leg, you’ll observe unique spike patterns and uncover how the brain organizes sensory information.

What Will You Learn?

  • How neurons encode touch information from different body parts.
  • Why action potentials are consistent in size and shape.
  • The concept of somatotopy and how the brain maps sensory input to specific body regions.
  • How neural signals from different parts of the body are processed and differentiated in the brain.

Stimulating the Neurons

Using a toothpick, gently touch the barbs (tiny hairs) on the cockroach leg. You might notice that many barbs don’t generate any spikes, but with patience, you’ll find a hair that does. When you touch the right hair, you’ll hear a burst of spikes almost instantly. This shows how quickly neurons respond to stimuli!

Now, explore more barbs. Notice that different barbs produce different spike patterns. Some have taller spikes, others shorter, and their shapes may differ. Interestingly, spikes from the same hair always look the same, highlighting an important principle: action potentials are consistent in size and shape for a single neuron. Different spikes in your recordings suggest activity from multiple neurons.

Discovering Somatotopy

As you switch between touching different barbs, you’re observing the concept of somatotopy in action. Neurons in the brain can differentiate signals from different body parts based on where the signal originates. In the cockroach, the brain knows whether a stimulus comes from one barb or another because of the unique spike patterns.

In humans, this organization is even more sophisticated. Touch receptors in your skin send signals through the spinal cord to the primary somatosensory (S1) cortex in the brain. This region is organized in a way that corresponds to your body, with neurons for different body parts arranged in a predictable pattern. For example, neurons for your fingers and tongue take up more space than neurons for your back, reflecting how sensitive these areas are to touch.

What Did You Learn?

By touching different barbs and recording their unique spike patterns, you’ve seen how neurons encode touch location. This experiment highlights somatotopy—the brain’s way of mapping sensory information to specific body parts. Think about how this process helps us navigate the world: your brain can tell whether you’ve touched something with your fingers, your foot, or your face. How do you think this might work in other animals?