# The “Cocombola Study”: A Physical Phantom Model for tDCS-Induced Electric Field Distribution

## TL;DR

This study introduces a low-cost watermelon model to map electric fields from tDCS, a brain stimulation technique.

## Contribution

A novel, inexpensive physical phantom using watermelons to qualitatively assess tDCS-induced electric field distribution.

## Key findings

- Voltage differences in watermelon electrodes matched expected tDCS electric field patterns in known montages.
- The watermelon model successfully approximated spatial EF distribution using polar coordinates.
- The model is proposed as a feasible alternative for studying non-invasive brain stimulation techniques.

## Abstract

Background: Transcranial direct current stimulation (tDCS)-induced electric fields (EFs) acting on brain tissues are hardly controllable. Among physical models used in neuroscience research, watermelons are known as head-like phantoms for their dielectric properties. In this study, we aimed to define an inexpensive and reliable method to qualitatively define the spatial distribution of tDCS-induced EFs based on the use of watermelons. Methods: After creating the eight cranial foramina and identifying the location of the 21 EEG scalp electrodes on the peel of a watermelon, voltage differences during stimulation were recorded in each of the 21 scalp electrode positions, one at a time, at four different depths. The recordings were graphically represented by using polar coordinates with the watermelon approximated to a perfect sphere. Results: To validate the model, we performed three experiments in well-known montages. The results obtained were in line with the expected behavior of the EFs. Conclusions: Watermelon might be a cheap and feasible phantom head model to characterize the EFs induced by tDCS and, potentially, even other non-invasive brain stimulation techniques.