Simplify the following text for a Grade 7 native English-speaking person.
Original: These early grew into international organizations such as the American Synesthesia Association , the UK Synaesthesia Association , the Belgian Synaesthesia Association , the German Synesthesia Association and the Netherlands Synesthesia Web Community .
Simplified: Synesthesia , or synaesthesia , is a condition where the brain mixes up the senses . People who have synesthesia are called synesthetes .