The air in the fungal Kingdom is saturated with spores, many of which encode complex information, a form of communication between citizens. For a fungal lifeform it is easy enough to understand, as their minds can ignore anything which is irrelevant or extraneous. For others, this barrage of information is overwhelming, stripping the sanity of most of those who experience it.
The first mushroom periapt was created for a prince of the Kingdom who had fallen for the lady Eldrigeth. He wanted to spend time with her in his realm but in order for this to happen, she would need to be protected from this influence. The periapt was designed to shield the mind of its wearer against the addling effects of spore language.
Their love affair was short lived.