The cause of involuntary emotional expression disorder (IEED) is unclear, but it is generally thought to result from an injury to the neurologic pathways that control emotional expression.

The neurochemistry of IEED is not fully understood, however some have implicated the glutamateric and monoaminergic neurotransmitter systems, which appear to be involved in the regulation of expression of emotions and may be involved in the manifestation of IEED. 

It is hypothesized that neurologic disease and injuries affect the excitatory action of glutamate, leading to excessive glutamatergic signaling and increased electrical activity in neurons.^{Bittigau P, Ikonomidu C}

Glutamate is the primary excitatory neurotransmitter in the central nervous system^{Bermack JE, Debonnel G}, including those networks that regulate emotional affect. Glutamate activity may be regulated through sigma-1 receptors and N-methyl-D aspartate (NMDA) receptors.^{Arciniegas DB, Lauterbach EC, Anderson KE, et al} 

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