Lethologica is a psychological disorder that inhibits an individual's ability to articulate his or her thoughts by temporarily forgetting

Forgetting

Forgetting refers to apparent loss of information already encoded and stored in an individual's long term memory. It is a spontaneous or gradual process in which old memories are unable to be recalled from memory storage. It is subject to delicately balanced optimization that ensures that...

 key words, phrases or names in conversation.
Lethologica was first identified as a serious, debilitating disorder by Swiss psychiatrist Carl Jung

Carl Jung

Carl Gustav Jung was a Swiss psychiatrist and the founder of Analytical Psychology. Jung is considered the first modern psychiatrist to view the human psyche as "by nature religious" and make it the focus of exploration. Jung is one of the best known researchers in the field of dream analysis and...

 in 1913 in his Wandlungen und Symbole der Libido (The Psychology of the Unconscious). Detailed studies of the disorder were first carried out by American psychiatrists in the 1950s.