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Thought Loop

by: Daniel Ha

A thought loop is a term used anecdotally by many online that is commonly described as being trapped thinking the same thought over and over again in a cyclical nature for a period lasting anywhere from a few seconds to a few hours. The term is popularly used to describe this experience while on a psychedelic drug[1], though there are also places online where the term "thought loop" is used to describe experiences not on a psychedelic drug.

Existing theories on thought loops

Though no academic literature exists on why thought loops occur, the most popular theory online is found at PsychonautWiki[2], an online encyclopedia project on topics related to psychedelic usage:

"This state of mind is most likely to occur during states of memory suppression in which there is a partial or complete failure of the person's short-term memory. This may suggest that thought loops are the result of cognitive processes becoming unable to sustain themselves for appropriate lengths of time due to a lapse in short-term memory, resulting in the thought process attempting to restart from the beginning only to fall short once again in a perpetual cycle."[3]

This theory however, is academically unsupported.

Terms in used in psychology that are similar to "thought loop"

A term used in academia to describe repeatedly having the same thought is "repetitive thought"[4]. In a paper by a professor of Psychology at the University of Exeter, Professor Edward Watkins categorizes several popularly used terms for experiences of repeated thought under the umbrella of "repetitive thought." None of these terms matched perfectly with the description of a thought loop, but all described experiences of thinking the same thought repeatedly. The uniqueness of the anecdotal description of thought loops compared to the other types of repetitive thought are two-fold: 1. thought loops are specified to be over a short period of time and 2. are highly associated with psychedelic drug use.

Despite the lack of a perfectly matching term, terms for repetitive thought are often used informally and inconsistently across research [5].

Repetitive thought [6] was shown to be highly associated with a lack of cognitive control associated with memory, suggesting that repetitive thought in general is likely caused by impariment of cognitive control.

Why thought loops commonly occur under the influence of psychedelic drug use

Psychedelic drugs affect the brain in largely the same way [7], producing its' effects mainly through agonizing the 5-HT2A receptor[8].

LSD has been shown to significantly impair executive functions such as cognitive flexibility and working memory[9]. Because of the common report of thought loops occurring under the influence of psychedelic drugs, it is possible that the impairment of executive functioning caused by being under the influence of psychedelic drugs causes the thought loop.

This theory is in conflict with the existing theory on PsychonautWiki which suggests that the loss of short-term memory leads to thought loops[10], executive function, which is impaired under the influence of psychedelic drugs, does not involve short-term memory[11].

Further evidence supports the idea that thought loops are much more likely to occur under the influence of psychedelic drugs because they impair executive function. Repetitive thought has been shown to be highly associated with impairment of cognitive control processes related to memory[12] and psychedelics have been shown to impair executive functioning (which are necessary for cognitive control)[13]. With these two pieces of information, categorizing thought loops as a type of repetitive thought experience, it is possible that thought loops are more likely to occur with impaired executive function (and thus cognitive control) caused by the influence of psychedelic drugs.

The most likely neurological mechanism for thought loops

Defining thought loops as an occurrence under the influence of psychedelic drugs, it is important to understand the relevant neurological effects that psychedelic drugs have to narrow down the neurological basis for thought loops. Psychedelic drugs such as LSD, lysergic acid diethylamide, have been shown to alter the functioning of 5-HT2AR receptors by binding to the receptor in a way that changes the receptor's functioning [14].

Alterations to the ways that serotonin receptors bind have also been shown to be associated with psychiatric disorders such associated with impaired cognitive control[15]. Being that the most likely theory for why thought loops occur under the influence of psychedelic drug use is that it is caused by an impairment of cognitive control, the most likely neurological mechanism for thought loops during psychedelic experiences lies in the altered functioning of serotonin receptors.