Any thought that occurs within our minds is undoubtedly our own thought – and when we say, "I think", there will be absolutely no mistake about the "I" to which we refer. In fact, only very few of us would even question whether we are thinking our own thoughts, and those who do are most likely pursuing a philosophical enquiry rather than physically questioning the nature of one's thinking. Isn't "I think, therefore I am" the most basic of all prerequisites for one's existence?
For a small minority, however, being able to think one's own thoughts is not always a given condition or even applicable to this "I." Some report having thoughts being put into their heads by another person, or simply "receiving" external thoughts originating from an outside source – an experience which, unsurprisingly perhaps, can be extremely frightening.
How is something like this even remotely possible? The answer is, it isn't. At least not with our current understanding of the laws of physics. As a result, this experience of severe interference is termed "thought insertion", and is defined as one of the key delusions – a "first-rank symptom" – indicative of a schizophrenic illness. Compared with some delusions that might just carry a hint of reality (such as believing neighbours are spreading rumours about you), thought insertion seems to be the most bizarre of them all.
Delusions as beliefs
Current psychiatric diagnostic systems view delusions as beliefs. For a certain idea to be delusional, someone must first believe in this idea, often with absolute conviction, even when faced with evidence to the contrary. In my view, however, thought insertions don't always fit in with this definition, and so don't qualify as delusions.
If one investigates the actual subjective experience of thought insertion – beyond what is written in clinical files and medical textbooks –- the richness and even reality of the experience begins to emerge. Orthodox definitions of delusion are being increasingly challenged by philosophically-minded researchers; psychotic or not, individuals experiencing external thoughts often find it extremely difficult to put into words "what it is like" to have such thoughts. Some of them report these thoughts as sensory, even auditory (but still claim they are thoughts and not voices); others can quite literally feel the "point of entry" to a certain locality inside their minds.
In fact, the boundary between thinking and perception is so blurred that one person used the term "thought-voices" to describe her experiences.
Then what is thought insertion, if it is not always a delusion? I argue that thought insertion is a duplex phenomenon which may or may not be a delusion.
The delusion may be created by having thoughts in which someone has lost their sense of agency (the feeling that a given thought is generated by one's self), and ownership, (the endorsement that this thought belongs to one's self). But agency and ownership are not all or nothing concepts, neither do they always come hand-in-hand – you can, for example, feel like you generated a thought but that it isn't yours, so though you have agency, there is no ownership.
Depending on how much of one's sense of agency and ownership is lost or damaged in relation to a given thought, it may feel unfamiliar or even alien. But it is only when an external attribution to another agent occurs, for example, "this thought is given to me by Chris", can we call it a delusion.
In other words, simply having a foreign thought is not a delusion in itself, even though it may very often lead to a delusional explanation.
The experience of thought insertion can be sensory, perceptual or physical. So, to me, it is more appropriate to say "delusions in thought insertion" rather than "delusions of thought insertion", and I am not just playing a game of lexicon. It is crucial to differentiate the processes that produce these acts of thinking and the thoughts that ensue, no matter how much such notions challenge our common sense.
Some of us may argue there is nothing about a delusion that is worth listening to, let alone explain, because the implausibility and apparent meaninglessness is beyond what a "rational" person could ever understand. But by acknowledging the complexity and mystery of thought insertion, clinicians might just be a little more understanding towards their patients' subjective experiences. By removing the assumption that all thought interference is delusional by nature, we close the gap between "us normal people" and "those mad people".
Even in cases where delusions are present, they still carry important meanings about the individual. Before we make assumptions and call someone delusional, perhaps we should question our own "reality" as well.
Explore further: Dreams, déjà vu and delusions caused by faulty 'reality testing'