What is an Intrusive Thought?


An intrusive thought is an unwelcome, involuntary thought, image, or unpleasant idea that may become an obsession, is upsetting or distressing, and can feel difficult to manage or eliminate.

When such thoughts are associated with obsessive-compulsive disorder (OCD), depression, body dysmorphic disorder (BDD), and sometimes attention-deficit hyperactivity disorder (ADHD), the thoughts may become paralysing, anxiety-provoking, or persistent. Intrusive thoughts may also be associated with episodic memory, unwanted worries or memories from OCD, post-traumatic stress disorder, other anxiety disorders, eating disorders, or psychosis. Intrusive thoughts, urges, and images are of inappropriate things at inappropriate times, and generally have aggressive, sexual, or blasphemous themes.



Many people experience the type of bad or unwanted thoughts that people with more troubling intrusive thoughts have, but most people can dismiss these thoughts. For most people, intrusive thoughts are a “fleeting annoyance”. Psychologist Stanley Rachman presented a questionnaire to healthy college students and found that virtually all said they had these thoughts from time to time, including thoughts of sexual violence, sexual punishment, “unnatural” sex acts, painful sexual practices, blasphemous or obscene images, thoughts of harming elderly people or someone close to them, violence against animals or towards children, and impulsive or abusive outbursts or utterances. Such thoughts are universal among humans, and have “almost certainly always been a part of the human condition”.

When intrusive thoughts occur with OCD, patients are less able to ignore the unpleasant thoughts and may pay undue attention to them, causing the thoughts to become more frequent and distressing. The suppression of intrusive thoughts often cause these thoughts to become more intense and persistent. The thoughts may become obsessions that are paralysing, severe, and constantly present, these might involve topics such as violence, sex, or religious blasphemy, among others. Distinguishing them from normal intrusive thoughts experienced by many people, the intrusive thoughts associated with OCD may be anxiety provoking, irrepressible, and persistent.

How people react to intrusive thoughts may determine whether these thoughts will become severe, turn into obsessions, or require treatment. Intrusive thoughts can occur with or without compulsions. Carrying out the compulsion reduces the anxiety, but makes the urge to perform the compulsion stronger each time it recurs, reinforcing the intrusive thoughts. According to Lee Baer, suppressing the thoughts only makes them stronger, and recognising that bad thoughts do not signify that one is truly evil is one of the steps to overcoming them. There is evidence of the benefit of acceptance as an alternative to the suppression of intrusive thoughts. In one particular study, those instructed to suppress intrusive thoughts experienced more distress after suppression, while patients instructed to accept the bad thoughts experienced decreased discomfort. These results may be related to underlying cognitive processes involved in OCD. However, accepting the thoughts can be more difficult for persons with OCD.

The possibility that most patients with intrusive thoughts will ever act on those thoughts is low. Patients who are experiencing intense guilt, anxiety, shame, and are upset over these thoughts are very different from those who actually act on them. The fact that someone is tormented by intrusive thoughts and has never acted on them before is considered an excellent predictor that they will not act upon the thoughts. Patients who are not troubled or shamed by their thoughts, do not find them distasteful, or who have actually taken action, might need to have more serious conditions such as psychosis or potentially criminal behaviours ruled out. According to Lee Baer, a patient should be concerned that intrusive thoughts are dangerous if the person does not feel upset by the thoughts, or rather finds them pleasurable; has ever acted on violent or sexual thoughts or urges; hears voices or sees things that others do not see; or feels uncontrollable irresistible anger.

Aggressive Thoughts

Intrusive thoughts may involve violent obsessions about hurting others or themselves. They can be related to primarily obsessional obsessive compulsive disorder. These thoughts can include harming a child; jumping from a bridge, mountain, or the top of a tall building; urges to jump in front of a train or automobile; and urges to push another in front of a train or automobile. Rachman’s survey of healthy college students found that virtually all of them had intrusive thoughts from time to time, including:

  • Causing harm to elderly people.
  • Imagining or wishing harm upon someone close to oneself.
  • Impulses to violently attack, hit, harm or kill a person, small child, or animal.
  • Impulses to shout at or abuse someone, or attack and violently punish someone, or say something rude, inappropriate, nasty, or violent to someone.

These thoughts are part of being human, and need not ruin the quality of life. Treatment is available when the thoughts are associated with OCD and become persistent, severe, or distressing.

A variant of aggressive intrusive thoughts is L’appel du vide, or the call of the void. Those with L’appel du vide generally describe the condition as manifesting in certain situations, normally as a wish or brief desire to jump from a high location.

Sexual Thoughts

Sexual obsession involves intrusive thoughts or images of “kissing, touching, fondling, oral sex, anal sex, intercourse, and rape” with “strangers, acquaintances, parents, children, family members, friends, co-workers, animals and religious figures”, involving “heterosexual or homosexual content” with persons of any age.

Common sexual themes for intrusive thoughts for men involve:

  • Having sex in a public place;
  • People I come in contact with being naked; and
  • Engaging in a sexual act with someone who is unacceptable to me because they have authority over me.

Common sexual intrusive thoughts for women are:

  • Having sex in a public place;
  • Engaging in a sexual act with someone who is unacceptable to me because they have authority over me; and
  • Being sexually victimised.

Like other unwanted intrusive thoughts or images, most people have some inappropriate sexual thoughts at times, but people with OCD may attach significance to the unwanted sexual thoughts, generating anxiety and distress. The doubt that accompanies OCD leads to uncertainty regarding whether one might act on the intrusive thoughts, resulting in self-criticism or loathing.

One of the more common sexual intrusive thoughts occurs when an obsessive person doubts their sexual identity. As in the case of most sexual obsessions, individuals may feel shame and live in isolation, finding it hard to discuss their fears, doubts, and concerns about their sexual identity.

A person experiencing sexual intrusive thoughts may feel shame, “embarrassment, guilt, distress, torment, fear of acting on the thought or perceived impulse, and doubt about whether they have already acted in such a way.” Depression may be a result of the self-loathing that can occur, depending on how much the OCD interferes with daily functioning or causes distress. Their concern over these thoughts may cause them to scrutinize their bodies to determine if the thoughts result in feelings of arousal. However, focusing their attention on any part of the body can result in feelings in that body part, hence doing so may decrease confidence and increase fear about acting on the urges. Part of the treatment of sexual intrusive thoughts involves therapy to help them accept intrusive thoughts and stop trying to reassure themselves by checking their bodies. This arousal within the body parts is due to conditioned physiological responses in the brain, which do not respond to the subject of the sexual intrusive thought but rather to the fact that a sexual thought is occurring at all and thus engage an automatic response (research indicates that the correlation between what the genitalia regard as “sexually relevant” and what the brain regards as “sexually appealing” only correlates 50% of the time in men and 10% of the time in women). This means that an arousal response does not necessarily indicate that the person desires what they are thinking about. However, rational thinking processes attempt to explain this reaction and OCD causes people to attribute false meaning and importance to these physiological reactions in an attempt to make sense of them. People can also experience heightened anxiety caused by forbidden images or simply by discussing the matter which can then also cause physiological arousal, such as sweating, increased heart rate and some degree of tumescence or lubrication. This is often misinterpreted by the individual as an indication of desire or intent, when it is in fact not.

Religious Thoughts

Blasphemous thoughts are a common component of OCD, documented throughout history; notable religious figures such as Martin Luther and Ignatius of Loyola were known to be tormented by intrusive, blasphemous or religious thoughts and urges. Martin Luther had urges to curse God and Jesus, and was obsessed with images of “the Devil’s behind.” St. Ignatius had numerous obsessions, including the fear of stepping on pieces of straw forming a cross, fearing that it showed disrespect to Christ. A study of 50 patients with a primary diagnosis of OCD found that 40% had religious and blasphemous thoughts and doubts – a higher, but not statistically significantly different number than the 38% who had the obsessional thoughts related to dirt and contamination more commonly associated with OCD. One study suggests that the content of intrusive thoughts may vary depending on culture, and that blasphemous thoughts may be more common in men than in women.

According to Fred Penzel, a New York psychologist, some common religious obsessions and intrusive thoughts are:

  • Sexual thoughts about God, saints, and religious figures.
  • Bad thoughts or images during prayer or meditation.
  • Thoughts of being possessed.
  • Fears of sinning or breaking a religious law or performing a ritual incorrectly.
  • Fears of omitting prayers or reciting them incorrectly.
  • Repetitive and intrusive blasphemous thoughts.
  • Urges or impulses to say blasphemous words or commit blasphemous acts during religious services.

Suffering can be greater and treatment complicated when intrusive thoughts involve religious implications; patients may believe the thoughts are inspired by Satan, and may fear punishment from God or have magnified shame because they perceive themselves as sinful. Symptoms can be more distressing for individuals with strong religious convictions or beliefs.

Baer believes that blasphemous thoughts are more common in Catholics and evangelical Protestants than in other religions, whereas Jews or Muslims tend to have obsessions related more to complying with the laws and rituals of their faith, and performing the rituals perfectly. He hypothesizes that this is because what is considered inappropriate varies among cultures and religions, and intrusive thoughts torment their sufferers with whatever is considered most inappropriate in the surrounding culture.

Age Factors

Adults under the age of 40 seem to be the most affected by intrusive thoughts. Individuals in this age range tend to be less experienced at coping with these thoughts, and the stress and negative affect induced by them. Younger adults also tend to have stressors specific to that period of life that can be particularly challenging especially in the face of intrusive thoughts. Although, when introduced with an intrusive thought, both age groups immediately look for ways to reduce the recurrence of the thoughts.

Those in middle adulthood (40-60) have the highest prevalence of OCD and therefore seem to be the most susceptible to the anxiety and negative emotions associated with intrusive thought. Middle adults are in a unique position because they have to struggle with both the stressors of early and late adulthood. They may be more vulnerable to intrusive thought because they have more topics to relate to. Even with this being the case, middle adults are still better at coping with intrusive thoughts than early adults, although it takes them longer at first to process an intrusive thought. Older adults tend to see the intrusive thought more as a cognitive failure rather than a moral failure in opposition to young adults. They have a harder time suppressing the intrusive thoughts than young adults causing them to experience higher stress levels when dealing with these thoughts.

Intrusive thoughts appear to occur at the same rate across the lifespan, however, older adults seem to be less negatively affected than younger adults. Older adults have more experience in ignoring or suppressing strong negative reactions to stress.

Associated Conditions

Intrusive thoughts are associated with OCD or OCPD, but may also occur with other conditions such as:

  • Post-traumatic stress disorder (PTSD).
  • Clinical depression.
  • Postpartum depression.
  • Generalised anxiety disorder and anxiety.

One of these conditions is almost always present in people whose intrusive thoughts reach a clinical level of severity. A large study published in 2005 found that aggressive, sexual, and religious obsessions were broadly associated with comorbid anxiety disorders and depression. The intrusive thoughts that occur in a schizophrenic episode differ from the obsessional thoughts that occur with OCD or depression in that the intrusive thoughts of people with schizophrenia are false or delusional beliefs (i.e. held by the schizophrenic individual to be real and not doubted, as is typically the case with intrusive thoughts) .

Post-Traumatic Stress Disorder

The key difference between OCD and post-traumatic stress disorder (PTSD) is that the intrusive thoughts of people with PTSD are of content relating to traumatic events that actually happened to them, whereas people with OCD have thoughts of imagined catastrophes. PTSD patients with intrusive thoughts have to sort out violent, sexual, or blasphemous thoughts from memories of traumatic experiences.[48] When patients with intrusive thoughts do not respond to treatment, physicians may suspect past physical, emotional, or sexual abuse. If a person who has experienced trauma practices looks for the positive outcomes, it is suggested they will experience less depression and higher self well-being. While a person may experience less depression for benefit finding, they may also experience an increased amount of intrusive and/or avoidant thoughts.

One study looking at women with PTSD found that intrusive thoughts were more persistent when the individual tried to cope by using avoidance-based thought regulation strategies. Their findings further support that not all coping strategies are helpful in diminishing the frequency of intrusive thoughts.


People who are clinically depressed may experience intrusive thoughts more intensely, and view them as evidence that they are worthless or sinful people. The suicidal thoughts that are common in depression must be distinguished from intrusive thoughts, because suicidal thoughts – unlike harmless sexual, aggressive, or religious thoughts – can be dangerous.

Non-depressed individuals have been shown to have a higher activation in the dorsolateral prefrontal cortex, which is the area of the brain that primarily functions in cognition, working memory, and planning, while attempting to suppress intrusive thoughts. This activation decreases in people at risk of or currently diagnosed with depression. When the intrusive thoughts re-emerge, non depressed individuals also show higher activation levels in the anterior cingulate cortices, which functions in error detection, motivation, and emotional regulation, than their depressed counterparts.

Roughly 60% of depressed individuals report experiencing bodily, visual, or auditory perceptions along with their intrusive thoughts. There is a correlation with experiencing those sensations with intrusive thoughts and more intense depressive symptoms as well as the need for heavier treatment.

Postpartum Depression and OCD

Unwanted thoughts by mothers about harming infants are common in postpartum depression. A 1999 study of 65 women with postpartum major depression by Katherine Wisner et al. found the most frequent aggressive thought for women with postpartum depression was causing harm to their newborn infants. A study of 85 new parents found that 89% experienced intrusive images, for example, of the baby suffocating, having an accident, being harmed, or being kidnapped.

Some women may develop symptoms of OCD during pregnancy or the postpartum period. Postpartum OCD occurs mainly in women who may already have OCD, perhaps in a mild or undiagnosed form. Postpartum depression and OCD may be comorbid (often occurring together). And though physicians may focus more on the depressive symptoms, one study found that obsessive thoughts did accompany postpartum depression in 57% of new mothers.

Wisner found common obsessions about harming babies in mothers experiencing postpartum depression include images of the baby lying dead in a casket or being eaten by sharks; stabbing the baby; throwing the baby down the stairs; or drowning or burning the baby (as by submerging it in the bathtub in the former case or throwing it in the fire or putting it in the microwave in the latter). Baer estimates that up to 200,000 new mothers with postpartum depression each year may develop these obsessional thoughts about their babies; and because they may be reluctant to share these thoughts with a physician or family member, or suffer in silence out of fear they could be “crazy”, their depression can worsen.

Intrusive fears of harming immediate children can last longer than the postpartum period. A study of 100 clinically depressed women found that 41% had obsessive fears that they might harm their child, and some were afraid to care for their children. Among non-depressed mothers, the study found 7% had thoughts of harming their child – a rate that yields an additional 280,000 non-depressed mothers in the United States with intrusive thoughts about harming their children.


Treatment for intrusive thoughts is similar to treatment for OCD. Exposure and response prevention therapy – also referred to as habituation or desensitisation – is useful in treating intrusive thoughts. Mild cases can also be treated with cognitive behavioural therapy, which helps patients identify and manage the unwanted thoughts.

Exposure Therapy

Exposure therapy is the treatment of choice for intrusive thoughts. According to Deborah Osgood-Hynes, Psy.D. Director of Psychological Services and Training at the MGH/McLean OCD Institute, “In order to reduce a fear, you have to face a fear. This is true of all types of anxiety and fear reactions, not just OCD.” Because it is uncomfortable to experience bad thoughts and urges, shame, doubt or fear, the initial reaction is usually to do something to make the feelings diminish. By engaging in a ritual or compulsion to diminish the anxiety or bad feeling, the action is strengthened via a process called negative reinforcement – the mind learns that the way to avoid the bad feeling is by engaging in a ritual or compulsions. When OCD becomes severe, this leads to more interference in life and continues the frequency and severity of the thoughts the person sought to avoid.

Exposure therapy (or exposure and response prevention) is the practice of staying in an anxiety-provoking or feared situation until the distress or anxiety diminishes. The goal is to reduce the fear reaction, learning to not react to the bad thoughts. This is the most effective way to reduce the frequency and severity of the intrusive thoughts. The goal is to be able to “expose yourself to the thing that most triggers your fear or discomfort for one to two hours at a time, without leaving the situation, or doing anything else to distract or comfort you.” Exposure therapy will not eliminate intrusive thoughts – everyone has bad thoughts – but most patients find that it can decrease their thoughts sufficiently that intrusive thoughts no longer interfere with their lives.

Cognitive Behavioural Therapy

Cognitive behavioural therapy (CBT) is a newer therapy than exposure therapy, available for those unable or unwilling to undergo exposure therapy. Cognitive therapy has been shown to be useful in reducing intrusive thoughts, but developing a conceptualisation of the obsessions and compulsions with the patient is important. One of the strategies sometimes used in Cognitive Behavioural Theory is mindfulness exercises. These include practices such as being aware of the thoughts, accepting the thoughts without judgement for them, and “being larger than your thoughts.”


Antidepressants or antipsychotic medications may be used for more severe cases if intrusive thoughts do not respond to cognitive behavioural or exposure therapy alone. Whether the cause of intrusive thoughts is OCD, depression, or PTSD, the selective serotonin reuptake inhibitor (SSRI) drugs (a class of antidepressants) are the most commonly prescribed. Intrusive thoughts may occur in persons with Tourette syndrome (TS) who also have OCD; the obsessions in TS-related OCD are thought to respond to SSRI drugs as well.

Antidepressants that have been shown to be effective in treating OCD include fluvoxamine (trade name Luvox), fluoxetine (Prozac), sertraline (Zoloft), paroxetine (Paxil), citalopram (Celexa), and clomipramine (Anafranil). Although SSRIs are known to be effective for OCD in general, there have been fewer studies on their effectiveness for intrusive thoughts. A retrospective chart review of patients with sexual symptoms treated with SSRIs showed the greatest improvement was in those with intrusive sexual obsessions typical of OCD. A study of ten patients with religious or blasphemous obsessions found that most patients responded to treatment with fluoxetine or clomipramine. Women with postpartum depression often have anxiety as well, and may need lower starting doses of SSRIs; they may not respond fully to the medication, and may benefit from adding cognitive behavioural or response prevention therapy.

Patients with intense intrusive thoughts that do not respond to SSRIs or other antidepressants may be prescribed typical and atypical neuroleptics including risperidone (trade name Risperdal), ziprasidone (Geodon), haloperidol (Haldol), and pimozide (Orap).

Studies suggest that therapeutic doses of inositol may be useful in the treatment of obsessive thoughts.


A 2007 study found that 78% of a clinical sample of OCD patients had intrusive images. Most people with intrusive thoughts have not identified themselves as having OCD, because they may not have what they believe to be classic symptoms of OCD, such as handwashing. Yet, epidemiological studies suggest that intrusive thoughts are the most common kind of OCD worldwide; if people in the United States with intrusive thoughts gathered, they would form the fourth-largest city in the US, following New York City, Los Angeles, and Chicago.

The prevalence of OCD in every culture studied is at least 2% of the population, and the majority of those have obsessions, or bad thoughts, only; this results in a conservative estimate of more than 2 million affected individuals in the United States alone (as of 2000). One author estimates that one in 50 adults have OCD and about 10-20% of these have sexual obsessions. A recent study found that 25% of 293 patients with a primary diagnosis of OCD had a history of sexual obsessions.

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What is Thought Suppression?


Thought suppression is a psychological defence mechanism. It is a type of motivated forgetting in which an individual consciously attempts to stop thinking about a particular thought.

It is often associated with obsessive-compulsive disorder (OCD). OCD is when a person will repeatedly (usually unsuccessfully) attempt to prevent or “neutralise” intrusive distressing thoughts centred on one or more obsessions. It is also thought to be a cause of memory inhibition, as shown by research using the think/no think paradigm. Thought suppression is relevant to both mental and behavioural levels, possibly leading to ironic effects that are contrary to intention. Ironic process theory is one cognitive model that can explain the paradoxical effect.

When an individual tries to suppress thoughts under a high cognitive load, the frequency of those thoughts increases and becomes more accessible than before. Evidence shows that people can prevent their thoughts from being translated into behaviour when self-monitoring is high; this does not apply to automatic behaviours though, and may result in latent, unconscious actions. This phenomenon is made paradoxically worse by increasing the amount of distractions a person has, although the experiments in this area can be criticised for using impersonal concurrent tasks, which may or may not properly reflect natural processes or individual differences.

Empirical Work (1980s)

In order for thought suppression and its effectiveness to be studied, researchers have had to find methods of recording the processes going on in the mind. One experiment designed with this purpose was performed by Wegner, Schneider, Carter & White. They asked participants to avoid thinking of a specific target (e.g. a white bear) for five minutes, but if they did, they were told then to ring a bell. After this, participants were told that for the next five minutes they were to think about the target. There was evidence that unwanted thoughts occurred more frequently in those who used thought suppression compared to those who were not. Furthermore, there was also evidence that during the second stage, those who had used thought suppression had a higher frequency of target thoughts than did those who had not used thought suppression; later coined the rebound effect. This effect has been replicated and can even be done with implausible targets, such as the thought of a “green rabbit”. From these implications, Wegner eventually developed the “ironic process theory”.

Improved Methodology (1990s)

To better elucidate the findings of thought suppression, several studies have changed the target thought. Roemer and Borkovec found that participants who suppressed anxious or depressing thoughts showed a significant rebound effect. Furthermore, Wenzlaff, Wegner, & Roper demonstrated that anxious or depressed subjects were less likely to suppress negative, unwanted thoughts. Despite Rassin, Merkelbach and Muris reporting that this finding is moderately robust in the literature, some studies were unable to replicate results. However, this may be explained by a consideration of individual differences.

Recent research found that for individuals with low anxiety and high desirability traits (repressors), suppressed anxious autobiographical events initially intruded fewer times than in other groups (low, high, and high defensive anxious groups), but intruded more often after one week. This difference in coping style may account for the disparities within the literature. That said, the problem remains that the cause of the paradoxical effect may be in the thought tapping measures used (e.g. bell ringing). Evidence from Brown (1990) that showed participants were very sensitive to frequency information prompted Clarke, Ball and Pape to obtain participants’ aposterio estimates of the number of intrusive target thoughts and found the same pattern of paradoxical results. However, even though such a method appears to overcome the problem, it and all the other methodologies use self-report as the primary form of data-collection. This may be problematic because of response distortion or inaccuracy in self-reporting.

Behavioural Domain

Thought suppression also has the capability to change human behaviour. Macrae, Bodenhausen, Milne, and Jetten found that when people were asked not to think about the stereotypes of a certain group (e.g. a “skinhead”), their written descriptions about a group member’s typical day contained less stereotypical thoughts. However, when they were told they were going to meet an individual they had just written about, those in the suppression group sat significantly farther away from the “skinhead” (just by virtue of his clothes being present). These results show that even though there may have been an initial enhancement of the stereotype, participants were able to prevent this from being communicated in their writing; this was not true for their behaviour though.

Further experiments have documented similar findings. In one study from 1993, when participants were given cognitively demanding concurrent tasks, the results showed a paradoxical higher frequency of target thoughts than controls. However other controlled studies have not shown such effects. For example, Wenzlaff and Bates found that subjects concentrating on a positive task experienced neither paradoxical effects nor rebound effects – even when challenged with cognitive load. Wenzlaff and Bates also note that the beneficiality of concentration in their study participants was optimised when the subjects employed positive thoughts.

Some studies have shown that when test subjects are under what Wegner refers to as a “cognitive load” (for instance, using multiple external distractions to try to suppress a target thought), the effectiveness of thought suppression appears to be reduced. However, in other studies in which focused distraction is used, long term effectiveness may improve. That is, successful suppression may involve less distractors. For example, in 1987 Wegner, Schneider, Carter & White found that a single, pre-determined distracter (e.g. a red Volkswagen) was sufficient to eliminate the paradoxical effect post-testing. Evidence from Bowers and Woody in 1996 is supportive of the finding that hypnotised individuals produce no paradoxical effects. This rests on the assumption that deliberate “distracter activity” is bypassed in such an activity.

Cognitive Dynamics

When the cognitive load is increased, thought suppression typically becomes less effective. For example, in the white bear experiment, many general distractions in the environment (for instance a lamp, a light bulb, a desk etc.) might later serve as reminders of the object being suppressed (these are also referred to as “free distraction”). Some studies, however, are unable to find this effect for emotional thoughts in hypnotized individuals when one focused distraction is provided. In an attempt to account for these findings, a number of theorists have produced cognitive models of thought suppression. Wegner suggested in 1989 that individuals distract themselves using environmental items. Later, these items become retrieval cues for the thought attempting to be suppressed. This iterative process leaves the individual surrounded by retrieval cues, ultimately causing the rebound effect. Wegner hypothesized that multiple retrieval cues not being forged explains, in part, the effectiveness of focused distraction (i.e. a reduction of mental load). This is because there may be an ideal balance between the two processes; if the cognitive demand that is not too heavy, then the monitoring processes will not supersede it.

Individual differences may also play a role in regards to the ironic thought process.

Thought suppression has been seen as a form of “experiential avoidance”. Experiential avoidance is when an individual attempts to suppress, change, or control unwanted internal experiences (thoughts, feelings, bodily sensations, memories, etc.). This line of thinking supports relational frame theory.

Other Methodologies

Thought suppression has been shown to be a cause of inhibition in several ways. Two commonly-used methods to study this relationship are the list method and the item method. In this list method, participants study two lists of words, one after the other. After studying the first list, some participants are told to forget everything that they have just learned, while others are not given this instruction. After studying both lists, participants are asked to recall the words on both lists. These experiments typically find that participants who were told to forget the first list do not remember as many words from that list, suggesting that they have been suppressed due to the instruction to forget. In the item method, participants study individual words rather than lists. After each word is shown, participants are told to either remember or forget the word. As in experiments using the list method, the words followed by the instruction to forget are more poorly remembered. Some researchers believe that these two methods result in different types of forgetting. According to these researchers, the list method results in inhibition of the forgotten words, but the item method results in some words being remembered better than the others, without a specific relation to forgetting.

Think/No Think Paradigm

A paradigm from 2009 to study how suppression relates to inhibition is the think/no think paradigm. In these experiments, participants study pairs of words. An example of a possible word pair is roach-ordeal. After all the word pairs are learned, the participants see the first word of the pair and are either told to think about the second word (think phase) or not to think about the second word (no think phase). The no think phase is when suppression occurs. Some pairs were never presented after the initial study portion of the study, and these trials serve as the control group. At the end of the experiment, the participants try to remember all of the word pairs based on the first word. Studies could also use the “independent probe” method, which gives the category and first letter of the second word of the pair. Typically, regardless of the method used, results show that the no-think trials result in worse memory than the think trials, which supports the idea that suppression leads to inhibition in memory. Although this methodology was first done using word pairs, experiments have been conducted using pictures and autobiographical memories as stimuli, with the same results.

Research has also shown that doing difficult counting tasks at the same time as a think/no think task leads to less forgetting in the no think condition, which suggests that suppression takes active mental energy to be successful. Furthermore, the most forgetting during the no think phase occurs when there is a medium amount of brain activation while learning the words. The words are never learned if there is too little activation, and the association between the two words is too strong to be suppressed during the no think phase if there is too much activation. However, with medium activation, the word pairs are learned but able to be suppressed during the no think phase.

fMRI studies have shown two distinct patterns of brain activity during suppression tasks. The first is that there is less activity in the hippocampus, the brain area responsible for forming memories. The second is an increase of brain activity in the dorsolateral prefrontal cortex, especially in cases where suppression is harder. Researchers think that this region works to prevent memory formation by preventing the hippocampus from working.

This methodology can also be used to study thought substitution by adding an instruction during the no think phase for participants to think of a different word rather than the word being suppressed. This research shows that thought substitution can lead to increased levels of forgetting compared to suppression without a thought substitution instruction. This research also suggests that thought substitution, while used as a suppression strategy during the no think phase, may work differently than suppression. Some researchers argue that thinking of something different during the no think phase forms a new association with the first word than the original word pair, which results in interference when using this strategy, which is different than the inhibition that results from simply not thinking about something.

Dream Influence

Dreams occur mainly during the rapid eye movement (REM) sleep and are composed of images, ideas, emotions, and sensations. Although more research needs to be done on this subject, dreams are said to be linked to the unconscious mind. Thought suppression has an influence on the subject matter of the unconscious mind and by trying to restrain particular thoughts, there is a high chance of them showing up in one’s dreams.

Ironic Control Theory

Ironic control theory, also known as “ironic process theory”, states that thought suppression “leads to an increased occurrence of the suppressed content in waking states”. The irony lies in the fact that although people try not to think about a particular subject, there is a high probability that it will appear in one’s dreams regardless. There is a difference for individuals who have a higher tendency of suppression; they are more prone to psychopathological responses such as “intrusive thoughts, including depression, anxiety and obsessional thinking”. Due to these individuals having higher instances of thought suppression, they experience dream rebound more often.

Cognitive load also plays a role in ironic control theory. Studies have shown that a greater cognitive load results in an increased possibility of dream rebound occurring. In other words, when one tries to retain a heavy load of information before going to sleep, there is a high chance of that information manifesting itself within the dream. There is a greater degree of dream rebound in those with a higher cognitive load opposed to those whose load was absent. With the enhancement of a high cognitive load, ironic control theory states thought suppression is more likely to occur and lead to dream rebound.

Dream Rebound

Dream rebound is when suppressed thoughts manifest themselves in one’s dreams. Self-control is a form of thought suppression and when one dreams, that suppressed item has a higher chance of appearing in the dream. For example, when an individual is attempting to quit smoking, they may dream about themselves smoking a cigarette. Emotion suppression has also been found to trigger dream rebound. Recurrence of emotional experiences act as pre-sleep suggestions, ultimately leading to the suppressed thoughts presenting themselves within the dream. One effecting factor of dream rebound is the changes in the prefrontal lobes during rapid-eye movement sleep. Suppressed thoughts are more accessible during REM sleep, as a result of operating processes having a diminished effectiveness. This leads to pre-sleep thoughts becoming more available “with an increased activity of searching for these suppressed thought[s]”. There are other hypotheses regarding REM sleep and dream rebound. For instance, weak semantic associations, post REM sleep, are more accessible than any other time due to weak ironic monitoring processes becoming stronger. More research is needed to further understand what exactly causes dream rebound.