In a Word - Impulsive vs Compulsive

In this Episode, I  continue an intermittent series called “In A Word.”  The difference between prior episodes and this one is that today I have two words.  I chose these words because I don’t really know the difference between them, and even after reading and trying to understand the difference, I am not sure that there is a clear difference.  The two words are Impulsive and Compulsive.

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References and readings (when available) are posted at the end of each episode transcript, located at psydactic.buzzsprout.com. All opinions expressed in this podcast are exclusively those of the person speaking and should not be confused with the opinions of anyone else. We reserve the right to be wrong. Nothing in this podcast should be treated as individual medical advice.

Transcript

Welcome to PsyDactic - Residency Edition.  Today is… I am a 4th year Psychiatry Resident in the National Capital Region.  That means that I am in my last year of training before taking my boards.  I say that to warn the listener that although I think I am smart enough to make a podcast, I am just one person.  My opinion is only my own and I don’t pretend to speak for anyone else, whether it be the federal government, the Department of Defense or the American Philatelic Society.  I also design this for an audience of other psychiatry residents or attendings, but I hope anyone can learn something from it.

Today I am continuing an intermittent series called “In A Word.”  The difference between prior episodes and this one is that today I have two words.  I chose these words because I don’t really know the difference between them, and even after reading and trying to understand the difference, I am not sure that there is a clear difference.  I think it is important as a psychiatrist that I am humble enough to admit that at times I don’t really know what I am saying, and I don’t think my entire field has a good grasp on what we are saying sometimes.  The two words I chose today are Impulsive and Compulsive.

If you think about the shared root of these words, -pul or -pel from the Latin, you may notice that there are many words that contain it.  Other than impulsive and compulsive, there are the words propulsive, repulsive, expulsive.  In astronomy there is a pulsar.  When something moves back and forth it is said to pulsate, and this is most often used to describe light or volume, like the volume of an artery or the lungs.  Using the derivative -pel which is just another form of -pul, there is impel, repel, dispel, compel, expel.  Pul- or Pel- represent some kind of forced or directed action.

Something moves or changes course.

When applied to psychiatry, this is basically referring to a behavior that has some kind of intent behind it. Not all behaviors are intentionally motivated.  Things like tremors, choreiform movements, alien limb movements lack intentional motivation.  Not all motivated behaviors are impulsive or compulsive.  Most are normal. When trying to really conceptualize my patients, I realized at some point that I don’t understand the difference between an impulsive motive and a compulsive motive?

The DSM even has chapters that use these words in the titles.  There is the Obsessive-Compulsive and Related Disorders, many of which were previously defined as either anxiety-related disorders or impulse control disorders.  There is the Disruptive, Impulse-Control and Conduct Disorders chapter.  Psychiatrists may also talk about substance use as either impulsive or compulsive type behaviors.  There are also disorders of sexual behavior that are variously described as impulsive or compulsive.  Personality disorders have criteria that include impulsive acts (especially borderline or antisocial personality disorders) and there is a personality disorder called obsessive compulsive personality disorder.  Surely so many things are not adequately or precisely differentiated by two meager words.  Let me discuss some of these diagnostic entities in a bit more detail.

Disruptive, Impulse Control and Conduct disorder diagnoses share the common factor that the behavior that a person exhibits violates social norms, such as killing pets for fun, setting their neighbor’s shed on fire (for no apparent reason), stealing garden gnomes (for no apparent reason), or screaming at someone in public (for no apparent reason).  Maybe impulsive actions are actions that happen for no apparent reason.  Unfortunately, this is not even close to universally the case.  Impulsive acts are nearly always preceded by some kind of urge or tension within the person who is committing the act that pushes them toward that act.

Interestingly, the DSM IV and 5 diverge in how they describe Obsessive-Compulsive Disorder by replacing the word impulses with the word urges.  For example, the definition of an obsession in DSM IV is “Recurrent and persistent thoughts, impulses, or images that are experienced, at some time during the disturbance, as intrusive and inappropriate and that cause marked anxiety or distress.” while the definition of an obsession in DSM 5 is “Recurrent and persistent thoughts, urges or images that are experienced, at some time during the disturbance, as intrusive, unwanted, and that in most individuals cause marked anxiety or distress.”  This find and replace continues.  Wherever “impulse” was used in the DSM IV for OCD, “urge” is stuck in its place.  It seems like an attempt to segregate the two terms (compulsive and impulsive) by not using one to define the other.

Another seemingly purposeful grammatical choice is the use of the term “tension” to describe the state of an individual driven to set fires or steal something of no apparent value prior to committing these acts.  What I am referring to here are the diagnostic criteria for pyromania and kleptomania.  The person experiences something prior to doing the act, and in the case of the “impulse control” disorders it is described as “tension.”  In the case of the obsessive-compulsive disorders, it is described as an “urge.”  

So I ask the question again:  “What is the difference between impulsive and compulsive behaviors?”  Is it that one results from tension and the other from urges? “Tension” seems a lot like “urge” to me.  If we define tension as a vague, ephemeral motive and urge as a specific, persistent motive, then maybe the DSM actually makes sense.  But this sounds like special pleading to me.

One way I try to think about this is that impulses are behaviors that happen before much thought or enough thought happens, while compulsions are the result of pesky thoughts that someone just can’t ignore.  Impulses are fast and precocious. Compulsions are tedious and inflexible.

As soon as we either imagine something or see something, our brain automatically plans out an action.  If you watch someone dancing, your brain is planning out those movements in your head, getting ready to execute them.  If you see something you want, your brain is pre-planning a path to that thing.  Controlling whether or not we do or don’t do that thing that our brain is mapping out is a critical skill.

The reason that I am making such a fuss about these words is because to be able to gain a deep understanding of our behaviors and develop novel treatments, we need to know the neural mechanisms that are at play.  Vague language doesn’t do much to help us understand even where to start looking.  Does using the term impulsive for addiction and sexual promiscuity and pyromania and antisocial behaviors really describe the same kind of thing?

The term impulsive likely refers to very different kinds of things.  It can refer to having some kind of bias toward action, like the brain is ready to act and it only takes a small impetus to make it do so.  We are disinhibited.  It could also refer to a problem with our ability to plan things out, take small steps toward our goal, to decide what is the next best thing to do instead of the easiest thing to do.  It could also describe being over-confident and acting too quickly, deciding what to do before we have enough information to make a good decision.

I stumbled across a paper in Neuropsychopharmacology from 2010, titled Probing Compulsive and Impulsive Behaviors, from Animal Models to Endophenotypes: A Narrative Review.  It identified those three types of impulsiveness that I just mentioned and also correlated them with different brain networks.

The kind of impulsiveness that is precocious, that is too ready to act, too easily induced into action, is thought to be the result of malfunction within the right inferior frontal (RIF) cortex and its subcortical connections.  The premotor region has planned out an action, and is rearin’ to go, but is being held back by something inhibiting inappropriate actions.  That hold signal involves the right inferior frontal cortex.  Psychological testing, in the form of stop signal reaction time, may be able to demonstrate this kind of impulsivity.  This type of impulsivity was proposed to be modulated most by the noradrenergic system and insensitive to serotonin, so SSRIs would not treat this kind of impulsivity.  SNRIs, NRIs, DNRIs, or stimulants would be helpful.

The second kind of impulsivity is related to what the authors describe as delaying gratification instead of choosing immediate small rewards that result in problems or failure of long term goals.  This kind of impulsivity is like missing the forest for the trees, getting distracted from the goal.  The belief is that this kind of impulsivity is mediated through orbitofrontal and connected cortical circuitry such as the VMPFC and the dorsal anterior cingulate gyrus and is proposed to be heavily influenced by serotonergic neurons.

The third kind of impulsivity is over-confident in a decision despite not having adequate information.  It is proposed to be related to dysfunction of the OFC and its connections.  I wonder if this is characteristic of people with conduct disorder or antisocial personality disorder.  Parts of the OFC if functioning correctly should act like an accountant or economist.  If calculating correctly, it should know whether or not all the variables that need to be accounted for are accounted for.  If not functioning correctly, then it may allow a decision that is not well thought through, that lacks available information.

If you remember some of my past episodes, you may say, “But Dr. O’Leary, you mentioned before that compulsive behaviors are related to malfunctioning of the OFC.  What gives?”  I’m not sure what gives.  We not have a very good understanding of the difference between the motives for impulsive and compulsive behaviors, and we also don’t understand the fine details of the neuroscience behind them.  We have some clues that someone who acts before considering any outcome may respond better to noradrenergic agents.  Those are the people with proposed dysfunction of the RIFG.  Alternatively there are those who are overconfident or who can’t incorporate new information, and they may respond better to serotonergic agents.

I haven’t even mentioned ADHD, which has been defined as an impulse control disorder before being put in the neurodevelopmental disorders.  The impulse control in ADHD is evidenced by hyperactivity, being excessively loud, talking out of turn, annoying others, etc.  It is also frequently an attention control disorder, where the person is under-responding to environmental cues, easily distracted by unimportant information.  A paper in Neuroimaging in 2010 called “The role of the right inferior frontal gyrus: inhibition and attentional control”  demonstrated that the right inferior frontal gyrus is very active when a person needs to respond to cues in the external environment regardless of whether it needs to inhibit action.  It makes sense, then, that stimulants or norepinephrine reuptake inhibitors treat ADHD, because these agents increase available norepinephrine, which may help the RIFG to both control attention and prevent pre-planned but not needed or inappropriate actions from actually happening.

I’ve spent the last few minutes explaining that there are different ways to conceptualize impulsivity actions that result from either an excessively low energy of activation or a paucity of information (either because immediate rewards become too distracting, or because we are overconfident).  Given that there are these, and likely other things people mean when they say impulsive, merely saying that a patient is impulsive does not really communicate anything specific.  Instead of simply saying impulsive, which could mean many things, a behavior or tendency could be better described.  For example, I could say, “Makes poor decisions due to not considering all available information.”  Or I could say, “Patient acts before thinking about the consequences and often regrets the choice.”  

I mentioned earlier that compulsiveness can be thought to differ from impulsiveness by being more a problem of too much of one thought, instead of not enough consideration of thoughts.  By that I mean that the motive force, or intention of the action is obsessive, the same information is considered again and again and again despite providing no new insight.  It is not a pre-potentiation problem, due to lack of inhibition of a preplanned motor response.  It is also not specifically a problem of not considering enough information (except when the obsessions are delusional in nature).  Instead, compulsivity is a problem with cognitive flexibility.  People with OCD have difficulty with reversal learning, which basically means adapting their future behaviors to new information.  Despite looking at the locked door for the 12th time, they cannot learn that the door is locked.  Despite their mom never dying when they step on a crack, they just can’t not avoid them.  How did you like that double negative?

People with OCD also have a problem with attention because they can’t switch their attention away from an obsession until the compulsion is sufficiently complete.  This means that the neurocircuits for impulsive and compulsive behaviors likely vastly overlap.  Both involve the need to inhibit a preplanned action, but the ways that the systems fail can be very different.

An article from 2015 in the Harvard Review of Psychiatry called “Comorbidity Between Attention Deficit/Hyperactivity Disorder and Obsessive-Compulsive Disorder Across the Lifespan” reported very high variability in the rates of comorbid ADHD and OCD reported in studies, and concluded that many of these associations are highly exaggerated.  This is due to how we diagnose things.  If we are not distinguishing between impulsivity and compulsivity or even different kinds of impulsivity itself, then we may be misled by the result: a patient is performing poorly in school or work, appears to do or say inappropriate things, and has a hard time concentrating.

Let me quote from this paper their characterization of one way to look at impulsivity versus compulsivity.    QUOTE  “When addressing the concept of comorbidity between ADHD and OCD, it is useful to consider the notion of an impulsive-compulsive continuum, as suggested by Hollander. According to this hypothetical scheme, the compulsive end of this continuum—which is associated with OCD—is characterized by harm avoidant and risk-aversive behaviors. Conversely, the impulsive end of the continuum is characterized by behavioral impulsivity (i.e., behaviors lacking forethought) and risk taking. According to Hollander, the concept of polarity between the two constructs is further supported by neurobiological and neurochemical differences. For example, on the neurotransmitter level, impulsivity is mediated by dopamine, whereas compulsivity is mediated by serotonin. In sum, ADHD and OCD appear to be remarkably different in terms of their phenomenology.”  UNQUOTE

I mentioned before some of the cortical regions implicated in ADHD and OCD and that there is overlap.  I haven’t yet highlighted that ADHD is consistently characterized by hypofunction of the RIFG and other frontal regions while OCD is associated with hyperfunction of the orbitofrontal cortex, so this makes Hollander’s continuum scheme seem appealing.  

However, to characterize OCD as “harm avoidant” I think only applies to some cases, and probably most cases, but it depends on the obsession.  Other OCD related disorders such as trichotillomania or skin picking disorder are associated with self harm.  It may be that self harm is meant to prevent some other kind of harm.

Also these authors point to dopamine as a driver of impulsivity.  Dopamine in our reward center drives us toward novelty and reward seeking.  We know that dopamine agonists, like those used in Parkinson’s disease can result in patients engaging in behaviors that they may never have done before, like gambling or sexual promiscuity.  We call these impulsive behaviors, though they are also and frequently excessively or rigidly goal driven.  Dopamine agonists also can result in repetitive behaviors that resemble compulsions.  Patients with OCD who don’t respond fully to a serotonergic agent may respond with addition of a dopamine blocker, but the response rates are not high.

Some drugs can result in a relative flood of dopamine in the nucleus accumbens.  Is dopamine-driven impulsivity the same as the impulsivity described with ADHD that we treat most effectively with dopaminergic and noradrenergic agents?  What I mean here is that I have often read that the mechanism of action of stimulants for ADHD is blocking dopamine reuptake or metabolism without any mention of norepinephrine.  However, this simplistic view gives dopamine too much of the credit.  It may be standing on the shoulders of norepinephrine to do its job.

I think to conceptualize impulsivity and compulsivity as a continuum is tempting, and if you enforce very specific definitions of the two terms, this could be accurate, but it will miss much of reality.  It relies on an oversimplified neurobiological model of brain function, OCD being associated with too much activity in the fronto-striatal circuit and relative serotonin deficiency and dopamine excess, and ADHD with too little activity in the fronto-striatal circuit and a relative dopamine deficiency. Embracing this model, you would need to downplay the role of norepinephrine and you would also need a lot more words for all the other things we currently call impulsive or compulsive that don't fit on that continuum.  Whew.  I need to take a breath.

While struggling with trying to define and differentiate compulsive and impulsive motives, I have discovered that they are likely not just two different things, but within themselves are different things.  However, they are also related things.  They are polyphyletic terms that draw a circle around things that do not have a single common antecedent but share common pathways.  Describing a behavior instead of merely reporting it as compulsive or impulsive will help prevent miscommunication and can inform treatment.  Looking for patterns in behaviors and asking what prompted the behavior is important.

We have some insight into how the brain decides what to do.  It appears that there is some tonic inhibition that involves the RIFG.  Loss of this inhibition due to hypoactivity of this region results in behaviors that are almost automatic, like blurting out answers, making annoying sounds, failing to adjust your volume, and also failing to identify or respond to important details or information.  Behaviors that require more decision making involve a broader region of the PFC and appear to be managed to some degree by the orbital frontal cortex.  These can range from being satisfied with only a little of the relevant information that is needed to being completely dissatisfied that the result you just quadruple-checked is real or durable.

If listening to this podcast has accomplished anything, I hope it is at least that the next time you speak the word impulsive or compulsive, you also have a voice in your head asking, “What actually is it that I mean by that?”

Thank you for listening.  I am Dr. O and this has been an episode of PsyDactic - Residency Edition.

References and readings

Neuropsychopharmacology (2010) 35, 591–604. doi:10.1038/npp.2009.185

Neuroimage. 2010 Apr 15; 50(3-3): 1313–1319. doi: 10.1016/j.neuroimage.2009.12.109

Compr Psychiatry. 2016 Jul:68:111-8. doi: 10.1016/j.comppsych.2016.04.010. Epub 2016 Apr 15.

Psychiatr Clin N Am 31 (2008) 587–591. doi:10.1016/j.psc.2008.06.007

Aust N Z J Psychiatry. 2019 Sep; 53(9): 896–907. Published online 2019 Apr 19. doi: 10.1177/0004867419844325

Harv Rev Psychiatry. 2015 Jul; 23(4): 245–262.  Published online 2015 Jul 8. doi: 10.1097/HRP.0000000000000050