Movement disorders: things that do go bump in the night.
Keywords: tics, pharmacotherapy, psychiatric, Tourette's disorder, involuntary, side-effects, intellectual disability
Q. Dr. Barnhill, many individuals with intellectual disability have abnormal movements, such as finger flicking or tics. Can you describe what these are and how they are identified?
A. We will be talking about involuntary abnormal movements. But first what do we know about movement in general and how do involuntary ones differ from voluntary ones?
At first blush this seems like an easy question to answer. But if we take a little time to think about it, things quickly get a bit blurred. Observable, volitional movements are the tip of an iceberg. Any voluntary movement is the culmination of hierarchical sequenced, highly regulated neurological activity. Even a simple voluntary movement like pointing at a bird requires the integration and coordination of sensory data such as target perception and selection; planning of specific actions; a fluid visual-spatial guidance system that gets the hand to where it should be; proprioceptive and kinesthetic feedback to make rapid adaptation to distance and motion factors; sequential alternating activation-inhibition of multiple muscle groups and coordination of signals that the action is complete, then stopping that act and getting ready for the next. It is also apparent that even pointing begins with global planning in the premotor cortex followed by a rapid progression through increasingly finely tuned visual, kinesthetic, and refined motor activity. All this occurs in milliseconds and is infinitely more complicated than a reflex movement away from a hot stove.
Consider a more complex task such as playing Rachmaninoff's Third Piano Concerto. Obviously to even consider this piece requires enormous skill and talent as well as years of practice. Functional brain imaging would reveal basic different patterns of brain activity during the early phases of practicing and learning this intricate piece than once it is mastered. By the time it is mastered by the pianist, most of the millions of different hand and finger movements are largely automatic. In short, those adjustments and variations of motor sequences are outside direct conscious awareness, allowing the concert pianist to rapidly merge technical skill with the expression of the intense emotion and power of this music.
For most of us, learning a new skill requires a different level of brain function than performing a well practiced one. Just think of how you feel when faced with the ominous label "some assembly required" on a child's toy. It is readily apparent to those of us who are "mechanically-challenged" and tremble in fear at this warning that learning new motor skills the night before or as is the case for real pros, intuiting how things fit together, is one challenge. Accomplishing the sequence of actions to complete the task under time pressure is another and reinforces this concept. Disorders of motor coordination, dyspraxias and movement disorders impact these cognitive-to-motor action transformations.
Q. So what happens during an abnormal movement?
A. Now imagine that somewhere in this complex process a short circuit occurs. Depending on where the error appears, different parts of the performance are affected. Mistakes can occur in the planning stages that are often labeled ideational and ideomotor dyspraxias. Another problem might arise due to the disorganization of gross motor actions as in cerebral palsy, paresis or paralysis. Suppose the short circuit occurs in the coordination of simple fragments of or activation/inhibition of multistep sequential volitional movements. Depending on the location of this particular short circuit, several things can go wrong. For example fragments of competing complex actions can breakthrough. There may be problems with initiation, persistence and timing of movements. Problems can arise due to confusing signals to activate and inhibit planned actions. Or there can be problems with learning new skills through practice or retrieving those previously mastered (procedural memory).
The majority of these abnormal movements result from errors within complex interconnecting pathways that involve the frontal-parietal and occipital cortices, the basal ganglia networks and cerebellum. This short list of potential short circuits not only is the substrate for abnormal movements; it also partly explains the many cognitive and behavioral problems often associated with movement disorders. We will explore this connection in a later "Ask the Doctor" segment.
Getting a step closer to answering your question, we need to distinguish between problems with various forms of motor planning and execution (dyspraxia) and motor coordination disorder, seizures, repetitive behaviors among individuals with intellectual disabilities and the types of abnormal movements pertinent to our discussion. We need to tell the difference between things that go bump in the night due to the joy of making noise, stumbling into furniture, or involuntary limb movement that unintentionally impacts something. The clinical reality of making these distinctions is also not as simple as it sounds. But, unfortunately, we will have to confine our discussion to things that go bump by accident.
Q. Why do clinicians sometimes have difficulty differentiating between voluntary and involuntary actions?
A. One way of thinking about this question is to borrow the basic concepts of functional behavioral analysis and apply it to the understanding of abnormal movements. If we begin with antecedents one major question comes to mind: what precipitates the movement? Put another way, what are the trigger stimuli that start the hierarchically sequenced chain of events noted earlier? Obviously they can be both internally and externally driven and directed. A thought or an external stimulus can trigger a focused goal directed voluntary action. Suppose there is neither a thought nor goal to direct the action. Let us consider complex tics. Many of these movements occur without thought or planning. Movements associated with other brain disorders may intrude upon a preferred or desired action. But focusing on complex tics, suppose the action has no specific external goal but is preceded by a growing premonitory sensation or urge to move. Depending on the qualities of the urge or sensation, the resulting action serves to relieve these sensory or cognitive antecedents but may not serve any useful instrumental purpose. In this sense the movement is not entirely voluntary nor is it completely involuntary. The term "involuntary" is often used to denote this dilemma.
This boundary problem is the essence of trying to understand the subtle differences between Tourette's disorder, compulsions and other types of repetitive behaviors. (1,2) In severe forms of 1,2 Tourette's disorder, automatic imitation of the actions of others (echolalia and echopraxia), purely involuntary, often unconscious, movements that lack pre-movement potentials on EEG and repetitive movements that satisfy an urge and stop when things feel right, can occur in the same individual. From this perspective, antecedents can evoke apparently voluntary movements with differing motivations as well as movements, including those that occur without rhyme, reason, goal or purpose. (3,4)
Q. So what about the function and consequences of abnormal movements?
A. It is pretty obvious that we have slipped from antecedents to function. This is a source of additional confusion. It is arguable that a simple tic has no specific function other than its own expression. On the other hand the movement itself may have intrinsic reinforcing properties. This may be stretching the analogy a bit thin, however, but if we look carefully at the neurobiology of a simple tic, we run up against another very interesting boundary problem. Under normal conditions there is a complex regulatory interaction between prefrontal cortex and basal ganglia. Both can put the breaks on different components of such intrusive movements. Depending on the focus of attention or intent, the prefrontal cortex plays a role in dampening the excitability of segments of the motor cortex via regulation of various components of the basal ganglia. Something goes wrong, perhaps due to injury, genetic risk, or medication induced, and the motivational, activation-regulation system malfunctions. This malfunction impacts the functional-instrumental integrity of goal directed actions and allows other motor actions to "slip out." (4)
From this model it is possible to grasp what happens in involuntary movements. It is also possible to see the connection between the substrates responsible for the overlap between abnormal movements and other repetitive or stereotypic behaviors. All of this suggests that there is a dimensional quality to repetitive behaviors that ranges from voluntary, involuntary, functional/meaningless, motivation and so forth. Included in the spectrum are factors that affect the threshold and tendency for these movements to both occur and continue. From this perspective there are is another metaphorical connection--one that suggests that there are differences between the neurobiological force mechanisms that initiate an abnormal movement from those that maintain it. (4,6)
Although we might not think of this as learning, we find overcommitted circuits devoted to a specific typology of tic or abnormal movement--the more you do it, the more likely it might be to recur or persist. This observation suggests that neuroplasticity, long term potentiation and sensitization of these pathways are occurring. Once these changes are solidified, we may see the roots of habit formation and associative conditioning. This process also seems to lie on a continuum that reawakens the voluntary, involuntary, "unvoluntary" debate noted earlier. (5)
The continuum of abnormal movements may explain why many patients respond to behavioral treatments and others require medication or both interventions. It is a bit too simplistic to define absolute treatment boundaries other than to say most medication interventions tend to impact neurobiological substrates, while habit reversal or exposure-response prevention addresses the overlearned or forces that drive or motivate the behaviors. But as we see clinically, even this generalization is suspect. This area is a particularly exciting arena for researchers in behavioral pharmacology and habit reversal and some exposure response prevention therapies.
Q. Most movement disorders are worsened by various forms of stressful or particularly challenging events. Does escape from this distress represent a function of the tic?
A. Although stress or other anxiety provoking settings or stimuli may increase the frequency and intensity of some abnormal movements, clinicians are not in the habit of addressing their functional role. Stress and activation of stress pathways in the limbichypothalamic networks affect many regions of the basal ganglia and increase the probability that abnormal movements will occur. But this vulnerability also reflects some breakdown in the normal regulatory functions of prefrontal/ executive functions. Many abnormal movements resemble some types of territorial, dominance and sexual display or grooming behaviors observed in mammals and primates. In this sense, they seem to be bits and pieces of highly conserved conflict or social communication rituals that are in essence, instinctual.
During our evolution, our hominid ancestors rewired these circuits and integrated them with our much expanded prefrontal cortex. As a result, many of these complex "ape-like" social behaviors are now disguised by the civilizing effects of culture and social conventions. Some neuroethologists consider compulsions, some rituals and abnormal movements as fragments of much older patterns of behavior that escape regulation. Thus we may find innate releasing mechanisms (types of stressors) that trigger these remnants of complex social behaviors. The real kicker comes from the overlapping neuroanatomy, physiology and neurochemistry of pathways that are also associated with compulsions, obsessions, tics and other movement disorders. So we can 5,6 argue that there is a substrate for certain abnormal movements that affects both conditioning and extinction.
Now back to your question--the link between stress and simple tics or movements is not an easy one to answer. The answer becomes more complicated as we move from simple movements to more complex, sequenced abnormal movements. Here the boundary between many repetitive behaviors becomes blurred. For example, it is repeatedly demonstrated that we can condition and extinguish eye blink to specific stimuli, usually potentially stressful stimuli. Eye blink tics or reduced eye blinking rates in a patient with Parkinson's disease are more difficult to extinguish, yet both are exacerbated by stressful stimuli. (3)
Many abnormal movements may have more in common with hiccups than voluntary actions that allows the individual to escape task demands or anxiety provoking settings. In short the link between antecedent, behavior and consequences becomes a bit blurred in the "motor" components of the basal ganglia networks. But if we look at repetitive behaviors that demonstrate limbic interconnections between the ventral basal ganglia, greater amygdala network, and regions involved in regulating these emotional-motivational pathways, we run into another complication. (2)
Q. It seems that these repetitive behaviors are like compulsions that relieve distress. How is this process like other escape behaviors, and where might negative reinforcement fit in?
A. Let's use Tourette's disorder as an example. A sensory tic or premonitory urge may be relieved by a particular movement that does allow temporary relief. Stretch this paradigm a step further and you can see a motor activity relieving anxiety or distress and all of a sudden you are butting up against obsessive compulsive symptoms. So in addition to varying typologies of motivational states we might also look at the ease of conditioning or habit formation operating in each of these actions. We might look at a continuum of conditioning thresholds, valence of reinforcement types (positive, negative, or associative conditioning experiences), and automatic motor actions that, although not appearing to operate under obvious learning principles, are subject to higher level operant processes. Some of these may evolve into habits that persist even after the original antecedents or conditioned stimulus-response associations are extinguished. (2,5)
I think it is becoming more apparent why the voluntary, involuntary question is not a straightforward one. We still have a lot to explore, and in the next Ask the Doctor, we can look at the clinical world of movement disorders in individuals with intellectual disabilities.
Q. What medications are related to the initiation or exacerbation of movement disorders in the intellectually disabled population?
A. We can explore this in greater depth in a later article, but the "simple" answer is that the neurobiology and neurochemistry of movement disorders is by no means simple. Some years ago, clinicians looked at movement disorders in terms of a ratio between dopamine (DA) and acetylcholine (ACH) in the basal ganglia--a simple DA/ACH ratio could be used to define disorders like Parkinson's or EPS and distinguish them from other disorders like Huntington's disease and tardive dyskinesia. For example, Parkinson's disease (PD) is characterized by loss of DA neurons in sections of the midbrain nucleus (substantia nigra). Thus, PD and antipsychotic induced EPS resulted from DA<<ACH. If you reversed this ratio (DA>>>ACH), you produced tardive dyskinesia, Tourette's disorder or Huntington's disease. (4)
Those were the good old days before we were flooded by new information from the neuroscience revolution. It is now apparent that for individuals with intellectual disability, the DA/ACH ratio is a gross oversimplification. For example, some movement disorders are drug induced. When I was a resident in psychiatry in the late 1970's, tardive dyskinesia was simply a hypersensitivity of DA neurons brought about by prolonged blockade and the development of something called "supersenstivity." Tics were always worsened by stimulants that increased the functional availability of DA. Although these mechanisms are important, there are many others, and both disorders are heterogeneous conditions. The same argument can be made for stereotypies, mannerisms and other repetitive behaviors. Although increases in DA can increase stereotypies, many individuals respond to other drugs, SSRIs or benzodiazepines, for example. This same argument can be applied to other movement disorders. (4)
Q. What medications can reduce movement disorders?
A. It is important not to consider all movement disorders to be defined by one or two specific abnormalities. We must first refine the typology/topography of the movements then focus on what we have learned about their neurochemistry to shape treatment decision making. For the sake of argument, for movements in which the DA/ACH= >1 (too much dopamine or too little acetylcholine), we have two options. We can block dopamine with neuroleptics or increase ACH tone (acetylcholine precursors or inhibitors of metabolism). This approach works in many conditions but may not work for all. This is where the neuroscience revolution comes roaring down the hallway.
(1.) Barnhill LJ, Antonacci DJ, Poindexter AR. Tic disorders. Disorders. In: Fletcher R, Loschen E, Stavrakaki C, First M (eds), Diagnostic Manual-Intellectual Disability (DM-IS): A Textbook of Diagnosis of Mental Disorders in Persons with Intellectual Disability. Kingston, NY: NADD Press, 2007:157-172.
(2.) Barnhill J, Horrigan JP. Tourette's syndrome and autism: A search for common ground. Ment Health Aspects Dev Disabil 2002;5:7-15.
(3.) Jankovic J, DeLeon ML. Basal ganglia and behavioral disorders. In: Schiffer RB, Rao SM, Fogel BS (eds), Neuropsychiatry: Second Edition. Philadelphia, PA: Lippincott, Williams & Wilkins, 2003:934-945.
(4.) Jankovic J, Tolosa E (eds). Parkinson's Disease and Movement Disorders: Fifth Edition. Philadelphia, PA: Lippincott, Williams & Wilkins, 2007.
(5.) Robertson MM. Tourette syndrome, associated conditions and the complexities of treatment. Brain 2000;123 425-462.
(6.) Saint-Cyr JA, Taylor AE, Nicholson K. Behavior and the basal ganglia. Adv Neurol 1995;65:1-28.
JARRETT BARNHILL, M.D.  & ANNE D. HURLEY, PH.D. 
 University of North Carolina School of Medicine, Chapel Hill, NC
 Tufts University School of Medicine and Harvard Vanguard Medical Associates, Boston, MA
CORRESPONDENCE: Jarrett Barnhill, M.D., Dept. of Psychiatry, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7160; email: Jarrett_Barnhill@med.unc.edu.
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|Title Annotation:||Ask The Doctor|
|Author:||Barnhill, Jarrett; Hurley, Anne D.|
|Publication:||Mental Health Aspects of Developmental Disabilities|
|Date:||Oct 1, 2008|
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