Intentional Inhibition and the “Alien Hand Syndrome”: How Self-Control Works

The ability to flexibly control our behavior is a hallmark of Homo sapiens and has played a significant role in our evolution. But what exactly is a voluntary act, and how does self-control work? How do neural mechanisms, including “intentional inhibition,” enable us to adapt our behavior to social contexts, adjust it according to long-term plans rather than immediate impulses? Can thoughts, emotions, and urges really be inhibited just like actions, and why does this work?

There should be a special word to describe the mixed feelings we get after hastily hitting the “Send” button. Annoyance, anger, or resentment are quickly replaced by the chilling realization that you sent the wrong thing, to the wrong person, at the wrong time—and it would have been better not to send it at all. What drove you when you wrote the message? What made you regret it? But more importantly—what could have stopped you in that moment?

Humans are unthinkable outside of a social context. Our interdependence with others is, if not absolute, at least life-defining in scale and nature. How did we, as higher primates who once lived in groups of a few hundred, manage to build a global civilization based on the closest interaction of millions?

Take a moment to think of a composite image of John von Neumann, Wernher von Braun, Edward Teller, and Dr. Strangelove, played by Peter Sellers in Stanley Kubrick’s film “Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb.” His hand seemed to have a life of its own, sometimes shooting up in a Nazi salute, sometimes trying to strangle its owner. Ideomotor apraxia, or “alien hand syndrome,” became known as “Dr. Strangelove syndrome” after the film. What do the development of complex societies and a neurological disorder have in common? The answer: what is necessary for the first and partially absent in the second—the ability to flexibly control one’s behavior.

How does the nervous system find a winning compromise between the short-term benefits of immediate stimuli and the long-term perspective of delayed rewards? Social psychologist Roy Baumeister, known for his work on the self and willpower, believes that self-control is a central element of the self and a necessary trait for success in life (Baumeister et al., 2007). But how is it achieved? What neural mechanisms allow us to adapt our behavior to social contexts?

Elisa Filevich, Simone Kühn, and Patrick Haggard propose “intentional inhibition” as the main process underlying self-control. In their view, the ability to delay a planned action and to adjust or stop an action already underway gives us the flexibility and strategic capacity to act (Filevich et al., 2012).

Studying Intentional Inhibition

The classic approach to studying action control divides actions into external ones, which are direct responses to imperative stimuli, and internal ones, initiated by the subject’s internal states (Goldberg, 1985; Jahanshahi et al., 1995; Jenkins et al., 2000). The standard definition of a voluntary act is “the absence of a preceding stimulus.” Intentional actions are triggered by desires and defined by the subject’s goals and intentions.

These desires and intentions, of course, often relate to the external world and serve as representations, acting as a link between the environment and behavior. Simply put, this mediation allows us to separate in time the cause (external and internal stimuli) and the effect (our actions). This temporal gap gives us “freedom from immediacy” (Shadlen and Gold, 2004).

But how can we study the mechanisms of intentional inhibition? Researchers face three methodological challenges:

1. Intentional inhibition does not produce any observable behavior that can be measured. Neuropsychology and neuroimaging can help detect processes associated with behavioral inhibition.
2. Intentional inhibition necessarily involves an internally, not externally, driven process, making it hard to manipulate stimuli. If classic experiments study behavioral responses to external stimuli, how can we study the internal generation and inhibition of behavior—something not accessible to outside observers?
3. Intentional inhibition must be the inhibition of something. There must be a process that would have led to action if it hadn’t been inhibited. But in the absence of observable behavior, how can we judge the presence of this process? In particular, it’s hard to distinguish between a situation where there was no intention at all and one where an action was planned or started but later inhibited.

Here, two possible reasons for the absence of action are identified:

• Early decisions—whether to start an action or not.
• Late decisions—whether to inhibit the resulting motor activity.

The first can be explained by action selection processes, while the second requires an additional process of intentional inhibition, specifically blocking motor output and suppressing an already prepared action (Brass and Haggard, 2008; Kühn et al., 2009). The following discussion focuses on the second case.

“Alien Hand Syndrome” and the Neuropsychology of Intentional Inhibition

Let’s return to Dr. Strangelove syndrome. Neurologist Sergio Della Sala describes the behavior of a patient with “alien hand syndrome” as follows:

“…the right hand often performs complex actions not desired by G.C. These actions are clearly purposeful and well-executed, but not wanted by the patient, who tries to stop them with her other hand. For example, when a cup of hot tea is in front of her, the right hand picks up the cup and brings it to her mouth, even though the patient knows the tea is too hot and has just said she’ll wait for it to cool. Nevertheless, her left hand had to intervene to put the cup back on the table. The desire to act differently was not enough to change the directed but inappropriate behavior of the right hand.” (Della Sala et al., 1991)

What is the primary problem here: inability to intentionally inhibit, or a hyperkinetic disorder? If inhibition were intact, patients with “alien hand syndrome” should perform adequately on tests of voluntary action. In fact, experiments show the opposite: inability to inhibit unintentional actions triggered by external stimuli is linked to reduced voluntary capacity for intentional actions (Cantagallo et al., 2010; Kritikos et al., 2005). Interestingly, another study found perseverative reactions of the “alien” hand to external stimuli. For example, when trying to make coffee, the alien hand persistently tries to do something inappropriate (Giovannetti et al., 2005).

This suggests that in a healthy brain, intentional inhibition must be a regular function, lasting as long as the motivation to act persists. A large number of perseverative errors were also observed when patients had to perform a parallel task, compared to standard conditions. It is logical to assume that intentional inhibition depends on the resources of the central executive system.

Summing up research on “alien hand syndrome,” the problem is not hyperactivity or excessive volition, but reduced intentional inhibition. Experimental results also suggest that an important aspect of voluntary control is the inhibition of competing, externally initiated actions. An effective voluntary act includes initiating the desired action and suppressing others. Without intentional inhibition, this can be difficult.

Neuroimaging of Inhibition

In a number of experiments, fMRI scans have shown the neural correlates of intentional inhibition and their connections to other inhibitory or goal-setting systems. Studies have also examined inhibition of higher-level processes, such as thoughts, and suggest that thoughts, emotions, and urges can be inhibited just like actions.

An unexpected link was found between inhibiting actions and inhibiting thoughts and emotions, for which there are good theoretical grounds. Some theories argue that language processes and speech are necessary for thinking (Davidson, 1975; McDowell, 1994; Wittgenstein, 1953). Others suggest that language is a system for transferring thoughts into and out of the mind (Cummins, 1996). Several studies show that the motor cortex is involved in processing “thoughts about actions” (Pulvermüller, 2005; Den Ouden et al., 2009; Meteyard et al., 2010).

Some emotion theories state that somatomotor activity and, in part, facial expressions are automatic components of experiencing emotion (James, 1884; Lange and Kurella, 1887; Wild et al., 2001; Sato and Yoshikawa, 2007). Thus, there may be a close link between emotions and observable motor responses, such as fear triggered by an image. It is also possible that inhibiting motor acts associated with emotions can suppress the emotions themselves.

Visualization of meta-analysis results of neural correlates: external inhibition, e.g., stop-signal reaction (red), action selection (blue), and intentional inhibition (green). Note the location of blue and red in the premotor and motor cortex, responsible for body movements. Also note the clear spatial separation between areas responsible for external inhibition (red, closer to the midline) and intentional inhibition (green, in the anterior dorsomedial prefrontal cortex).

The key takeaway: the process of intentional inhibition in the brain is functionally and spatially-physiologically distinct from processes of external inhibition and action selection.

The Functional Role of Intentional Inhibition

Intentional inhibition contributes to behavior generation as an “extension” of the computational models the brain uses to control and adjust simple goal-directed actions (Haruno et al., 2001). Their operation is based on a predictive feedback loop that checks whether the predicted outcomes of the current command match intentions and goals. Any mismatch triggers an adjustment of motor commands, and the process repeats until the goal is achieved. The diagram below shows the structure of the intentional inhibition system, consisting of two “functional loops”: the “internal” or motor loop, responsible for executing the action, and the “external” or distal loop, which makes adjustments, giving us that “freedom from immediacy.”

Here’s a practical example. It’s Saturday night, and you have to get up early tomorrow to drive your father-in-law or mother-in-law to the country (a distal goal). You think about treating yourself tonight, since Sunday is already spoken for. You start planning who to invite for drinks (planner), get ready to type a message in a messenger (body movement), your brain has already calculated the consequences (motor prediction)—an hour or so and the party is on. Then your distal evaluation loop kicks in, assessing whether your short-term actions align with your long-term goals (impact prediction). You reason that partying will mean no sleep, a killer hangover, and not being in the best shape to drive relatives—hardly the best outfit for a chauffeur. With this in mind, Sunday goes from bad to worse. At this point, intentional inhibition (shown as a dashed line in the diagram) comes into play, closing the two loops. The short-term action is stopped (you change your mind, the party doesn’t happen), your long-term interests are preserved (you don’t suffer all Sunday), and no one gets hurt.

Now, take a moment to imagine the importance of the brake pedal in the context of humanity’s use of cars. The electrical activity of neuron clusters in the frontal cortex of our brain is not just a brake pedal, but a “cubic centimeter of chance,” as the old and cunning Yaqui Indian told Carlos Castaneda—a chance to act differently.