Similarities and differences between normal urges and the urge to tic

Besides sneezing, yawning, and scratching, other types of more complex behaviors can be considered urges for action, in that they are both compelling and can be overtly inhibited. Many behaviors increasing the survival rate of self and species have this instinctual (although not compulsory) nature. We feel a terrible urge to catch a newborn falling from a table, although we could choose not to do so. The hypothesis is advanced that both insula and cingulate cortex participate in social behaviors such as contagious yawning, laughing, and crying, but are not necessarily involved in the urge to cough, for example. Jackson and coauthors state that motor reflexes (as in recoiling from fire) are different from urge-for-action in that they cannot be cortically inhibited (or temporally postponed). They also characterize urges for actions as different from desires because of their highly implicit and not overly conscious nature. These characterizations are insightful and correct in principle, but the authors focus on very specific and peculiar urgefor-action types, such as the urge of urination, and of yawning and scratching, which are far from homogeneous. The urge to urinate is one of the many signals that originate in the brain upon hypothalamic impulses and that are involved in the homeostatic regulation of physiological parameters (such as blood oxygen, delta sleep-inducing peptide levels, and plasma concentration of glucose (Burdakov, Luckman, & Verkhratsky, 2005). In this view, the urge to eat in a person with very low glucose levels cannot be considered a reflex (it can be cortically guided, inhibited, or deferred) and is not necessarily a conscious desire (e.g., as with someone who is working and is very concentrated); therefore, it can be legitimately considered an urge-for-action. Similarly, the urge to breathe when there is a lack of oxygen (at high altitude, or in badly air-conditioned places), or, again, the urge to lie down when cerebral blood pressure is low and we feel faint; the urge to quickly undress when it is too hot, or to wrap up when it is freezing; the urge to move arms and legs when we are drowning; and the urge to cough if we are suffocating can all legitimately be considered types of urgesfor-action. We are not sure that insula and mid-cingulate cortex are crucially involved in all these behaviors. It is possible that contagious yawning might share more similarities with other human behaviors reflecting the processing of social information (such as contagious crying and laughing). Indeed, we know that both insula and cingulate cortex play a very important role in empathy, in response to crying (Lang, Yu, Markl, Mü & Kotchoubey, 2011; Sander, Frome, & Scheich, 2007) or to the sight of suffering people (Proverbio, Adorni, Zani, & Trestianu, 2009). Possibly, these structures are responsible for other urges-for-actions such as those regulating instinctual parental behavior (catching a baby falling from a table, for example), aimed at increasing the survival rate of individuals (brushing an insect away from a child) or of the species. Finally, I would make a distinction between spontaneous yawning and contagious yawning. Spontaneous yawning is thought to have the important function of increasing oxygen blood levels, by expanding the lungs and stretching the muscles (Thompson, 2011). It is also known to lower brain temperature, thus favoring increase in sleepiness and passage to the sleep stage (Gallup & Gallup, 2007). Overall, yawning is probably involved in the circadian and homeostatic control of sleep and wakefulness. Contagious yawning, on the other hand, is thought to be based on the activity of mirror neurons, with the purpose of synchronizing and regulating the behavior of cohabitant individuals, similarly to contagious laughing and crying (Geangu, Benga, Stahl, & Striano, 2010). In this view, the urge to yawn when another does so would stimulate regions involved in theory of mind and empathy, such as the cingulate cortex (Platek, Mohamed, & Gallup, 2005), as was found by Jackson and coauthors. * * * 244 COMMENTARIES D ow nl oa de d by [ N ew Y or k U ni ve rs ity ] at 2 2: 51 0 9 Fe br ua ry 2 01 5 Similarities and differences between normal urges and the urge to tic Beth A. Belluscio, Sule Tinaz, and Mark Hallett Human Motor Control Section, National Institute of Neurological Disorders and Stroke, Bethesda, MD,