Sharing More Than the Sofa

Abstract

Following an initial act of self-control, human performance on subsequent tasks that also require self-control exertion is impaired. This phenomenon, termed ego depletion, is constrained by beliefs and perceptions in humans. Interestingly, this effect has also been observed in dogs, which arguably do not share similar belief systems. This observation suggests that a common biological mechanism might underlie the phenomenon for both species. It also suggests that we can learn something about human self-control by conducting research with dogs. In this article, we relate findings on the depletion effect in dogs to the different mechanisms that are proposed to explain the effect in humans. Finally, we elaborate on practical implications for working dogs.

Keywords

self-control ego depletion glucose canine

Just about every dog owner has demanded the following: “Sit! Stay! Do not eat until I say OK!”—and nearly every pet dog has learned to respond appropriately. In other words, owners expect their dogs to control themselves, and dogs often meet this expectation. This outcome is not surprising, since dogs are similar to humans in their need to inhibit and control their behavior in order to maintain social relationships, coordinate actions with others, and obtain delayed rewards (Marshall-Pescini, Virányi, & Range, 2015). Nevertheless, dogs are not human and have no sense of “self,” so how are they exerting “self”-control? Research suggests that dogs are probably much more like humans than often thought and that self-control by both species is fundamentally similar. This similarity can help to shed light on what it means to exert self-control and how self-control might be fatigued and facilitated in dogs and humans.

Self-control refers to the effortful regulation of emotions, thoughts, and behaviors that is often necessary to obtain delayed benefits. In both humans and dogs, self-control is related to prefrontal activity in the brain (Cook, Spivak, & Berns, 2016). Self-control has a genetic basis (Connolly & Beaver, 2014), but it can also be improved through targeted practice (e.g., Muraven, 2010).

In contrast to the long-term beneficial consequences of self-control training, there are short-term temporary deficits that are incurred immediately after self-control exertion. These effects are typically studied using a sequential-task paradigm, in which participants are required to conduct two consecutive tasks. Completing a first task requiring self-control, compared to an initial task that requires little self-control exertion, typically results in diminished performance on a second task also requiring self-control. This observed phenomenon, termed ego depletion¹ by Baumeister, Bratslavsky, Muraven, and Tice (1998), is somewhat surprising, as one could expect the opposite—that is, performing the first task would prime the mental representations necessary to perform the second task (Muraven, Tice, & Baumeister, 1998). Nevertheless, an initial act of self-control exertion has been found to negatively affect a variety of executive functions in dozens of studies (for a meta-analysis, see Hagger, Wood, Stiff, & Chatzisarantis, 2010), though it deserves noting that some studies have been unable to replicate these findings (Boyle et al., 2016; Hagger et al., 2016), and a recent meta-analysis has challenged the reliability and validity of the phenomenon (Carter, Kofler, Forster, & Mccullough, 2015).

A potential explanation for why some researchers have failed to observe depletion is that it may be dependent on beliefs and expectations. According to expectancy models, the depletion effect occurs because participants believe that exerting self-control will fatigue them (Job, Dweck, & Walton, 2010). There is ample evidence supporting this claim. If you believe, or are induced to believe, the opposite—that self-control is inexhaustible—you will not show the depletion effect (e.g., Job et al., 2010), and the effect might even reverse if you are induced to believe that performance increases after effort (Martijn, Tenbült, Merckelbach, Dreezens, & de Vries, 2002). Convergent evidence thus supports the hypothesis that beliefs do indeed influence the depletion effect, although the depletion effect appears independent of beliefs after the performance of multiple self-control tasks (Vohs, Baumeister, & Schmeichel, 2013).

An interesting approach for testing whether expectation models can account for the full range of depletion effects is to examine whether depletion can be observed in dogs, a species that arguably does not share human belief systems. Nevertheless, these animals live in the human environment, often being treated as part of the human family. Unlike lab animals, dogs can perform self-control tasks that are not food-dependent. For example, dogs can be trained to exert self-control for praise rewards. The same cannot be said for laboratory rats, which might be an otherwise interesting animal to use in behavioral tests, given the extensive research that has been conducted on them in behavioral neuroscience.

Miller, Pattison, DeWall, Rayburn-Reeves, and Zentall (2010) were the first to investigate the depletion effect in dogs. They found that dogs persisted less on an unsolvable puzzle task after completing a 10-minute sit-and-stay task, compared to being caged for the same duration (see also Miller, Pattison, Laude, & Zentall, 2015). Moreover, exerting self-control to stay still not only reduced subsequent persistence but also decreased search accuracy (Miller, 2013). It was also found that staying still increased approach behavior toward an aggressive conspecific, which is the dominant, more impulsive response (Miller, DeWall, Pattison, Molet, & Zentall, 2012). These results mirror those obtained with humans. The fact that dogs are affected similarly suggests that the depletion effect does not result from beliefs about the consequences of self-control exertion and that another mechanism common to dogs and humans might be involved.

The Resource Model

The most influential theory proposed to account for the depletion phenomenon is the limited-resource theory (Muraven & Baumeister, 2000). According to this theory, the exertion of self-control depletes a common energy resource, leaving less energy available for subsequent acts of self-control. Because self-control is an executive function that relies on prefrontal cortical activity, and because glucose is the primary supply of energy to the brain, it has been argued that the depletion effect might be the result of glucose depletion in the brain (for a review, see Gailliot, 2015). From this idea, it was hypothesized that the consumption of glucose might counteract the depletion effect by restoring glucose levels. Research in both humans and dogs has shown that the depletion effect can indeed be counteracted by administering glucose. Dogs that performed the sit-and-stay task and consumed glucose before the second task persisted longer than dogs that drank a sweetened calorie-free drink and as long as dogs that did not have to exert self-control (Miller et al., 2010; Miller et al., 2015). These findings, however, do not indicate that glucose will always counteract the depletion effect. An excessive dose of glucose can diminish food motivation in dogs, masking the positive effect of glucose ingestion on self-control exertion (Miller, 2013). Taken together, the studies in dogs indicate that the consumption of specific doses of glucose can counteract the depletion effect, which is in line with the limited-resource theory.

That the ingestion of glucose can counteract the depletion effect, however, does not necessarily mean that the depletion effect itself is caused by brain glucose depletion. The brain prioritizes its own energy supply over that of the peripheral organs (Kurzban, 2010). Moreover, blood and brain glucose can fluctuate independently (McNay, McCarty, & Gold, 2001). For these reasons, it has been argued that the consumption of glucose can counteract the depletion effect because it acts as a motivational cue for control. In line with this hypothesis is the observation that merely rinsing the mouth with glucose, which cannot restore glucose levels, is sufficient to counteract the depletion effect (e.g., Molden et al., 2012). This finding has resulted in a revision of the original limited-resource theory, which now argues that depletion effects result from the allocation of energy to tasks with high priorities rather than from the depletion of a physical resource (Baumeister & Vohs, 2016).

Motivational Models

According to motivational models, depletion results from a shift in motivation rather than from a depleted resource (Inzlicht & Schmeichel, 2012). Kurzban, Duckworth, Kable, and Myers (2013) have stated that the motivation to perform a specific task is related to the benefits associated with performing that task relative to the benefits of alternative opportunities. A shift in motivation is then explained by assuming that the benefits and costs of a specific task change during the prolonged exertion of self-control. Accordingly, the depletion effect will not occur as long as an individual is sufficiently motivated to perform the task (i.e., as long as the costs of the task do not outweigh the benefits). This explains why cues that increase motivation, such as the offer of an unexpected gift (Tice, Baumeister, Shmueli, & Muraven, 2007), can counteract the depletion effect.

Given that the depletion effect in dogs is not prone to expectancy explanations, the question arises whether motivational models can account for depletion effects in dogs. Possibly, dogs may experience temporary shifts in both motivation and attention after prolonged self-control exertion, as proposed by Inzlicht and Schmeichel (2012). However, it is less clear how dogs would compute the benefits and costs of competing tasks, as proposed by the opportunity-cost model (Kurzban et al., 2013). Yet it is conceivable that shifts in motivation in dogs can also be explained by a cost-benefit trade-off at a more basic level. Future research needs to clarify more specifically how the benefits and costs of different tasks are calculated and compared in order to determine whether motivational accounts provide a sufficient explanation for the depletion effect in dogs. Although these motivational models might thus provide a promising avenue for explaining the depletion effect in dogs, it seems unlikely that they can fully explain the effect. An interesting observation with regard to this is that hungry dogs persist less to obtain food from an unsolvable puzzle toy (Miller et al., 2010; Miller et al., 2015) and search less accurately for hidden food (Miller, 2013) after sitting still for 10 minutes. In contrast to this observation, motivational accounts would have predicted that hungry dogs should maintain a high motivation to obtain food because hunger motivates humans to work harder for food (Orquin & Kurzban, 2016). Hence, existing motivational models lack the specification to explain how motivation can account for the depletion effects found in dogs.

Physiological Mechanisms

Kurzban and colleagues (2013) also put forward an explanation at the level of the brain, focusing on the role of dopamine. During task performance, dopamine signals reward. Prolonged self-control exertion might cause a decrease in dopamine release. This would, in turn, decrease the motivation to perform the second task and consequently result in the depletion effect. This explanation is supported by the observation that people focus more on cues signaling reward after having exerted self-control (Schmeichel, Harmon-Jones, & Harmon-Jones, 2010). Other research has suggested that the reason why both glucose and motivational cues can counteract the depletion effect might be that they activate dopaminergic pathways in the prefrontal cortex (Chambers, Bridge, & Jones, 2009). In dogs, there is currently no research that has investigated whether dopamine release is associated with the depletion effect, although it has been observed that motivational cues can elicit dopamine release in dogs (Odendaal & Meintjes, 2003). Whether this can also counteract the depletion effect has yet to be investigated.

Recently, it was found that the ingestion of fructose can also counteract the depletion effect in both humans and dogs (Miller et al., 2015). Whereas fructose cannot cross the blood-brain barrier, and thus cannot fuel the brain directly, it can increase dopamine release in the prefrontal cortex (Malkusz et al., 2012). Therefore, it could be that the intake of fructose affects the depletion effect by triggering dopaminergic pathways.

An alternative mechanism that has been proposed to account for the depletion effect is the activation of the vagus nerve. The vagus nerve is the primary parasympathetic nerve that connects the heart and the gastrointestinal system to the prefrontal cortex, which is known to be critically involved in self-control (Thayer, Hansen, Saus-Rose, & Johnsen, 2009). The hypothesis that the vagus nerve plays an important role in self-control exertion is substantiated by the observation that successful self-control exertion is accompanied by greater vagal nerve activation, as reflected in elevated heart rate variability (Segerstrom & Nes, 2007). Activation of the vagus nerve can also explain why certain substances can counteract the depletion effect. Both glucose and fructose, for example, activate the vagus nerve (Tsurugizawa et al., 2009). Positive emotions do the same for both humans (Kok et al., 2013) and dogs (Kuhne, Hößler, & Struwe, 2014), which can explain how motivation increases self-control exertion. Because the vagus nerve is activated by these different cues, it has been suggested that the vagus nerve communicates information about different aspects of the bodily state, including nutrient availability, to prefrontal brain areas. Based on this information, the brain might alter its self-control exertion to maintain energy homeostasis (Evans, Boggero, & Segerstrom, 2015). Transfer of this information could occur through the release of noradrenaline or serotonin (Dorr & Debonnel, 2006). Serotonin, like dopamine, is involved in self-control exertion in both humans and dogs (Wright, Mills, & Pollux, 2012).

As should be clear from the previous discussion, research with dogs can shed light on the biological mechanisms that underlie the depletion effect. However, clearly, more research is needed to further elucidate the mechanisms at play. Most prominently, future research should aim to investigate directly whether the depletion effect can be counteracted by dopamine and serotonin levels using novel techniques. For example, to study the direct effects of dopamine and serotonin, tracers designed to track these neurotransmitters in a dog model could be adopted (Peremans et al., 2006). Another promising avenue for future research could be to examine whether the depletion effect can be directly linked to the vagus nerve by using transcutaneous vagus nerve stimulation. Though similar research could be conducted with humans, the canine research would control for expectations and other conscious mental processes.

Practical Applications

Using dogs to test the depletion effect might not only provide better insight into the mechanism underlying the effect but also deliver practical advice for handling dogs, in particular working dogs that constantly need to inhibit their impulses to successfully perform their tasks. For example, the aforementioned research suggests that it might be best to let dogs rest immediately before an important task. Moreover, once dogs are too depleted to continue performing tasks at the required level, it might prove useful to engage in a procedure that has been demonstrated to counteract the depletion effect, such as by administering a carbohydrate drink. From this perspective, it would be of interest to investigate to what extent different types of stimulation (e.g., motivation, vagus nerve stimulation) can counteract the depletion effect.

Conclusion

There is currently some debate concerning the reliability of the depletion effect in humans. We propose that this might reflect that the phenomenon is constrained by human-specific factors, such as beliefs. It is for this reason that a canine model can substantially clarify our understanding of this phenomenon. Dogs, like humans, face self-control demands in everyday life, and they are similarly affected by the exertion of self-control. Testing dogs might help us to understand the mechanism underlying the depletion effect, and this research in turn might have practical applications for working dogs.

Footnotes

Declaration of Conflicting Interests

The authors declared that they had no conflicts of interest with respect to their authorship or the publication of this article.

Funding

Sarah Beurms is supported by a PhD fellowship from the Research Foundation Flanders (FWO; Grant 11N8115N).

Notes

References

Kurzban

Duckworth

Kable

J. W.

Myers

(2013). (See References). Proposes a motivational model to explain the depletion effect, explaining the potential role of dopamine in more detail than the current article.

Miller

H. C.

Pattison

K. F.

DeWall

C. N.

Rayburn-Reeves

Zentall

T. R.

(2010). (See References). The first article that reported the phenomenon of ego depletion in dogs, demonstrating that dogs persisted less after a stay task compared to a caged control condition.

Miller

H. C.

Pattison

K. F.

Laude

J. R.

Zentall

T. R.

(2015). (See References). A recent article investigating the effects of the administration of glucose and fructose after initial self-control exertion in dogs.

Muraven

Baumeister

R. F.

(2000). (See References). Explains the resource model of ego depletion, in which glucose is proposed as the limited resource, in more detail than the current article.

Wright

H. F.

Mills

D. S.

Pollux

P. M. J.

(2012). (See References). A study that investigated impulsivity in dogs, using owner reports and behavioral tests, and correlated impulsivity with urinary metabolites of dopamine and serotonin.

Baumeister

R. F.

Bratslavsky

Muraven

Tice

D. M.

(1998). Ego depletion: Is the active self a limited resource? Journal of Personality and Social Psychology, 74, 1252–1265. doi:10.1037/0022-3514.74.5.1252

Baumeister

R. F.

Vohs

K. D.

(2016). Strength model of self-regulation as limited resource: Assessment, controversies, update. In Olson

J. M.

Zanna

M. P.

(Eds.), Advances in experimental social psychology (pp. 67–127). New York, NY: Academic Press. doi:10.1016/bs.aesp.2016.04.001

Boyle

N. B.

Lawton

C. L.

Allen

Croden

Smith

Dye

(2016). No effects of ingesting or rinsing sucrose on depleted self-control performance. Physiology & Behavior, 154, 151–160. doi:10.1016/j.physbeh.2015.11.019

Carter

E. C.

Kofler

L. M.

Forster

D. E.

Mccullough

M. E.

(2015). A series of meta-analytic tests of the depletion effect: Self-control does not seem to rely on a limited resource. Journal of Experimental Psychology: General, 144, 796–815. doi:10.1037/xge0000083

10.

Chambers

E. S.

Bridge

M. W.

Jones

D. A.

(2009). Carbohydrate sensing in the human mouth: Effects on exercise performance and brain activity. The Journal of Physiology, 587, 1779–1794. doi:10.1113/jphysiol.2008.164285

11.

Connolly

E. J.

Beaver

K. M.

(2014). Examining the genetic and environmental influences on self-control and delinquency: Results from a genetically informative analysis of sibling pairs. Journal of Interpersonal Violence, 29, 707–735. doi:10.1177/0886260513505209

12.

Cook

P. F.

Spivak

Berns

(2016). Neurobehavioral evidence for individual differences in canine cognitive control: An awake fMRI study. Animal Cognition, 19, 867–878. doi:10.1007/s10071-016-0983-4

13.

Dorr

A. E.

Debonnel

(2006). Effect of vagus nerve stimulation on serotonergic and noradrenergic transmission. The Journal of Pharmacology and Experimental Therapeutics, 318, 890–898. doi:10.1124/jpet.106.104166

14.

Evans

D. R.

Boggero

I. A.

Segerstrom

S. C.

(2015). The nature of self-regulatory fatigue and “ego depletion”: Lessons from physical fatigue. Personality and Social Psychology Review. Advance online publication. doi:10.1177/1088868315597841

15.

Gailliot

M. T.

(2015). Energy and psychology. Global Journal for Research Analysis, 4(7), 253–255. doi:10.15373/22778160/July2015/131

16.

Hagger

M. S.

Chatzisarantis

N. L. D.

Alberts

Anggono

C. O.

Birt

Brand

. . . Cannon

(2016). A multilab preregistered replication of the ego-depletion effect. Perspectives on Psychological Science, 11, 546–573.

17.

Hagger

M. S.

Wood

Stiff

Chatzisarantis

N. L. D.

(2010). Ego depletion and the strength model of self-control: A meta-analysis. Psychological Bulletin, 136, 495–525. doi:10.1037/a0019486

18.

Inzlicht

Schmeichel

B. J.

(2012). What is ego depletion? Toward a mechanistic revision of the resource model of self-control. Perspectives on Psychological Science, 7, 450–463. doi:10.1177/1745691612454134

19.

Job

Dweck

C. S.

Walton

G. M.

(2010). Ego depletion—Is it all in your head? Implicit theories about willpower affect self-regulation. Psychological Science, 21, 1686–1693. doi:10.1177/0956797610384745

20.

Kok

B. E.

Coffey

K. A.

Cohn

M. A.

Catalino

L. I.

Vacharkulksemsuk

Algoe

S. B.

. . . Fredrickson

B. L.

(2013). How positive emotions build physical health: Perceived positive social connections account for the upward spiral between positive emotions and vagal tone. Psychological Science, 24, 1123–1132. doi:10.1177/0956797612470827

21.

Kuhne

Hößler

J. C.

Struwe

(2014). Emotions in dogs being petted by a familiar or unfamiliar person: Validating behavioural indicators of emotional states using heart rate variability. Applied Animal Behaviour Science, 161, 113–120. doi:10.1016/j.applanim.2014.09.020

22.

Kurzban

(2010). Does the brain consume additional glucose during self-control tasks? Evolutionary Psychology, 8, 244–259. doi:10.1177/147470491000800208

23.

Kurzban

Duckworth

Kable

J. W.

Myers

(2013). An opportunity cost model of subjective effort and task performance. Behavioral & Brain Sciences, 36, 661–726. doi:10.1017/S0140525X12003196

24.

Malkusz

D. C.

Banakos

Mohamed

Vongwattanakit

Malkusz

Saeed

. . . Bodnar

R. J.

(2012). Dopamine signaling in the medial prefrontal cortex and amygdala is required for the acquisition of fructose-conditioned flavor preferences in rats. Behavioural Brain Research, 233, 500–507. doi:10.1016/j.bbr.2012.05.004

25.

Marshall-Pescini

Virányi

Range

(2015). The effect of domestication on inhibitory control: Wolves and dogs compared. PLoS ONE, 10(2), e0118469. doi:10.1371/journal.pone.0118469

26.

Martijn

Tenbült

Merckelbach

Dreezens

de Vries

N. K.

(2002). Getting a grip on ourselves: Challenging expectancies about loss of energy after self-control. Social Cognition, 20, 441–460. doi:10.1521/soco.20.6.441.22978

27.

McNay

E. C.

McCarty

R. C.

Gold

P. E.

(2001). Fluctuations in brain glucose concentration during behavioral testing: Dissociations between brain areas and between brain and blood. Neurobiology of Learning and Memory, 75, 325–337. doi:10.1006/nlme.2000.3976

28.

Miller

H. C.

(2013). The effects of initial self-control exertion and subsequent glucose consumption on search accuracy by dogs. Revista Argentina de Ciencias Del Comportamiento, 5(2), 21–29. Retrieved from http://www.revistas.unc.edu.ar/index.php/racc/article/view/5144

29.

Miller

H. C.

DeWall

C. N.

Pattison

Molet

Zentall

T. R.

(2012). Too dog tired to avoid danger: Self-control depletion in canines increases behavioral approach toward an aggressive threat. Psychonomic Bulletin & Review, 19, 535–540. doi:10.3758/s13423-012-0231-0

30.

Miller

H. C.

Pattison

K. F.

DeWall

C. N.

Rayburn-Reeves

Zentall

T. R.

(2010). Self-control without a “self”? Common self-control processes in humans and dogs. Psychological Science, 21, 534–538. doi:10.1177/0956797610364968

31.

Miller

H. C.

Pattison

K. F.

Laude

J. R.

Zentall

T. R.

(2015). Self-regulatory depletion in dogs: Insulin release is not necessary for the replenishment of persistence. Behavioural Processes, 110, 22–26. doi:10.1016/j.beproc.2014.09.030

32.

Molden

D. C.

Hui

C. M.

Scholer

A. A.

Meier

B. P.

Noreen

E. E.

D’Agostino

P. R.

Martin

(2012). Motivational versus metabolic effects of carbohydrates on self-control. Psychological Science, 23, 1137–1144. doi:10.1177/0956797612439069

33.

Muraven

(2010). Building self-control strength: Practicing self-control leads to improved self-control performance. Journal of Experimental Social Psychology, 46, 465–468. doi:10.1016/j.jesp.2009.12.011

34.

Muraven

Baumeister

R. F.

(2000). Self-regulation and depletion of limited resources: Does self-control resemble a muscle? Psychological Bulletin, 126, 247–259. doi:10.1037/0033-2909.126.2.247

35.

Muraven

Tice

D. M.

Baumeister

R. F.

(1998). Self-control as limited resource: Regulatory depletion patterns. Journal of Personality and Social Psychology, 74, 774–789. doi:10.1037/0022-3514.74.3.774

36.

Odendaal

J. S. J.

Meintjes

R. A.

(2003). Neurophysiological correlates of affiliative behaviour between humans and dogs. Veterinary Journal, 165, 296–301. doi:10.1016/S1090-0233(02)00237-X

37.

Orquin

J. L.

Kurzban

(2016). A meta-analysis of blood glucose effects on human decision making. Psychological Bulletin, 142, 546–567. doi:10.1037/bul0000035

38.

Peremans

Goethals

De Vos

Dobbeleir

Ham

Van Bree

. . . Audenaert

(2006). Serotonin transporter and dopamine transporter imaging in the canine brain. Nuclear Medicine and Biology, 33, 907–913. doi:10.1016/j.nucmedbio.2006.07.013

39.

Schmeichel

B. J.

Harmon-Jones

(2010). Exercising self-control increases approach motivation. Journal of Personality and Social Psychology, 99, 162–173. doi:10.1037/a0019797

40.

Segerstrom

S. C.

Nes

L. S.

(2007). Heart rate variability reflects self-regulatory strength, effort, and fatigue. Psychological Science, 18, 275–281. doi:10.1111/j.1467-9280.2007.01888.x

41.

Thayer

J. F.

Hansen

A. L.

Saus-Rose

Johnsen

B. H.

(2009). Heart rate variability, prefrontal neural function, and cognitive performance: The neurovisceral integration perspective on self-regulation, adaptation, and health. Annals of Behavioral Medicine, 37, 141–153. doi:10.1007/s12160-009-9101-z

42.

Tice

D. M.

Baumeister

R. F.

Shmueli

Muraven

(2007). Restoring the self: Positive affect helps improve self-regulation following ego depletion. Journal of Experimental Social Psychology, 43, 379–384. doi:10.1016/j.jesp.2006.05.007

43.

Tsurugizawa

Uematsu

Nakamura

Hasumura

Hirota

Kondoh

. . . Torii

(2009). Mechanisms of neural response to gastrointestinal nutritive stimuli: The gut-brain axis. Gastroenterology, 137, 262–273. doi:10.1053/j.gastro.2009.02.057

44.

Vohs

K. D.

Baumeister

R. F.

Schmeichel

B. J.

(2013). Motivation, personal beliefs, and limited resources all contribute to self-control. Journal of Experimental Social Psychology, 49, 184–188. doi:10.1016/j.jesp.2012.08.007

45.

Wright

H. F.

Mills

D. S.

Pollux

P. M. J.

(2012). Behavioural and physiological correlates of impulsivity in the domestic dog (Canis familiaris). Physiology & Behavior, 105, 676–682. doi:10.1016/j.physbeh.2011.09.019