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61 Pages·2016·0.84 MB·English

Florida State University Libraries
2016
Caffeine and Self-Control: Does Adenosine
Play a Role in Ego Depletion?
Heather M. Maranges
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FLORIDA STATE UNIVERSITY

COLLEGE OF ARTS AND SCIENCES

CAFFEINE AND SELF-CONTROL:
DOES ADENOSINE PLAY A ROLE IN EGO DEPLETION?

By

HEATHER M. MARANGES

A Thesis submitted to the
Department of Psychology
in partial fulfillment of the
requirements for the degree of
Master of Science

2016
Heather M. Maranges defended this thesis on May 4, 2016.
The members of the supervisory committee were:

Roy F. Baumeister
Professor Directing Thesis

James K. McNulty
Committee Member

Lisa A. Eckel
Committee Member

The Graduate School has verified and approved the above-named committee members, and
certifies that the thesis has been approved in accordance with university requirements.
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TABLE OF CONTENTS

List of Tables ................................................................................................................................. iv
Abstract ............................................................................................................................................v

INTRODUCTION ...........................................................................................................................1

THE PRESENT RESEARCH .......................................................................................................11

GENERAL DISCUSSION ............................................................................................................36

APPENDIX A: IRB APPROVAL ................................................................................................43

APPENDIX B: INFORMED CONSENT FORM .........................................................................47

References ......................................................................................................................................48

Biographical Sketch .......................................................................................................................55

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LIST OF TABLES

1 Study 1 Descriptive Statistics ..................................................................................................15

2 Anagram Performance in Study 2 ............................................................................................23

3 Cognitive Reflection Test Performance in Study 2 .................................................................26

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ABSTRACT

What biological processes underlie self-control, such that this adaptive skill differs among
people and appears to be functionally limited? The current research aims to answer this question
by proposing that adenosine, an inhibitory neurotransmitter that helps to link the rate of energy
expenditures to available energy resources in the brain, signals self-control depletion. Two
studies were conducted to test the adenosine hypothesis, taking advantage of caffeine’s ability to
block adenosine’s action. A first, correlational study furnished evidence for the hypothesis that
people who can benefit most from a boost in self-control (i.e., who have lower trait self-control
and higher demands for self-control at work) would consume and depend on caffeine to improve
their performance in domains which require self-control more than people with sufficient self-
control resources (i.e., who have higher self-control and lower demands for self-control at work).
A second, experimental study using a self-control depletion manipulation tested whether caffeine
directly improves self-control and counteracts ego depletion. However, Study 2 did not furnish
support for the adenosine hypothesis. Implications and future directions are discussed.
(174 words)
Keywords: Self-Control, Ego Depletion, Caffeine, Adenosine, Practice Effects

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INTRODUCTION
Self-control is the ability to override a prepotent response or competing action tendency
and replace it with a different one (Baumeister & Vohs, 2007; Muraven & Slessareva, 2003).
Some people have higher trait levels of self-control than others (Tangney, Boone, & Baumeister,
2004). Self-control also appears to be functionally limited: after using self-control during one
task, people find it more difficult to employ self-control during another task, a state known as
ego depletion (Baumeister et al., 1998; Muraven, Tice, & Baumeister, 1998; Schmeichel, 2007;
for meta-analysis, see Hagger, Wood, Stiff, & Chatzisarantis, 2010). Every day, people use self-
control to resist fattening foods, be polite in the face of rudeness, exercise, control their thoughts,
regulate their emotions, and concentrate on work. Further, better self-control leads to better
outcomes in academics, career, relationships, and health (Tangney, Baumeister, & Boone, 2004).
What is going on in the brain such that self-control, a process so important to humans’
success, might fail? The purpose of the present research was to test whether processes of
inhibition associated with the action of adenosine, a messenger molecule active in the central
nervous system (CNS), can account for individual differences in trait self-control and self-
control’s limited nature. The approach to testing these hypotheses took advantage of the
neurochemical profile of caffeine, a widely used drug which blocks adenosine from exerting its
effects. The following sections include an outline of the rationale for my adenosine hypothesis,
an explanation of how caffeine facilitates analysis of that hypothesis, the derivative caffeine
hypotheses, and tests of those hypotheses using correlational and empirical methods.
Self-Control, Depletion, and Glucose
Self-control (used interchangeably with self-regulation in this paper) is the ability to
override and alter thoughts, emotions, behavior, or competing action tendencies that are not
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consistent with short- or long-term goals (Baumeister & Vohs, 2007; Muraven & Slessareva,
2003). Trait (chronic) self-control varies among people and predicts a variety of outcomes,
including academics, occupational accomplishments, stability and satisfaction of relationships,
adjustment, mental and physical health, curbing prejudice, addiction, criminal and violent acts,
positive emotionality, and longevity (Baumeister, Heatherton, & Tice, 1994; Daly, Baumeister,
Delaney, & MacLachlan, 2014; Finkel, DeWall, Slotter, Oaten, & Foshee, 2009; Gottfredson &
Hirschi, 1990; Mischel, Shoda, & Peake, 1988; Moffitt et al., 2011; Muraven, 2008, 2010; Shoda,
Mischel, & Peake, 1990; Tangney, Boone, & Baumeister, 2004).
Occupational success, happiness, and healthy relationships reflect what people consider to
be a good life and depend upon people’s self-control (Tangney, Boone, & Baumeister, 2004).
People with higher self-control experience these outcomes to a greater extent than do people with
lower self-control, presumably because they are able to regulate their emotions, cognitions, and
behavior in pursuit of these goals on a daily basis. For example, self-control serves occupational
goals by helping people work productively, avoid distractions at work, and perform well in their
given field every day (Schmidt & Diestel, 2015). Likewise, the daily pursuit of happiness, which
requires downplaying negative feelings (e.g., Gailliot, Schmeichel, & Baumeister, 2006) and
promoting positive feelings, depends on self-regulation (Tice & Bratslavsky, 2000). Graceful
social interactions, which help to build relationships, are also associated with successful emotion
regulation (Lopes, Salovey, Côté, Beers, & Petty, 2005). Further, self-control promotes healthy
relationships by allowing people to reduce the effect of external stressors on their social
interactions (e.g., Neff & Buck, 2012). Accordingly, people with lower trait self-control may be
motivated to seek self-control support in general, to be productive at work, and to improve their
mood and friendliness as compared with people with higher self-control. One of the potential
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sources to which people may turn to improve self-control is caffeine, and this hypothesis will be
further discussed below.
State (situational) self-control levels can fluctuate. It has been well established that after
initial self-control use, people may become less motivated or less able to use self-control on
additional tasks (Baumeister et al., 1998; Muraven, Tice, & Baumeister, 1998; Schmeichel, 2007;
for meta-analysis, see Hagger, Wood, Stiff, & Chatzisarantis, 2010). This state in which people
cannot or do not successfully employ self-control is known as ego depletion (Baumeister,
Bratslavsky, Muraven, & Tice, 1998). The strength model suggests that self-control is like a
muscle, which depends on a limited resource and can become fatigued (Baumeister, Vohs, &
Tice, 2007).
The implication of ego depletion for people’s daily goal pursuit is that people who have
more tasks that require self-control may become depleted and be less able to work productively
toward their goals throughout the day. For example, some people work in environments that are
especially demanding of their self-control and they must resist impulses, ignore distractions, and
regulate their emotions (Schmidt & Diestel, 2015). For people with higher self-control demands
at work, job performance, mood, and sociability may suffer relative to people with lower self-
control demands at work because they are becoming more ego depleted. Accordingly, people with
more demanding work environments may be seek out support for their self-control in general, to
be productive at work, and to improve their mood and friendliness relative to people with lower
demands on their self-control at work. One potential source of support they may seek out is
caffeine, and the rationale for hypothesis will be reviewed below.
What biological processes account for the findings that some people become more
depleted than others and that self-control, a process so important to humans’ success, might fail at
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all? Glucose, a simple sugar that serves as the brain’s primary energy source, was one candidate
for the limited resource on which self-control relies. Indeed, in a set of eight studies, Gailliot and
colleagues (2007) found that using self-control (i.e., to control attention, override prejudice,
perform the Stroop task, or regulate emotions) can lead to decreases in blood glucose levels, that
lower blood glucose levels predict diminished performance on tasks that require self-control (i.e.,
the Stroop task or an unsolvable figure-tracing task), and that consuming new glucose can
counteract ego depletion effects. The rationale for Gailliot and colleagues’ study was that self-
control requires more metabolic resources than other, simpler mental processes and that glucose is
the brain’s primary metabolic resource.
That rationale is consistent with findings in cognitive neuroscience and biology. For
example, it has been established that self-control relies on relatively metabolically expensive
cortical (as opposed to sub-cortical) brain regions (Botvinick, Cohen, & Carter, 2004; Vilberg &
Rugg, 2008), particularly the prefrontal cortex (PFC) (for review, see Robinson, Schmeichel, &
Inzlicht, 2010; Aron, Robbins, & Poldrack, 2004; Miller & Cohen, 2001; Monsell, 2003). Further,
the energy used in the brain (in the form of adenosine triphosphate, ATP) comes from the
metabolism of glucose (Rich, 2003). Although Gailliot and colleagues’ theory was consistent with
biological theory, the project itself was criticized because blood glucose levels are different from
brain glucose levels and researchers were unable to replicate its findings (Kurzban, 2010; Lange
& Eggert, 2014). Criticisms of Gailliot et al.’s methods do highlight the importance of measuring
brain glucose, but they do not undermine the theory itself— that decreases in brain glucose
resulting from increased glucose metabolism may signal to the brain that it cannot sustain
continued self-control.

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