ABSTRACT

Frontal Cortical Asymmetry and Impulsive Aggression

Sarah Laurie Lake, M.A.

Thesis Chairperson: Matthew S. Stanford, Ph.D.

The present study uses individuals who display impulsive aggressive outbursts

and measures resting frontal cortical activity. Impulsive aggression (IA) is described as a

reactive or emotionally charged aggressive response characterized by a loss of behavioral

control. Previous physiological studies have found IAs have sensory and informational

processing deficits. Undergraduate volunteers were recruited for an 8min resting EEG

with 1min blocks of eyes open or closed. Age- and gender-matched controls reported no

aggressive outbursts and a score below 4 on the BDHI. Statistical differences were found

between IAs and controls in both the midfrontal [t(22) = 2.743, p < .01] and lateral

frontal [t(22) = 2.365, p < .05] regions, with IAs having more right resting activity than

controls. Due to the nature of IA as a trait in the current sample, this study lends evidence

towards resting frontal asymmetry as a marker for susceptibility to psychopathology.

Page bearing signatures is kept on file in the Graduate School.

Frontal Cortical Asymmetry and Impulsive Aggression

by

Sarah Laurie Lake, B.S.

A Thesis

Approved by the Department of Psychology and Neuroscience

___________________________________

Jaime L. Diaz-Granados, Ph.D., Chairperson

Submitted to the Graduate Faculty of

Baylor University in Partial Fulfillment of the

Requirements for the Degree

of

Master of Arts

Approved by the Thesis Committee

___________________________________

Matthew S. Stanford, Ph.D.

___________________________________

Sara L. Dolan, Ph.D.

___________________________________

Jon E. Singletary, Ph.D.

Accepted by the Graduate School

December 2011

___________________________________

J. Larry Lyon, Ph.D., Dean

Copyright © 2011 by Sarah Laurie Lake

All rights reserved

iii

TABLE OF CONTENTS

LIST OF FIGURES v

LIST OF TABLES vi

ACKNOWLEDGMENTS vii

CHAPTER ONE: Background and Significance 1

Behavioral Approach/Withdrawal 1

Frontal EEG Cortical Asymmetry 3

CHAPTER TWO: Methods 13

Background and Neuropsychological Measures 13

Physiological Measurement 16

Data Reduction and Analysis 17

CHAPTER THREE: Results 19

CHAPTER FOUR: Conclusions 24

REFERENCES 28

iv

LIST OF FIGURES

Figure 1: Resting activity difference score means 21

Figure 2: Resting activity difference score means with anger covaried 21

Figure 3: Resting activity difference score means with impulsivity covaried 22

v

LIST OF TABLES

Table 1: Means and standard deviations of self-report measures 20

vi

ACKNOWLEDGMENTS

This project would have been impossible without the direction and support of my

mentor, Dr. Matthew S. Stanford; chair, Dr. Jaime L. Diaz-Granados; committee

members Dr. Sara L. Dolan and Dr. Jon E. Singletary; as well as the remaining faculty

and graduate students in the Psychology and Neuroscience Department at Baylor

University. Their support, patience, and input were crucial to the understanding and

completion of this study.

Along with superb faculty support, many graduate students have assisted in data

collection and analysis. Thanks to Baylor colleagues Nathaniel Anderson, Robyn

Baldridge, Megan Johnson Shen, Jordan LaBouff, and Joanna Price for their assistance,

grace, and compassion. Finally, a special thanks to Nicholas Saltarelli and my family,

Liz, Wally, Scott, and Sandra for their everlasting support and inspiration.

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CHAPTER ONE

Background and Significance

Behavioral Approach/Withdrawal

The abundance of previous research on affective traits indicates the importance of

individual personality on behavior. Both positive and negative affective traits have been

studied, but the distinction between what constitutes positive or negative affect has been a

source of constant debate (Hagemann, Naumann, Thayer, & Bartussek, 2002), along with

the specific brain mechanisms involved. Research generally focuses on either particular

affective traits that moderate brain mechanisms (e.g. Ekman, 1992) or the underlying

systems that assist in the affective experience and mediate brain mechanisms (e.g. Carver

& White, 1994; Coan & Allen, 2004).

Carver and Harmon-Jones (2009) define affect as “a hedonic experience, a sense

of valence, a subjective sense of positivity or negativity arising from an event,” (p. 183).

Thus, those experiencing positive affect would sense a feeling of satisfaction, and those

experiencing negative affect would feel displeasure. Preceding affect is valence, or the

event that elicits the emotion (Carver & Harmon-Jones, 2009; Davidson, 1998). Most

recently, this valence has been viewed in terms of motivational systems that trigger affect

(Alloy et al., 2009a; Carver & Harmon-Jones, 2009; Coan & Allen, 2003; Harmon-Jones,

2003a; Harmon-Jones, 2003b).

Originally, three types of motivational direction were thought to exist: the

behavioral approach system (BAS), the behavioral inhibition system (BIS), and the fight-

flight-freeze system (FFFS) (Gray, 1972; 1987; 1990). The BAS was hypothesized to

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relate to positive emotion, BIS was thought to resolve goal conflicts, and FFFS system

was believed to be sensitive to all aversive stimuli (Alloy et al., 2009b; Gray, 1990; Gray

& McNaughton, 2000). The approach motivation system (BAS) organizes behaviors

involved in approaching desired rewards (Carver & White, 1994; Davidson, Ekman,

Saron, Senulis, & Friesen, 1990). This system is the pathway for goal-directed

movement, nonpunishment, and escape of punishment (Carver & White, 1994). That is,

the approach motivation system is used for behavior that is optimal for pursuit and

obtainment of rewards. The BIS is the aversive motivational system, organizing

behaviors involved in avoiding unfavorable outcomes (Carver & White, 1994). This

system is the pathway for behavior avoiding punishment as well as resolving goal

conflicts (Alloy et al., 2009b).

Originally, Carver and White (1994) developed the Behavioral Inhibition

System/Behavioral Activation System Scale (BIS/BAS Scale) in reference to positive and

negative affective valence. In other words, the Behavioral Inhibition System was thought

to involve strictly negative affect whereas the Behavioral Activation System involved

behaviors pertaining to positive affect. Thus, the BIS/BAS Scale was intended to

measure valenced affect. However, Harmon-Jones and colleagues (Harmon-Jones &

Allen, 1998; Harmon-Jones & Sigelman, 2001) demonstrated that the Behavioral

Activation System was activated during anger, an affect previously thought to be

negatively valenced, showing that simply affective valence does not fully explain

behavioral motivation tendencies.

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Frontal EEG Cortical Asymmetry

Studies using frontal resting electroencephalogram (EEG) activity either 1)

examine asymmetry as an individual difference related to traits or trait-like measures; 2)

investigate asymmetry as an individual difference that can predict state-related emotional

responses; 3) examine asymmetry as an individual difference related to psychopathology;

or 4) investigate state-related changes in asymmetry as a function of state changes in

emotion (Coan & Allen, 2004). The first three studies focus on trait-like properties,

assuming frontal EEG activity is an inherent biological characteristic specific to the

individual. The fourth presumes emotional state changes in asymmetry are observable

and recordable. Differences in frontal asymmetry have been shown in a variety of

research, such as cognitive tasks (Davidson, Chapman, Chapman, & Henriques, 1990),

autism (Orekhova, Stroganova, Prokofiev, Nygren, Gillberg, & Elam, 2009), eating

disorders (Silva, Pizzagalli, Larson, Jackson, & Davidson, 2002), memory encoding

(Floel et al., 2004), manic or depressive symptomology (Harmon-Jones et al., 2002;

Peterson & Harmon-Jones, 2009), and trait anger (e.g. Harmon-Jones, 2007; Harmon-

Jones & Allen, 1998; Harmon-Jones, Gable, & Peterson, 2009; Harmon-Jones &

Sigelman, 2001; Harmon-Jones, Sigelman, Bohlig, & Harmon Jones, 2003). The

majority of previous literature focuses on individual personality traits with frontal

asymmetry, including anger (Carver & Harmon-Jones, 2009; Harmon-Jones, 2007),

disgust and happiness (Davidson et al., 1990b), positive and negative affective situations

(Gable & Harmon-Jones, 2008), stress (Verona, Sadeh, & Curtin, 2009), and aggression

(Verona et al., 2009).

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The majority of research agrees that resting frontal cortical activity is indicative of

affective style in terms of general approach or withdrawal tendencies (Coan & Allen,

2004; Coan, Allen, & McKnight, 2006; Davidson, 1993; Davidson 1998a,b). This

resulted in Davidson’s (1993; 1998a,b) proposed model of approach/withdrawal

motivational in regards to resting EEG activity, with left frontal activity—either as a state

or trait—indicating a predisposition to approach a stimulus, and right frontal activity

relating to withdrawing from a stimulus. Theories abound as to the importance of frontal

asymmetry in regards to association with state or trait effects (Coan et al., 2006), but

researchers agree emotion is the main factor. Most of the replicated research centers on

trait-dependent hypotheses in positive and negative affect research (Gable & Harmon-

Jones, 2008; Tomarken, Davidson, Wheeler, & Doss, 1992). Generally, it is believed that

half of the variance found during frontal cortical activity is due to state influences

whereas the residual half is due to trait influences (Hagemann et al., 2002). It is

important to note that frontal EEG activity refers to a tonic recording of frontal EEG

processes, not a change in activity due to provocation (“activation”) (Coan & Allen,

2004).

Accepting the presupposition that frontal asymmetry is indicative of an

individual’s tendency to use approach- or withdrawal-related tendencies (Coan et al.,

2006) and related to affective trait research, Harmon-Jones (2003b) proposed three

models of frontal asymmetry in response to the research thus far. The valence model

hypothesizes that the left frontal cortical region is involved with the expression of

positive affect, whereas the right frontal region is involved in the experience of negative

affect. The motivational direction model states that asymmetry in the frontal lobe is due

5

to motivational direction and supposes that left frontal cortical region is involved with

approach-related motivational directions, whereas the right region is involved with

withdrawal-related motivational directions. Lastly, the valenced motivation model posits

that there is an interaction between motivational direction and affect. In this model, the

left frontal cortical region is theorized to involve the expression of positive, approach-

motivated affect and the right is concerned with the experience of negative, withdrawal-

motivated emotion. However, Harmon-Jones (2003b) notes that not all emotions act in

this valenced motivational way, as anger is negative in valence but evokes left frontal

cortical region activity (e.g., Carver & Jones, 2009; Harmon-Jones, 2004a; Harmon-

Jones, 2004b). Much of the previous research has confounded valence with motivational

direction, thus research that separates these is necessary.

In line with Gray’s (1994) biological basis, Davidson (1998a,b) proposed that

both withdrawal and approach motivation are represented in two separate neural circuits.

The withdrawal system aids withdrawal from aversive stimuli and produces negative

affect, whereas the approach system facilitates appetitive behavior and generates positive

affect. Although interaction occurs between both systems, they have been conceptualized

as independent from each other (Davidson, 1998b). Davidson and colleagues (Henriques

& Davidson, 1990; Henriques & Davidson, 1991) have suggested that the levels of

activation in the brain’s circuitry influence individual differences, and those differences

are the contributing cause of affective style. With regard to depression, it was suggested

that individual differences in prefrontal cortical activity bias a person’s affective style and

subsequently modulate their vulnerability to develop depression (Davidson 1998a,b).

Davidson (1998b) notes that his model is not intended to be a model of depression or

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psychopathology, but as a model of affective style that related to vulnerability to

psychopathology and abnormality of emotion.

Biological Basis

Behavioral motivation has been tied to the septo-hippocampal system and its

associated structures, including the septal region, fimbria, fornix, alveus, dentate gyrus,

entorhinal cortex, CA1, CA3, thalamus, hippocampus, amygdala, and hypothalamus

(Gray, 1987). The septo-hippocampal system is related to the medial prefrontal cortex,

which also has ties to the limbic system and is critical for motivation (Miller & Cohen,

2001). Both withdrawal and approach systems are comprised of the dorsolateral

prefrontal cortex, the ventral medial prefrontal cortex, nucleus accumbens, basal ganglia,

amygdala, anterior temporal cortex, parietal cortex, and the hypothalamus (Davidson,

1998b). The amygdala has been most specifically related to withdrawal motivation

(Davidson 1998a,b). Monoaminergic afferents that are sent from the brainstem to the

frontal lobe have been hypothesized to be a part of the behavioral inhibition system

(Gray, 1987). Two possible routes of inhibition have been proposed: inhibition of motor

projections from the subiculum to the cingulate cortex; or inhibition of fixed action

patterns in the pathway from the lateral septal area descending to the hypothalamus

(Gray, 1987). These pathways are hypothesized to allow a person to use inhibition with

their motor actions if necessary.

In contrast, the catecholamine-related reward center has been shown to be a vital

part in the behavioral approach system (McClelland, Davidson, Saron, & Floor, 1980).

The behavioral approach system has been linked to the ascending mesolimbic

dopaminergic fibers that mediate the effects of reward (Gray, 1987). When an individual

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performs an act that is rewarding, such as reaching a goal, the dopaminergic pathways

inhibit the rewarded instrumental behavioral through projection to the ventral striatum.

An increase in dopamine then leads to greater reward-seeking behavior to maintain the

satisfying feeling dopamine produces. The nucleus accumbens, most specifically the shell

region, has been particularly indicated in the approach motivation system (Davidson,

1998a,b).

Apart from the anatomy of the frontal lobe and behavioral motivation-related

structures, not much is known about the neural substrates that cause frontal lobe cortical

asymmetry. The frontal lobe’s relation to behavioral inhibition and cortical activity was

discovered serendipitously, thus research has focused more on the outcome and less on

the underlying factors that are the source of frontal lobe asymmetry (Pizzagalli,

Sherwood, Henriques, & Davidson, 2005). No literature has been found attempting to

relate the cause of frontal lobe asymmetry to date.

Anger

Anger is characterized as an emotion brought on by frustration in regards to

expectations (Siegel, 1986). Usually, anger is regarded as a negatively valenced emotion

(Harmon-Jones, 2003b). Anger could be used in defensive situations (Tomarken &

Davidson, 1994) and consequently be regarded as positive, but generally, anger is viewed

as having negative valence (Buss & Perry, 1992).

Harmon-Jones and Allen (1998) used the Buss Perry Aggression Questionnaire

(BPAQ: Buss & Perry, 1992) to assess trait anger while recording resting frontal activity

in adolescents. High levels of anger related to increased left cortical activity and

decreased right activity, specifically in frontal regions. This initiated a movement of

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research on frontal asymmetry and anger, as the left frontal cortical region had previously

been thought to be strictly positively valenced and approach-motivated. Harmon-Jones

(2004a) replicated these results, showing that at mid-frontal and lateral-frontal sites, trait

anger related to greater left frontal cortical activity. It was postulated that the individuals

perceived anger as a positive trait and thus cortical activity reflected this subjectivity. To

test this conjecture, the Attitudes Towards Anger scale (ATA: Harmon-Jones, 2004a) was

comprised and given to participants. Although ATA was valid and reliable, a positive

attitude towards anger did not correlate with left frontal cortical activity. It was

concluded that the relationship between trait anger and left frontal cortical activity was

not due to a positive attitude toward anger, but rather an approach-motivated direction

(Harmon-Jones, 2004a; Harmon-Jones, 2004b). Harmon-Jones and colleagues (2003)

found that during an angering situation, participants who believed they had an

opportunity to remedy the situation had increased left frontal activity. Thus, angry

feelings may not lead to increased left frontal activity per se, but the chance to rectify

them may.

Salience of personal relevance and approach-related behavior was studied using

frontal cortical activity (Harmon-Jones, Lueck, Fearn, & Harmon-Jones, 2006). The

researchers recorded EEGs while manipulating the salience of prejudice by using

affective pictures. Approach-related manipulation was also used, as individuals were

asked to write an essay on why they believed racism was wrong. During prejudice-

evoking pictures along with the expectation of approach-related behavior, relative left

frontal activity was increased along with anger. Expanding this work, Harmon-Jones

(2007) hypothesized that individuals higher on trait anger would show greater left frontal

9

cortical activity in response to anger-evoking affective pictures. Using the BPAQ (Buss

& Perry, 1992), individuals who scored highly on self-reported anger demonstrated

greater relative frontal cortical activity to pictures eliciting anger than pictures intended to

show fear, disgust, positive, or neutral reactions (Harmon-Jones, 2007).

Frontal asymmetry was found to be susceptible to manipulation through hand

contractions as well (Harmon-Jones, 2006). Right-handed participants were asked to

squeeze a rubber ball in one hand for two 45-second baseline periods before testing and

then while watching a 2.5-minute computer broadcast in which they were asked to

squeeze continuously. Participants then completed a survey of emotional reactions to the

broadcast, along with a measure of approach-related affect. It was found that hand

contractions produced cortical differences at mid-frontal regions, with right hand

contractions causing greater relative left frontal activity. It was hypothesized that

because self-reported approach affect was the only trait that correlated with frontal

asymmetry (sadness, guilt, happiness, and anger did not), the manipulation of brain

activity influenced the affective experience.

After effectively demonstrating frontal cortical activity manipulation, Peterson,

Shackman, and Harmon-Jones (2009) used hand contractions and a behavioral measure

of aggression by number of administered noise bursts after provocation during frontal

asymmetry recordings. Greater left frontal cortical activity related to greater behavioral

aggression. They concluded these results demonstrated that not only does the prefrontal

cortex inhibit aggressive behavior, but also greater activity of the left prefrontal region is

involved in causing situational behavioral aggression.

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Aggression

Anger has been shown to closely relate to aggression (Buss & Perry, 1992;

Jensen-Campbell, Knack, Waldrip, & Campbell, 2007), and a negative consequence of

anger is aggression (Berkowitz, 2000). As anger has been demonstrated as an approach-

motivated behavior, Harmon-Jones (2003a) found that when using the BIS/BAS Scales

(Carver & White, 1994), trait aggression was related negatively to BIS and positively to

BAS. He concluded, “These results are consistent with the hypothesis that individual

differences in physical aggression are positively associated with individual differences in

approach motivation” (p. 1002, Harmon-Jones, 2003a). It was also shown that BIS did

not negatively correlate with anger, suggesting that the BIS inhibits physical aggressive

behaviors only. Indeed, Coan and Allen (2003) also found that high levels of trait BAS

sensitivity are associated with a higher likelihood of aggressive behavior.

Harmon-Jones and Sigelman (2001) purposefully offended participants and then

asked them to assign an aversive-tasting drink to the insulter. After the insult, the

tendency among high left frontal cortically activated individuals was to designate a more

bitter taste to the offender, in which the researchers defined as an aggressive act. It was

hypothesized that anger and the behavioral approach system were associated with

offensive aggression only (Harmon-Jones & Sigelman, 2001).

Impulsive aggression. Impulsive aggression involves unplanned, immediate

responses to minimal provocation (Stanford, Greve, & Gerstle, 1997). Impulsive

aggression is considered reactive and emotional, accompanied by poor regulation of

physiological arousal as well as loss of behavioral control (Barratt, 1991; Houston,

Stanford, Villemarette-Pittman, Conklin, & Helfritz, 2003). Neuropsychological findings

11

have demonstrated that impulsive aggression is correlated with executive dysfunction

(Chambers, 2010), including a lack of impulse control (Stanford et al., 1997) and deficits

in verbal strategic processing (Villemarette-Pittman, Stanford, & Greve, 2002).

Psychophysiological results show that impulsive aggressive individuals have

reduced EEG P3 amplitude (Barratt, Stanford, Kent, & Felthous, 1997; Mathias &

Stanford, 1999) and increased P3 latency (Mathias & Stanford, 1999), demonstrating

sensory and informational processing deficits. The P3 is a component of the event-

related potential (ERP) wave that occurs approximately 300ms after the presentation of a

low probability stimulus. Impulsive aggressors also have increased latency and reduced

amplitude on the late positive potential, a measure of emotional processing (Conklin &

Stanford, 2002), indicating that impulsive aggressors have difficulty processing

emotional stimuli. Individuals identified as impulsively aggressive also have a higher

heart rate during a challenging task than nonaggressive controls (Pitts, 1997).

Relative left frontal activity related to an experience of experimentally

manipulated anger during an approach-motivated setting only (Harmon-Jones, 2003b).

Impulsive aggressors have problems with strategic processing and executive dysfunction

(Stanford et al., 1997); they have a tendency to view situations in an approach-motivated

context, an immediate means to an end. In a positron emission tomography study using

impulsive murderers compared to predatory murderers, impulsive murderers had lower

prefrontal function during a continuous performance task (Raine, Meloy, Bihrle,

Stoddard, LaCasse, & Buchsbaum, 1998).

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Hypotheses

Because prefrontal cortical dysfunction is associated with impulsive aggressive

behavior (Hirono, Mega, Dinov, Mishkin, & Cummings, 2000; Meyer-Lindenberg et al.,

2006), it was predicted that impulsive aggressors would have increased left prefrontal

activity at both mid-frontal and lateral-frontal cortical regions. Because aggression and

anger are related personality traits (Jensen-Campbell et al., 2007) and both correlate with

executive control functions such as behavioral inhibition, it was also hypothesized that

higher left prefrontal cortical activity would be positively correlated to the BAS Scale

(Carver & White, 1994).

13

CHAPTER TWO

Research Design and Methods

Background and Neuropsychological Measures

Inclusion/Exclusion Criteria

Demographic and background questionnaire. This questionnaire solicited

information about participants’ age, gender, year in school, ethnicity, first language, and

medical history including previous major head injuries and current use of psychoactive

medications.

Participant Selection

Individuals completed initial measures to determine eligibility for participation in

psychophysiological measures. The Impulsive Aggression Quick Screen (IA-QS:

Stanford, Greve, & Dickens, 1995) was the determinant for categorization into groups.

To be classified as impulsively aggressive, an individual must meet four criteria: 1)

Identifying several episodes of impulsive aggression with loss of behavioral control in the

past six months; 2) The aggressive act was disproportionate to the provocation or

preceding event; 3) At least two impulsive aggressive acts occurred during the previous

30 days; and 4) A score 8 or higher on the Irritability subscale of the Buss-Durkee

Hostility Inventory. Age- and gender-matched controls did not report any episodes of

aggression with loss of behavioral control in the previous six months. Along with an

absence of an aggressive history, all controls had a score of 3 or less on the Irritability

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subscale of the Buss-Durkee Hostility Inventory. In addition, females were matched in

regards to menstrual stages, with EEGs recorded during the late luteal phase (days 21-28

of cycle) (Accortt & Allen, 2006; Hwan, Wu, Chen, Yeh, & Hsieh, 2009).

Trait Measures.

Impulsive Aggression Quick Screen. The IA-QS (Stanford et al., 1995) is used to

classify an individual as predominately impulsively aggressive. This measure uses DSM-

IV-TR criteria for Intermittent Explosive Disorder combined with the Irritability subscale

from the Buss-Durkee Hostility Inventory (BDHI; Buss & Durkee, 1957). The IA-QS

was designed to assess a person’s aggressive behavior over the previous six months.

Lifetime History of Aggression Questionnaire. The Lifetime History of

Aggression Questionnaire (LHA; Coccaro, Berman, & Kavoussi, 1997) is used to assess

the extent of aggressive history of the participant. Participants were asked to rate the

frequency of eleven antisocial behaviors since the age of thirteen such as “How many

times would you say you got into physical fights with other people” to produce three

subscales: aggression, self-directed aggression, and antisocial behavior. A total score

indicates the level of history with a higher score indicating a more extensive aggressive

history.

Barratt Impulsiveness Scale. The BIS-11 (Patton, Stanford, & Barratt, 1995) is a

self-report measure that assesses general impulsiveness and produces six first-order

factors (attention, motor, self-control, cognitive complexity, perseverance, and cognitive

instability) and three second-order subscales (attentional, motor, and non-planning).

15

Items such as “I do things without thinking” and “I am self controlled” are scored on a

four-point Likert scale with 1 = Rarely/Never and 4 = Almost Always/Always. A total

impulsiveness score is acquired by summing the 30 items with higher total scores

representing more general impulsiveness.

Buss-Perry Aggression Questionnaire. The BPAQ (Buss & Perry, 1992) is a 29-

item self-report measure that measures trait aggression. Participants answered questions

like “Once in a while I can’t control the urge to strike another person” on a five-point

scale with 1 = Extremely uncharacteristic of me and 5 = Extremely characteristic of me,

with four subscales measuring individual components of aggression: physical aggression,

verbal aggression, anger, and hostility.

Alcohol Use Disorders Identification Test. The AUDIT (Babor, de la Fuente,

Saunders, & Grant, 1989) is a short, 10-item questionnaire intended to assess quantitative

drinking behavior, frequency of consumption, and alcohol-related problems. The first

eight items, such as “How many standard drinks containing alcohol do you have on a

typical day when drinking?” are rated as: 0 = Never, 1 = Monthly or Less, 2 = Two to

Four Times a Month, 3 = Two or Three Times a Week, and 4 = Four or More Times a

Week. The last two questions, “Have you or someone else been injured as a result of

your drinking” and “Has a relative, friend, doctor, or other health worker been concerned

about your drinking or suggest you cut down?” are rated as: 0 = No, 1 = Yes but Not in

the Last Year, and 2 = Yes During the Last Year. A total score is calculated by summing

the responses, with higher scores indicating a higher degree of alcohol usage.

16

Drug Abuse Screening Test. The DAST-20 (Skinner, 1982) is a short self-report

measure to measure the presence and severity of drug use in the previous year, intended

for use in clinical and research settings. This 20-item yes-or-no test with items like

“Have you abused prescription drugs?” can be summed by counting all “yes” responses,

with higher scores indicating more drug-related problems.

Behavioral Inhibition Scale/Behavioral Activation Scale. The BIS/BAS Scale

(Carver & White, 1994) measure individuals’ tendency to use either the behavioral

approach system (BAS) or the behavioral inhibition system (BIS). The BAS is a system

that regulates approach motivation in response to goals such that a person will attempt to

attain reward by moving towards them. The BAS Scale measures energetic pursuit of

rewards and positive emotional reactivity to rewarding events. The BIS is a system that

regulates withdrawal motivation in response to fear. The BIS Scale measures self-

perceived proneness to anxiety in the presence of threat cues. The BIS/BAS Scale is

comprised of four subscale scores (BAS Drive, BAS Fun Seeking, BAS Reward

Responsiveness, and BIS) with 24 self-report items rating agreement on a 4-point scale,

including items like “I have very few fears compared to my friends” and “When I want

something I usually go all-out to get it.”

Physiological Measurement

Resting EEG

Psychological recordings were measured in the evening 4:00PM-8:00PM) to

control for diurnal scalp variations (Peterson & Harmon-Jones, 2009). After giving

informed consent, participants’ scalps were prepared with rubbing alcohol and a slightly

17

abrasive gel (NuPrep) to increase scalp conduction. Then, heads were fitted with a

Neuroscan Quick-Cap with 64 tin electrodes (International 10-20 system) with standard

and intermediate positions. To allow for removal of data contaminated by the eye and

facilitate differentiation of artifact, four electrodes around the participant’s eye will be

used to record blinks and movement. One electrode was placed on each mastoid for data

referencing. Impedance for each electrode maintained at less than 5 k!. EEGs will be

digitized at a sampling rate of 1,000 samples per second and amplified by SYNAMPS2

amplifiers (Compumedics Neuroscan, Charlotte, NC). A bandpass filter was set at 0.1 Hz

to 35 Hz to separate out unnecessary frequencies. Participants were seated in a padded

chair in a radio frequency anechoic chamber and a resting EEG was recorded. The EEG

lasted for eight minutes with one-minute blocks of eyes open or closed in one of two

counterbalanced orders (OCCOCOOC or COOCOCCO) and a 15-second buffer between

blocks for participants to switch conditions.

Data Reduction and Analysis

For each individual, a spatial filter was used to filter out eyeblinks, which uses an

average blink to correct electrodes that were affected by the blinks. Data with excessive

artifact due to participant movement were rejected and not included in data reduction.

Due to the ambiguity of “frontal region” (Tomarken & Zald, 2009), the midfrontal

cortical region was examined comparing F3 and F4, whereas the lateral frontal region

was examined comparing F7 and F8. Average alpha powers at each site of interest were

transformed using a natural log. All artifact-free data were analyzed with a fast Fourier

transformation (FFT) with a Hamming window of 1 second and 50% overlap similar to

previous research (e.g. Coan & Allen, 2003; Harmon-Jones et al., 2004; Schmidt, Fox,

18

Perez-Edgar, & Hamer, 2009). Each participant’s hemispheric asymmetry was calculated

by region of interest (ln[right] – ln[left]), producing a hemispheric index similar to

previous research (e.g. Coan & Allen, 2003; Harmon-Jones, Vaughn-Scott, Mohr,

Sigelman, & Harmon-Jones, 2004). Because alpha activity correlates inversely with

cortical activity (Lindsle & Wicke, 1974), higher asymmetry index scores are indicative

of increased left cortical activity.

19

CHAPTER THREE

Results

Although N = 28 participants were tested, four participants classified as Impulsive

Aggressive were not included in analyses. Two participants were excluded due to lack of

verbal reporting of physical aggression during the Lifetime History of Aggression

Questionnaire interview, one participant had a metal plate in his face, and one participant

disclosed a head injury during conversation that was not reported on the prescreen

survey. Thus, a total of N = 24 participants were used in the statistical analyses. There

were no differences in age [t(22) = -.086, ns] between the Impulsive Aggressive group (n

= 10) and controls (n = 14).

Comparisons of the two groups showed significant differences on the BIS-11

Attentional subscale [t(22) = -6.003, p = .000], BIS-11 Total [t(22) = -3.297, p < .01], all

subscales on the BPAQ [Physical Aggression t(22) = -9.571, p = .000; Verbal

Aggression t(22) = -4.441, p = .000; Anger t(22) = -7.897, p = .000; Hostility t(22) = -

5.420, p = .000], and all subscales on the LHA [Aggression t(22) = -9.260, p = .000; Self-

Directed Aggression t(22) = -4.414, p = .000; Consequences and Antisocial Behavior

t(22) = -6.318, p = .000; Total t(22) = -11.066, p = .000]. There were clear statistical

differences between Impulsive Aggressors and controls on all aggression and anger self-

report measures; means and standard deviations are reported on Table 1.

20

Table 1

Means and Standard Deviations of Self-Report Measures

Control Group IA Group

Measure M SD M SD t p

BIS-11

Attentional 13.77 3.27 21.60 2.95 -5.93 .000

Motor 21.85 3.76 24.00 4.47 -1.26 ns

Nonplanning 21.15 7.52 25.60 4.43 -1.66 ns

Total 56.77 11.66 71.20 8.46 -3.30 .000

BPAQ

Physical Aggression 14.00 4.97 34.80 4.78 -10.12 .000

Verbal Aggression 11.08 3.04 19.10 4.23 -5.30 .000

Anger 10.46 3.38 24.40 4.90 -8.08 .000

Hostility 14.15 5.57 26.30 8.18 -4.24 .000

Total 49.69 14.62 104.60 16.76 -8.38 .000

AUDIT 0.71 1.49 2.20 2.49 -1.83 ns

DAST-20 1.08 1.94 3.80 3.58 -2.17 .049

BIS/BAS

Behavioral Inhibition 15.08 2.96 13.50 3.57 1.16 ns

BAS Reward 8.31 2.36 7.80 2.25 0.52 ns

BAS Drive 9.15 1.95 8.60 1.35 0.77 ns

BAS Fun Seeking 8.69 1.97 6.40 2.37 2.53 .019

LHA

Aggression 3.46 2.30 14.40 3.37 -9.26 .000

Self-Directed Aggression 0.31 0.86 2.70 1.70 -4.41 .000

Consequences/Antisocial 0.46 0.78 4.00 1.83 -6.32 .000

Total 4.23 3.06 21.30 4.35 -11.07 .000

Note. Scales are as follows: Barratt Impulsiveness Scale-11 (BIS-11: Patton et al., 1995);

Buss-Perry Aggression Questionnaire (BPAQ: Buss & Perry, 1992); Alcohol Use

Disorders Identification Test (AUDIT: Babor et al., 1989); Drug Abuse Screening Test

(DAST-20: Skinner, 1982); Behavioral Inhibition/Activation Scale (BIS/BAS: Carver &

White, 1994); Lifetime History of Aggression (LHA: Coccaro et al., 1997).

Regarding hemispheric asymmetry, statistical differences were found between

Impulsive Aggressors and controls in both the midfrontal [t(22) = 2.743, p < .01] and

lateral frontal [t(22) = 2.365, p < .05] locations. Examining the means of hemispheric

asymmetry indexes, Impulsive Aggressors had lower asymmetry indexes (midfrontal M =

-.0424, SD = .085; lateral frontal M = -.1158, SD = .228) and thus more right activity

during a resting state than controls (midfrontal M = .0630, SD = .098; lateral frontal M =

.0508, SD = .114) (Figure 1).

21

Figure 1. Resting activity difference score means; midfrontal t(22) = 2.743, p < .01;

lateral frontal t(22) = 2.365, p < .05.

Because previous research has confounded anger with “aggression,” anger and

impulsivity were covaried out of the statistical analyses. After controlling for anger using

the BPAQ Anger subscale, significant differences were found between Impulsive

Aggressors and controls at both sites as well [midfrontal F(2) = 3.859, p < .05; lateral

frontal F(2) = 4.992, p < .02, see Figure 2].

Figure 2. Resting activity difference score means with anger covaried; Buss-Perry

Aggression Questionnaire (BPAQ: Buss & Perry, 1992) Anger subscale as anger

covariate; midfrontal F(2) = 3.859, p < .05; lateral frontal F(2) = 4.992, p < .02.

22

Thus there are still significant physiological differences between Impulsive

Aggressors and controls even after controlling for anger. After controlling for self-

reported impulsivity using the BIS-11 Total, both hemispheric indexes were statistically

different between groups as well [midfrontal F(2) = 4.588, p < .05; lateral frontal F(2) =

3.510, p < .05, see Figure 3]. These results demonstrate physiological differences in

frontal hemispheric activity at a resting state even after controlling for anger and

impulsivity, showing clear biological differences between Impulsive Aggressors and

controls.

Figure 3. Resting activity difference score means with impulsivity covaried; Barratt

Impulsiveness Scale Version 11 (Patton et al., 1995) Total score as impulsivity covariate;

midfrontal F(2) = 4.588, p < .05, lateral frontal F(2) = 3.510, p < .05.

When looking at behavioral motivation, however, results were not statistically

different between Impulsive Aggressors and controls for three of the four subscales of the

BIS/BAS [Behavioral Inhibition t(22) = 1.264, ns; BAS Reward t(22) = .294, ns; BAS

Drive t(22) = .586, ns]. For BAS Seeking, results were statistically significant [t(22) =

2.288, p < .05], with controls scoring higher on the subscale (M = 8.43, SD = 2.138) than

Impulsive Aggressors (M = 6.22, SD = 2.438), and was positively correlated with the

23

hemispheric index at midfrontal sites (r = .523, p < .01) suggesting that controls engaged

in more reward-seeking behavior than Impulsive Aggressors, and that higher BAS

Seeking scores were related to more left frontal activity at a resting state. This positive

correlation disappeared when all three BAS subscales were collapsed (r = .237, ns).

24

CHAPTER FOUR

Conclusions

Contrary to hypotheses, results indicated that Impulsive Aggressors had more

right frontal cortical activity than controls. This is the opposite of Harmon-Jones and

colleagues (Harmon-Jones, 2003a,b,2004a; Harmon-Jones & Sigelman, 2001) with their

research on anger. Harmon-Jones (2004a) used the Anger subscale of the Buss Perry

Aggression Questionnaire and found that higher scores on related to more left frontal

EEG activity. Clear groups of controls and Impulsive Aggressors were used in the

current study and BPAQ Anger was covaried out, suggesting trait anger may not be

approach motivated in an Impulsive Aggressive sample. Furthermore, there was a

positive correlation between higher left frontal EEG activity and the Behavioral

Activation System scores on the Fun-Seeking subscale, indicating controls were related

to higher scores of self-reported approach motivational style. This is congruent with

Harmon-Jones’ (2004a) results, showing that left frontal EEG activity at a resting state is

related to higher approach motivation.

Although left hemispheric activity is usually indicative of positive affect, it was

hypothesized that Impulsive Aggressors would have greater left frontal cortical activity

due to using more motivational approach. Because they had greater right frontal cortical

activity, it was concluded that Impulsive Aggressors tend to use more withdrawal

motivation. Delving further into the literature, previous research has found that stimuli

intended to elicit approach motivation produced greater left frontal activity in babies

(Davidson & Fox, 1982) and adults (Coan, Allen, & Harmon-Jones, 2001; Ekman,

25

Davidson, & Friesen, 1990). Complementary, disgust films used as stimuli intended to

elicit withdrawal motivation produced greater right frontal activity in adults (Davidson et

al., 1990). This research focuses on laboratory stimuli to produce the motivational

direction and does not mention the properties of individual brain differences as biological

traits.

In fact, the studies in which right hemispheric activity is dominant show clear

similarities in regards to psychopathology and abnormality in emotional processing.

Besides being linked to previous diagnoses of depression (Henriques & Davidson, 1990),

current clinical diagnoses of depression (Henriques & Davidson, 1991), self-reported

measures of depression (Schaffer, Davidson, & Saron, 1983), and eating disorders (Silva

et al., 2002) greater relative right frontal activity at a resting state was found to relate to

social inhibition and lower scores on measures of social competency (Fox et al., 1995).

The current study may show increased right frontal asymmetry as a marker of

psychopathology due to the sample’s trait-like impulsive aggressive behavior (Davidson,

1998a,b). Although a university sample was used, previous studies have shown clear

psychopathology in Impulsive Aggressors in a college sample (Helfritz & Stanford,

2006).

A biological basis of right frontal EEG activity has been hypothesized to be due to

high cerebrospinal fluid concentrations of corticotropin-releasing hormone (CRH) (Kalin,

Shelton, & Davidson, 2000). In rhesus monkeys, Kalin and colleagues (2000) found

right frontal EEG activity was related to high CRH concentrations, thus higher levels of

stress responses. Although this was an animal model, it lends evidence that resting right

cortical activity is related to an abnormal biological predisposition.

26

Even Gray (1994) admits that the definitions of the systems underlying

withdrawal motivation are indistinct. The hypothetical systems for withdrawal

motivation are thought to cause withdrawal from aversive stimuli, whereas those that

underlie the Behavioral Inhibition System are presumed to interrupt behavior, increase

arousal, and increase attention (Gray, 1994; Coan & Allen, 2004). These blurry

definitions for both withdrawal motivation and the BIS, which are hypothesized to utilize

the same system, make a definitive conclusion hard to construct. However, it makes sense

that Impulsive Aggressors, defined to lack inhibition, cannot appropriately use the BIS

and thus overreact to minimal provocation in an aggressive manner. This would explain

the decrease in left frontal resting activity along with the lack of correlation with the BAS

Scale subscales.

One limitation to the current study is the lack of clear definitions for the causes

behind frontal asymmetry at a resting state. Although it is generally agreed upon that

frontal lobe asymmetry is related to emotional processing, it appears that definitions for

what constitutes approach motivation opposed to withdrawal motivation and how they

relate to the Behavioral Activation/Inhibition System is ambiguous at best. An

explanation as to why the outcomes using the BIS/BAS Scales did not result in statistical

significance could be a limited sample size, but considering the psychophysiological

results showed statistical differences, it may simply be that the scale lacks psychometric

validity for use in a psychopathological sample. Lastly, the use of alpha power and EEGs

as measures of activity was restrictive, as although EEGs produce excellent temporal

resolution, limited spatial information can be provided. Future studies should utilize

more spatially accurate measures to show specific brain mechanisms involved.

27

To conclude, it was demonstrated that Impulsive Aggressors had higher resting

right frontal cortical activity as measured by EEGs than controls. This was probably a

result of the inherent trait-like properties the current sample had, as all Impulsive

Aggressors reported an extensive aggressive history but were not induced to an

aggressive state at the time of testing. Due to the nature of impulsive aggression as a trait

in the current sample, this study lends evidence towards resting frontal lobe asymmetry as

an inherent marker for susceptibility to psychopathology.

28

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