Heart Rate Variability Predicts Emotional Flexibility in Response to Positive Stimuli

doi:10.4236/psych.2012.38086

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Psychology

2012. Vol.3, No.8, 578-582

Published Online August 2012 in SciRes (http://www.SciRP.org/journal/psych) http://dx.doi.org/10.4236/psych.2012.38086

578

Heart Rate Variability Predicts Emotional Flexibility in Response

to Positive Stimuli

To momi Fujimura1,2, Kazuo Okanoya1,2,3*

1Japan Science Technology Agency, ERATO, Okanoya Emotional Inform ati on Project, Saitama, Japan

2RIKEN Brain Science Institute, Saitama, Japan

3Department of Life Sciences, Graduate School of Arts and Sc ien ces , The University of Tokyo, T okyo, Japan

Email: *[email protected]

Received May 7th, 2012; revised June 7th, 2012; accepted July 10th, 2012

Flexible adaptation to constantly changing environments is linked to mental health and psychological

functioning. Heart rate variability (HRV), an index of autonomic flexibility, has been implicated in emo-

tional flexibility, the ability to generate contextually dependent emotional responses in accordance with

situational demands. The current study investigated whether HRV during rest is associated with experi-

enced emotion, one of the measures of emotional flexibility. To assess experienced emotion in response to

changing events, three types of stimuli sets were created by presenting two stimuli successively. First, two

stimuli represented the same valence (i.e., negative/negative or positive/positive). Second, two stimuli

represented opposite valences (i.e., negative/positive or positive/negative). Third, a neutral stimulus was

followed by negative or positive stimulus (i.e., neutral/negative or neutral/positive). Psychological ratings

for experienced emotion to the second stimulus were collected with regard to valence and arousal. The

results showed that subjects with lower resting HRV experienced more aroused states in response to suc-

cessive positive stimuli. Resting HRV may be a proxy of emotional flexibility indexed by subjective

arousal states to positive events.

Keywords: Heart Rate Variability; Emotional Flexibility; Psychological Ratings

Introduction

Life involves constantly changing events in the external en-

vironment. Rapid and adequate adaptation to these changes is

vital for organisms to survive. Recent research has focused on

emotional flexibility, the ability to flexibly respond to positive

and negative events and to regulate emotion effectively (Waugh,

Thompson, & Gotlib, 2011; Westphal, Seivert, & Bonanno,

2010). Individuals with greater emotional flexibility have posi-

tive reactivity to positive events and negative reactivity to

negative events, in accordance with situational demands. These

context-dependent emotional responses are characterized by

flexible autonomic, somatic, and psychological responses to

changing events.

Heart rate variability (HRV), an index of autonomic flexibil-

ity, is positively associated with good psychological and

physiological functioning (Thayer & Lane, 2000). HRV is cal-

culated by R-R wave intervals produced by electrocardio-

graphic data. In healthy individuals, heart rate fluctuates during

resting states due to the different frequency characteristics of

sympathetic and parasympathetic neural modulations of heart

rate. Therefore, HRV is indicative of autonomic balance be-

tween sympathetic and parasympathetic activity. Low HRV is

associated with a number of psychological disorders character-

ized by poor emotion regulation and behavioral inflexibility

(see Thayer & Brosschot, 2005 for a review). Given that emo-

tional flexibility can be defined by autonomic and behavioral

reactivity, it is possible that HRV assesses an individual’s emo-

tional flexibility, or how well an individual responds to emo-

tional events and generates contextually dependent emotional

responses.

Individual differences in regulated emotional response can be

predicted by baseline HRV (see Appelhans & Luecken, 2006

for a review). For example, subjects with low resting HRV

showed a more exaggerated startle reflex potentiated by the

threat of shock compared with subjects with high resting HRV

(Melzig, Weike, Hamm, & Thayer, 2009). Furthermore, the

emotion-modulated startle reflex was higher in subjects with

low HRV than in those with high HRV and subjects with low

HRV showed no difference in startle magnitude during negative,

positive, and neutral foregrounds (Ruiz-Padial, Sollers, Vila, &

Thayer, 2003). This evidence suggests that individuals with low

resting HRV have a tendency to produce an exaggerated startle

reflex regardless of valence, reflecting an inappropriate re-

sponse to situational demands.

Attention allocation, which involves the selection of mean-

ingful information from the external environment, is also asso-

ciated with resting HRV (Thayer & Brosschot, 2005). A previ-

ous study reported that individuals with low HRV could not

shift their attention away from negative stimuli, resulting in

prolonged response initiation after the presentation of negative

stimuli (Krypotos, Jahfari, van Ast, Kindt, & Forstmann, 2011).

In relation to this, Johnsen, Thayer, Laberg, Wormnes, Raadal,

Skaret, Kvale, and Berg (2003) found increased attentional bias

to threat-related words (i.e., dental-related words for dental

phobics) in subjects with low HRV. This evidence indicates

that HRV during rest is associated with sensitivity to threat

signals. Because attentional control is important for adapting to

a constantly changing environment, excessive sensitivity to

*Corresponding author.

T. FUJIMURA, K. OKANOYA

threat signals interferes with the processing of subsequent

events, leading to emotional inflexibility.

The aforementioned studies have revealed that resting HRV

predicts individual differences in emotional flexibility by mea-

suring reflexes and attention to emotional stimuli directly or

indirectly. However, it remains unknown whether subjective

emotions measured by psychological ratings are related to rest-

ing HRV, although subjective emotion is one of the indices to

assess emotional flexibility. Waugh et al. (2011) demonstrated

that high-resilient people who exhibited emotional flexibility,

compared to low-resilient people, showed a greater difference

in self-reported affect between current negative and positive

pictures. Given that emotional flexibility is characterized by

context-dependent experienced emotion, HRV, an index of

flexibility, is associated with experienced emotion as measured

by psychological ratings. That is, people with low HRV may

show poor emotional experiences to positive and negative

stimuli.

The present study aimed to examine whether resting HRV

predicts individual differences in the experience of subjective

emotion. To assess emotional flexibility, experienced emotion

was evaluated in response to target stimuli followed by three

types of prime stimuli. In the first case, the prime and target

stimuli represented the same valence (i.e., negative/negative or

positive/positive). In the second case, the prime and target

stimuli represented opposite valences (i.e., negative/positive or

positive/negative). In the third case, a neutral prime stimulus

was followed by negative or positive target stimuli (i.e., neu-

tral/negative or neutral/positive). Participants were asked to rate

their experienced emotion when viewing the picture that was

presented second (i.e., the target picture). We hypothesized that

subjects with high resting HRV, in comparison with subjects

with low resting HRV, would have stronger experiences of

pleasantness or unpleasantness in response to the target stimu-

lus, regardless of which stimulus was presented first. In addi-

tion to valence ratings, arousal ratings for experienced emotion

were collected. Individuals with low resting HRV are charac-

terized by chronic autonomic hyperarousal and diminished

response habituation (Friedman & Thayer, 1998). Accordingly,

experienced arousal may be exaggerated in individuals with

low resting HRV. Furthermore, this tendency may be promi-

nent in the congruent condition in which same-valence stimuli

were presented successively because individuals with low HRV

are unlikely to habituate these emotional stimuli. In the present

study, we expected that individual difference in resting HRV

would translate into positive and negative reactivity, assessed

by experienced emotion.

Method

Participants

Forty-three adults (24 men and 19 women; mean ± SD age,

25.02 ± 6.74 years) participated in the study. The participants

were recruited by advertisements placed with an intermediary

company, and their occupational backgrounds varied widely.

They received compensation for participating in the experiment.

All of the participants had normal or corrected-to-normal vi-

sion.

Stimulus Material

The stimuli were 35 pictures selected from the International

Affective Picture System (IAPS: Lang, Bradley, & Cuthbert,

2008), consisting of 10 pleasant, 5 neutral, and 10 unpleasant

pictures. The mean of valence/arousal ratings were: 7.63/5.10

for the pleasant pictures, 4.99/2.45 for neutral pictures, and

2.73/5.23 for unpleasant pictures. Arousal ratings were equiva-

lent for pleasant and unpleasant pictures. All pictures were

presented in full color.

Apparatus and Physiological Measurement

Experimental events were controlled by a program written in

Inquisit 3.0 (Millisecond) and were implemented on a computer

(Vostro 420, Dell) using the Microsoft Windows XP operating

system. Stimuli were presented on a 19-inch LCD monitor

(E1902S, Iiyama; 1024 × 768 pixels, 75 Hz refresh rate) and

subtended a visual angle of abou t 20.8˚ × 28.1˚.

The electrocardiogram (ECG) was recorded with a data ac-

quisition system (MP150 system; BIOPAC sy stems Inc., Goleta,

CA) with electrodes placed in a Lead II configuration. The

ECG signals were .5 to 35 Hz bandpass filtered and amplified

using a BIOPAC amplifier (ECG100C; BIOPAC systems Inc.,

Goleta, CA) and were digitized with a sampling rate of 1000

Hz.

Procedure

Experiments were conducted individually in an electronically

shielded and sound-attenuated room. Upon arrival, participants

were told that the electrodes were harmless and that they could

withdraw from the experiment at any time. All participants

completed the informed consent form and successfully partici-

pated in the experiment. After all sensors were attached, task

instructions were provided.

To assess baseline values of HRV in a resting period, ECG

was measured for 5 min during a resting state. Participants were

asked to relax into a chair but not to close their eyes to avoid

falling into sleep.

After the measurement of resting HRV, a picture evaluation

task was conducted. For each trial, two pictures were consecu-

tively displayed. To assess experienced emotion elicited by the

second picture (i.e., the target stimulus) preceded by the first

picture (i.e., the prime stimulus), three types of conditions in-

cluding pairings of pictures were produced. The first pairing

consisted of negative/negative or positive/positive stimuli. The

second pairing consisted of negative/positive or positive/ negative

stimuli. The third pairing consisted of neutral/negative or neu-

tral/positive stimuli. These six pairings were arranged into three

blocks according to the hedonic content of the prime stimuli

(positive, neutral, and negative blocks). Each prime stimulus

was presented two times within a block. In each block, 10 pair-

ings of pictures were presented, including five positive pictures

and five negative pictures as target stimuli. The target stimuli

were identical across the three blocks. The three blocks were

randomly conducted across participants.

A trial began with a 2-s fixation point followed by two suc-

cessive pictures presented for 6 s each. After a 6-s blank screen,

the rating screen was displayed until the participant responded.

The inter-trial interval was 6 s. The psychological rating task

was the 9 × 9 Affect Grid, which assessed affect along the di-

mensions of valence and arousal (Russell, Weiss, & Mendel-

sohn, 1989). Participants were asked to rate how they felt when

T. FUJIMURA, K. OKANOYA

580

Figure 1.

Scatter plots for functions of psychological ratings and RMSSD and correlation coefficients for each relation: (a) Valence ratings and RMSSD; ( b)

Arousal ratings and RMSS D.

T. FUJIMURA, K. OKANOYA

they viewed the picture that was presented second by indicating

a square on a two-dimensional emotional space using a com-

puter mouse. All the participants used the right hand to rate the

feeling.

Data analysis

To evaluate HRV, inter-beat intervals (IBI) were derived

from ECG signals using software for analysis (Acknowledge

4.1; BIOPAC systems Inc., Goleta, CA). First, IBI were

checked in a tachograph and corrected if the R-wave triggers

were misplaced. To evaluate a time domain of HRV, the root

mean square successive difference (RMSSD) (see the Task

Force of the European Society of Cardiology and the North

American Society of Pacing Electrophysiology, 1996) was

calculated from IBI for a 5-min resting period for each partici-

pant.

For the psychological ratings, valence and arousal ratings on

a 9-point scale were collected for each trial.

Results

The mean of the RMSSD calculated by IBI during the 5-min

resting period across participants was 40.84 ms (SD = 20.53).

Figure 1 shows scatter plots by function of valence or arousal

ratings and RMSSD. To determine the relationship between

subjective states elicited by emotional stimuli and baseline

HRV, correlation coefficients were calculated for each condi-

tion. We found a significant negative correlation between

arousal ratings for positive stimuli preceded by positive stimuli

and RMSSD (r = –.325; t(41) = 2.20, p < .05). There were no

other significant correlations.

Discussion

In the current study, we investigated whether resting HRV is

associated with experienced emotion elicited by multiple emo-

tional events. The results showed that individuals with lower

HRV experienced more aroused states when viewing succes-

sive positive stimuli. This is the first evidence indicating an

association between resting HRV and subjective experienced

emotion by measuring psychological ratings.

Resting HRV was negatively associated only with arousal

ratings, not valence ratings, when viewing successive two posi-

tive pictures. This result showed that lower resting HRV led to

higher arousal states in response to multiple positive stimuli.

This finding is consistent with previous findings suggesting that

individuals with low HRV are in states of hyperarousal and

diminished habituation by various autonomic measures (Frie-

dman & Thayer, 1998). Furthermore, low HRV during rest has

been shown to resist habituation, even to non-threat stimuli, due

to hypervigilance (Thayer, Friedman, Borkovec, Johnsen, &

Molina, 2000). According to this evidence, subjects with low

HRV fail to adapt to successive positive stimuli, resulting in

feelings of relatively high arousal instead of pleasantness. This

finding suggests that individuals with low HRV show poor

habituation and assess their subjective emotional states as

aroused. Resting HRV may be associated with the ability to

control subjective arousal states rather than to enhance pleas-

antness or unpleasantness when confronting emotional stimuli.

Another explanation of the relationship between reduced HRV

and high arousal states is that HRV is positively related to good

emotion regulation (Porges, 2007; Porges & Byrne, 1992;

Thayer & Lane, 2000, 2009). Emotion regulation involves the

process by which people manage both negative and positive

emotions (Gross, 1998). Successful emotion regulation, by

either reappraisal or suppression, has been shown to lead to

increased vagally mediated HRV (Butler, Wilhelm, & Gross,

2006; Di Simplicio, Costoloni, Western, Hanson, Taggart, &

Harmer, 2011). Furthermore, participants with a high baseline

of vagally mediated HRV spontaneously use emotion regula-

tion strategies more often during emotional conversation than

participants with a low baseline of vagally mediated HRV

(Butler et al., 2006). Consistent with these findings, our results

suggest that high arousal states in response to positive stimuli

result from failures of emotion regulation in subjects with lower

HRV.

Notably, our findings indicated that resting HRV was related

to emotional experience elicited by positive stimuli, not nega-

tive stimuli, although most previous studies have shown an

association between resting HRV and the processing of threat-

ening or negative stimuli (Appelhans & Luecken, 2006; John-

sen et al., 2003; Krypotos et al., 2011; Melzig et al., 2009).

However, individuals with low resting HRV produced an ex-

aggerated emotion-modulated startle reflex in response to neu-

tral and positive pictures (Ruiz-Padial et al., 2003). This ten-

dency could be due to sensitivity to non-threat signals. In this

study, it is possible that the misperception of safety (i.e., posi-

tive stimuli) in individuals with low HRV caused higher arousal

states compared to individuals with high HRV. This finding

provides evidence of emotional inflexibility in response to mul-

tiple positive stimuli. Thus, resting HRV may predict emotional

flexibility indexed by the experience of high arousal to positive

events.

In summary, the current study revealed that resting HRV is a

good proxy of emotional flexibility indexed by subjective ex-

perienced emotion. Individuals with lower HRV experienced

more arousal states when faced with multiple positive stimuli.

This may be due to emotional inflexibility derived from sensi-

tivity to non-threat signals and/or failure of emotion regulation.

HRV may indicate how individuals respond to positive events

effectively and successfully. Future research should investigate

the use of resting HRV as a proxy of emotional flexibility by

measuring psychological, autonomic, and behavioral indices.

Resting HRV provides useful information to understand indi-

vidual differences in emotional flexibility.

Acknowledgements

We thank Kentaro Katahira and for assistance with ed-

iting this manuscript.

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