Subacute and chronic low back pain differentially modulate the
perceived value of reward
1
Parks ,
1
Petre ,
1,
2
Apkarian
Elle L.
Bogden
A. Vania
1Dept of Physiology, 2Dept of Anesthesiology, Northwestern University, Chicago, IL 60611
INTRODUCTION
Experiment 1
We previously demonstrated that chronic pain impairs emotional decisionmaking during a monetary gambling task (Apkarian et al., 2004). Here we
utilize two tasks, gains vs. losses and gains vs. time, to independently
measure specific components of decision-making. In Experiment 1, we
compare healthy subjects with different populations of low back pain
patients, and examine the perception of value as it relates to pain
characteristics and gender. In Experiment 2 we investigate the same
parameters in a longitudinal study to further elucidate the time course of
pain’s impact on behavior.
Task 1: Pain modulates behavioral loss aversion
differently in males and females
PM 082
IASP 2010
Montreal
Experiment 2
Sub-acute back pain patients’ perception of reward does not change 9 months later
METHODS
Example loss aversion data shown for two subjects (A, B), with Session 1 and Session 2 conducted 9 months apart.
Pain intensity was tracked for 1 year; dates of Session 1 and Session 2 testing marked in gray. Color-coded heatmaps
represent probability of gamble acceptance for each gain/loss combination presented in Task 1 (white indicates high
willingness to accept the gamble, black indicates low willingness to accept the gamble).
• Participants completed two tasks involving the perception of monetary
• Loss aversion behavior (Task 1) did not significantly change over a period of nine months (lambda p=0.5,
sensitivity to gains p=0.7, losses p=0.5). Temporal discount rates (Task 2) were also unchanged (p=0.3) (n=10).
Experiment 1
reward (see below for description of task design). We compared healthy
subjects with three populations of people suffering from subacute (pain
durations of 2-4 months, 4-6 months, and 6-12 months) and chronic (pain > 5
years) low back pain. (See Panels 1 and 2 for a breakdown of subjects.)
• Decision-making behavior was examined in relationship to pain
characteristics, duration of pain, and gender.
Experiment 2
• Here we tracked decision-making behavior for the same tasks in a
longitudinal study of low back pain (n=10). Subjects’ pain characteristics were
followed over the course of one year. Tasks were performed twice, with
Session 2 completed nine months after Session 1.
5 x 2 ANOVA shows a significant interaction effect between pain duration
and gender on decision-making. As pain duration increases, females
become more behaviorally loss averse (A), whereas males become more
sensitive to absolute gains (B). A trend for females to become more
sensitive to absolute losses was also observed (C).
Task 2 : Temporal discounting of future rewards
Task Design
under risk (Tom et al., 2007).
Data were fit with a straight line using the size of each potential gain and loss
as independent variables and acceptance/rejection as the dependent variable.
The resulting regression coefficients for loss and gain variables served as
individual measures of loss and gain sensitivity. The ratio of loss to gain
responses was then used to calculate the level of behavioral loss aversion (λ)
for each participant .
At Session 1, loss aversion and temporal
discounting of future rewards did not correlate
with pain characteristics (not shown). Nine
months later, both behaviors show evidence for
modulation by reported pain intensity (A, B).
Session 2 performance also correlates with the
change in pain between sessions (C, D).
The observed trends suggest that increased
pain is associated with decreased loss aversion
and a greater tendency to discount the value of
future rewards.
Task 1 investigated the magnitude of loss aversion during decision-making
Participants decided to accept or reject gambles
offering a 50/50 chance of gaining or losing differing
amounts of money. Trials began with a red dot
followed by a display showing the amount of potential
gain (in green) and loss (in red); values ranged from
$10 to $38 for gains and $5 to $19 for losses.
Reward perception is increasingly modulated by pain characteristics over time
No significant group effects were observed between healthy subjects’,
subacute and chronic back pain patients’ decision-making behavior for
perception of future rewards.
Decision-making behavior is not correlated with pain
intensity in subacute back pain patients
CONCLUSION
• Behavioral loss aversion is modulated by the chronicity of pain differently in males and females.
• Temporal discounting does not show modulation by pain chronicity.
• However, performance on both tasks becomes better correlated with perceived pain intensity after
living with chronic pain for long periods of time, even for individuals whose pain decreases.
Task 2 investigated the subjective value of delayed monetary rewards (Kable
• These results have important implications for our understanding of long-term consequences of
experiencing pain and the classification of pain into subacute and chronic states.
& Glimcher, 2007).
Trials displayed a choice amount of money (range
$32-$60) with a specific time delay (range 1–90
days). Participants then chose to either accept the
delayed reward presented in the trial or reject it for a
smaller but immediate reward of $30.
Subject-specific temporal discount rates (k) of monetary value were calculated
with a single parameter hyperbolic function (subjective value = 1/(1+k*delay)
and then compared between groups.
No significant correlations were observed between pain intensity and
decision-making about reward during Task 1 (A) or Task 2 (B) in
subacute back pain patients (pain duration < 1 year). Subdividing by
gender and/or duration group had no effect.
Chronic back pain patients (males, n=5) exhibited a trend relating pain to
increased loss aversion (p = 0.08) and increased sensitivity to absolute
gains (p=0.02) (not shown).
• We are currently examining the neural mechanisms underlying these effects and their modulation by
gender.
Funded by NIH NINDS NS35115