Psychopharmacology
Electronic Supplementary Material 1
The effects of nicotine dependence and acute abstinence on the processing of drug and non-drug
rewards
Lawn, W.1, Freeman, T.P1, Hindocha, C.1, Mokrysz, C.1, Das, R.K.1, Morgan, C.J.A. 1,2, & Curran,
H.V.1
1
Clinical Psychopharmacology Unit, University College London, Gower Street, London, WC1E 6BT,
United Kingdom.
2
School of Psychology, University of Exeter, Washington Singer Building, Perry Road, Exeter, EX4
4QG, United Kingdom.
Statistical Analyses
CO data were investigated via a mixed ANOVA with a between-subjects factor of group (dependent
and occasional) and a within-subjects factor of smoking-condition (ad libitum and abstinent). The
time since last smoked was analysed using non-parametric comparisons as the data were nonnormally distributed. MNWS, craving (from MNWS) and SHAPS scores were investigated via mixed
analyses of variance (ANOVA) with a between-subjects factor of group (dependent and occasional)
and within-subjects factors of smoking-condition (ad libitum and abstinence) and time (pre-task and
post-consumption).
We also conducted an exploratory analysis into the time taken to choose each reward-type1. This
analysis was conducted in order to determine if certain rewards were chosen more quickly than others
and therefore perhaps elicited a response with greater motivation. The time taken to choose each
reward was averaged across all trials and a mixed ANOVA with a between-subjects factor of group
and within-subjects factors of reward-type (cigarette, music and chocolate), reward-magnitude (large
and small) and smoking-condition was carried out. Paper was not included in this analysis as 19
participants never chose paper.
Furthermore, we also conducted an exploratory analysis into whether the average number of buttonpresses (BP) for the chosen reward was dependent upon the alternative reward that was foregone. This
analysis was conducted in order to determine whether motivation for each reward (as measured by
BP) was affected by the reward option that was rejected. It therefore provided information on the
relationship between choice and BP data. Separate ANOVAs for cigarette, music and chocolate were
carried out with a between-subjects factor of group and a within-subjects factor of alternative-reward
(cigarette, chocolate, music and paper). We collapsed across reward-magnitude and smokingcondition for these three ANOVAs. Missing data for both of these exploratory analyses were imputed
by separately calculating the mean for the relevant cell in each group.
Results
State measures
Carbon monoxide (CO) and hours since last smoked (Table 1)
The dependent group’s CO level was greater in the ad libitum condition compared with the abstinent
condition (t18=7.915, p<0.001). The occasional group’s CO level did not differ between conditions.
1
We would like to thank two anonymous reviewers for suggesting the two exploratory analyses described
here.
Dependent smokers had smoked more recently before the experiment during the ad libitum condition
compared to during abstinence (W19=3.827, p<0.001) but, as expected, there was no difference for
occasional smokers.
Minnesota Nicotine Withdrawal Scale (MNWS), Craving (from MNWS) and SHAPS (Table 2)
Dependent smokers had smoked more recently before the experiment during the ad libitum condition
compared to during abstinence (W19=3.827, p<0.001) but, as expected, there was no difference for
occasional smokers.
Group, smoking-condition and time all significantly affected overall MNWS and the craving item.
The dependent group’s MNWS score was greater than the occasional group’s score only during
abstinence and at pre-task (t38=3.905, p<0.001). The dependent group’s craving decreased between
pre-task and post-consumption during both abstinence (t19=7.192, p<0.001) and, to a lesser extent,
during ad libitum smoking (t19=2.667, p=0.011), whereas there were no changes between pre-task and
post-consumption for the occasional smokers.
SHAPS data were analysed using the original scoring system (Snaith-Hamilton et al., 1995). There
were significant interactions between smoking-condition, time and group (F1,38=10.195, p=0.003,
ηp2=0.212), smoking-condition and time (F1,38=8.162, p=0.007, ηp2=0.177), time and group
(F1,38=6.306, p=0.016, ηp2=0.152) and smoking-condition and time (F1,38=4.347, p=0.044,
ηp2=0.1033). Furthermore, there were main effects of smoking-condition (F1,38=7.823, p=0.008,
ηp2=0.171) and group (F1,38=5.698, p=0.022, ηp2=0.130). The groups only differed during abstinence
at pre-task (t38=3.178, p=0.009) and the dependent group’s score only differed between pre-task and
post-consumption during abstinence (t38=4.731, p<0.001).
Time to choose each reward (Figure. 1)
There was an interaction between group, reward-type and reward-magnitude (F1.664, 63.226, p=0.016,
ηp2=0.110) and a main effect of reward-magnitude, with larger rewards chosen faster than smaller
rewards (F1, 38=12.317, p=0.001, ηp2=0.245). Exploration of the group X reward-type X rewardmagnitude interaction showed that the dependent group were faster to choose large compared to small
rewards for music (t19=2.940, p=0.006) and chocolate (t19=3.265, p=0.002), but not for cigarettes. On
the other hand, the occasional group were faster to choose large compared to small rewards for
cigarettes (t19=2.591, p=0.014) and music (t19=2.036, p=0.049), but not for chocolate.
Average button-presses (BP) for the chosen reward affected by the alternative reward (Figure. 2)
For music BP, there was a main effect of alternative-reward (F1, 38=3.687, p=0.030, ηp2=0.088). BP
was greater when music was chosen over cigarettes than when music was chosen over paper
(t39=2.530, p=0.047).
For chocolate BP, there was a main effect of alternative-reward (F1, 38=3.873, p=0.025, ηp2=0.092). BP
was greater when chocolate was chosen over cigarettes than when chocolate was chosen over paper
(t39=2.867, p=0.020).
For cigarette BP, there was an interaction between alternative-reward and group (F1.665, 63.288=5.889,
p=0.007, ηp2=0.134) and a main effect of alternative-reward (F1.665, 63.288=5.917, p=0.007, ηp2=0.135).
Exploration of the interaction showed that, within the occasional group, BP was greater when
cigarettes were chosen over chocolate than when cigarettes were chosen over paper (t19=3.251,
p=0.007) and BP was greater when cigarettes were chosen over chocolate than when cigarettes were
chosen over music (t19=4.297, p<0.001). Contrastingly, there were no significant differences within
the dependent group for cigarette BP as a function of foregone reward. The main effect was due to BP
being greater when cigarettes were chosen over chocolate than when cigarettes were chosen over
music (t39=4.409, p<0.001), when collapsing across groups.
Table 1 Group means (SDs) of CO and time since last smoked. CO = carbon monoxide.*p<0.05;
***p<0.001 within-subjects significance; o p<0.05, ooo p<0.001 overall between-subjects significance.
Bold numbers identify which within-subject difference the significance refers to. Between-subject
differences are collapsed across smoking-condition and time and so represent overall differences
Dependent
Occasional
Abstinent
Ad Libitum
Abstinent
Ad Libitum
CO***, ooo
5.15 (2.13)
14.95 (6.75)
2.80 (1.06)
2.95 (1.50)
Last Smoked
14.52 (3.38)
0.50 (0.54)
89.73 (77.20)
83.28 (102.65)
(hours)***,ooo
Table 2 Group means (SDs) of state measures at times pre-task and post-consumption. MNWS = Minnesota Nicotine Withdrawal Scale; SHAPS = SnaithHamilton Pleasure Scale. *p<0.05; ***p<0.001 within-subjects significance; o p<0.05, ooo p<0.001 overall between-subjects significance. Bold numbers
identify which within-subject difference the significance refers to. Between-subject differences are collapsed across smoking-condition and time and so
represent overall differences
Dependent
Occasional
Abstinent
Pre-task
Ad Libitum
Post-
Pre-task
consumption
Abstinent
Post-
Pre-task
consumption
Ad Libitum
Post-
Pre-task
consumption
Postconsumption
MNWS***
13.55 (7.75)
3.85 (3.13)
4.55 (4.38)
2.55 (3.0)
5.65 (4.67)
4.55 (3.47)
4.65 (3.28)
3.55 (3.55)
Craving (from
2.80 (1.40)
0.70 (0.80)
1.10 (1.165)
0.50 (0.61)
0.75 (0.91)
0.30 (0.47)
0.50 (0.61)
0.40 (0.75)
4.15 (4.08)
1.45 (2.19)
1.60 (2.23)
1.60 (2.14)
0.80 (2.35)
0.85 (1.95)
0.70 (1.59)
0.60 (1.23)
MNWS)***, ooo
SHAPS***, o
Fig. 1 Average time taken (in seconds) to choose each reward type (cigarette small, cigarette large,
music small, music large, chocolate small, chocolate large) in the DReaM-Choice task, collapsed
across smoking-condition. Error bars represent ± standard error.
Time to choose each reward
2
1.8
1.6
Time (s)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Small
Large
Small
Dependent
Large
Occasional
Cigarette
Music
Chocolate
Fig. 2 Average number of button-presses (BP) in 7 seconds for each reward: a) music b) chocolate c)
cigarettes as a function of the foregone reward (cigarette, music, chocolate, paper). Error bars
represent ± standard error.
Average number of button-presses
a) BP for music
40
35
30
25
20
15
10
Dependent
Over Cigarette
Occasional
Over Chocolate
Over Paper
Average number of button-presses
b) BP for chocolate
40
35
30
25
20
15
10
Dependent
Over Cigarette
Occasional
Over Music
Over Paper
Average number of button-presses
c) BP for cigarettes
40
35
30
25
20
15
10
Dependent
Over Music
Occasional
Over Chocolate
Over Paper