Although Amphetamine Significantly Affected All of These Variables Except Zygomatic EMG

Addendum to “Results,” section, Wardle and de Wit

To further explore relationships between the effects of amphetamine on subjective mood and the effects of amphetamine on emotional reactivity, we constructed change scores capturing the effects of amphetamine on mood and responses to the pictures by subtracting placebo scores on the variables on interest from scores at the 10 mg and 20 mg session, and then correlating those change scores. We conducted both Pearson correlations, and Spearman rank-–order correlations (which relax assumptions about normality and linearity of relationships).

The Pearson correlations of 20 mg change scores are presented in Table S1. Although amphetamine significantly affected all of these variables except zygomatic EMG to positive pictures, the correlations between the drug’s effects on subjective mood and ratings of the pictures or EMG activity to the pictures were low. Furthermore, although amphetamine produced consistent effects on arousal and positivity ratings, and marginally (p = =.06) consistent effects on corrugator and zygomatic responses, the correlations between its effects on ratings and on psychophysiological reactions were low. Examining the Spearman correlations (Table S2), the results are substantively similar, with one exception, a significant positive correlation between amphetamine effects on POMS arousal and zygomatic activity.

The Pearson correlations of 10 mg change scores are shown in Table S3. Here, we observed similar but slightly attenuated relationships as at the 20 mg dose. One exception is a significant correlation between MAP and zygomatic EMG, which was attributable to a single participant with a notably low blood pressure response to the 10 mg amphetamine. Examining the table of Spearman correlations (Table S4), the relationships are substantively similar. Importantly, relaxing the assumptions of linearity and normality did not produce any significant relationships between POMS Arousal and zygomatic activity at the 10 mg dose.

In summary, the subjective effects of amphetamine on POMS Arousal, POMS Elation, and amphetamine-like effects are moderately to highly correlated at both doses. Interestingly, these subjective effects do not correlate closely with reports of feeling a drug effect (DEQ Feel), suggesting participants may at times misattribute feelings produced by the drug to other sources. The subjective effects also did not correlate significantly with either the cardiovascular effects, or with the measures of emotional reactivity to pictures (ratings and psychophysiological responses). The sole exception was a significant Spearman correlation between POMS Arousal and zygomatic activity change with the 20 mg dose.

Although these generally null findings cannot establish independence of the two effects in question, they do suggest that the effects are not strongly related. Furthermore, the significant Spearman correlation suggests that if relationships do exist between these effects, they may not be linear in nature. For example, individuals with lower levels of drug response may tend to attribute the positive feelings generated by the drug to the pictures, creating a positive relationship between drug response and picture responses for these individuals, while individuals with a higher and thus more subjectively evident response to the drug may attribute the positive feelings to the drug, producing no relationship between subjective effects and picture responses. Future studies aimed at elucidating the relationship between subjective mood and reactivity to emotional stimuli should thus consider multiple possible forms for this possible relationship. Lastly, changes in corrugator and zygomatic reactivity to the pictures were, as expected, modestly negatively related. However, changes in ratings of the pictures and changes in psychophysiological responses were not significantly related, suggesting possible sub-groups, such that some individuals experience subjective changes in their reactivity to the pictures with amphetamine, while others experience more psychophysiological changes.

Table S1 t-Tests and Pearson correlations of effects of amphetamine at placebo vs. the 20 mg session

20 mg vs. Placebo t-tests / Correlations of 20 mg placebo change scores
POMS Arousal / ARCI / DEQ / MAP / Positive ratings / Arousal ratings / CR EMG / ZG EMG
Typical effects
POMS Elation AUC / t(34)=5.16, p<.001 / .70** n=35 / .70** n=35 / .16 n=35 / -.19 n=35 / .12 n=35 / .06 n=35 / .04 n=34 / .22 n=33
POMS Arousal AUC / t(34)=5.26, p<.001 / – / .71** n=35 / .14 n=35 / .17 n=35 / .25 n=35 / .20 n=35 / -.04 n=34 / .31 n=33
ARCI A AUC / t(34)=4.96, p<.001 / – / .44* n=35 / .15 n=35 / .07 n=35 / .07 n=35 / .08 n=34 / .24 n=33
DEQ “Feel” AUC / t(34)=5.65, p<.001 / – / .04 n=35 / -.27 n=35 / -.14 n=35 / .17 n=34 / .21 n=33
MAP AUC / t(35)=5.96, p<.001 / – / -.04 n=36 / .08 n=36 / -.13 n=35 / .01 n=33
Emotional reactivity
Positivity ratings, all pictures / t(35)=2.80, p=.008 / – / .80** n=36 / -.22 n=35 / .16 n=33
Arousal ratings, all pictures / t(35)=2.53, p=.02 / – / -.19 n=35 / .08 n=33
Corrugator EMG positive pictures / t(34)=-2.26, p=.03 / – / -.33+ n=33
Zygomatic EMG positive pictures / t(32)=1.78, p=.08 / –

AUC Area under the curve, POMS elation profile of mood states elation scale, ARCI A addictions research center inventory amphetamine scale, DEQ drug effect questionnaire, MAP mean arterial pressure, CR corrugator, ZG zygomatic, EMG electromyography

** p.001, * p.01; + Marginal, p=.06

Table S2 Spearman correlations of effects of amphetamine at placebo vs. the 20 mg session

Spearman correlations of 20 mg placebo change scores
POMS Arousal / ARCI / DEQ / MAP / Positive ratings / Arousal ratings / CR EMG / ZG EMG
Typical effects
POMS Elation AUC / .72** n=35 / .61** n=35 / .14 n=35 / -.20 n=35 / -.003 n=35 / .004 n=35 / .10 n=34 / .29 n=33
POMS Arousal AUC / – / .60** n=35 / .18 n=35 / .14 n=35 / .11 n=35 / .20 n=35 / -.09 n=34 / .48** n=33
ARCI A AUC / – / .50* n=35 / .09 n=35 / -.08 n=35 / .06 n=35 / .17 n=34 / .29 n=33
DEQ “Feel” AUC / – / -.004 n=35 / -.28 n=35 / -.13 n=35 / .18 n=34 / .19 n=33
MAP AUC / – / -.09 n=36 / .03 n=36 / -.13 n=35 / .17 n=33
Emotional reactivity
Positivity ratings all pictures / – / .80** n=36 / -.28 n=35 / .23 n=33
Arousal ratings all pictures / – / -.27 n=35 / .12 n=33
Corrugator EMG positive pictures / – / -.10 n=33
Zygomatic EMG positive pictures / –

** p<.001, * p<.01; + Marginal, p=.06

Table S3 t-Tests and Pearson correlations of effects of amphetamine at placebo vs. the 10 mg session

10 mg vs. Placebo t-tests / Correlations of 10 mg placebo change scores
POMS Arousal / ARCI / DEQ / MAP / Positive ratings / Arousal ratings / CR EMG / ZG EMG
Typical effects
POMS Elation AUC / t(34)=3.57, p=.001 / .77** n=35 / .57** n=35 / -.06 n=35 / -.29 n=35 / -.06 n=35 / -.04 n=35 / -.07 n=34 / .25 n=33
POMS Arousal AUC / t(34)=2.59, p=.01 / – / .45** n=35 / -.12 n=35 / -.13 n=35 / -.02 n=35 / -.06 n=35 / -.05 n=34 / .21 n=33
ARCI A AUC / t(34)=3.09, p=.004 / – / .46* n=35 / -.24 n=35 / -.18 n=35 / .06 n =35 / .07 n=34 / .13 n=33
DEQ “Feel” AUC / t(34)=1.37, p=.18 / – / -.07 n=35 / -.33 n=35 / -.16 n=35 / .04 n=34 / -.02 n=33
MAP AUC / t(35)=3.88, p<.001 / – / -.27 n=36 / -.15 n=36 / -.41 n=35 / -.43* n=33
Emotional reactivity
Positivity ratings all pictures / t(35)=1.18, p=.25 / – / .53** n=36 / -.19 n=35 / .003 n=33
Arousal ratings all pictures / t(35)=1.14, p=.16 / – / -.19 n=35 / .08 n=33
Corrugator EMG positive pictures / t(34)=-1.83, p=.08 / – / -.43* n=33
Zygomatic EMG positive pictures / t(32)=2.40, p=.02 / –

** p.001, * p.01; + marginal, p=.06

Table S4 Spearman correlations of effects of amphetamine at placebo vs. the 10 mg session

Spearman correlations of 10 mg placebo change scores
POMS Arousal / ARCI / DEQ / MAP / Positive ratings / Arousal ratings / CR EMG / ZG EMG
Typical effects
POMS Elation AUC / .75** n=35 / .42** n=35 / -.15 n=35 / -.38 n=35 / -.007 n=35 / -.05 n=35 / -.12 n=34 / .09 n=33
POMS Arousal AUC / – / .41** n=35 / -.10 n=35 / -.14 n=35 / -.06 n=35 / -.16 n=35 / -.10 n=34 / .19 n=33
ARCI A AUC / – / .49* n=35 / -.13 n=35 / -.11 n=35 / .12 n=35 / .003 n=34 / .07 n=33
DEQ “Feel” AUC / – / -.04 n=35 / -.27 n=35 / -.13 n=35 / -.07 n=34 / .01 n=33
MAP AUC / – / -.15 n=36 / -.15 n=36 / .22 n=35 / -.42 n=33
Emotional reactivity
Positivity ratings all pictures / – / .56** n=36 / .05 n=35 / .009 n=33
Arousal ratings all pictures / – / -.17 n=35 / .11 n=33
Corrugator EMG positive pictures / – / -.39+ n=33
Zygomatic EMG positive pictures / –

** p.001, * p.01; + marginal, p=.06