The data collected in this study, contrary to our hypothesis, suggested a negative relationship between impulsivity and stimulation following alcohol, such that individuals who performed more impulsively on a response-inhibition task reported the least stimulation following alcohol consumption. Additionally, there was a negative relationship between impulsive behavior and arousal following alcohol consumption, with individuals who performed more impulsively also reporting less arousal following alcohol consumption. These data suggest that individuals with lower levels of state impulsivity actually endorse more reinforcing effects (i.e. arousal and stimulation) following alcohol consumption compared with higher impulsive individuals, contrary to what was hypothesized.
Previous research has suggested that aggressive impulsive individuals are under aroused at rest, but—in response to photic stimulation—show increased arousal (as measured by evoked electrical potentials) compared with non-aggressive controls (Houston and Stanford, 2001
). Although our results fail to show greater arousal in impulsive individuals following alcohol administration, methodological differences between studies (objective physiological measure versus subjective measures) and the possible interaction between impulsivity and aggression in the previous study may have led to divergent findings. The results of this study do suggest that individuals with high levels of impulsive behavior may be less sensitive to the stimulating effects of alcohol, and need more alcohol to experience the same level of stimulation as their less impulsive counterparts. To our knowledge, there has not been a study that has directly tested and confirmed this hypothesis in human populations. However, animal studies have suggested that more impulsive animals are less sensitive to motor stimulation following alcohol administration (Mitchell et al., 2006
). Additionally, similar results have been found in human studies, although with amphetamine rather than alcohol. In these studies, individuals with higher lapses of attention (a proposed dimension of impulsivity; de Wit, 2009
) reported less liking and desire for more of the drug following amphetamine administration (McCloskey et al., 2010
). Those who perform more impulsively on a response-inhibition task following acute alcohol administration consumed more alcohol in an ad lib
consumption procedure (Weafer and Fillmore, 2008
), perhaps to experience the positive stimulating effects of alcohol. A positive correlation exists between impulsivity and consumption of alcohol (Grau, 1999
). Impulsive individuals may need to consume more alcohol per drinking occasion to achieve the stimulating effects of alcohol. Future studies are needed that assess the relationship of impulsivity and subjective response to alcohol using a full dose range of alcohol.
The time points at which the subjective effects of stimulation and sedation following alcohol consumption were measured differed between this study and previous studies. Previous studies measured stimulation and sedation at multiple time points within the range of 10–60 (Thomas et al., 2003
), 15–165 (King et al., 2002
) and 30–180 min (Holdstock et al., 2000
) following the first sip of alcohol. This study measured stimulation and sedation (BAES) at only one time point, which was 50 min following completion of alcohol consumption (Fig. ; corresponding to 170 min following first sip of alcohol). At this time point, the mean breath alcohol (± SEM) for the group was ~0.08% ± 0.01. A differentiator model suggests that individuals who are at risk for alcohol problems experience the greatest stimulation during the ascending limb of the breath alcohol curve and fewer sedative-like effects during the descending limb (Newlin and Thomson, 1990
), suggesting that the subjective effects of stimulation and sedation can vary according to the time points on the breath alcohol curve in which these measurements are captured. Although stimulation and sedation were measured following the peak of the breath alcohol curve, measures of mood (POMS) were collected closer to the peak of the breath alcohol curve (20 min following alcohol administration; Fig. ) and revealed a negative association with impulsivity and arousal. Perhaps, if subjective ratings of stimulation and sedation following alcohol consumption were collected at additional time points along the breath alcohol curve, a different directional relationship between impulsivity and subjective effects of alcohol would have emerged.
It is of interest that state impulsivity, but not trait impulsivity, predicted sensitivity to the stimulating effects of alcohol. The differentiation between the predictive values of trait versus state impulsivity in this context may be due to either less self-reporting of impulsive behaviors or the selection of non-problematic alcohol drinkers. Perhaps higher levels of trait impulsivity would have been found if the sample included individuals with a more extensive drinking history or levels of alcohol use disorders. Previous studies have shown that high levels of trait impulsivity are found in those populations who suffer from alcohol dependence (Bjork et al., 2004
; Mitchell et al., 2005
). Future studies to determine the role of trait impulsivity and sensitivity to the subjective effects of alcohol need to be conducted, perhaps in populations who suffer from alcohol-use disorders, to understand the interactions between these risk factors further.
Previous studies that have found increased sensitivity to the stimulating effects of alcohol have observed this phenomenon in heavy drinkers, alcoholics or individuals with a family history of alcohol problems (Holdstock et al., 2000
; King et al., 2002
; Schuckit, 1994
; Thomas et al., 2003
). Two studies in which heavy drinkers reported greater stimulation following alcohol consumption had individuals who averaged roughly 12–24 drinks per week and engaged in approximately 45 binge drinking episodes across a 6-month period (Holdstock et al., 2000
; King et al., 2002
). Participants in this study drank on average 12 drinks per week and engaged in approximately four binge drinking episodes across a 3-month time span. As part of inclusion criteria for this study, an AUDIT cutoff of 12 was imposed. This cutoff was chosen as it has previously been shown as adequate for excluding individuals who may be dependent upon alcohol (Conigrave et al., 1995
). By employing this AUDIT cutoff, we may have excluded individuals with the highest risk for developing alcohol dependence. If individuals at higher risk for alcohol dependence were included in the sample, the hypothesized increased sensitivity to the stimulating effects of alcohol in higher impulsive individuals may have been observed. It should be noted though that we did not find any significant relationships between level of alcohol consumption (drinks per week) and subjective responses to alcohol (sedation, stimulation and arousal) in this sample.
Another important consideration when comparing the results from this study to the aforementioned studies is the pacing of alcohol administration. The present study administered a 0.8 g/kg dose of alcohol in a binge-like fashion, in which participants consumed four alcoholic drinks over a period of 2 h, which corresponded to BrAC of 0.08%. The aforementioned studies administered doses of alcohol that ranged from 0.4 to 0.8 g/kg consumed within 10–25 min (Holdstock et al., 2000
; King et al., 2002
; Thomas et al., 2003
). While administering alcohol in a binge-like manner (according to the NIAAA definition of a binge drinking episode) resulted in breath alcohol curves similar to bolus administration of alcohol, consuming alcohol over a longer time period (2 h versus 10–25 min) may affect the subjective effects of alcohol. There is evidence to suggest that the pacing of drink administration influences the subjective effects of alcohol, such that stimulant effects increase with speed of consumption (Morean and Corbin, 2010
). The BAES measurements were recorded when BrAC were between 0.07 and 0.08%, though the slower absorption and slower onset of the pharmacological effects may have led to differences in reports of stimulation and sedation compared with studies that employed a bolus dosing procedure. The differences in subjective effects when alcohol is administered in a bolus dose versus multiple doses over a longer time period has not been well characterized and represents a question that warrants additional research.
In summary, results from this study suggest that with respect to impulsivity, a significant positive relationship with self-reported sedation and a significant negative relationship with self-reported stimulation and arousal following alcohol consumption exists. These findings may suggest that individuals with high levels of impulsive behavior are less sensitive to the stimulation effects of the dose of alcohol (0.8 g/kg) administered in this study. While a decreased sensitivity to the stimulating effects of alcohol may lead impulsive individuals to consume higher doses of alcohol to achieve the desired effect, the data from this study cannot fully support that assumption. Future studies should be aimed at assessing higher doses of alcohol and subjective stimulation at multiple time points along the breath alcohol curve in impulsive individuals. Also, future studies should examine whether the relationship between impulsivity and subjective response to alcohol differs in those individuals with a family history of alcohol problems. As it stands, the results from this study suggest that these impulsivity-based differences in the subjective effects of alcohol may reflect differing motivations for alcohol use. Understanding these motivations may provide insight on how to reduce risky drinking in impulsive populations.