Trait impulsivity and poor inhibitory control are well-established risk factors for alcohol misuse, yet little is known about the associated neurobiological endophenotypes. Here we examined correlations among brain physiology and self-reported trait impulsive behavior, impaired control over drinking, and a behavioral measure of response inhibition. A sample of healthy drinkers (n=117) completed a pulsed arterial spin labeling (PASL) scan to quantify resting regional cerebral blood flow (rCBF), as well as measures of self-reported impulsivity (Eysenck I7 Impulsivity scale) and impaired control over drinking. A subset of subjects (n=40) performed a stop signal task during blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging to assess brain regions involved in response inhibition. Eysenck I7 scores were inversely related to blood flow in the right precentral gyrus. Significant BOLD activation during response inhibition occurred in an overlapping right frontal motor/premotor region. Moreover, impaired control over drinking was associated with reduced BOLD response in the same region. These findings suggest that impulsive personality and impaired control over drinking are associated with brain physiology in areas implicated in response inhibition. This is consistent with the idea that difficulty controlling behavior is due in part to impairment in motor restraint systems.
Impulsivity, which refers broadly to acting without thinking, is a widely accepted risk factor for alcohol abuse (Potenza and de Wit, 2010). Measuring impulsive personality traits encompasses several distinct conceptual and methodological factors. One such factor that has been repeatedly implicated in alcohol abuse is difficulty controlling or inhibiting inappropriate behavior. Such poor behavioral control can be assessed by both self-report personality inventories and behavioral laboratory measures. On personality inventories, greater self-reported difficulty controlling behavior or acting without forethought is associated with increased drug and alcohol use (Petry, 2001 and Finn, 2002). Behavioral measures of inhibitory control include stop signal and go/no-go tasks, which measure the ability to inhibit prepotent or instigated motor behavior, such as a finger press. Poor response inhibition on these tasks has also been repeatedly linked with greater alcohol use and problems (Bjork et al., 2004, Nigg et al., 2006 and Rubio et al., 2008).
One potential explanation for the increased risk of alcohol-related problems in impulsive individuals is a specific instance of impaired impulse control: impaired control over drinking. Impaired control refers to a decreased ability to limit or abstain from alcohol consumption despite persistent intentions to do so (Heather et al., 1993). Impaired control is a well-established feature of problematic alcohol use, with two DSM-V criteria for alcohol use disorders that reflect impaired control (i.e., drinking greater amounts than intended and inability to quit or control drinking; American Psychiatric Association, 2013). Moreover, impaired control is becoming increasingly recognized as a problem for young adult drinkers, as this is one of the first symptoms endorsed by those transitioning from social- to dependent-drinking (Leeman et al., 2012 and Leeman et al., 2014).
Impaired control and impulsivity/behavioral under-control are conceptually linked, in that impaired control refers to difficulty controlling the specific behavior of alcohol consumption. As such, it is reasonable to assume that individuals who have a general difficulty controlling behavior or inhibiting inappropriate responses might also display impaired control over drinking. Indeed, initial studies show correlations between impaired control and both self-report and behavioral measures of inhibitory control (for review, see Leeman et al. (2012)). However, little is known about the neurobiological endophenotypes of trait impulsivity in general, and impaired control specifically. Understanding the neural correlates of impulsive traits and impaired control could have important implications for identifying individuals at risk for alcohol use disorders, and for developing treatments.
In a reasonably large sample of 117 healthy subjects who spanned a range of drinking, the current study examined anatomic regions in which measures of brain physiology were correlated with self-reported trait impulsive behavior in general, impaired control over drinking specifically, and a behavioral measure of motor response inhibition. Specifically, we identified regions where impulsive personality and impaired control correlated with resting cerebral blood flow. Additionally, we examined fMRI blood oxygenation level-dependent (BOLD) activation during a response inhibition (stop signal) task as a function of impaired control. Given previous evidence about brain areas involved in response inhibition (Congdon et al., 2010, Bari and Robbins, 2013 and Rae et al., 2014), we expected trait impulsivity and impaired control to be associated with less activity in right frontal regions.
