Study authors say these findings may reflect dysfunction in brain regions that govern how humans relate to their environment and make adaptive decisions, which may in turn facilitate the development of alcoholism through maladaptive, disinhibited behavior.
"Despite their often subtle nature, emotional reactions hold a central position in determining how the brain regulates behavior," said Robert Miranda, Jr., a National Institute on Alcohol Abuse and Alcoholism postdoctoral fellow at Brown University and first author of the study.
"Through integration with cognitive processes, emotional reactions play an important role in learning and memory, evaluating variable environmental contingencies, and motivating adaptive behavior. There is considerable variability among individuals in terms of how emotionally reactive we are to different types of situations and events. These differences may indicate vulnerability to certain psychiatric conditions, such as mood and anxiety disorders and addictions. In the case of antisocial behavior and addictions, there may be diminished reactions to cues that signal aversive events, including punishment."
Individuals who do not experience the appropriate amount of anxiety or negative emotion when threatened are unlikely to alter their behavior in response to the threat, said Peter R. Finn, professor of psychology at Indiana University, Bloomington.
"Psychopaths, for example, are a subset of people with ASPD who show hyporesponsiveness to aversive stimuli. This study looks at reduced or 'hypo' reactivity to aversive stimuli as evidence for poor inhibition, which may result in increased vulnerability to a wide range of problems, including criminal, alcohol and/or drug problems. In other words, this hyporesponsivity may be manifesting itself in the antisocial behavior as well as the excessive use of alcohol."
Researchers examined 62 males, divided into three groups: 24 were alcohol dependent; 17 were alcohol dependent and had ASPD; and 21 "controls" were neither alcohol dependent nor had ASPD. All of the participants completed self-report questionnaires, clinical interviews, and had their eye-blink electromyograms measured to acoustic startle probes while viewing color photographs rated as pleasant, neutral and unpleasant. (The startle response is a defensive reflex that is evoked when a person is presented with an abrupt event, such as a loud, unexpected noise. The reflex – in this case, the eye blink – is influenced by emotional states. It is "normally" larger when an individual is presented with unpleasant pictures, sounds or odors, and smaller when presented with pleasant stimuli.)
"We found that persons with co-existing alcoholism and ASPD are different from alcoholics without ASPD and non-ASPD, non-alcoholic controls in their responsiveness to emotional cues," said Miranda. "The control and non-ASPD alcohol-dependent groups showed the normal linear increase in the eye-blink component of the startle reflex from pleasant to neutral to unpleasant stimuli. In contrast, alcoholics with ASPD did not show the typical increase of startle in response to the unpleasant stimuli or the decrease in response to pleasant stimuli. In short, their emotional responses appeared to be blunted. Importantly, all three groups rated the photographs similarly, ruling out the likelihood that response differences were due to altered subjective experiences of the photographs."
Finn said these findings have both immediate and future applications. "Alcoholics tend to get into trouble a lot," he said. "Yet these individuals simply may not be as affected by the prospects of negative outcomes, and may in fact have problems inhibiting their behavior to avoid such outcomes. So, how are you going to provide treatment to antisocial alcoholics?" Future studies, he added, need to focus on "children who show evidence of behavioral problems but have yet to develop alcohol problems. We also need to understand what impact their environments may have on their emotional responsiveness," he said.
Miranda agrees. "Conduct disorder (CD), the childhood predecessor to ASPD, is the most robust psychiatric risk factor for adolescent alcohol and drug use," he said. "Numerous studies point to a consistent relationship between conduct problems in early and middle childhood and later drug use; those who show more conduct problems have higher levels of drug use and higher rates of drug-related problems."
