Visual–spatial attention in alcoholics and illicit stimulant abusers: effects of nicotine replacement

Abstract

Reports of alcohol or illicit drug-related cognitive impairments have frequently disregarded the potentially confounding effects of smoking status and nicotine withdrawal on these measures. This study addressed this issue by measuring visual–spatial attention via an adaptation of the Posner paradigm in three groups of tobacco smokers: controls without a history of alcoholism or illicit drug use (n=27; 20 male), chronic alcoholics (n=22; 18 male), and illicit stimulant abusers (n=36; 21 male). Throughout testing, nicotine levels were stabilized by the double-blind administration of a high (14 or 21 mg) or low (7 mg) dose transdermal nicotine patch. A significant effect of group was observed for number of correct responses to restriction trials (F=5.48, 2/79 df; p=.006). Performance was normalized in the illicit stimulant group, and alcoholic participants exhibited superior performance relative to both illicit stimulant abusers (p=.002) and controls (p=.01). These findings support the hypothesis that nicotine may have a compensatory or normalizing effect on attentional functions in substance abusers. Whether these results reflect the central nervous system-activating effects of nicotine or merely alleviation of nicotine withdrawal is a topic of ongoing research.

Introduction

Chronic alcoholism has been associated with subtle deficits of information processing in tasks involving attention, perceptual-motor skills, visual–spatial functions, learning and memory, and abstraction and problem solving (Ahveninen et al., 2000, Nixon and Phillips, 1999, Oscar-Berman and Ellis, 1987, Parsons and Nixon, 1993, Polo et al., 2003). Recent studies have sought to examine other preexisting or comorbid factors, which might contribute to these findings. In particular, investigations utilizing subgroups of alcoholics who also abuse illicit substances are particularly timely given the prevalence of polysubstance use among treatment-seeking alcoholics (SAMHSA, 2000).

Of particular interest are the rates of illicit stimulant abuse with or without concurrent alcoholism. Although cocaine-related treatment rates have stabilized or declined in most regions of the United States, abuse of methamphetamine has increased dramatically (SAMHSA, 2000). Cocaine and methamphetamine are often used concurrently, with up to 20% of street-available stimulants containing a mixture of both substances (Albertson et al., 1999). In general, abuse of and/or dependence upon illicit stimulants have been associated with a pattern of deficits similar to that of chronic alcoholism, with particular focus on attentional decrements (Simon et al., 2000, Simon et al., 2002, Salo et al., 2002, McKetin and Mattick, 1998, McKetin and Solowij, 1999, Beatty et al., 1995, O'Malley et al., 1992). Although illicit stimulants and alcohol are frequently coabused (Bunney et al., 2001, Grant and Harford, 1990), the literature remains inconsistent with respect to the long-term effects of separate and combined abuse of these substances on cognitive functioning (see Bolla et al., 2000, Lawton-Craddock et al., 2003).

Legal stimulants, such as nicotine, also demonstrate measurable effects on cognitive functioning. In smoking participants, nicotine administration potentiates attentional functioning, sensory and motor abilities, and other cognitive skills (Heishman, 1998). Rodway et al. (2000) suggest that nicotine may enhance attentional functioning by increasing participants' ability to inhibit irrelevant information. An analogous function has been defined in our laboratory as the concept of cognitive efficiency or the ability to ignore irrelevant information while maintaining focus on relevant stimuli within a specified time frame (Nixon and Bowlby, 1996, Nixon and Parsons, 1991). Significant impairment of cognitive efficiency has been noted in alcoholics and alcoholic polysubstance abusers (Ceballos et al., 2003, Nixon et al., 1998, Nixon et al., 2002). Thus, the concomitant use of nicotine, alcohol, and illicit stimulants in treatment-seeking populations presents a potential confound in neurocognitive studies, as nicotine is known to enhance some aspects of cognitive functioning, which are typically impaired in these substance-abusing groups.

Conversely, nicotine withdrawal may be associated with measurable cognitive impairment following abstinence periods as short as 4 h (Pickworth et al., 1996, Snyder et al., 1989). This issue is particularly important given the high rates of smoking among alcoholics and illicit stimulant abusers (Le, 2002, Fertig, 2002, Tidey et al., 2000, Chait and Griffiths, 1983, Henningfield and Griffiths, 1981). Hence, effects of nicotine withdrawal may confound experimental results obtained via protocols in which participants are denied adequate access to nicotine throughout the testing session. Furthermore, substance abuse studies in which control groups are recruited without regard to smoking status could introduce significant bias, particularly given that alcoholics are three times more likely than the general population to be heavy smokers (Fertig, 2002, Le, 2002).

To date, the potentially compensatory and/or interative effects of acute nicotine administration on alcohol and illicit stimulant-related neurocognitive deficits have not been adequately examined. Thus, this study was designed to assess cognitive functioning, specifically visual–spatial attention, in regular tobacco smokers with and without a history of chronic alcohol or illicit stimulant abuse. Throughout testing, nicotine levels were stabilized by the double-blind administration of a low (7 mg) or high (14 or 21 mg) dose transdermal nicotine patch. An adaptation of the Posner paradigm (Carter et al., 1995, Posner et al., 1982, Posner, 1988, Posner, 1995, Hillyard et al., 1995, Hillyard et al., 1994, Luck et al., 1994) was employed, in which participants are required to covertly shift visual–spatial attention to detect both the presence and location of a target proceeded by a valid (i.e., relevant), invalid (i.e., irrelevant), or neutral cue. Because of our focus on cognitive efficiency, dependent variables of interest included accuracy and reaction time measures of the attentional subprocesses of disengagement and restriction (Posner, 1988, Posner, 1994, Posner, 1995, Posner and Dehaene, 1994). Previous studies have suggested that these components may be sensitive to nicotine administration and/or compromised in alcoholic polysubstance abusers (Murphy and Klein, 1998, Witte et al., 1997, Ceballos et al., 2000, published abstract).

The authors hypothesized that, within a sample of regular tobacco smokers, acute nicotine administration might act to normalize deficits of visual–spatial skill and attention associated with alcoholism and illicit stimulant abuse (Ahveninen et al., 2000, Nixon and Phillips, 1999, Oscar-Berman and Ellis, 1987, Parsons and Nixon, 1993, Polo et al., 2003, Simon et al., 2002, Beatty et al., 1995, O'Malley et al., 1992). A secondary hypothesis predicted that, based on previous research (Nixon et al., 1998, Lawton-Craddock et al., 2003), illicit stimulant abusers might exhibit decreased cognitive efficiency relative to other groups.