Int. J. Environ. Res. Public Health 2009, 6 2009 occurs unbeknownst to the participants, seamlessly, and without warning. In delay conditioning the CS and the US overlap in time and terminate simultaneously. In trace conditioning, there is a silent trace period of no stimulation between the CS and the US. Given the neuropathological evidence of cerebellar and frontal system deficits associated with alcoholism, we predicted that alcoholics’ impairments on these learning tasks would increase systematically as task difficulty increased. Alcoholics would be more impaired in reversal learning (both delay and trace) than in simple discrimination learning. Furthermore, introduction of a silent trace interval was expected to further reduce alcoholics’ ability to acquire a simple discrimination as well as reverse that discrimination as compared to delay conditioning. 2. Experimental Section 2.1. Participants A total of 37 currently abstinent alcoholic’s (ALC) were recruited to participate in this study. All were naïve to the eyeblink classical conditioning procedures, meaning they had no prior training in eyeblink conditioning. The participants in this study were recruited from the Geriatric Research, Education, and Clinical Center (GRECC) at the Veterans Affairs Boston Healthcare System, Boston, MA, by way of distribution of flyers at local institutions, advertisements in local newspapers, and by referral from area hospitals. Abstinent alcoholic participants were screened to be free of any neurological disease or illness. Participants were also excluded for any CNS drugs, major head injury, hospitalization in a psychiatric facility > one week, or any medications for/history of severe psychiatric disorders (e.g., schizophrenia, chronic intractable obsessive compulsive disorder, agoraphobia, current major depression). History of substance abuse/dependence other than alcohol, except nicotine (current or lifetime) and cannabis (lifetime), was cause for exclusion. Cannabis use in the year prior to testing was cause for exclusion. To meet criteria for inclusion, the abstinent alcoholic participants met one or more of the three criteria delineated below: (1) positive SMAST, (2) positive DIS-IV for DSM-IV diagnostic criteria, or (3) reported a history of ≥ 21 drinks per week for five years or longer (Oscar-Berman, personal communication). All participants were self-described alcoholics. Participants were required to have abstained from drinking for at least one month prior to participating in the study. Drinking characteristics of the sample are provided in detail below and in Table 5. Delay Conditioning ALCs. Twenty abstinent alcoholic individuals were included in the delay discrimination reversal task (8 men, 12 women). The mean age of the delay ALC group was 49 years (standard deviation, SD = 8.4), the mean education in years was 13 (SD = 3.4), and the mean verbal intelligence as measured by the Wechsler Adult Intelligence Scale, Third Edition (WAIS-III) [19] was 100 (SD = 20.8). The mean duration of abstinence prior to testing was 4.2 years (SD = 5.3), but ranged from 1 month to 19 years (see Table 1). On the Lifetime Drinking History (LDH) [20], abstinent alcoholics reported a significant history of alcohol abuse that ranged in duration from 4 years to 46 years. The mean length of abuse was 24 years (SD = 11.0). This measure yields an estimate of total lifetime exposure to alcohol using standard drink conversions (grams absolute alcohol) via two methods: (1) total lifetime