Effects of prolonged ethanol exposure on neurophysiological measures during an associative learning paradigm

Long-term ethanol exposure has been reported to produce electrophysiological and cognitive impairments in some alcoholics. This study assessed the effects of chronic ethanol exposure on neurophysiological indices of associative learning in rats. Male Wistar rats (46) were exposed to ethanol vapor (EtOH group) or air (control group) for 6 consecutive weeks. After the animals were withdrawn from ethanol, electrodes were implanted in the frontal and parietal cortices and in the amygdala. Following a prolonged abstinence from ethanol (10-15 weeks), rats were exposed to a classical conditioning paradigm in which a food pellet was paired with the presentation of an auditory stimulus. During the first five sessions (conditioning phase), food pellet presentation was paired with the presentation of an infrequently presented tone. During the second five sessions (extinction phase), the association between food pellet presentation and the infrequently presented tone was weakened by no longer presenting food pellets following the infrequent tone. During selected test sessions, event-related brain potentials (ERPs) elicited by each tone (i.e. food-paired tone, non-paired tone) were recorded and analyzed. These analyses revealed differences in ERP responses between the groups. The latency of the N1 and P2 ERP components in the cortex of the control group, but not the EtOH group, increased during sessions when the association between food pellet delivery and tone presentation was being established or extinguished. These data support the hypothesis that chronic ethanol treatment results in a loss of responsivity in ERP components sensitive to changes in food-tone associations, even following a prolonged period of withdrawal from ethanol.