Piracetam impairs the overshadowing of background stimuli by an informative CS

The effects of Piracetam (100 mg/kg) on passive avoidance learning was investigated in a situation in which rats received multiple conditioning trials. The test was based on the untrained preference of rats for a dark, rather than a brightly lit compartment. After the initial black-white preference was tested, rats were restricted to the black compartment for conditioning. Different groups received different percentages of tone-shock pairings. After the conditioning trials the black-white preference was again tested. The saline-injected rats showed overshadowing of the background stimulus by the tone, in the group that had received 100% tone-shock pairings; and an acquired aversion to the background stimuli in the group that had received 0% tone-shock pairings. In the rats injected with 100 mg/kg Piracetam associative strength was partitioned indiscriminately between the tone and the background stimuli, regardless of the tone-shock pairings that had been received during conditioning.