The proportion of rats that preferred lever C (i.e., mean selection of lever C of the last 3 days>60%) after preference reversal did not differ significantly from that recorded in initially drug-naïve rats (8.3 versus 2.3%, z<1.96).
The proportion of rats with prolonged access to cocaine that preferred lever C after 10 days of choice did not differ from that recorded in initially drug-naïve rats (0.0 versus 2.3%, z<1.96).
Under the S-/C+ condition, rats displayed no preference until day 9, when they shifted toward preferring lever C.
However, regardless of the dose available, rats continued to prefer lever S over lever C [F 2,20) = 0.07, NS] (Fig. 4b).
Regardless of this residual tendency to choose lever C, the present study nevertheless clearly demonstrates that rats largely prefer lever S when it is rewarded by taste sweetness.
Since December of 2008, the Fed's preferred policy lever, the federal funds rate, has rested between 0% and 0.25%: effectively the lowest possible level, since the zero return on cash means that the central bank could not effectively deploy negative interest rates.
But 3 months after their last drink, they always preferred the risky lever, even when they payoff was poor, the researchers report this week in the Proceedings of the National Academy of Sciences.
As expected, following the training period, animals significantly preferred the L5 lever delivering the large reward (L5 choice: 88.9% ± 1.5).
This increase was not sufficient, however, to reverse the preference for lever S in favor of lever C. Thus, rats preferred saccharin even when its delay was equal to or above the delay of cocaine effects.
You flipped tiny levers next to your preferred candidates.
While the most subordinate monkeys clearly preferred cocaine to saline, the dominant monkeys' lever-pressing for cocaine "was not significantly different" from their lever-pressing for saline, says Nader, whose study appears in February's issue of Nature Neuroscience.
