Asymmetrical stimulus generalization following differential fear conditioning

Rodent ultrasonic vocalizations (USVs) are ethologically critical social signals. Rats emit 22 kHz USVs and 50 kHz USVs, respectively, in conjunction with negative and positive affective states. Little is known about what controls emotional reactivity to these social signals. Using male Sprague–Dawley rats, we examined unconditional and conditional freezing behavior in response to the following auditory stimuli: three 22 kHz USVs, a discontinuous tone whose frequency and on–off pattern matched one of the USVs, a continuous tone with the same or lower frequencies, a 4 kHz discontinuous tone with an on–off pattern matched to one of the USVs, and a 50 kHz USV. There were no differences among these stimuli in terms of the unconditional elicitation of freezing behavior. Thus, the stimuli were equally neutral before conditioning. During differential fear conditioning, one of these stimuli (the CS⁺) always co-terminated with a footshock unconditional stimulus (US) and another stimulus (the CS⁻) was explicitly unpaired with the US. There were no significant differences among these cues in CS⁺-elicited freezing behavior. Thus, the stimuli were equally salient or effective as cues in supporting fear conditioning. When the CS⁺ was a 22 kHz USV or a similar stimulus, rats discriminated based on the principal frequency and/or the temporal pattern of the stimulus. However, when these same stimuli served as the CS⁻, discrimination failed due to generalization from the CS⁺. Thus, the stimuli differed markedly in the specificity of conditioning. This strikingly asymmetrical stimulus generalization is a novel bias in discrimination.     

Temporal discounting in "gain now-lose later" and "lose now-gain later" conditions

Studies on temporal discounting typically involve choosing between two outcomes of the same sign, i.e., positive or negative. For example, participants often are given a choice between a smaller, sooner gain and a larger, but later gain, or (less commonly) the options may be a sooner, larger loss and a later, but smaller loss. In contrast, participants in this study (N= 129; 66 women and 63 men, volunteers from Warsaw, Poland, all employed, with college education, ranging in age from 23 to 50 years, M=32.3 yr., SD=7.4) had to make a yes-or-no decision as to whether they would accept a financial offer involving a combination of a gain and a loss. This offer could be either an immediate gain to be followed later by a larger loss or an immediate loss followed later by a larger gain. Despite the substantial differences between the options in the present study and those in typical discounting studies, the same hyperboloid discounting function that describes choice between immediate and delayed gains also accurately described choice in the substantially different situations presented in the present study. In addition, steeper discounting was observed with a smaller delayed outcome than with a larger delayed outcome.