The presentation of tone and shock stimuli in all training and testing sessions was controlled by GraphicState software (Coulbourn Instruments).
Briefly, the subjects were placed in a basic Skinner box module (Coulbourn Instruments, Allentown, USA) and left undisturbed for 2 min. Then, a training session consisting of 7 presentations of tone (7 s, 1000 Hz, 70 dB) (CS), coterminating with an electric foot shock (2 s, 1 mA) (US), was delivered with intervals of 30 s. immediately afterwards, the animals were returned to their home cage.
In the 129SVE strain, freezing behavior before presentations of tone-shock pairings was minimal and did not differ across the genotypes (F2,51=0.53, P=0.589), but significantly less freezing was observed in both heterozygous and knockout mice, compared with their wild-type littermates, in the periods following the three tone-shock associations and after the third association.
The rats received two types of ambiguous probe-testing: presentation of single tones of a frequency different to the reference tones with which they were trained (single-frequency probes), and simultaneous presentation of the two reference tones (dual-frequency probes).
Ambiguity tests involving simultaneous presentation of training tones correlated strongly with tests using a single ambiguous tone presentation and could be used in future as new measures of attention bias.
A speaker connected to a sound generator was also mounted at the top of the sound-attenuating chamber for the presentation of discrete tones.
Although tones have been used extensively in research as a conditioned stimulus, we do not know of any report that mere presentation of unconditioned tones is rewarding in rats.
Simultaneous presentation of acoustic tones with electrical stimulation led to suppression of the electrically evoked response, which increased with increasing acoustic level.
The rate of excitatory presynaptic events (EPSPs) was measured during monaural ipsi- or contralateral presentation of pure tones at different frequencies.
