Neurophysics of temporal discrimination in the rat: a mismatch negativity study.

Behavioral estimates of time discrimination threshold on animals might be contaminated by the conditioning procedure used and by attentional effects. To avoid such side effects, we measured time discrimination by recording the rat electroencephalographic response to small temporal variations. Freely moving rats were presented with repetitive sounds, some of them being occasionally shorter than the standard, to produce a Mismatch Negativity (MMN) which is known to primarily involve preattentive processes. The smallest difference eliciting a MMN located the discrimination threshold between 16% and 33% of the standard, without attentional confound. Being observed in several species, MMN can be used to decipher both the phylogenetic and ontogenetic evolution of time discrimination, without attentional confound.