Discrimination learning of amplitude modulated tones in Mongolian gerbils

Abstract

Discrimination learning of 100% sinusoidal amplitude modulated tones (AM) was investigated in adult Mongolian gerbils using a footshock motivated shuttle box avoidance go/no go paradigm. AM stimuli to be discriminated had identical carrier frequency (2 kHz) but differed in modulation frequency ( f m) by one octave. Six groups of gerbils were trained to discriminate AM-pairs with f m ranging from 10 to 640 Hz. Learning proceeded faster and discrimination performance was slightly better for low f m, up to 80 Hz, than for high f m, above 80 Hz. These results may be related to cortical AM encoding (Schulze, H. and Langner, G., J. Comp. Physiol. A, 181 (1997) 651–663), which is temporal for low f m (synchrony code) and spatial for high f m (rate-place code). This may implicate different neuronal learning strategies or distinct behavioral meanings influencing the discrimination training.