Acoustic imprinting leads to differential 2-deoxy-D-glucose uptake in the chick forebrain

This report describes experiments in which successful acoustic imprinting correlates with differential uptake of D-2-deoxy[14C]glucose in particular forebrain areas that are not considered primarily auditory. Newly hatched guinea chicks (Numida meleagris meleagris) were imprinted by playing 1.8-kHz or 2.5-kHz tone bursts for prolonged periods. Those chicks were considered to be imprinted who approached the imprinting stimulus (emitted from a loudspeaker) and preferred it over a new stimulus in a simultaneous discrimination test. In the 2-deoxy-D-glucose experiment all chicks, imprinted and naive, were exposed to 1.8-kHz tone bursts for 1 hr. As shown by the autoradiographic analysis of the brains, neurons in the 1.8-kHz isofrequency plane of the auditory "cortex" (field L) were activated in all chicks, whether imprinted or not. However, in the most rostral forebrain striking differences were found. Imprinted chicks showed an increased 2-deoxy-D-glucose uptake in three areas, as compared to naive chicks: (i) the lateral neostriatum and hyperstriatum ventrale, (ii) a medial magnocellular field (medial neostriatum/hyperstriatum ventrale), and (iii) the most dorsal layers of the hyperstriatum. Based on these findings we conclude that these areas are involved in the processing of auditory stimuli once they have become meaningful by experience.