Memory in the Chick: Multiple Cues, Distinct Brain Locations

Training chicks on a one-trial passive avoidance task results in memory-dependent synaptic remodeling in the intermediate medial hyperstriatum ventrale (IMHV) and lobus parolfactorius (LPO). Because pretraining IMHV lesions are amnestic and posttraining IMHV lesions are not, the functional significance of this remodeling requires explanation. Chicks use various cues to classify and remember objects. If the IMHV were concerned with memory for only one such cue, then posttraining IMHV lesions would not lead to "amnesia" because animals would still avoid the aversive bead using other contextual cues. This hypothesis was tested using a color discrimination task. IMHV lesions, but not LPO lesions, impair color discrimination, suggesting that the IMHV may be involved in classifying and remembering the bitter bead on the basis of color. Thus, even simple associations are stored in the brain in the form of multiple, dispersed representations.