The effects of superior colliculus lesions in hamsters: feature detection versus spatial localization

This study was aimed at further documenting the effects of collicular lesions in exploratory activity in the hamster. Following habituation to a set of four objects placed in an open field, collicular and sham-operated hamsters were confronted to a change in the initial situation in which one object was replaced by a new one in a familiar location or in a new location, or a familiar object was moved to a new location, or was left in the same location (control condition). Hamsters sustaining lesions of the superior colliculus and sham-operated hamsters were found to habituate at the same rate. The surgical treatment modified the reactions to the spatial change. Intact hamsters reacted selectively to the new object, whatever its location. In contrast, collicular animals did not react to the familiar object when it was in a new location. Nevertheless, they were able to detect the new object when it replaced a familiar object at the same location. However, when the new object was at a new location, there was only a tendency in collicular hamsters to react to this change. When no change was made in the initial situation, no change in exploratory activity was observed in either group. These results, together with others, suggest that the rodent's superior colliculus is not directly involved in object discrimination, but plays a crucial role in the attentional components of spatial behavior.