DISSOCIATION OF "WHAT" AND "HOW" INFORMATION IN RODENTS

Visual processing in the brain is divided into two major pathways: the dorsal “where” stream critical for spatial awareness, and a ventral “what” stream mediating object recognition. Consistent double-dissociations of these types of information is seen across many mammalian species, including rats, with knockdown of components of the dorsal stream such as the postrhinal cortex (POR) impairing processing of the spatial location of objects, while knockdown of ventral regions such as the perirhinal cortex (PER) impairs object recognition. However, evidence in humans and non-human primates shows that the dorsal stream is also critical to plan interactions with objects, leading to this pathway also being labelled the “how” pathway. Whether a homologous distinction exists in non-primates remains unknown. To address this question, rats were given selective lesions to POR or PER, or sham lesions. Using a combination of spontaneous object recognition and object-in-place tests, we have replicated previous observations of a double dissociation between “what” and “where” information – POR-lesioned animals showed impaired location recognition, while PER-lesioned rats showed impaired object recognition. In addition, we adapted the protocol of Goodale (1994) to rats – rats were rewarded for displacing a set of 12 uniquely-shaped objects. Like people, intact rats predominantly grasp these objects through their center of mass. Those with POR lesions, however, showed far less consistency in their grip of objects. These results suggest that the “what” vs “how” distinction is conserved in the visual processing streams of non-primates.