Higher visual responses in the temporal cortex of mice.

The visual cortex of mice is a useful model for investigating the mammalian visual system. In primates, higher visual areas are classified into two parts, the dorsal stream ("where" pathway) and ventral stream ("what" pathway). The ventral stream is known to include a part of the temporal cortex. In mice, however, some cortical areas adjacent to the primary visual area (V1) in the occipital cortex are thought to be comparable to the ventral stream in primates, although the whole picture of the mouse ventral stream has never been elucidated. We performed wide-field Ca imaging in awake mice to investigate visual responses in the mouse temporal cortex, and found that the postrhinal cortex (POR), posterior to the auditory cortex (AC), and the ectorhinal and temporal association cortices (ECT), ventral to the AC, showed clear visual responses to moving visual objects. The retinotopic maps in the POR and ECT were not clearly observed, and the amplitudes of the visual responses in the POR and ECT were less sensitive to the size of the objects, compared to visual responses in the V1. In the ECT, objects of different sizes activated different subareas. These findings strongly suggest that the mouse ventral stream extends to the ECT ventral to the AC, and that it has characteristic response properties that are markedly different from the response properties in the V1.