From the Highest Echelons of Visual Processing to Cognition

Supplementary content at http://bit.ly/364H8WR The inferior temporal cortex (ITC) is the highest echelon within the visual stream concerned with processing visual shape information. The Felleman and Van Essen diagram (Chapter 1, Figure 1.5) places the hippocampus at the top. While visual responses can be elicited in the hippocampus, people with bilateral lesions to the hippocampus can still see very well. A famous example is a patient known as H. M., who had no known visual deficit but gave rise to the whole field of memory studies based on his inability to form new memories. The hippocampus is not a visual area and instead receives inputs from all sensory modalities (Chapter 4). The history of how the inferior temporal cortex became accepted and described as a visual area is fascinating and follows the refinements in the ability to make more precise lesions and controlled behavioral experiments. In stark contrast to the hippocampus, bilateral lesions to the ITC are associated with impairment in visual object recognition in macaque monkeys (Section 4.7), and with several object agnosias in humans (Section 4.8). We are beginning to decipher the neural code that represents how visual scenes are interpreted.