No abstract

Evidence from functional neuroimaging of the human brain indicates that information about salient properties of an object-such as what it looks like, how it moves, and how it is used-is stored in sensory and motor systems active when that information was acquired. As a result, object concepts belonging to different categories like animals and tools are represented in partially distinct, sensory- and motor property-based neural networks. This suggests that object concepts are not explicitly represented, but rather emerge from weighted activity within property-based brain regions. However, some property-based regions seem to show a categorical organization, thus providing evidence consistent with category-based, domain-specific formulations as well.

The cognitive and neural mechanisms underlying category-specific knowledge remain controversial. Here we report that, across multiple tasks (viewing, delayed match to sample, naming), pictures of animals and tools were associated with highly consistent, category-related patterns of activation in ventral (fusiform gyrus) and lateral (superior and middle temporal gyri) regions of the posterior temporal lobes. In addition, similar patterns of category-related activity occurred when subjects read the names of, and answered questions about, animals and tools. These findings suggest that semantic object information is represented in distributed networks that include sites for storing information about specific object attributes such as form (ventral temporal cortex) and motion (lateral temporal cortex).

An intriguing and puzzling consequence of damage to the human brain is selective loss of knowledge about a specific category of objects. One patient may be unable to identify or name living things, whereas another may have selective difficulty identifying man-made objects. To investigate the neural correlates of this remarkable dissociation, we used positron emission tomography to map regions of the normal brain that are associated with naming animals and tools. We found that naming pictures of animals and tools was associated with bilateral activation of the ventral temporal lobes and Broca's area. In addition, naming animals selectively activated the left medial occipital lobe--a region involved in the earliest stages of visual processing. In contrast, naming tools selectively activated a left premotor area also activated by imagined hand movements, and an area in the left middle temporal gyrus also activated by the generation of action words. Thus the brain regions active during object identification are dependent, in part, on the intrinsic properties of the object presented.

No abstract