A study examining the brain of a person with object agnosia, a defect in the inability to recognize objects, is providing a unique window into the sophisticated brain mechanisms critical for object recognition. The research, published by Cell Press in the July 14 issue of the journal Neuron, describes the functional neuroanatomy of object agnosia and suggests that damage to the part of the brain critical for object recognition can have a widespread impact on remote parts of the cortex.
Object agnosia is caused by an injury to the brain that does not include damage to the eyes or a general loss in intelligence. However, there is some controversy about the specific part of the brain that is linked with object agnosia. "Understanding the neuroanatomical basis of object agnosia promises to elucidate the neural correlates of object agnosia and to shed light on the mechanisms critical for normal object recognition," explains lead study author, Dr. Christina Konen from Princeton University.
To gain new insight into the neural basis of object agnosia, Dr. Konen and colleagues used neuroimaging and behavioral investigations to study visual and object-selective responses in the cortex of healthy controls and a patient called SM who, following selective brain damage to the right hemisphere of the brain, exhibited object agnosia.
The researchers discovered that the functional organization of the "lower" visual cortex, where the image from the retina is initially processed, was similar in SM and control subjects. However, SM exhibited decreased object-selective responses in the brain tissue in and around the brain lesion and in more distant cortical areas that are also known to be involved in object recognition. Unexpectedly, the decrease in object-selective responses was also observed in corresponding locations of SM's structurally intact left hemisphere. There also appeared to be some functional reorganization in intact regions of SM's damaged right hemisphere, suggesting that neural plasticity is possible even when the brain is damaged in adulthood.
The authors conclude that an area of the brain called the right lateral fusiform gyrus is critically involved in object recognition and that damage to this area can affect distant cortical regions. "To our knowledge, this study constitutes the most extensive functional analysis of the neural substrate underlying object agnosia and offers powerful evidence concerning the neural representations mediating object perception in normal vision," says Dr. Konen.