Humans have an uncanny ability to skim through text, instantly recognizing words by their shape--even though writing developed only about 6000 years ago--long after humans evolved. Thus, neuroscientists have hotly debated whether an area of the cortex called the Visual Word Form Area (VWFA) is truly a specific and necessary area for recognizing words.
Functional MRI scans have shown that the area specifically activates when people read, as opposed to recognizing other objects, such as faces or houses. And people with lesions in the region lose the ability to recognize whole words--reduced to letter-by-letter reading. However, fMRI studies cannot demonstrate a causal role for the VWFA, and lesions involving the VWFA invariably involved other regions as well.
Now, a patient whose surgery to relieve epilepsy specifically disrupted the VWFA has given researchers, led by Laurent Cohen of the Hôpital de la Salpêtrière, an opportunity to demonstrate that the region does indeed play a causal role in the ability to recognize words.
The researchers reported in the April 20, 2006, issue of Neuron the results of reading, language, and object recognition tests both before and after the surgery on the 46-year-old man. They found his reading capability before surgery to be normal. However, tests after surgery showed very different results.
"Although we studied reading more extensively than the perception of other types of visual stimuli, our patient presented a clear-cut reading impairment following surgery, while his performance remained flawless in object recognition and naming, face processing, and general language abilities," reported the researchers. "Such selectivity may be difficult to observe in patients with more customary lesions resulting from strokes or tumors, which often affect a larger extent of cortex and white matter. The small size of the present lesion thus provides precious support to the idea of partial regional selectivity for word perception in the ventral cortex," they wrote.
Importantly, the researchers observed that before the surgery, the patient could recognize long words as quickly as short ones; but after the surgery, the recognition time increased linearly as a function of word length. Such findings indicated that the patient had been reduced to recognizing words letter by letter.
"How could there be a piece of neural tissue dedicated to a recently invented cognitive skill like word recognition?" wondered Alex Martin in a preview of the paper in the same issue of Neuron. Nevertheless, Martin commented, Cohen and his colleagues "report a unique set of findings in favor of the existence of the VWFA that will surely add fuel to the debate." He concluded that "The single case study…provides compelling evidence that the VWFA plays a causal role in the chain of neural events that underlie normal reading."
The researchers include Raphaël Gaillard of INSERM in Orsay, France and AP-HP, Hôpital de la Salpêtrière in Paris, France; Lionel Naccache of INSERM in Orsay, France and AP-HP, Hôpital de la Salpêtrière and Université Paris VI in Paris, France; Philippe Pinel of INSERM in Orsay, France; Stéphane Clémenceau and Emmanuelle Volle of AP-HP, Hôpital de la Salpêtrière in Paris, France; Dominique Hasboun, Sophie Dupont, and Michel Baulac of AP-HP, Hôpital de la Salpêtrière and Université Paris VI in Paris, France; Stanislas Dehaene of INSERM in Orsay, France; Claude Adam of AP-HP, Hôpital de la Salpêtrière in Paris, France; and Laurent Cohen of INSERM in Orsay, France and AP-HP, Hôpital de la Salpêtrière and Université Paris VI in Paris, France.
Gaillard et al.: "Direct Intracranial, fMRI, and Lesion Evidence for the Causal Role of Left Inferotemporal Cortex in Reading." Publishing in Neuron, 50, 191-204, April 20, 2006. DOI 10.1016/j.neuron.2006.03.031 www.neuron.org
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