the university of pittsburgh

the university of pittsburgh

Disordered reading with stimulation to the left mid-fusiform gyrus

1mo ago
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In a new paper from our lab at the University of Pittsburgh, Hirshorn et al. PNAS, we shed light on critical aspects of how the brain reads, demonstrating a causal relationship between the activity in an area of the fusiform and skilled reading. We show that we can read out what word a person is reading at a particular moment from the activity recorded from electrodes surgically implanted in this area and that disrupting the activity in this region temporarily causes profoundly disordered word and letter recognition. In this study, the role of this area in reading was studied using electrodes placed within the brains of patients who chose to have surgical treatment for drug-resistant epilepsy. The electrodes were surgically implanted in the left fusiform gyrus and other brain regions. These electrodes were used to continuously monitor the patients’ brain activity for 1-2 weeks, so that the dysfunctional tissue causing their seizures could be precisely localized and then later removed. The patients also kindly volunteered to participate in research, which provided an unprecedented opportunity to understand how the brain recognizes printed words. First, mild electrical brain stimulation through these electrodes was used while patients read words and letters. This stimulation causes the brain tissue near the electrodes to temporarily act abnormally, and therefore disrupt the normal functioning of the stimulated area. When stimulation was delivered to the target area in the fusiform gyrus, patients’ ability to read words was profoundly disturbed, despite both patients being otherwise proficient readers. One patient reported thinking about two different words at the same time, and trying to combine them, despite only one word (illegal) being on the screen. In another case, she reported thinking that there was an “n” in the word message. The effects were even more dramatic in a second patient: he misperceived letters. When the letter “X” was on the screen, he first responded “A” and when the letter “C” was on the screen, he confidently reported seeing the letters “F” then “H”. When stimulation was delivered elsewhere, both patients could name words and letters without trouble. Also, stimulation to this fusiform region did not alter their ability to name pictures and faces. The patients’ reading disruptions can be seen in the video above. In addition to stimulating through these electrodes, the activity from the area was recorded while the patients read words. Using sophisticated techniques for pattern analysis, it was possible to use the recorded data to determine what word a patient was reading at a particular moment. This suggests that neural activity in the area codes knowledge about learned visual words that can be used to discriminate even visually similar words from each other. Taken together, the results of this study provide strong evidence that an area of the left fusiform gyrus becomes shaped by reading experience and plays a critical role in the accurate recognition of printed words. These results have important implications for our understanding of the neurobiological basis of many reading disorders and suggests a potential neural target for reading disorder therapies. See https://youtu.be/FvP1qeJHs8E and https://youtu.be/BfLyn4IH38c for full videos including control trials. For more information on this and our other research see http://lcnd.pitt.edu/ . See also: http://www.pnas.org/content/early/2016/06/17/1604126113.abstract EA Hirshorn, Y Li, MJ Ward, RM Richardson, JA Fiez, and AS Ghuman (In Press). Decoding and Disrupting Word Individuation in the Left Mid-Fusiform Gyrus. Proceedings of the National Academy of Sciences.