Thursday, March 20, 2008
Cool ECoG recording study on word perception by Canolty et al.
A study by Ryan Canolty and a host of other co-authors including Bob Knight, and our friend Nina Dronkers, published in the online journal, Frontiers in Neuroscience, used electrocorticogram (ECoG) recordings to monitor the spatiotemporal dynamics (such a fancy sounding phrase) of word perception. ECoG strikes me as a method that is highly under-utilized in cognitive neuroscience research. We are all so interested in getting both high spatial and temporal resolution, yet very few people have used ECoG, which has both (Dana Boatman is one person who comes to mind as having used this method). The downside is that to record electrical signals directly from the surface of the brain, you have to implant electrode grids, and you can only do this in patients with neurological diseases, such as epilepsy. Usual caveats aside regarding the generality of findings from such populations, the method seems to have a lot of promise.
Canolty et al. summarize their main findings more eloquently that I could, so I'll just quote them:
"Word processing involves sequential activation of the post-STG, mid-STG, and STS and these results validate previous spatial results regarding the cortical regions involved in word processing, and, in turn, language comprehension. These neuroanatomical results support lesion and neuroimaging studies which have shown word-related activity to occur in the post-STG, mid-STG, and STS (Belin et al., 2002; Binder et al., 2000; Démonet et al., 1994; Dronkers et al., 2004; Dronkers et al., 2007; Fecteau et al., 2004; Giraud and Price, 2001; Indefrey and Cutler, 2005; Mummery et al., 1999; Petersen et al., 1988; Price et al., 1992; Price et al., 1996; Scott and Wise, 2004; Vouloumanos et al., 2001; Wise et al., 2001; Wong et al., 2002; Zatorre et al., 1992). However, these results also reveal the temporal flow of information between these distinct brain regions and support a component of serial processing in language. This study complements and extends Binder and colleagues (2000) by demonstrating that word processing first activates the post-STG, then the mid-STG, and finally the STS."
This is interesting, particularly because it doesn't show much activity in anterior temporal regions which some have argued as being critical to word-level processing (e.g., Scott et al. 2000). The authors of the ECoG study suggest that STS activation, which tended to arrive at the party a bit late relative to STG regions, are involved in word meaning-related functions, because real word stimuli modulated activity there relative to non-words. They suggested that this finding may contradict the Hickok & Poeppel view of the STS supporting phonological functions. It may, or may not. For example, their STS activations could reflect activation of networks involved in processing or representing phonological word forms. Whatever the correct interpretation, it is nice to have decent spatiotemporal resolution in the process of word recognition. (Too bad they couldn't implant grids bilaterally!)