From anatomy to behavior

Our ultimate goal is to understand the function of the human corpus callosum. But the experimental arsenal for studying the microphysiology of the corpus callosum is still limited. The method of choice is still ERP (see the next section). The application of TMS methodology has been useful but limited (e.g., Pascual-Leone, Walsh, and Rothwell, 2000), recording from depth electrodes during behavior is still in its infancy (cf. Fried, MacDonald, and Wilson, 1997), and PET methodology still has crude spatial resolution that prevents a precise regional analysis.

One unique data set comes from recording electrical activity on the exposed cortex while stimulating different points on the midsagittal callosum area during callosal section for epilepsy (Chen, 1986). Behavioral methods for studying callosal function are better developed for sensorimotor integration through the corpus callosum (witness the Poffenberger paradigm) than for cognitive and control functions (see Part III). There remains the anatomy of the corpus callosum, visualized by ever improving methodology of brain imaging. But how do we analyze the structure of the corpus callosum? And how do we study its structure/function relationship? The standard approach has been to analyze the size and shape of the midsagittal cross-section of the corpus cal-losum. But analysis of the structure of the corpus cal-losum off the midsagittal plane and volumetric measures of the corpus callosum may have differential functional organizational significance. They are likely to receive increased morphometric attention in the next decade.

Consider the anatomical approach. Two questions immediately arise: what to measure and how to measure it.

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