Optical Imaging of Cortical Activity: Real-time imaging using extrinsic dye-signals and high resolution imaging based on slow intrinsic-signals

The processing of sensory information, coordination of movement and other higher brain functions are carried out by millions of neurons that form elaborate networks. Individual neurons are synaptically connected to hun­ dreds or thousands of other neurons that shape their response properties. How these neurons and their intricate connections endow the brain with its remark­ able performance is one of the central questions in neurobiology. In the mammalian brain, cells that perform a given function or share common functional properties are often grouped together (e.g., the orienta­ tion and ocular dominance columns of the visual cortex). Attaining an under­ standing of the three dimensional functional organization of such groups of cells is a key step towards revealing the mechanisms of information process­ ing in a given cortical region. Thus, especially promising are experimental methods that allow the visualization of the functional organization of a cortical region, particularly methods that provide high spatial and temporal resolution. Currently there is a surge of interest in several imaging techniques that yield information about the spatial distribution of active neurons in the brain. These methods include the 2-deoxyglucose method (2-DG), radioactive imaging of changes in blood flow, electroencephalography, magnetoencepha­ lography, positron emmision tomography (PET), nuclear magnetic resonance imaging (MRI), and thermal imaging. Each technique has advantages as well