Delineating brain regions

[SandyaS72]

So if there's not a really precise delineation of regions of the brain, when there are studies that talk about the size of regions being different between groups, or even talking about the size of a hippocampus for example, on what basis can they draw that conclusion?

[kittyzxu]

One way to "map" out a region is to sample different parts within the target region and record the neurons in that region. Then you compare/examine the firing patterns of those neurons until their shared features become less and less.Then you go back to your original recording notes and write down the x,y,z coordinates of these regions and a "map" will gradually become obvious. Needless to say, this way of mapping is tedious and requires lots of work...imagine mopping a basketball court with a toothbrush. We sometimes further confirm the mapping using anatomical MRI in addition. --- An electrophysiologist's confession on brain "mapping"

[akim1]

In gross anatomy sense, the hippocampus is well-delineated. It has a very different texture (that you can both feel and see) from the rest of the cortex. I guess the point made in lecture was more specifically in the microscopic sense. If you were to look under a microscope, the boundaries are less clear, and hippocampal cells will frequently encroach into non-hippocampal territory. Given this, measuring the size of hippocampus (by mass or length) is trivial (if the person is dead) as long as you're not looking for microgram/micron resolution. I'm not sure how prominent it is on the different imaging modalities.

The delineation given by the homunculus (connection between your body and the different parts of the cortex), on the other hand, is very vague and ambiguous. There is really no precise boundary but general regions where a stimulus could cause neuronal activity.

[michaelseung]

Piggybacking off of kittyzxu's comment, recent imaging technology (e.g. Electroencephalography) allows scientists to monitor brain activity while the patient conducts specific tasks, like speaking. Over multiple trials, specific regions of the brain will be determined and this brain mapping can be achieved. With this, region sizes can be discussed, but like the above comments, I think the precise boundaries become unclear under the microscope in most circumstances.