Nature of (wo)Man
By nature, men are nearly alike; by practice, they get to be wide apart.
Confucius

Courteously of Patrick Bermudez the picture above provides a glimpse into the stuff of our humanity. Shown here are horizontal slices from an identical cross section of magnetic resonance images from a sample of healthy adults involved in Bermudez's research (Neuroscience of Music). Briefly, the images have been meticulously coregistered and aligned in order to carry out statistical analysis in a standardized space. Careful attention was paid to preserve individual variability. It's time consuming and computationally intensive for researchers to play around in Procrustes' bed, but Patrick does it well. The resulting image is beautiful testament to the diversity that lends credit to Confucius' keen observation.
The human brain is literally an extension of the mammilian brain composed of two largely symmetrical hemispheres. Respectively, the left & right hemispheres of the human brain monitor and control the right and left sides of the body. On a finer structural level the two hemispheres consist of homologous structures which are assymetrical. The most noted homologous assymetry between the hemispheres are the peri-Sylvian regions involved in the production and comprehension of language.
In the MRI images the grey areas represent nerual nuclei and the white areas is primarily myelinated neural axons which connect different nuclei both within and across hemispheres. Commonly nurons and axons are referred to as grey and white matter in the brain. The most outer layer of grey matter in the human brain is known as the neocortex. The neocortex consists of a heavly interconnected seven layer columnar arrangement of neurons. On average the human brain weighs between 1.3-1.4 Kg which consititutes about 2% of total body weight for someone weighing 150 pounds. The brain consists of circa 100 billion neurons; 19.3 billion neurons in the neocortex in females and 22.8 billion in males.
Structural differences like the one just mentioned are plentiful and constatnly debated in the field of Neuroscience. Essentially, the blueprint & scaffolding for human brain structure is largley determined and regulated by genetic information. Inherent to this fine superstructure is a extensive degree of plasticity which enables the human brain and inturn the individual to adapt to different environments, learn and modify behavior based on experiences. Mechanisms underlying brain plasticity are the focus of intense research, however it is safe to presume that brain plasticity is governed by molecular processes that drive the shaping of interconnectivity within the brain.
Hypothetically, the structural differences visibile in the MRIs can in part be due to form and genetics naturally commen to humans. On a finer level of analysis the individual differences between MRIs may be in part consequent to the interconnectivity between brain regions that is shaped by the individuals experiences. Thus, by practice individuals grow wide apart.