blood'-brain' barrier
Pronunciation: (blud'brān'),

This is the infamous impenetrable wall that for a long time gave scientist the belief that this just would not be an area where the first non-invasive brain treatment would be ale to take place.  a layer of tightly packed cells that make up the walls of brain capillaries and prevent substances in the blood from diffusing freely into the brain: passage across the cell membranes is determined by solubility in the lipid bilayer or recognition by a transport molecule.  Because of the introduction of ultrasound to utilize along with electromagnetism; this allows for the first time the ability to transverse the BBB.  Sonography molecules are small enough to slip through the heretofore impenetrable  barrier and thus make a larger pathway for electromagnetism to follow in its wake.  Without ultrasound the EBA mechanism simply would not work.  This a main reason why Transcranial Magnetic Stimulation continues to have difficulty in reaching its goals regarding the alleviation of depression.  TMA does not utilize sonography; and cannot without full permission from the Behavior Research Institute.