
The anatomic conventions of the Talairach Atlas are that anatomic right, 
superior and anterior directions are positive, while left, inferior and 
posterior directions are negative (Talairach Atlas Landmarks). Talairach 
Atlas Lanmarks are used to define the registration are as follows: 

1. The Anterior Commissure (AC), defined as the origin of the Talairach 
  Atlas coordinate system, is assumed to be at location (0, 0, 0). 

2. The Posterior Commissure (PC) is assumed to be at location ( 0, -24, 0 ). 

3. The point where the AC-PC line intersects the posterior extent of the 
  brain at the AC-PC level. This point is designated as the landmark 
  "Posterior to the Posterior Commissure" (PPC), and is assumed to be at 
  location ( 0, -102, 0 ). 

4. The point where the AC-PC line intersects the anterior extent of the 
  brain at the AC-PC level. This point is designated as the landmark 
  "Anterior to the Anterior Commissure" (AAC), and is assumed to be at 
  location ( 0, 68, 0 ). 

5. The point where a "horizontal" line passing through the AC intersects 
  the left extent of the brain in the coronal plane containing the AC. 
  This point is designated as the landmark "Left of the Anterior Commissure" 
  (LAC), and is assumed to be at location ( -62, 0, 0 ). 

6. The point where a "horizontal" line passing through the AC intersects 
  the right extent of the brain in the coronal plane containing the AC. 
  This point is designated as the landmark "Right of the Anterior 
  Commissure" (RAC), and is assumed to be at location ( 62, 0, 0 ). 

7. The point where a "vertical" line passing through the AC intersects the 
  superior extent of the brain in the coronal plane containing the AC. This 
  point is designated as the landmark "Superior to the Anterior Commissure" 
  (SAC), and is assumed to be at location ( 0, 0, 72 ). 

8. The point where a "vertical" line passing through the AC intersects the 
  inferior extent of the brain (i.e., the inferior extents of the temporal 
  lobes) in the coronal plane containing the AC. This point is designated 
  as the landmark "Inferior to the Anterior Commissure" (IAC), and is 
  assumed to be at location ( 0, 0, -42 ). 

In order to best place the landmarks according to the assumptions used to 
determine their locations in Talairach Atlas space, it is recommended that 
you locate and place landmark vertices in specific orthogonal views, as follows: 

  AC, PC: Use sagittal and transverse views 

  SAC, IAC, RAC, LAC: Use coronal view 

  AAC, PPC: Use transverse view 

[END MedX quote]
