Neuroanatomy and Cortical Landmarks

Prior to any type of functional mapping, a profound knowledge of neuroanatomy is mandatory. Focusing on the clinical applications of fMRI, this chapter will present methods to identify characteristic anatomical landmarks, and describe the course and shape of some gyri and sulci and how they can be recognized on MR imaging. As anatomy will be presented in neuro-functional systems, some redundancy is desired in order to course over cortical landmarks. If fMRI is not performed during clinical routine imaging, usually a 3D data set is acquired to overlay the results. Nowadays, fMRI is performed using echo planar imaging (EPI) with anisotropic distortion, whereas 3D T1-weighted data sets, such as MPRage (magnetization prepared rapid acquisition gradient echo) or SPGR (spoiled gradient recalled acquisition in steady state) sequences, are usually isotropic. Normalization of the fMRI data may reduce this systemic error to some extend that is more pronounced at the very frontal aspect of the frontal lobe and the very posterior aspect of the occipital lobe. However, for individual data, normalization and overlaying fMRI results on anatomy remains crucial. No two brains, not even the two hemispheres within one subject, are identical at a macroscopic level, and anatomical templates represent only a compromise (Devlin and Poldrack 2007). Usage of templates like the Talairach space (based on the anatomy of one brain) or the MNI template (based on 305 brains) can cause registration error as well as additional variation, and reduce accuracy; indeed, it does not warrant the shammed anatomical precision in the individual case.