Docteur de l'université Automatic Segmentation and Shape Analysis ...

6 Chapter 1 Introduction
1.1.2 Hippocampus and its role in AD
Hippocampus has been the subject of particular interests to physiologists and neu-
roscientists due to its role in the memory, as well as its involvement in the neu-
rological disorders such as AD and epilepsy. Information concerning its function
and anatomy maybe found in texts and reference works on neurology and neu-
roanatomy of the subject (Duvernoy, 2005; Andersen et al., 2006; Taupin, 2008).
Hippocampal formation, including hippocampus proper (also known as cornu Am-
monis 1 , CA), subiculum, and dentate gyrus, is located in the limbic lobe on the
medial aspect of the hemisected brain. It belongs to the most primitive archicor-
tex of the cerebral cortex. In the description by Santiago Ramón y Cajal (1911;
for English translations, see Ramón y Cajal, 1995, also Ramón y Cajal, 1968), the
hippocampal proper is stratified into alveus, stratum oriens, stratum pyramidale,
stratum radium, stratum lacunosum, and stratum modeluare, which are usually
grouped into three archicortical layers, viz. molecular (stratum radium, stratum
lacunosum and stratum modeluare), pyramidal (stratum pyramidale), and poly-
morphic layers (stratum oriens), from deep to superficial, with ventricular surface
covered by the alveus.
Based on the cell morphology, Lorente de Nó (1934) divided the hippocampus
proper into 4 subfields, namely CA1–4 (see Figure 1.4). CA1, extending from
subiculum, is the largest subfield, characterized by pyramidal cells with triangular
cell body, in contrast to larger and ovoid cell bodies in CA2 and CA3. CA1 is also
known as the ‘vulnerable sector’ or Sommer’s sector, because of its inordinate sen-
sitivity to ischemia and hypoxia, while CA3 as the ‘resistant sector’ or Spielmeyer
sector. CA2 is a narrow region between CA1 and CA3, of which the characteriza-
tion and the distinct existence have been subject to discussion, while now can be
distinguished by molecular and genetic criteria (Lein et al., 2005; Mercer et al.,
2007). The CA4 subfield originally described by Lorente de Nó is the polymorphic
layer of the dentate gyrus, consisting of interneurons.
1 Latin for ‘Ammon’s horn’, after the Egyptian deity imn ‘Ammon’.