been assumed throughout much of the twentieth century, neuroge-
nesis is now known to occur in limited but measurable ways even
in the adult vertebrate brain. These neurogenic processes have been
best studied in the rodent brain but are also known to take place in
the adult human brain, particularly within a structure called the
hippocampus. Recent research has estimated that about fourteen
hundred new neurons are added each day within the two hippocampi
of the human brain.
The hippocampus is a bilateral structure located beneath the sur-
face of the temporal lobe known to play a pivotal role in the formation
and stabilization of memories (see Chapter 19). The name derives
from the perceived similarity between the shape of this structure in
the human brain and the shape of a seahorse, a fish with the genus
name Hippocampus (Fig. 10.7). The seahorse genus name comes from
a sea beast of ancient myth having the head and front legs of a horse
(Greek hippos = horse) and the posterior of some kind of weird fishlike
swimming creature (Greek kampos = sea monster).
HippocampusFigure 10.7. Left: hippocampus, the brain structure, revealed by exposing the
medial (interior) temporal lobe region. Right: Hippocampus, the seahorse.