effect is not always straightforward. For example, the amount of serotonin
released and recycled (serotonin turnover) predicts the chance of such diverse
behaviors as violence, suicide, and depression (Kalat, 2016, pp. 368–9). The
role of neurotransmitters will be considered in the context of the neuroscien-
tific study of rituals and religious experience (see especially section 7.7),
among others.
There are a hundred billion (also written as 10^11 ) neurons in the brain, in
addition to which there are many more glial cells that support the neurons.
The“gray matter”near the surface of the brain consists of cell bodies whereas
the“white matter”below it is made up of glial cells and the axons of neurons
travelling to other neurons. Many of the axons are covered by a fatty layer
called the myelin-sheath, which speeds up the spread of the action potential.
As we proceed deeper toward the lower part of the brain and the spine we
reach increasingly more archaic layers of the brain. Since the major divisions
of the brain were positioned horizontally one behind another in the evolu-
tionary history of animals, they are called the forebrain, the midbrain, and the
hindbrain. In this survey, we will only consider the forebrain, the most recent
part. Before we get started, it is also useful to mention a couple of standard
anatomical terms there are used to designate directions and positions in the
brain (cf. England & Wakely, 2006, pp. 19–22). The meaning of some of the
expressions can be easily deduced from Latin, such asanterior(toward the face),
posterior(toward the back of the head),superior(toward the top of the head),
andinferior(toward the feet). Further,lateralis something that is positioned at
the side of the brain andmedialis something that is toward the inside symmetry
plain of the brain. A bit less intuitive are the termsdorsalandventral:aswiththe
main divisions of the brain, these directions make sense if we think of animals
walking on four legs. Thusventralis something that is toward the stomach and
dorsaloriginally means something that is toward the back; in humans, however,
the dorsal direction is found toward the top of the head.
In humans, the cerebral cortex covers most other parts of the brain (see
Figure 3.2). The cerebral cortex is divided into two symmetric halves called the
cerebral hemispheres, which are connected by the corpus callosum and a few
smaller bundles of neurons (commissures). Interestingly, many neuronal
pathways of the body are connected to the opposite side of the brain (Kalat,
2016, pp. 424–32). For example, the muscles on the left side of the body are
connected to the right hemisphere. The situation is more complicated in the
case of vision: the left hemisphere sees only the right half of the visualfield,
receiving information about the right visualfield from both eyes (and vice
versa). In various cognitive tasks one of the two hemispheres takes part more
intensely, a division of labor that is calledlateralization. For example, under-
standing and producing language mostly relies on the left hemisphere (Mildner,
2008, pp. 99–137; Denes, 2011, pp. 44–7). The right hemisphere, in contrast,
plays a dominant role in reading emotional clues and comprehending spatial
54 Cognitive Science and the New Testament