1. Introduction: A Historical Perspective
The degree to which sex differences extend to human brain anatomy has
been investigated in many studies. The first postmortem studies on brain
sex differences have reported larger and more asymmetrical male than
female brains (Swaab DF and Horfman MA, 1984). During that period, brain
sexual differences in neuroscience were exclusively restricted to the
hypothalamus, sex hormones, and sexual behavior (Siva NL and Boulant JA,
1986; Levine S, 1966). Later, a surge of research focused on the
influence of sex hormones on different brain regions such as the
amygdala, hypothalamus, and hippocampus (Siva NL and Boulant JA, 1986),
as well as brain sensory motor and cognitive functions including memory,
emotion, navigation, and pain perception in healthy and diseased
condition (Kimura D et al., 1996). By the 20thcentury, the development of neuroimaging techniques (MRI, PET, TMS, EEG)
has extensively advanced our understanding of the differences between
male and female brains during normal development, from childhood,
through adolescence, to adulthood. Neuroimaging highlighted the
differences in behaviors, cognitive and emotional functions, and pointed
out the risk and consequences of various neurological and psychological
disorders (Arnold AP et al., 2017). Analyzing such differences has a
wide range of implications, from studying fundamental neuroscience to
practical guidelines in the diagnosis, prognosis, and treatment of brain
disorders. As research continues to deepen our knowledge of biological
sex differences, a newly emerging field is intended to address the
diagnostic and clinical needs of both sexes: sex-based biology and
medicine. The overall purpose of this review paper is to combine the
findings from neuroscience, neuroimaging, brain research,
neurobehavioral, neonatology, and neurodevelopment studies covering all
aspects of neonate brain development from volumetric, to microstructure
and functional connectivity. We aim to provide the investigators with a
global and precise overview on this topic to help the exploration of sex
differences in normal brain development. This review research allows for
a better understanding of the pathophysiology of brain abnormalities
observed in various sex-linked diseases such as neural tube defects,
neonatal seizures, autism spectrum disorder (ASD), and brain tumor, that
develop early in life.