Lastly, to beat a dead bush:
FETAL BRAIN &
COGNITIVE DEVELOPMENT
Rhawn Joseph, Ph.D.
Brain Research Laboratory,
ABSTRACT
The human brainstem is fashioned around the 7th week of gestation and
matures in a caudal to rostral arc thereby forming the medulla, pons,
and midbrain. The medulla mediates arousal, breathing, heart rate, and
gross movement of the body and head, and medullary functions appear
prior to those of the pons which precede those of the midbrain. Hence,
by the 9th gestational week the fetus will display spontaneous
movements, one week later takes its first breath, and by the 25th week
demonstrates stimulus-induced heart rate accelerations. As the pons,
which is later to mature, mediates arousal, body movements, and
vestibular and vibroacoustic perception, from around the 20th to 27th
weeks the fetus responds with arousal and body movements to
vibroacoustic and loud sounds delivered to the maternal abdomen. The
midbrain inferior-auditory followed by the superior-visual colliculi is
the last to mature, and in conjunction with the lower brainstem makes
fine auditory discriminations, and reacts to sound with fetal heart
rate (FHR) accelerations, head turning, and eye movements--around the
36th week. When aroused the fetus also reacts with reflexive movements,
head turning, FHR accelerations, and may fall asleep and display rapid
eye movements. Thus fetal-cognitive motor activity, including auditory
discrimination, orienting, the wake-sleep cycle, FHRs, and defensive
reactions, appear to be under the reflexive control of the brainstem
which also appears capable of learning-related activity.
FETAL BRAIN-BEHAVIOR AND COGNITIVE DEVELOPMENT
It is now well established that the human fetus is capable of some
degree of behavioral complexity. In fact, as early as the 9th week of
gestation the fetus is able to spontaneously move the extremities,
head, and trunk (de Vries, Visser, & Prechtl, 1985). It has also
been suggested that the near term fetus may be endowed with some degree
of cognitive capability (e.g., Hepper & Shahidullah, 1994;
Kisilevsky, Fearson & Muir, 1998). Cognition has been inferred
based on alterations in fetal heart rate (FHR) and habituation to
airborne sound (Kisilevsky & Muir, 1991), response-declines to
vibroacoustic stimuli (Kisilevsky et al., 1998; Kuhlman, Burns, Depp,
& Sabagha, 1988), and what appears to be neonatal preferences for
the maternal voice as well as melodies and stories presented up to six
weeks prior to birth (DeCasper & Fifer, 1980; DeCasper &
Spence, 1986; DeCasper, Lecanuet, Busnel, Granier-Deferre &
Maugeais, 1994; Lecanuet, Granier-Deferre, & Busnel, 1989).
As will be detailed below, the behavior of the fetus and newborn is
likely a reflection of reflexive brainstem activities which are
produced in the absence of forebrain-mediated affective or cognitive
processing, i.e. thinking, reasoning, understanding, or true
emotionality (Joseph, 1996a, 1999; Levene, 1993; Sroufe, 1996). It is
the much slower to develop forebrain which generates higher order
cognitive activity and purposeful behaviors, and which is responsible
for the expression and experience of true emotions including pleasure,
rage, fear and joy and the desire for social-emotional contact (Joseph,
1992, 1996ab, 1999; MacLean, 1990).
At birth and for the ensuing weeks, the forebrain is so immature that
its influences are limited to signaling distress in reaction to hunger
or thirst; a function of the immature hypothalamus (Joseph, 1982, 1992,
1999) in conjunction with the midbrain periaqueductal gray (e.g.
Larson, Yajima, & Ko, 1994; Zhang, Davis, Bandler, & Carrive,
1994). Although various limbic nuclei become functionally mature over
the course of the first several postnatal months and years (Benes,
1994; Joseph, 1992, 1999), the neocortex and lobes of the brain take
well over seven, ten, and even thirty years to fully develop and
myelinate (Blinkov & Glezer, 1968; Conel, 1939, 1941; Flechsig,
1901; Huttenlocher, 1990; Yakovlev & Lecours, 1967).
It is rather obvious that the neonate is able to scream and cry and can
even slightly lift the corners of the mouth as if smiling. However,
these do not appear to be true emotions (Sroufe, 1996; however, see
Izard, 1991). In fact, smiling, as well as screaming and crying can be
produced from brainstem stimulation even with complete forebrain
transection or destruction (Larson et al., 1994; Zhang et al., 1994;
reviewed in Joseph, 1996a). Hence, neonatal and premature infant
"smiling" or distress reactions to noxious stimulation (e.g. heel
lance) are also likely brainstem mediated, particularly in that they
may be triggered in the absence of any obvious stimulus source and
following forebrain destruction or lack of development (anencephaly).
However, as brainstem maturation continues in a caudal-rostral arc
(Debakan, 1970; Langworthy, 1937), at term and over the following weeks
and months, the immature hypothalamus (which sits atop the midbrain),
and thus the forebrain, increasingly contributes to and gains control
over these behaviors (Joseph, 1992, 1999).
The progression in behavioral complexity that begins with spontaneous
fetal movements and which culminates with presumed preferences for the
sound of mother's voice, also appear to reflect maturational events
taking place in the brainstem, followed by forebrain structures.
Indeed, the brainstem is first fashioned around the 33rd day of
gestation (Bayer, 1995; Marin-Padilla, 1988; Sidman & Rakic, 1982)
and nearly completes its cycle of development and myelination around
the 7th gestational month (Gilles, Leviton, & Dooling, 1983;
Langworthy, 1937; Yakovlev & Lecours, 1967). However, in contrast
to the forebrain, the brainstem is incapable of cognition such as
reasoning, comprehension, or thought (Joseph, 1996c), but instead
reflexively reacts to a variety of stimuli in an exceedingly complex,
albeit stereotyped fashion (Blessing, 1997; Cohen, Rossignol &
Gillner, 1988; Cowie, Smith, & Robinson,1994; Steriade &
McCarley, 1990).
(The rest of the study is here: http://brainmind.com/FetalBrainDevelopment.html)
Just to show I don't pull random things out of my behind.
