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Prenatal memory
Prenatal memory,
also called
fetal memory,
is important for the development of memory in humans. Many
factors can impair fetal memory and its functions, primarily maternal actions. There are multiple techniques
available not only to demonstrate the existence of fetal memory but to measure it. Fetal memory is vulnerable
to certain diseases so much so that exposure can permanently damage the development of the fetus and even
terminate the pregnancy by aborting the fetus. Maternal nutrition and the avoidance of drugs, alcohol and other
substances during all nine months of pregnancy (especially the critical period when the nervous system is
developing) is important to the development of the fetus and its memory systems. The use of certain substances
can entail long-term permanent effects on the fetus that can carry on throughout their lifespan.
Contents
Background Information and Functions
Development
Functions
Measurement techniques
Classical Conditioning
Habituation
Exposure Learning
Implications
Diseases and conditions affecting fetal memory
Intrauterine hypoxia
Hypothyroidism
Rubella
Fetal Nutrition and Memory
Longitudinal Memory Effects of Prenatal Drug Exposure
Pregnancy Category
Alcohol
Cocaine
Heroin
Methamphetamine
See also
References
Background Information and Functions
There is some evidence that fetal memory may begin within the second trimester after conception. Substantial
evidence for fetal memories has been found at around 30 weeks after conception.
[1]
Fetal memory is important
for parental recognition, and facilitates the bond between child and parents. One of the most important types of
memory is that which stores information contributing to the maternal bond between infant and mother. This
form of memory is important for a type of development known as attachment.
[2]
Fetal memory is thus critical
to the survival of the fetus both prenatally (in the womb) and after birth
as an infant.
Development
The Central Nervous System (CNS) and memory in the fetus develop
from the ectoderm following fertilization via a process called neurulation.
Fetal memory is integral to
The ectoderm is the outermost layer of the embryo. This happens
mother-infant attachment.
towards the end of the third week of gestation (time period when the
embryo is carried in the women's uterus) and ends with the start of the
development of the neural tube, an important structure crucial to
development of the central nervous system. Some evidence suggests memory is actually responsible for
carrying out the development of the CNS during neurulation. However, much more research needs to be done
on this. Fetal memory and brain development can be impaired by a number of maternal implications. Rubella,
intrauterine hypoxia and hypothyroidism are some of the more researched examples. Alcohol and other
substances such as hard drugs can affect this process as well.
Functions
Once neurulation is complete and has given rise to the nervous system, fetal memory becomes responsible for
a variety of tasks. One of its main functions at this point is to control breathing in the fetus. Also noted, was its
ability to control eye movement and coordination during all nine months of development. There is evidence
that these are practiced in the womb and carried out similarly after birth. Learning language as an infant also
requires fetal memory. It is now known that the mother's voice is clearly heard from inside the womb and that
the fetus can differentiate speech sounds, particularly the phonemes (a single segment of sound) in speech.
This is evident in the baby when born, showing many signs of early language comprehension. It has also been
shown that infants prefer their mother's native language after being exposed to it in the womb. Evidence also
exists that the infant, when born, prefers its mother's smell from having memorized her scent as a fetus.
Memory is critical for the recognition process that takes place between the mother and infant through
breastfeeding. Breast milk contains contents recognizable by the infant that they were exposed to through
amniotic fluid (fluid that encompasses the fetus and is responsible for its nutrition in the womb) in the fetal
stage. Since the baby is so dependent upon the mother, maternal nutrition also plays a large role in the infant
developing healthy brain functioning; including memory function, which the infant cannot live without. Thus,
fetal memory is critical to the survival and healthy development of the infant before and after birth. Many of
these functions are measured through methods such as classical conditioning, habituation and exposure
learning, being the most popular.
[2]
Measurement techniques
There are considered to be three paradigms used to investigate fetal learning and memory. They are: classical
conditioning, habituation and exposure learning.
[3]
Classical Conditioning
Classical conditioning is described as the pairing of a conditioned stimulus (CS) (such as a vibration) with an
unconditioned stimulus (US) (such as a loud noise) to evoke a conditioned response (CR) (agitation). In this
pairing, the vibration will be presented immediately followed by a loud noise. Initially, the presentation of the
loud noise (US) would cause the unconditioned response (UR) (natural agitation) without prior classical
conditioning. However, the continuous pairing of the loud noise (US) with the vibration (CS) converts the
unconditioned response (UR) into a (CR) as the fetus learns that the presentation of a vibration will be
followed by a loud noise. Eventually, the fetus will respond to the vibration (CS) without being exposed to the
loud noise (US); this is when conditioning has occurred. Conditioning has been demonstrated in as few as 12-
15 pairings of the vibration (CS) with the loud noise (US) in fetuses as early as 32 weeks of gestation.
[3]
Another study replicated these findings.
[2]
Fetuses between 32 and 39 weeks gestation were presented a pure tone (CS), which was paired with a
vibroacoustic stimulus (US). A vibroacoustic stimulus is a low bass sound frequency that is felt by the fetus as
a mechanical vibration.
[4]
After 10-20 pairings, approximately 50% of the fetuses showed successful
conditioning, unrelated to age or sex of the fetus. It is suggested that poorly prepared experimental set up,
inaccurate or inappropriate response measures and unsuitable stimuli could all contribute to failed conditioning,
as opposed to lack of fetal memory.
[2]
Reasons for some fetuses demonstrating conditioning, while others do
not, remains undetermined.
Habituation
The second paradigm, habituation, is one of the most successful ways of
investigating fetal memory. Habituation has been demonstrated in fetuses
as early as 22 weeks and corresponds to the onset of fetal auditory
abilities.
[5][6][7][8]
Both auditory and vibroacoustic stimulation have been
used in habituation. Vibroacoustic stimulation is a technique involving
the repetitive stimulation of the fetus, by applying a vibroacoustic
stimulus (in predetermined intervals) to the abdomen of the mother. The
movement and reaction of the fetus, in response to the stimulus, is
Evidence shows that newborns in
recorded using ultrasound technology. This process is repeated until
the neonatal period, like above,
habituation, defined as a lack of response to the stimulus by the fetus, is
are habituated to auditory stimuli
reached. Stimulation trials continue into the neonatal period (first 28 days
experienced while a fetus.
after birth) by presenting the same auditory stimulus, to test whether or
not the fetus has memory of the stimulation events. A scientific control
group of babies in the neonatal period, having not been exposed to the stimulus as a fetus, are used in neonatal
trials to serve as a comparison.
Results from another recent study suggest that fetuses were able to form both short and long-term memories.
[9]
This conclusion was drawn from the fact that habituation rates (number of stimuli needed to habituate) were
higher in babies in the neonatal stage that had not previously undergone fetal stimulations when compared to
those who had: therefore demonstrating the memory of the stimulus in its fetal stage being carried into the
neonatal stage.
Exposure Learning
The final experimental technique used to investigate fetal learning and memory is exposure learning. This
technique allows the experimenter a lot of control over the presentation of the stimulus and following
testing.
[2]
Exposure learning is the act of presenting the fetus with a stimulus, such as a television theme tune,
repeatedly while in the womb and then testing recognition (learning) of that tune after birth. One experiment
was conducted where fetuses were exposed to the television theme tune from the show "Neighbours" while in
the womb.
[10]
In the first condition of the experiment, newborns age 2–4 days who were exposed to the tune
while in the womb were presented with the tune after birth. Upon hearing the tune, these newborns showed
physiological changes, such as a decrease in heart rate. This observed change did not happen with unfamiliar
tunes, or to newborns that were not exposed to the tune in the womb; so the tune had to be learned in the
womb. Recognition of the tune was strong 2–4 days after birth, however, diminished after the age of 21 days
without repeated exposure.
[10]
A second exposure learning experiment, using the television theme tune, was conducted to determine when
learning and memory could first take place in utero. It was determined that by 30–37 weeks of gestation,
fetuses previously exposed to the theme tune were more active when presented with the tune than those who
had no previous experience with the tune. This demonstrates that stimulus recognition begins no earlier than
30 weeks of gestation.
[11]
Implications
Overall, studies indicate that there is an ability for fetal learning and memory, and through classical
conditioning, habituation and exposure learning that memory can be measured. It is important to note that
certain periods in fetal development allow for different learning and memory abilities, which should be taken
into consideration when determining if fetal memory exists. Auditory stimuli presented in the womb can be
retained and recognized (learned) into the days following birth and that learning is specific to familiar auditory
stimuli.
[12][13]
Measuring learning and memory in the fetus has only been discussed in terms of healthy
pregnancies; however, many factors such as disease affect these delicate processes.
Diseases and conditions affecting fetal memory
Much research and literature has shown that endocrine, neurological and most other diseases a mother or father
carries can have adverse effects on a fetus's development.
[14]
The majority of the research done regarding fetal
brain development, and consequently its memory after birth, has focused on one condition or state and two
main diseases: intrauterine hypoxia, hypothyroidism and rubella.
Intrauterine hypoxia
Intrauterine hypoxia is a condition or state caused by insufficient oxygen
levels reaching a fetus during gestation, having detrimental effects on the
development of its central nervous system (CNS).
[15]
In many cases,
intrauterine hypoxia results in the death of the fetus. Commonly known,
the CNS is vital to the communication and response transmissions
between the brain and all of the body parts within an organism. Due to
dysfunction in this system such things as cognitive functioning and
attention capacity are impeded, resulting in a poor ability to decode or
encode information and form memories.
[16]
It has also been discovered
that lower levels of oxygen reaching the developing fetus may, in fact,
decrease the amount of grey matter produced within its brain
[17]
and
The frontal lobe (highlighted in
increase the amount of sulcal (referring to a sulcus: a fissure within the
red) is one part of the fetus's
surface of the brain) cerebrospinal fluid (CSF); importantly in the frontal
brain that can be negatively
[18]
The later
lobe and temporal lobe, which are critical memory centers.
affected by decreased levels of
point regarding sulcal CSF has been linked to schizophrenia (a mental
oxygen due to intrauterine
hypoxia.
disorder affecting thought processes). Grey matter is a large component
of the CNS and is related to: muscle control, sensory perceptions,
memory, emotions and speech; please follow this link for more
information regarding the different brain structures and their effects on human function.
[19]
Hypothyroidism
Hypothyroidism is a disease that may have severe, adverse effects on the brain development in a fetus. These
problems are often caused by a "passing-down" from the mother or from an external neurotoxin causing
impaired cognitive ability and, in extreme cases, mental retardation.
[20]
Hypothyroidism is usually caused by an iodine deficiency that results in the under production of thyroid
hormones or an underdeveloped thyroid gland with similar effects.
[15]
Thyroid hormone release is regulated
by a stimulating hormone called thyrotropin (TSH) in a normal functioning person. In abnormal cases when
there are lowered levels of thyroid hormone, TSH levels increase to compensate, thus doctors and medical
researchers can measure TSH levels to predict hypothyroidism.
[21]
If interested, a good explanation of this
process and the consequences of abnormal levels of TSH can be found under this link.
[22]
Reduced levels of
thyroid hormones have many physical and cognitive implications for a fetus once fully developed. Because of
ethical reasons, most research has been carried out on rats and other mammals. However, in the hypothyroid
rat brain, numerous malformations were found: reduced myelin of neurons in the CNS, deficiency of neurons
in the cerebral cortex, the visual cortex and auditory cortex, hippocampus and cerebellum, which relate to
general learning and motor skill acquisition.
[23]
Rubella
Rubella, synonymous with German measles, is a disease caused by a virus with the same name and is highly
contagious. It is often combated using preventative measures, typically through vaccination. For children and
adults it can be overcome quite easily once vaccinated, however, if the fetus is exposed to the virus, especially
during the first trimester (the first three months of pregnancy), major implications can occur.
[24]
Fetal Nutrition and Memory
Fetal nutrition has implications for both the short term and long-term development of the brain. Due to ethical
reasons, studies, which may result in diminished physical functioning or short/long-term damage, are generally
done on animals before being deemed safe for human trials.
There are two points in rodent brain development during which treatment with choline, a neurotransmitter,
produces lifelong enhancement of spatial memory.
The first point is at 12–17 days into embryo development, and the second
is between 16 and 30 days after the rat has been born. Baby rats, from
mothers fed a diet lacking in choline during these two periods of
pregnancy, have poorer memory function than baby rats from mothers
who received choline. Choline, when given during these critical periods,
causes a major improvement in memory performance when rats are being
trained in a maze. Even in older rats, these memory changes persist and
Choline, a neurotransmitter
can be used to easily identify which rats came from mothers that received
important for spatial memory.
enough choline. Supplementation with choline appears to reduce the
speed at which memory declines with age. Choline before pregnancy is
also related to changes in the birth, death, and migration of cells in the hippocampus during the development of
the baby rats in the womb. Choline is also associated with the different location and shape of neurons involved
in memory storage within the brain.
[25]
In another study using rats, it was found that the size of the hippocampus (the central region in memory
functioning) was affected by protein malnutrition. More specifically, only the CA1 region of the hippocampus
seemed to demonstrate a significant reduction in size. The CA1 subsection of the hippocampus was 20%
smaller in offspring from mothers who were fed a protein deficient diet while pregnant. Because the region of

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