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.
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. 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. 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. The ectoderm is the outermost layer of the embryo. This happens towards the end of the third week of gestation (time period when the embryo is carried in the woman'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.
Measurement techniques There are considered to be three paradigms used to investigate fetal learning and memory. They are: classical conditioning, habituation and exposure learning.
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. Another study replicated these findings.
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. 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. 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. 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 recorded using ultrasound technology. This process is repeated until habituation, defined as a lack of response to the stimulus by the fetus, is reached. Stimulation trials continue into the neonatal period (first 28 days 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. 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. 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. 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.
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.
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. 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. 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. 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). 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. 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 and increase the amount of sulcal (referring to a sulcus: a fissure within the surface of the brain) cerebrospinal fluid (CSF); importantly in the frontal lobe and temporal lobe, which are critical memory centers. The later point regarding sulcal CSF has been linked to schizophrenia (a mental 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.
Hypothyroidism