The human brain can be seen as one of nature's finest miracle. An object that weights merely three pounds is responsible for how we perceive reality, feel emotions, remember events and learn new things. For the past two decades, scientists and researchers have explored this hot field of neuroscience in hopes of finding some answers to how something so small is able to hold a lifetime of information. How exactly does the human brain retain experiences, thoughts, and memories? The answer to this has yet to be discovered.
From the time I was young, I have always been fascinated about the processes of the brain and how the mind is able to remember and recollect memories. For almost two years now, I have been fortunate enough to be able to observe the actions and development of my little sister Michelle. From infant to toddler, I have observed the how the brain constantly refines her motor and hand-eye coordination skills.
From her first words to her half Burmese/half Chinese complete sentences it is amazing to be able to watch her master difficult tasks such as learning a language, not to mention two languages, at the same time. How is it that she remembers to differentiate between the language she chooses to speak and the person to whom she is speaking? For example, when she talks with my grandmother, she seems to know to speak only Chinese or Burmese so she will understand. But when she speaks to my brother in Chinese and he doesn't respond, she will repeat it in Burmese or English. One instance of this I observed just recently. Ever since Michelle was little, she has been fascinated with computers and would ask us to show her the picture images saved onto the computer. But when my brother came home and used the computer one weekend, she became territorial and asked him to politely move aside in Chinese. When that didn't work, she dropped the polite part and just told him to move in Chinese. But still, she got no response from my brother who can't understand a word of Chinese. So as she was pushing and clawing her way onto the seat, she took a moment to step away from him and said, "koko (brother in Chinese), eckoo me." Although not too articulate, she got her point across of her wanting him to move by saying excuse me to someone who was not able pick up any Chinese hints. What is the molecular basis that allows for her to learn and retain words from different languages? How does the brain store and recall information from past experiences? How do we learn from past experiences? Is the brain solely responsible for making each person who they are? I don't have the answers to any of those questions, but I do have an opinion on the last question. No, I don't think the brain is what is completely responsible for the action or behavior of a person. I believe it is greatly influenced by a person's genome. So the next question is, how do genes code for things such as the level of emotional behavior or the quickness of your temper? I don't have answers to that question either, but I have been able to make interesting observations in both my sister and I, which could unscientifically imply some sort of correlation.
I have always believed I am more similar to my dad than my mom in many ways. Like my dad, I can have great patience and tolerance for many things but am very short tempered when enough is enough. On the other hand, my mom is always reasonably tolerant and does not lose her temper quite as easily. My sister, however is a combination of both. She chooses to get either very angry when things aren't going her way, or chooses to simply ignore the situation or the person at hand. We know that if she does not want to do something she is told, she will simply turn around and head in the other direction pretending not to hear, or will stay and ignore your request and pretend to not understand. She has caught on to our bribes of sweets and rides in the car and will not do something if she does not want to. My parents say she got this stubbornness from me, but I know otherwise. Aside from this, I have been told that there are many little traits and characteristics about Michelle that resemble me. We both live to climb and jump over anything and everything. Even when we are walking, she'll add a hop or two in between her steps. She will climb any stair, chair, or table she can get her hands on and slide or jump down over and over again. She even learned to walk before she mastered crawling. Although my parents find us similar in our actions and behavior as toddlers, the environment in which I was raised in and the one in which Michelle is raised in is very different. The first three years of my life, I grew up in Burma (Myanmar) where the environmental conditions are almost completely opposite of that in the United States. It is interesting to see how or if our genes and the environment interact to influence behaviors and personalities.
Researchers have experimented and studied some of the cellular and molecular mechanisms involved in brain function. One particular study conducted by Scott Swartzwelder, a clinical professor of psychology and behavioral science, found the nutrient choline plays a vital role in wiring the brain for memory and learning. Choline is a precursor of the neurotransmitter acetylcholine, a chemical used in the transmission of brain impulses between nerves, muscles and organs. In this case, choline is involved directly with cognition, stimulus response, and long and short-term memory (1). The study showed that feeding choline supplements to pregnant rats resulted in the production of offspring with increased memory capacity and learning rates. Although this is not to say that pregnant women should start increasing their dietary levels of choline, which can be found naturally in eggs, nuts, milk and liver, this study does show improved capacity of brain cells in rats for long-term potentiation. Choline, which is used to make the memory-managing messenger chemical acetylcholine, helped improve the preparation of the brain to receive similar messages in the future (2). A region of the brain, which is crucial for the sorting of short-term memories into long-term memories, is the hippocampus. The hippocampus is a horseshoe shaped region of the subcortical brain. Located in the temporal lobe, it has been found to have a role in emotion and sexuality (3). It also contains "place cells" that construct mental maps of position, which is implicated in the learning and remembering of spatial orientation. This 3-D "mental map" of the world around us is crucial for our ability to move around our surroundings. Studies in monkeys have shown that damage to this region causes the inability to navigate through familiar areas. In mice, the hippocampus of the brain contains about a million of these large nerve "place cells" which also enable mice to record their location in space.
Memories are probably first processed and kept in the hippocampus for several weeks before they are transferred to the cerebral cortex for permanent storage. This may explain why people with damage to the hippocampus region of the brain are able to retain previous memories of faces and places, which is stored in the cortex, but have difficulty forming new short-term memories. The hippocampus is a center for short-term memory. It weighs the importance of each incident or circumstance and then chooses or decides which should be kept as memory. This is absolutely crucial in the process of learning, allowing for the rapid knowledge of new items.
Diseases such as Alzheimer's cause damage to the hippocampal region, resulting in a failure to remember spatial layouts of landmarks. In a 4-year study of 405 elderly volunteers, de Leon and coworkers have found that cases of probable Alzheimer's disease usually emerge in people who start off with a small hippocampus and mild memory problems. This study showed a 20 to 50 percent decline of hippocampal volume in victims of Alzheimer's compared to healthy controls. Stroke patients who suffered brain damage to the parahippocampal gyri, an area connected to and just below the hippocampus, experience navigation problems. After stroke damage to this region, which is crucial to the storage and recollection of spatial information, the patient often loses the ability to learn new routes or to travel familiar routes.
In any case, the hippocampus seems to play an important role in the formation of new memories. It seems as though all new experiences must pass their way through this region on their way to forming new memories. Many patients with hippocampal damage can remember events that occurred before the injury, but not since. In which case, patients become prisoners of their past. Yet they can still learn new skills such as playing bridge and improve their playing skills each time they play, although they will think it is their first time playing the game. This suggests that the memory of skill development is controlled by a different part of the brain.
The human brain is something to be marveled at. It is incredible to imagine that an object that consists of billions of neural connections and is made up of three pounds of brain cells is responsible for how we perceive reality, feel emotions, remember events and learn new things. Most of who we are lies inside this small organ which sits on top of our heads. Understanding how the mind retains a lifetime's worth of memories is still one of the toughest problems in biology.
(1) Smart Basics Glossaries-CHOLINE1)
(2) Prenatal Choline Supplements May Boost Memory In Children
(3) The Hippocampus
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This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.