Blurring Science and Reality: The Hope of Photographic Memory

Ever hoped Harry Potter had an instantaneous memory spell for you right before exams? Well, there is currently no memory spell, but what you really need is Memory Bread. Born from Japanese science fiction anime Doraemon, Memory Bread captures every Asian student’s fantasies. When the bread is pressed into any page of a book, the bread owner will develop immediate photographic memory of the book. Too good to be true? Research into memory and its enhancements tell us that the Memory Bread may not be too far from reality.

A Brief History
Memory is the ability to retain, reactivate, and reconstruct experience-dependent information. Memory has been an enigma to philosophers and scientists throughout human history. As early as around 400 BC, Plato wrote about his view of memory in Theaetetus. To Plato, memory is analogous to the impressions on the “wax tablet” of our malleable mind left by the weight of our experiences. This idea of memory as a “wax tablet” was disagreed with later by many other prominent thinkers. One of the greatest philosophers of the twentieth century, Bertrand Russell, said that “this analysis of memory is probably extremely faulty, but I do not know how to improve it” (1).

Early writings about memory from the nineteenth century focused on different types of learning and memory processes and disagreed on whether an integral system of memory exists. These writings were largely based on philosophical and psychological theories. Few discussions related memory to the biological processes inside the brain. However, rigorous inquiry into the neuropsychological function of the brain began with Brenda Milner, a British neuropsychologist who conducted a series of tests on patients suffering from “medial temporal lobe amnesic” syndrome. This syndrome is a type of amnesia in which the patient is incapable of acquiring new long-term memory, but the patient’s past memories and other cognitive abilities such as language, short-term memories, perception, and reasoning are intact (2). Following Milner’s footsteps, modern neuroscientists started looking into the precise functions of neurons and their contributions to different types of memories.

Classification
It is intuitive to see that memories exist in different forms. Remembering an event or a person’s face is very different from recalling that five plus five equals ten, which is also distinct from the memory of how to brush one’s teeth. Even more drastic is the difference between long-term and short-term memories: hearing a series of numbers and trying to reproduce them after a few seconds is different from retrieving your house number from long-term memory. In the former case, it is likely that you are going to forget the series of numbers after having a little stretch and going out for a meal; in the latter case, however, you probably would not forget your address even after months of journey away from home.

In 1968, psychologists Richard Atkinson and Richard Shiffrin proposed their multi-memory model. The model states that there are three types of memory stores dominating a human brain: sensory memory, short-term memory, and long-term memory (3). Sensory memory is the momentary retention of information in our sensory organs (less than two seconds) after the external stimulus has ceased. Sensory memory also allows our brain to select the aspects of inputs to be processed in our short-term and long-term memories later.

Short-term memory is the retention of information for a short period of time (which is comparatively longer than the transient sensory memory). Information in the short-term memory remains in the consciousness after it has been produced. Short-term memory has a limited capacity. For example, it requires short-term memory for a reader to understand what this sentence is about, because the reader’s brain has to retain information about the words that construct this sentence. And if a sentence is too long, readers may have much more difficulty understanding the meaning of it.

Today, neuropsychologists often use the idea of working memory instead of short-term memory. They recognize that the human brain has the ability to manipulate short-term memories, integrate and analyze information logically, and control its own attention-all of these are underrepresented by the idea of passive retention and repetition of the term “short-term memory.” Studies have shown that similar to short-term memory, working memory can only sustain for a short period of time, unless it is constantly rehearsed by the mind until it is stored as a long-term memory. Working memory is encoded in the neuronal activities during the delay period, which is a period after external stimuli have vanished but during which information of the stimuli is still retained in the brain (4).

Long-term memory contains information about events and facts that have left the consciousness but are stored in one or multiple locations in the brain. This long-term memory can be retrieved for further usage even after a long period of inactivity (3). Long-term memory can be classified into declarative and non-declarative memories. Declarative memory is a way our memory represents the world. It can be about facts such as “Dartmouth is in Hanover.” This type of declarative memory is called the semantic memory. Another type of declarative memory is known as episodic memory, which contains our memories of events and of people. The distinctive feature of declarative memories is that they are either true or false.

In contrast to declarative memories, non-declarative memories, such as the memory of how to brush your teeth, are expressed through performances and procedures other than recollection. This kind of memory also does not require conscious retrieval-non-declarative memories come almost automatically to an organism. Figure 1 shows the different classes of non-declarative and declarative memories (5).
Scientific researches into amnesic patients as well as normal human brains have found the active sites for some of the types of memories classified above. The relevant parts of the brain have been shown in the last row of Figure 1. Also see Figure 2 for brain anatomy (6).

The medial temporal lobe and the hippocampus are generally believed to be the places where declarative memory storage and retrieval take place (7). Yet recent research has revealed that patients with an impaired hippocampus, but an intact parahippocampal cortex, were still capable of retaining and recalling certain declarative memory, although they were no longer able to remember new events and people. This shows that the process of storing declarative memory may not be based entirely in the hippocampus (8). Scientists are not able to pinpoint with certainty where semantic knowledge is processed and stored. Some claim that such memory is scattered across all brain areas. Others, however, resort to the “grandmother cell theory.” This hypothesis states that certain brain cells have the whole package of complex mnemonic functions about an entity. These cells are stimulated whenever a person is asked to recognize that entity. To put it simply, when one is asked to look at his or her grandmother’s photo or to hear her voice, the “grandmother cell” in the person’s brain will be activated when the person recollects memories about the grandmother. The grandmother cell theory, in spite of its playful name, found proof in a 2005 study from California. The study showed that certain cells are responsive to pictures or even just names of famous people, such as Bill Clinton or Jennifer Aniston (9).

Enhancement
Modern neuroscience certainly helps us understand the inner workings of human memory better. It also allows mnemonic experts to justify various methods of memory enhancement practiced throughout the centuries by professionals and scholars. In the sixteenth century, an Italian missionary Ricci Matteo went to China to spread the western mnemonic techniques. He was surprised by the rote learning ability of many Chinese scholars. After years of memorizing the traditional texts, these scholars achieved almost perfect photographic memory-an exact memory of every word and punctuation in the texts (10). Not everyone is born with the ability of photographic memory. However, Arthur Bornstein, the founder of the Bornstein Memory School, claims that normal people like the Chinese scholars can be trained to have almost perfect memory (11).

The key to enhancing one’s working memory is to practice attention control. Absentmindedness is, according to Daniel Schacter, the chairman of Harvard University’s Psychology Department, one of the “seven sins of memory” (12). In a study of brain activity from the University of California, Berkeley, researchers showed that working memory is closely related to the parietal lobe, the superior frontal gyrus, and the middle frontal gyrus (see Figure 2). The first two areas are also active when the subject of an experiment practices controlled attention. Working memory and attention control are thus inseparable functions of our brains. One practical exercise for attention control is meditation (4). A study from 2007 comparing thirteen Zen meditation practitioners and thirteen controls found that the meditators performed better on a computerized test of controlled attention, and that meditators had much slower decline in gray matter volume and reaction time as they aged (4).

Memory is like a muscle; the more it is used, the more robust it becomes. Like the ability to play a musical instrument or to excel in a sport, constant practice is another way to enhance one’s working memory. A study examining the changes in brain structure in a group of subjects after three months of juggling courses showed that the area in charge of perception of motion had been enlarged. This meant that the group of people who juggled regularly for three months could learn motions and skills involving the perception of motion more easily than people who did not go through the juggling courses (4). Since the perception and remembrance of motion are closely related to procedural long-term memory, the capacity of our memory may be increased through practice.

For many students, retaining information in working memory is not enough. Working memory can only hold a limited amount of knowledge, and less when the brain is under stress or fatigue. A greater problem is that working memory is fleeting. In order to be able to retrieve the memory days later, we have to turn short-term memories into long-term ones.

In the past, people used the repetition of information combined with mnemonic skills to consolidate their memories. Remembering the acronyms of several items, creatively linking the material with songs or images, and repetition and revision of the materials all help to consolidate the memory. The question that arises here is how we can assess the effectiveness of the consolidation tools.

In 1988, Ericsson proposed three requirements for good memory skills (13): 1) meaningful encoding, 2) retrieval structure, and 3) speed-up. “Meaningful encoding” means that the information should be understood and processed in a familiar context so that it is meaningful to the subject. Cues such as visual images or rhyming words should also be stored with the memory. The more imaginative and elaborate the cues are, the easier it is to retrieve the associated memories. Elaborating on the material to find mnemonic cues is understood as the “retrieval structure.” “Speed-up” refers to how fast the process of retrieval memory is. With the three criteria in hand, one can not only evaluate whether certain mnemonic tricks are useful, but also design one’s own techniques for memorizing any material.

Although the exploration into memory consolidation skills took place long before Ricci Matteo embarked on his missionary trip to the Ming dynasty, scientists only began to discover the biological process of memory consolidation in recent decades. The process of memory consolidation originates in the hippocampus, which later transfers the memories to other parts of the cerebral cortex for long-term storage (14). Information in our brain is transported through neurons. Mammalian neurons communicate by releasing neurotransmitters-molecules that travel in the small space, also known as the synapse, between two neurons. Experiments have found that when a strong external stimulus is applied to the synapse, the synapse is made more sensitive so that the communicating neurons may be more responsive to future release of neurotransmitter, or release a larger quantity of neurotransmitter. Such increase in the synaptic strength is often related to the improvement of mammalian memory (15).

This process of long lasting enhancement in signal transmission following stimulation of the synapse is termed long term potentiation (LTP). LTP has proven to be the most viable candidate so far for a cellular mechanism of memory storage (16). LTP is thus the important linkage between our philosophical understanding and the biophysical aspect of our memory and learning.
Since the discovery of LTP, huge advances have been made in understanding exactly how it works. The major transmitter in the brain is glutamate, which when released binds to AMPA receptors across the synapse, causing positively charged ions to rush into the cell. If enough receptors are stimulated by glutamate, a threshold charge will build up inside the cell, and the neuron will pass the signal on down the network. LTP works by increasing the amount of receptors available to detect glutamate release, so that the next time the same stimulus comes around it will pass the signal on even more easily. For example, if you have a bad reaction to shellfish one day, your neurons will undergo LTP so that you will never go near shellfish again.

The implication of the aforementioned experiments is that neuropsychologists may be able to control LTP using pharmachology and specific stimulation. If that is possible, all the memory tricks we used in the past pale in comparison to the potential of targeted LTP stimulating. LTP may allow working memories to be stored as long-term memories with much more speed and accuracy than traditional mnemonic skills. However, to control human memory, or even to totally dissect and understand mammalian intelligence will demand a long period of strenuous scientific endeavor. While research into the storage of memory and the processing of information in the human brain still remains rather rudimentary, potential LTP memory treatments provide amnesic patients hope. Perhaps one day, scientists will be able to create our Memory Bread and attain perfect photographic long-term memory for all of us.

References

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