Learning and Cognition
PSYC3500 Learning and Cognition
Dr. Brian Uldall
Sunday, December 11, 2011
Wisdom, as the application of knowledge, must be grown and cultivated in the garden of our lives. Thousands of years of human history recorded for our digestion, for our conservation, lay at our feet. As the famous maxim attributed to George Santayana goes: those who do not learn from history are doomed to repeat it.
At a universal level, this thought can be applied to civilizations, to societies, to governments, but even more appropriate to our discussion, this aphorism is succinctly relevant to the challenge of humanity. I charge that nary has an individual who quoted the saying “what you don’t know won’t hurt you” has truly believed this in their heart, except such that it be applied to someone other than themselves.
How many years and decades do we spend, in our lives, trying to obtain knowledge, to transfer it to wisdom, to better our lives and the lives of those around us, only to forget that which we felt so near and dear to us? Yet, memory is not the enemy, time is the enemy. As Gollum, in J.R.R. Tolkien’s book The Hobbit riddles, time is that which “devours [all things]: Birds, beasts, trees, flowers; Gnaws iron, bites steel; Grinds hard stones to meal; Slays king, ruins town, And beats high mountain down (Tolkien, 1995).”
The control of time, as yet, still seems to be beyond our grasp. In fact, it is perhaps even difficult to prove time in existence, as we all sit within its postulated construct, as one staring out of a brightly lit room into a darkly muted sky. The laws of nature govern this relentless drive forward on the continuum of existence; the controlling of our memories, however, is much closer within our grasp.
Unfortunately for those of us who sit here reading this document, the biological or genetic breakthroughs allowing us to retain and more importantly recall an infinite amount of knowledge as individuals, may yet be beyond our reach. How therefore can we use the tools that have been discovered, the strategies science has uncovered to absorb and secrete the knowledge and histories that we, as individuals have been exposed to? How can we, as individuals, use this gift of consciousness to increase our learning and retention capabilities allowing us to enrich our own lives and the lives of those around us?
In this paper, while the transformation of knowledge to wisdom is far out of scope, we will begin by discussing the problems of memory retention and recall, and will examine the ways in which we can personally influence our predisposed capabilities to learn and recall information through the application of strategies from applied Metamemory research.
Problem Statement and Research Questions
Have you ever opened your mouth and began to say something, but completely forgot what you were about to say? In many cases we can laugh at this failing at the expense of our humanity, i.e. “I’m only human”. What, however, happens if the information you were going to unveil was critical to your job, your family, or to your livelihood?
In another scenario, you are late for work and you stand in awe at your inability to recall where you placed your keys, perhaps only to find them in your pocket after overturning couch cushions, recliners and blaming your family members, who stare at you in disbelief.
Further evidence of our memory failings is when we go out of our way to complete a task only to forget what it was we were doing or intending on doing. Take another example: being asked a question, and being absolutely sure you know the answer, but not being able to recall with clarity what the answer is!
To add insult to injury perhaps you have a memory that is so vivid you can only see it in your mind’s eye, taste it and feel it; only to find incontrovertible evidences that the memory itself was an illusion and an internal deception. How about the feeling of Déjà vu: being sure from a consistency within your external and internal senses that you have seen, felt or experienced a particular situation before, but having no solid recollection of the actual time and place of its occurrence.
These human operational failings, such as having an idea on the tip of the tongue (TOT) but out of reach, seem to be so universal that research has identified evidences of over 45 languages that articulate the concept (Terry, 2009). As a result of the commonality of these failings, there is much research dedicated to understanding the source of things such as the feeling of knowing (FOK), the tip of the tongue (TOT) experience, and false memories (Terry, 2009).
The question remains then, how do we increase our abilities as individuals to create, or recall memories. Are there any means by which we can influence our natural genetic and biological capabilities to increase our capacity for learning? What type of strategies can we employ that help us conquer the frustrations of FOK, TOT and false memories?
Significance of Research Questions
Solomon, the King of Israel wrote his book of Wisdom for the purpose of:
“… gaining wisdom and instruction; for understanding words of insight; for receiving instruction in prudent behavior, doing what is right and just and fair; for giving prudence to those who are simple, knowledge and discretion to the young. Let the wise listen and add to their learning, and let the discerning get guidance, for understanding proverbs and parables, the sayings and riddles of the wise… but fools
despise wisdom and instruction (NIV).”
As Solomon states, so I would espouse that only a fool would despise the acquisition of wisdom and knowledge. However, would we say that it is an attribution of wisdom to persist in a futile pursuit? Why should we spend time in intellectual pursuits that would allow us to better our lives and the lives of those around us, if we are only to forget the majority of what we have learned? As discussed, time is our enemy, and constrained in what we as individuals can pursue in our limited lifetimes, we must be intentional in our consumption of the economies of time.
However, would people strive to better themselves if retention was increased? What if there were biological modifications and strategies which allowed people to rise above the din of normality and perform as polymaths, culminating and integrating a plethora of knowledge into all aspects of life and society?
As knowledge increased, ignorance would decrease, and with it, I believe, the decrement of problems caused by ignorance, problems such as how to integrate peace into homes, families, and our workplaces in ways that are conducive to effective functionalism. Through knowledge we can solve problems such as how to apply theories of conservative economics to increase the health and welfare of our personages, our homes and our economies.
Unlike the decision ultimately made by Yentl, shown in the award winning movie of the same name, the pursuit of knowledge should expand beyond just learning for the sake of learning. It is with knowledge and the application of this knowledge, combined with self-examination that we can truly obtain the good life (Socrates as written by Plato).
It is therefore with expressed interest in understanding how to obtain this good life that we draw the conclusion that the pen-ultimate purpose and meaning of life is learning through the pursuit, acquisition, retention and recollection of knowledge.
Report of Research Findings
With this goal in mind, it is now time to turn to a discussion on the means by which we can increase and enhance our learning capabilities. Within our discussion we shall address two such approaches: behavioral modifications and learning strategies.
Science, in its current state, does not provide for the possibility of humans modifying their genetic code to increase innate and inborn capabilities, however, there are some behavioral actions we can perform that have been shown to provide positive benefits to our biological predispositions. This first section examines those behaviors by which we can influence our inborn learning and cognitive capabilities through modifications of human behaviors.
Most, if not all of us have heard that “An apple a day keeps the doctor away”, or “You are what you eat”. It has been understood in various capacities throughout human history that the food we eat has a direct impact on the health and stability of our vitals. When examining food intake, there are studies and anecdotal evidences alike that discuss how certain elements and nutrients like calcium, niacin, vitamins A, D or K are required for healthy growth and function of the human body.
It therefore should come as no surprise that studies such as those outlined by Gómez-Pinilla identify certain foods and ingredients, like Omega-3 that help increase cognitive abilities. Other food products such as Ginkgo Biloba (U. Rigney, 1999) and Green Tea catechin (Unno, et al., 2007) have also been shown to have positive effects on human cognition.
Further references also indicate, perhaps surprisingly, that the act of eating itself induces various hormones and peptides that stimulate portions of the body associated with learning capabilities and cognitive processes (Gómez-Pinilla, 2008), although some food substances like saturated fats and calcium that can reduce cognitive abilities, especially in the elderly (2008). Diet, therefore is an important biological behavior that is part of identifying ways in which we can influence and increase our own learning capabilities.
Apart from a healthy diet, full of brain-enhancing nutrients, another behavior shown to affect cognitive abilities is that of exercise. Walz, et al., examines how Nerve Growth Factor (NGF) and basic fibroblast growth factor (bFGF) proteins have been found to help increase short and long term memory capabilities in various doses (Walz, et al., 2005). Further studies indicate that brain-derived neurotrophic factor (BDNF) and Nerve Growth Factor (NGF) are increased through exercise (Neeper, Gómez-Pinilla, Choi, & Cotman, 1996).
Both of the aforementioned studies indicate that the changes in bFGF, NGF and BDNF affect the hippocampus, an area of the brain shown to be associated with human memory (Eichenbaum, 2003). Additional studies by Ahmadiasl, Alaer and Hanninerr, have identified that physical activity has positive affects on the hippocampus and has been shown to increase spatial learning as well (2003). In conjunction with physical exercise, exercising the brain has also been found to stimulate neuropathic growth and increase cognitive capabilities (Gilkey & Kilts, 2007).
As seen above, exercise, both physical and mental, is another important way in which we can influence of cognitive capabilities.
In addition to diet and exercise, sleep is another important behavior that seems to impact our cognitive abilities. The correlation of sleep and memory, according to Blissitt, is very complex (2001). As a result, while sleep and memory is the focus of a significant amount of studies, the results of such studies are often contradictory or inconclusive (Blissitt, 2001). Despite some contradictory findings, certain conclusions seem to be undisputed, such as the finding that sleep after a learning activity seems to increase memory, while learning after sleep seemed to decrease the amount of information retained (Blissitt, 2001).
Other studies have indicated that circadian cycles have a direct effect on the ability for people to learn new information, although the actual cycle seemed to have a variation based on age, preference and even culture (Terry, 2009).
In the case of sleep, while discovered information is still difficult to summarize in a universal pattern, it can be seen that sleep is another human biological behavior that can influence our ability to learn in a very personal way.
Up to this point we have discussed ways in which we can impact our biology or neurology to help increase our individual capacity to learn. Apart from the physical strategies discussed above, there are also learning strategies. While the previous biological approach represents mild cognitive enhancement, learning strategies themselves represent a significant weighting in the ability to increase learning capabilities. The following section outlines various learning strategies and techniques that can be applied by individuals to enhance cognitive retention.
Mnemonics may be the most familiar strategy for increasing learning. The term Mnemonics comes from the name of the titaness Mnemosyne, a Greek god who represented memory and mothered the nine Muses. Mnemosyne had a very long memory, and taught her children to use encoding strategies to learn the history of the world, hence the common use of the word Mnemonics.
Mnemonics, according to Terry, are strategies used to aid encoding and retrieval (2009). There are various forms of Mnemonics including first-letter and acronym mnemonics where the first letter is used to create an acronym that triggers the terms that are to be remembered. Examples of first-letter and acronym mnemonics are those such as are used to learn the order of mathematical operations (i.e. PPMDAS). Other types of mnemonics such as keyword, narrative story, method of loci or peg word mnemonics are also commonly used (Terry, 2009).
Keyword mnemonics are used to create a cognitive bridge between two ideas, where one word will remind you of another word that in turn causes you to recall the target word. Take the word panache for example. For me, panache sounds similar to the Haitian Kreyole word for walk (mache), which sounds similar to the word march, and when people march around they often are dressed in very flamboyant costumes. This is the way I have encoded the word panache, which means to be flamboyant and recklessly courageous.
Another type of mnemonic is the narrative story method. In the narrative story method, we use keywords that we need to remember in a certain order and hang a story off of the keywords. For example, if you need to remember the birth order of your friends five children you can make up a story including the names of the five children in the correct order.
Other forms of mnemonics are the method of loci, where you can attach a visual walk through of a well-known location to the words you need to remember, and when recalling those words, you can walk back through those locations in your mind to elicit the terms you are trying to member. Peg word, another form of mnemonics, is commonly used to put terms to a rhyme to help remember. For example the old children’s rhyme to help learn the numbers: “one, two, buckle my shoe, three, four, shut the door, five, six, pickup sticks… etc.”
Perceptual learning is a phenomenon that describes prior learning and how prior learning has been shown to increase our ability to learn new information. Perceptual learning authenticates that the statement “the more you know, the more you can know” is indeed a verifiable truism.
There are many different techniques associated with perceptual learning, such as making a conscious effort in associating information you are learning to information you already know, applying personalized meaningfulness to the information you are learning such as how this information could have helped you in past circumstances, or how it can help other people you know. Perceptual learning is also found in using various other techniques such as those discussed by Goldstone called attention-weighting, imprinting, differentiation and unitization (1998)
Attention-weighting is the practice of paying closer attention to ideas that are more important to the topic and filtering out information that is less important. In some ways, we all perform attention-weighting distinctively. Have you ever noticed that once you buy a certain type of car, that car begins to show up everywhere, as if, taking cue from you, the world has realized how exception this particular vehicle is and has thus gone out and purchased one too!
The reality is, more than likely, everyone else already owned this car for a long time, and you are now just noticing it for the first time (unless of course Daemon-Chrysler is giving away cars again!). This concept of selective perception shows that we are often practicing attention-weighting intrinsically in our daily interactions.
The second concept, imprinting, revolves around the idea that studies show that the more you are exposed to a specific stimulus, the more your cognitive thought processes can respond with “speed, accuracy and general fluency” (Goldstone, 1998). This type of learning helps explain how accuracy can increase on an assembly line over time. As these studies show, practice, through continued exposure, can increase performance, so perhaps there is a reason sports coaches make you run plays over and over again during practice!
The other forms of perceptual learning discussed above, differentiation and unitization have to do with the ability to draw distinctions between certain stimuli or create overarching categories that would lump other stimuli together to form memories. For example, when first learning how to crochet, it is important to create a distinctive understanding of the differences between a slip stitch, a single, half-double, double and treble crochet stitch.
From a differentiation perspective, performing exercises against the nuances defined by the differences between these stiches creates a stronger bonding in the memory of how to perform each stitch (spatial learning). However, once the differentiation is learned, unitization is preferable, as rather than remembering that a half double stitch consists of two chain loops on the turn stitch, drawing the yarn over, then inserting back into the third chain from the hook, drawing the yarn over again, pulling through, and drawing the yarn over the hook a third time and pulling through all three loops, an individual can unitize the whole process into a single memory called the half-double crochet stitch.
Elaboration, mental imagery, and imagery rehearsal
Another learning technique focuses on the depth of processing. Elaboration, mental imagery and imagery rehearsal are all techniques used to increase the level of which individuals must think about what they are learning. Often, as an example, individuals might be lead to believe that underling and note taking help with learning and memory, however, studies have shown that this technique often produces no more retention than in its absence (Terry, 2009).
In contrast, elaboration includes techniques that require individuals to think in a more personalized manner which helps contribute to perceptual learning goals such as meaningfulness and association (Terry, 2009). Through elaboration, learners are asked to respond to questions, or to put information in their “own words”. Terry continues to describe how this approach requires learners to associate the new information with existing information, and identifies that studies show this approach increasing long term retention (2009).
Other forms of elaboration referred to as mental imagery have been shown to be very powerful in increasing learning and retention. Studies performed by Sanders, et al, Holmes, and Mackintosh, and Paivio, display that imagining and rehearsing exercises in the mind, are often as efficacious and sometimes more so than the studying of exercises to be performed (Sanders, et al., 2007-2008) and (Holmes & Mackintosh, 2008) and (Paivio, 1969). Rehearsing information by memory elicitation and review has also been shown to strengthen memories and increase retention over time (Terry, 2009).
Learning variables: incentives, interest and arousal.
While it seems obvious in the concepts of learning, studies have also shown that certain forms of incentives, interest and arousal impact the ability for knowledge retention. Individuals that are more interested in a topic, perhaps because of perceptual learning techniques, or elaboration or rehearsal, retain knowledge on a given topic more readily than those who are less interested (Terry, 2009). Additionally, this increase in interest facilitates emotional arousal, which is another factor that has been shown, at least in small doses, to help increase learning and retention (Holmes & Mackintosh, 2008) and (Terry, 2009).
Our final topic around increasing our learning capabilities is the idea of spaced-learning versus exam-cramming. When examining the ability to influence long term retention, studies have shown that while exam-cramming may increase the knowledge of information in the immediate state, this form of learning technique has a higher rate of failure to retrieve over time (Terry, 2009). To help facilitate long term retention, studies have shown that spacing out study sessions or topic exposure has a dramatic effect on the long term retention of knowledge (Terry, 2009). Additionally, perhaps due to concepts discussed in elaboration, studies have also shown that learners are more likely to benefit from a practice test with review than another study session (Terry, 2009).
Before coming to conclusion, our discussion would not be complete without touching on the strategies for knowledge retrieval. As previously discussed, after spending a significant amount of time in the pursuit of knowledge, there is nothing more frustrating than forgetting what you have learned, except for experiencing the feeling of knowing (FOK) and the tip of the tongue (TOT) phenomena. The following section describes a few topics and techniques to bring clarity and present strategies that will help increase our ability to retrieve information that we have learned but are having a hard time recalling.
The tip of the tongue phenomenon seems to be a universal grievance when discussing memory recall. Have you ever tried to think of something you are sure you know, and it seems like it is right there, just beyond your reach, however, the harder you try and remember this particular piece of knowledge, the further out of reach it seems as other thoughts and pieces of knowledge crowd into your conscious mind.
An interpretation of this problem is related to cue recall, and is described as Terry as a problem related to neuronal pathways in memory storage (2009). As you search, perhaps unconsciously at first, through your memory, to retrieve the sought after information, nerve pathways are accessed and information is brought into working memory. At some point during this process, the brain will settle on the location your desired information is stored, however, the cues that have brought you to this information have a stronger activation in memory than the desired information itself.
The harder you try and think about the desired information, the stronger the activation for the associated cues becomes, until there is a point where you can’t think of anything but the unwanted cues! One suggested approach to overcoming this difficulty is to stop trying to recall the sought after information, but keep the question “in the back of your mind”. Eventually, the activation of the associated cues will return to normal, at which point, the often-experienced “Oh, I remember now” reaction will result in the conscious recall of the sought after information into working memory.
Another type of failure to retrieve, similar to the previously mentioned TOT phenomenon is the feeling of knowing (FOK) experience. In this case, you are fairly confident you know the answer to the question, but are unable to retrieve the answer from your memory. While sometimes, the FOK results in the recognition of false memory (i.e. you really didn’t know in the first place), in other instances, there is some mental block at work preventing you from retrieving the desired information.
One such example of the FOK experience is when you have put your keys down, but you can’t remember exactly where you put them. All things being equal (i.e. if you don’t have children or a spouse in your house that is constantly moving your keys), it is likely that you are experiencing a mental block for information you do know, but just cannot recall.
One approach to overcoming this type of failure to retrieve is wrapped up in the idea of encoding specificity. Encoding specificity is a theory in which information can be recalled by mentally placing yourself back into the same situation as when the memory was first encoded into memory (Terry, 2009). For example, if you have lost your keys, replay in your mind driving into the driveway, getting out of the garage and coming into the house. The more information you can reproduce around the experience of encoding, the more likely you are to remember where you left those keys (unless someone else did move them!).
Contextual, state and mood dependent learning.
Similar to the idea of encoding specificity, another concept has an applied impact on capabilities of retrieval. Although providing a weaker influence to retrieval capabilities, studies have shown that replicating the physical context in which learning occurs, the physical and emotional state of the individual during learning, and even the mood of the individual while learning can help aid in retrieval (Terry, 2009).
In summary through the application of these various techniques and strategies of learning and recall, the learner can increase their acquisition and access to knowledge.
Connection to Personal and Professional Goals
For my personhood,
both independent verifications such as the StrengthFinders assessment co-created by Marcus Buckingham and the Gallup Poll organization, as well as my own intrapersonal awareness of myself as a human, proclaims that I am a lifelong leaner. One of my primary drivers in life is to learn as much as I can about as many things as I can, so that I can transition this knowledge into the wisdom necessary to better my life, and the lives of those around me.
As previously discussed, the intellectual battle that each human undertakes is not the inability to remember information that we have learned, nor the inability to learn information in the first place, rather it is our constant struggle against the relentless enemy of time. With infinite time, I believe humans with normal brain function would be able to learn and retain the information that they felt most important to their lives regardless of their own biological capabilities. With infinite time, even information once known but ‘forgotten’ could be relearned in less time than originally required, as continued retrieval and re-encoding strengthens memories creating resiliency to future deterioration (Terry, 2009).
Due to my own personal drive, I spend a significant amount of my life learning eclectic, unrelated information. I desire to be as one perhaps archaically described like an Oracle, like the wise Socrates. I desire to learn obtain the silos of knowledge held in individuals spread across all disciplines, across the world, and through a synthesis of these silos help better myself, help better my friends and family, and perhaps through these efforts, find in my own way, the immortality so sought after by the near and ancients alike.
From a future goal perspective, reaching into the past, I held off obtaining any degrees for almost 15 years after leaving high school, as I understand knowledge and the pursuit of knowledge to be free if one so chooses. However, that chosen path presented only a small audience of influence as many consider the un-papered, unlearned. Therefore, apart from the difficulties of financing an education just for the sake of an education, I believe, should my hardware and software hold out, and the means present themselves, in the years to come I will complete a masters and doctorate, as there will be no cessation for my hungry desire for knowledge. What specialization however, yet I cannot tell, for how can one chose to be an expert in one thing, when they desire the breadth and depth of all.
Discussion, Recommendations, and conclusions
To conclude my didactic overview of human learning and cognition, let me explain, no, rather let me sum up, for those that are intimidated against reading my entire proposition. Here lay before you some of the main proposals and further research topics that will bring forth effective learning and recall of human knowledge, based on our scientific inquiry as it has been so far advanced within this century.
Limited, but effectual biological behaviors are one of the ways in which we can actively influence our learning capabilities. Science suggests that eating healthy foods, such as the food substances including Ginkgo Biloba, Green Tea and Omega-3 fatty acids, and abstaining from certain foods, such as saturated fats, will help provide the most fertile brain for intellectual pursuits.
Exercise is also found to increase the capabilities around both short and long term memory retention, and therefore exercise should be part of your weekly regimen, as well as light routines before undertaking specific learning activities.
While sleep has been shown to contribute a variance among studied participants, it can also influence learning capabilities. Most specifically, it is known that individual circadian rhythms facilitate more appropriate times to learn (e.g. morning, afternoon or evening), as well as solid evidences showing that retention is higher when learning activities are undertaken before sleep rather than after awakening (Terry, 2009).
Furthermore, while some-what limited in our ability to influence biology, learning strategies themselves have been shown to be extremely effective in increasing learning and cognition. Within this paper we have examined many different ways to use effective learning strategies, but of the most importance is our ability to implement perceptual learning techniques, such as attention-weighting, imprinting, differentiation and unitization (Goldstone, 1998). Additional techniques such as mental rehearsal, elaboration, association and appropriate spacing for study will also have a significant impact on our ability to learn and retain information.
After learning is complete, the failure to recall information, while frustrating, can be overcome by implementing certain strategies such as minimizing associative interference, utilizing encoding specificity and reproducing emotional, and contextual states in which the original learning occurred.
Until such medical breakthroughs as those fantasized in movies such as Johnny Mnemonic where humans have their own personalized techno-biologically interfaced digital storage space, the combined techniques described in this paper will give each of us an edge on learning and retaining the world and all the knowledge therein. Go forth, and know yourself and the world around you better!
Ahmadiasl, N., Alaer, H., & Hanninerr, O. (2003). Effect of Exercise on Learning, Memory and Levels of Epinephrine in Rats’ Hippocampus. Journal of Sports Science and Medicine, 106-109.
Blissitt, P. A. (2001). Sleep, memory and Learning. Journal of Neuroscience Nursing, 208-215.
Eichenbaum, H. (2003). How does the hippocampus contribute to memory? Trends in cognitive sciences, 427 – 429.
Gilkey, R., & Kilts, C. (2007). Cognitive Fitness. Harvard Business Review, 53-66.
Goldstone, R. L. (1998). Perceptual Learning. Annual Review of Psychology, 585-618.
Gómez-Pinilla, F. (2008). Brain foods: the effects of nutrients. Nature Reviews. Neuroscience, 568-578.
Holmes, E., & Mackintosh, B. (2008). The Causal Effect of Mental Imagery on Emotion Assessed Using Picture-Word Cues. Emotion, 395-409.
Neeper, S., Gómez-Pinilla, F., Choi, J., & Cotman, C. W. (1996). Physical activity increases mRNA for brain-derived neurotrophic factor and nerve growth factor in rat brain. Brain Research, 49-56.
Paivio, A. (1969). Mental Imagery in Associative Learning and Memory. Psychological Review.
Sanders, C., Sadoski, M., Wasserman, R., Wiprud, R., English, M., & Bramson, R. (2007-2008). Comparing the Effects of Physical Practice and Mental Imagery Rehearsal on learning Basic Venipuncture By Medical Students. Imagination, Cognition and Personality, 117-127.
Socrates as written by Plato, T. b. (2007). Six Great Dialogues. New York: Dover Publications, INC.
Terry, W. S. (2009). Learning & Memory : Basic Principles, Processes, and Procedures. Boston: Pearson Education.
Tolkien, J. R. (1995). The Hobbit, or, There and back again. New York: HarperCollins Publishers, Inc.
U. Rigney, S. K. (1999). The effects of acute doses of standardized Ginkgo biloba extract on memory and psychomotor performance in volunteers. Phytotheraphy Research, 408-415.
Unno, K., Takabayashi, F., Yoshida, H., Choba, D., Fukutomi, R., Kikunaga, N., . . . Hoshino, M. (2007). Daily consumption of green tea catechin delays memory. Biogerontology, 89-95.
Walz, R., Roesler, R., Reinke, A., Martins, M. R., Quevedo, J., & Izquierdo, I. (2005). Short- and Long-term Memory and Differentialy Modulated by Hippocampal Nerve Growth Factor and Fibroblast Growth Factor. Neurochemical Research, 185-190.