Lecture 1: Historical background

Welcome back to the course Brain, Behaviour, and Dentistry. Now we begin the second session of the course, which will focus on the issues of memory of dental patients. In the first class of this session, you will learn to identify the key concepts of memory formation and the major methods of memory research. Before the topics of memory, let’s begin with some stories about forgetting. More than 100 years ago, a German psychologist Ebbinghaus investigated the capacity of human memory by taking himself as the subject. He tried to memorize a list of three-letter syllables, such as AUQ and SYF, and after a fixed period of time, he tested himself how many syllables he could still recognize accurately.

A critical finding here is that the ‘forgetting curve’, i.e., the curve of the decayed memory, is a non-linear one. As you can see in this diagram, sometime after the learning task, memory decayed dramatically. Of course, the forgetting curve may vary between different individuals, and now we know some behavioural factors, such as sleeping and stress, will influence the shape of this curve. Though the study by Ebbinghaus was done 100 years ago, it inspires the research of human memory.

Forgetting seems to be part of human nature. However, there are some people whose memory is so good that they never forget! Another famous psychologist Luria has reported the story about Shereshevsky, a man with a super memory. Luria has become a good friend to him due to this study. It said that 30 years after, Luria talked to Shereshevsky about the first time they met, ‘Hey, did you remember on the first day we met, I tested your memory by offering you a telephone book. You just memorize everything from that book.’ And then Shereshevsky answered ‘Yeah, I know, that telephone book’ and he started to recite every item from that book – 30 years after he memorized it.

Now we know the secret of super memory. Some people with super memory, the mnemonist, has a unique ability we called synesthesia, i.e., to link the information processing between different perceptual modalities. For example, when reading words, they can see ‘colours’ from the letters. In other words, they not just read a passage but watch an image related to the passage. Notably, such a linkage between different ways of information processing can also be found in ordinary people. For example, we sometimes link auditory and visual images together, such as the case of ‘Bouba Kiki effect’. When children are shown with these two figures, most of them would link the Bouba with the rounded one and Kiki with the sharped one.

The perceptual experience is also linked to meanings. For example, children may feel the rounded one is very funny, and Bouba just sounds funny. These cases reveal that when we memorize something, we build links, and meaningful links, between these things.

After years of research, researchers have gradually built up a theoretical framework to explain the information processing of memory.

A typical information-processing theory consists of three stages: encoding, storage, and retrieval. First, when we start to memorize something, we need to collect the information. For example, we need to pay attention to the source stimuli first. Then the information is stored in our brain – exactly speaking, the information is processed and consolidated. Finally, the piece of information can be recalled to our mind, a stage named memory retrieval. Any problem with this information processing may lead to forgetting. For example, we may forget something because we don’t even encode the information at the beginning. Or, we collect the information but it does not consolidate or integrate into our mind.

Or, we just cannot recall what it is, i.e., a problem from the retrieval stage. Here I would like to explain further the concept of memory consolidation, which is key to the formation of long-term memory. Again, not every trace of memory is worthy of putting into our long-term memory. For example, when I attended a course on dental anatomy, I was more impressed by the lame jokes from professors, than the lecture on dental morphology. However, the memory of these jokes was not consolidated into my long-term memory. In contrast, I can still recall the knowledge of dental morphology, which becomes part of my long-term memory. Here ‘consolidation’ is usually associated with some efforts.

For example, I need to rehearse the knowledge of dental morphology so that they become consolidated. Of course, I did not rehearse the professor’s lame jokes. My memory about the jokes just decayed quickly, according to the forgetting curve!