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Mecanics of Memory
The mechanics of memory
Caoilainn Doyle explains why we remember and forget
Memory is what situates you in time and place. It gives you a sense of who you are, and where you are going. A particularly vivid memory for me is the day of my first communion. After the ceremony, my mother brought me to the toy shop and allowed me to buy whatever I liked. You can only imagine the bliss of a 7 year old being let loose in a toy shop with what felt like unlimited cash. I bought a skateboarding Barbie doll which brought me endless hours of enjoyment. It is true that living through this experience resulted in a memory of the event being stored. But is living through an experience enough for it to be stored as a memory? ‘If you want to keep your memories, you first have to live them’ Bob Dylan
Much of our knowledge about memory comes from a famous case study of a man named H.M, who despite living through his experiences could not store them as new memories. In 1953 at the age of 27, H.M underwent a surgical procedure which removed much of his hippocampi (plural of hippocampus) and surrounding cortices in the medial temporal lobe of his brain in an attempt to cure his intractable epilepsy (see Figure 1). Although the procedure helped with his epilepsy, the consequences for his memory function were devastating. H.M demonstrated severe anterograde amnesia as a result of the surgery which left him incapable of forming new memories of his lived experiences.
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Before the development of technology to capture images of the brain such as fMRI, rare cases like H.M’s were the only way to learn about how the structures of the human brain related to memory. As the scientific enquiry of H.M’s peculiar case ensued, it was discovered that although H.M couldn’t create new long term memories, his ability to hold information (short-term memory) and manipulate information (working memory) over brief periods remained intact. An example of short-term memory would be briefly holding a mathematical operation (2+4-5) in your mind, while an example of working memory would be the manipulation of such information in the mind to answer the equation. H.M showed us that memory is not a unitary process. In fact, there are three different types of memory: long-term, short-term and working (see Figure 2). Because H.M’s medial temporal lobe was removed we know that this structure is important for long-term memory, but not for short-term or working memory.
24 Senior Times l May - June 2020 l www.seniortimes.ie Further research on H.M’s case revealed that although he could not store new memories about events or facts he did show evidence of new motor learning (such as reduced errors on a maze tracing task). This in turn helped us to understand that there are different types of long-term memory: declarative and non-declarative (see Figure 2). Declarative memory corresponds to information about events and facts which we can access through conscious awareness, whereas non-declarative is memory is a type of procedural or skill based learning which cannot be accessed through conscious awareness, such as knowing how to ride a bike. This discovery helped us to understand that the hippocampi in the medial temporal lobe of the brain are important for the formation of declarative, but not non-declarative memories. As shown Figure 2, declarative memory can be further broken down into semantic memory which represents facts and concepts, such as the name of the toyshop I bought my Barbie in; and episodic memory which represents your lived experience of events, such as the day I bought my Barbie. Autobiographical memory is a type of declarative memory which corresponds to one’s memory of one’s lived experience or autobiography. Your autobiographical memory is what gives you your identity and sense of self.
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뻴 䰀攀愀瘀攀 愀 䰀攀最愀挀礀 䜀椀椀 䄀昀琀攀爀 昀愀洀椀氀礀 愀渀搀 昀爀椀攀渀搀猀 愀爀攀 氀漀漀欀攀搀 愀昀琀攀爀Ⰰ 氀攀愀瘀椀渀最 愀 最椀昀琀 琀漀 挀栀愀爀椀琀礀 椀渀 礀漀甀爀 眀椀氀氀 椀猀 愀 眀漀渀搀攀爀昀甀氀 眀愀礀 琀漀 猀甀瀀瀀漀爀琀 愀 昀愀瘀漀甀爀椀琀攀 挀愀甀猀攀 椀渀 琀栀攀 昀甀琀甀爀攀⸀ 䄀猀 礀漀甀 挀漀渀猀椀搀攀爀 礀漀甀爀 瀀氀愀渀猀Ⰰ 眀攀 愀猀欀 礀漀甀 琀漀 愀氀猀漀 挀漀渀猀椀搀攀爀 椀渀挀氀甀搀椀渀最 愀 最椀昀琀 琀漀 吀栀攀 䠀漀瀀攀 䘀漀甀渀搀愀琀椀漀渀 椀渀 礀漀甀爀 眀椀氀氀⸀
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吀栀愀渀欀 礀漀甀℀
Figure 2. Different types of Memory
What is of interest with H.M is that although he had difficulty forming new long term (declarative memories), his recall of events prior to his surgery remained relatively intact. This suggests that the medial temporal lobe (in particular the hippocampi) is important for the formation of new declarative memories, but may not be the ultimate storage site of our lived experiences in the brain. This view is in line with the classical theory that memories are created in the hippocampi but over time gradually transition to other brain regions for storage, with no trace of the memory remaining in the hippocampi. However, another theory suggests that when we recall information from memory both the hippocampi and other brain regions for storage are active. It is important to note that although H.M’s case supports the classical theory, the jury is still out on which is the best explanation of memory in the brain and much remains unknown about how memory functions in the brain.
Although it is incredibly rare that we would experience a case of severe amnesia such as H.M’s, it is likely that we will experience a decline in memory function as we age. Healthy aging is associated with a decline in memory and executive control processes carried out by brains, which may negatively impact wellbeing. Executive control processes are important for the regulation of behaviours and emotions, and play a role in retrieval of true memories. Episodic autobiographical memory appears to decline more than semantic with healthy aging and this degradation can range in severity from healthy aging, to mild cognitive impairment and more severe conditions such as dementia. Autobiographical memory is not only vulnerable to the loss of true memory, but is increasingly susceptible to false memories as we age due to the decline in cognitive processes carried out by frontal brain regions. Although more marked in dementia, even healthy aging is associated with an increased susceptibility to false memories.
Given this knowledge, what can we do to protect the contents and accuracy of our true memories as we age? In a similar way to how our life experiences can be knitted into our brain structure as stored memories, so too can we use our experience to hack the brain’s memory capabilities. A phenomena known as experience dependent plasticity suggests that our brains can change in response to the experiences we engage with. Although plasticity was once thought to be possible only in the developing brains of children, recent research suggests that the aging brain is also capable of experience dependent plasticity. Intervention studies aimed at improving autobiographical memory recall suggest that engaging with activities such as music therapy, gratitude, forgiveness and mindfulness-based cognitive training, are effective for enhancing the richness of autobiographical recall.
enhance autobiographical richness, buffer against age-related cognitive decline, and induce observable change in the brain areas responsible for autobiographical memory. Reminiscence therapy, which involves recalling and sharing one’s personal autobiography of life, often in a group setting, has been shown to improve the richness of autobiographical memory in healthy older adults, and those with mild cognitive impairment and dementia. This suggests that it may be a useful tool for protecting the accuracy and contents of our memory as we age. However, much more research is needed to establish the impact of reminiscence therapy on autobiographical memory, wellbeing, cognition and the brain in order to understand how these improvements occur and what is happening in the brain to facilitate them.
A team of researchers at Maynooth University and Trinity College Dublin are currently conducting a research project which aims to address how reminiscence therapy impacts autobiographical memory, wellbeing, cognition and the brain, to establish whether it is a useful tool to protect our memory as we age.
We are currently holding 6-week groups exploring positive memories from history and people’s pasts. If you are aged 60 years or over and would like to take part, contact Andrew Allen at Andrew.Allen@mu.ie or at 0899526518.
