Memory Sticks

 
 

Memory mechanisms have more of a focus in health studies today than ever before, but we still know so little about how we remember. Do we take it for granted? James Kelly investigates.

The ability to remember is one of the most abused faculties of the student body, second only to the metabolic processes of the liver, but with major assessment not yet even a smudge on the horizon why give it a thought? Why not? The importance it has in our lives, from the trivialities of daily life to abstractions on the most complex concepts, cannot be overstated.

Memory enables us to easily sail through life both temporally, through learning, and physically, through coordinated movement. It’s involved in everything from reading music to riding a bike. Despite the multifaceted role memory plays, its underlying mechanisms are still poorly understood. However with neuroscience and cognitive psychology growing ever more intimate, we’re starting to gain a greater understanding of how our memory behaves.

Memory as an abstract concept has been pondered over for millennia, but it wasn’t until this century (with its more rigid adherence to empiricism) that good models for memory were proposed, and memory as a field of study was given physical grounding. Towards the end of the 19th century it was becoming clear that certain mental functions, such as perception and voluntary motor control, could be related to the neural circuit. From this the search for a discrete memory circuit arose.

It wasn’t until the 1950s when the case of Henry Molaison arose (known in the field as HM) that any major breakthroughs came. HM had his hippocampus almost completely removed as treatment for severe epilepsy. Before this, little was known about the hippocampus, a structure located in the temporal lobes at the sides of the brain. Following surgery, he was unable to form new long-term memories but could still remember much from before the operation. He was entirely capable of learning new motor skills, while unable to remember actually learning them.

As a result of these findings, it was proposed that the hippocampus is essential for the formation of long-term memories but not for storing them – with the exception of memories involving motor skills. Decades of research and study on memory in animal models and individuals with brain trauma have since been spent on the cause. This has led to a greater understanding of the topography of memory, both physically and psychologically, but the map is still far from detailed.

From a basic psychological stand point, memory can be broken up into three forms: working, short term and long term memory. Working memory involves the retention of transitory information, which can then be manipulated for a direct purpose such as reasoning or comprehension. It requires short-term memory, but is separate from it. Short-term memory is the storage of very limited amounts of information, in a readily available state for a short time. Long term memory, our subject of interest and the form that ‘memory’ most commonly refers to, is structurally and functionally distinct from the other two. It deals with the mental preservation of facts, events, skills and even conditioning. It provides the information we require to function socially and, to an extent, physically.

Long term memory can be broken in two categories – explicit and implicit. Explicit memory deals with the conscious remembrance of facts and events, when you think of Paris being the capital of France, that is done using explicit memory. It requires a deliberate effort to be recalled. It’s extremely flexible, forming in such a way that separate pieces of information can form associations, even if acquired at different times. Implicit memory deals with skill-based/nonverbal memories. It’s recalled unconsciously. Implicit memory can be subdivided into procedural memory (how to ride a bike), associative memory (conditioning to stimuli, such as fear response) and non-associative memory (like reflexes).

The brain isn’t like a hard drive or, if we’re being honest with ourselves, USB. Instead, the different forms of long term memories are associated with different brain regions. These areas of storage reflect the functions facilitated by the memory – explicit memory and the temporal lobes (also linked to language), procedural memory and the striatum (involved in movement), associative memory and the amygdala  (involved in emotion), non-associative and the reflex pathways (involved in reflexes).

But how is it that a lump of living matter can encode, store and retrieve all this information? That’s the big question, and the answer is we’re not really sure. Obviously our senses and their related neural areas take in and process the information, but it’s less obvious how that information is actually encoded.

The most promising model involves changes in the strength of synaptic connections, the connections between neural cells in the brain. It is thought that when a particular set of neural connections are activated by a signal, resulting from a new piece of information, those neural connections strengthen. The inverse of this process is when unused connections result in loss of the information. The strengthening and weakening of neural connection definitely occurs in the brain, but just how these changes in connection pattern represent a memory, how the change move between brain regions while forming, and how the pattern is then ‘read’ for recall is less certain.

Much of the recent neurological studies on our memories have been centred on the understanding of short-term memory loss, and diseases that impair our ability to remember. John Cooper, a stem cell scientist at the Institute of Psychiatry in the UK, recently commented that “knowing anything about the memory mechanism is important progress in understanding Alzheimer’s disease”. But there’s still a lot yet that we have to learn about memory.

The roads are missing from our mental map.

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