Understanding the Nature of Long-Term Memory

Having an understanding of the nature of long-term memory is essential to anyone interested in studying the brain and the human mind. There are many theories about the formation of long-term memories,and what makes them more powerful than other forms of memory.

Engrams in the nervous system

Until recently,studies of engrams in the nervous system and long-term memory were based on either tissue lesion or pharmacological disruption. However,with the development of advanced intervention techniques,researchers can now image engrams in cell ensembles. This can provide important insights into how memories are formed and maintained.

Competition is a fundamental property of many biological systems,and engrams are no different. When an experience occurs,a small fraction of eligible neurons are primed to become part of an engram. The neuron with the highest relative excitability is awarded a place in the engram. The engram is then allocated to support the memory of that experience. As the number of eligible neurons increases,the engram grows and changes.

Semon proposed the engram theory,stating that engrams must possess certain properties to be effective in memory. He described an engram as a complex of functionally connected engram cell ensembles that are dispersed across multiple brain regions.

In the nervous system and long-term memory,engrams may also be physically redundant,which can enhance retrievability. Physical redundancy allows engrams to survive the death of one or a few neurons.

Retrieval attributes

Using new technologies to study the neurobiological basis of memory retrieval has helped to unlock some of the mysteries of the human brain. Among these discoveries are the encoding and retrieval attributes of long-term memory.

In the field of cognitive psychology,the term engram was first introduced by Richard Semon,a German scientist at the turn of the twentieth century. He defined an engram as a change in the nervous system representing an event. In a natural state,these engrams are inaccessible. However,researchers have been able to manipulate engrams in mice through genetically encoded actuators.

The encoding attribute of long-term memory is the ability to store information over time. While this may seem trivial,it is important to remember that people use different strategies to store information. The encoding process forms links between memories and facilitates retrieval.

Aside from the storage,the retrieval attribute of long-term memory is the ability of a person to recall an episode from their past. The memory retrieval process involves the reconstruction of a specific episode based on schema knowledge.

cLTM formation

During the last few years,researchers have been experimenting with a host of effectors that can be used to modulate neural activity. These include small molecules like c-Kin,s-Kin,and c-Ets to name a few. Although many have been demonstrated,the jury is still out on the effectiveness of these nanomedicines in humans.

The fact of the matter is that the fabled “cLTM” may be a fiction in the grand scheme of things. The main reason is that this particular sub-cellular structure is highly interconnected with other brain regions. To wit,the LAL aka LAL (or LAL) is highly correlated with the superior medial protocerebrum,which is the target of the MB output neurons. As a result,the MB is a critical processing area for long-term associative memory formation.

However,the MB is only one of many input and output brain regions. For instance,the LAL also receives a significant number of sensory inputs,mainly from the visual and auditory senses. In the long term,these inputs are stored as mental representations of the world.

cLTM vs meaningless pictures

Several studies have examined the effects of time and repetition on the performance of old-new recognition of pictures. Four studies investigated the effects of the retention interval (i.e.,the length of time between the first and second presentations of an item) on old-new recognition. The results are consistent with the predictions of image sampling models.

In one study,the same test item was presented twice at input. Half of the items were shown in the same orientation the second time. The other half of the items were reversed at the test. The mean number of falsely recalled items was 0.25 in Tukey’s HSD. This is not a surprising finding because the number of falsely recalled items was the same between the real objects and the pictures. However,this finding does not explain the asymmetry in the performance of the real objects and the photographs.

Moreover,there is no evidence to suggest that the differences in the performance of the two groups are due to asymmetric memory. Instead,it is likely that the performance of the real objects is superior because of their better knowledge of the study material.