Title:Associative memory and symptoms of Asperger’s syndrome

Title:Associative memory and symptoms of Asperger’s syndrome

タイトル：　アスペルガー症候群と連想記憶

Introduction

We have formulated the hypothesis that, in Asperger’s syndrome, the function of associative memory, which manages associativity, is poorer than usual. This leads to the assumption that some characteristic symptoms occur in Asperger’s syndrome. This paper discusses symptoms on which this assumption is built and associative memory.

Memory is divided into episodic memory and semantic memory; associative memory is considered to have a function to memorize things as episodic memories. In associative memory, memories are triggered one after another from one memory. For example, suppose one remembers the whole of a painting. In associative memory, the mere sight of a fragment of it triggers recollection due to association, making it possible to visualize the whole painting.

In episodic memory, the memories associated with an event experienced are linked in a network. When one recalls the episodes experienced in the past, the memories associated with them are triggered one after another from the fragments of a certain memory. Thus, it is episodic memory in which associated memories are linked in a network, triggered as a whole from their fragments. This suggests that episodic memory is formed based on the function of associative memory.

In contrast with episodic memory, there is semantic memory.

In semantic memory, concrete memories other than the very meaning of a word are discarded, not left at all. Episodes--how, when, and where a certain word was remembered--were not stored in semantic memory. It cannot be said that a memory is connected to another memory in a network.  This suggests that semantic memory works based on a different function from that of associative memory. Since semantic memory works in a similar way to the computer, which memorizes input data just as is, here we call semantic memory direct memory, in contrast with associative memory.

Associative memory	Episodic memory
Direct memory	Semantic memory

It is known that semantic memory is dominant in one’s childhood and that episodic memory becomes dominant as advancing ages.

Further, rote memorization is what children are good at; one becomes poor at it in the adulthood.

Savant syndrome is observed in Asperger’s syndrome patients.

It is characterized by prodigious memory and outstanding numeracy. We infer that the way of memorizing things in Savant syndrome patients is semantic memory. Abilities such as memorizing a huge amount of telephone numbers correctly is not the memory involving understanding but rote memorization. Probably, it is far more difficult for an adult to memorize multiplication table than for a child to automatically memorize it. These facts indicate that, in the so-called rote memorization, things are memorized as semantic memories. 

There is no evidence that if one of associative memory and direct memory is good the other is poor. However, symptoms of Asperger’s syndrome are explicable on the hypothesis that Asperger’s syndrome patients are excellent in direct memory and poor in associative memory.

Memorization and calculation are what the computer is good at. Conversely, understanding of the abstract is what the latest computer is poor at. Asperger’s syndrome patients are poor at understanding of the abstract.

The relation between understanding of the abstract and associative memory is deduced from the difference between realistic painting and abstract painting. Suppose one paints a picture of a lion in comics or a stuffed lion by seeing a photograph (realistic painting) of a lion. Emphasis and transformation (deformation) of a real object is abstract painting. What an abstract painting or a rough drawing represents is known only after association. One can identify it as a lion through association with the characteristics. Realistic painting does not require association; since realistic painting represents the life itself, one can identify it as a lion as long as one has seen one before.

Associative memory	Abstract painting	Abstract
Direct memory	Realistic painting	Realistic

We believe that the fact that Asperger’s syndrome patients have difficulty in understanding abstract concepts is explicable by impairment of associative memory. In some cases, a person without Asperger’s syndrome requires time to understand abstract concepts. An abstract text cannot convey what it means correctly when it is interpreted literally. First, based on the literal meaning of the text, association occurs in the head with several recollections, among which the most appropriate is chosen.

There is another reason for which associative memory is required. It is because the brain generalizes that one can understand abstract concepts. Presumably, realistic direct memory is poor at memorizing things by generalizing them. Direct memory is not a vague memory but an exact memory. Naturally, a vague memory would find it difficult to memorize a huge amount of figures.

In the associative memory model using perceptron networks, it is possible to have neuronal circuits memorize patterns by layering them. However, since memorization does not take place individually as the computer does, layering similar patterns causes confusion in the memory. For this reason, associative memory is not suitable for memorization of a huge amount of figures or the like. The poorer an organism is at generalization, the more exact memory it has. Asperger’s syndrome patients, in whom direct memory is dominant, are poor at generalization, thereby having difficulty in understanding the abstract.

One of the characteristics of Asperger’s syndrome is circumlocution: being apt to give a detailed account in explaining the whole of something. It is realistic to express details of the whole. The ability of generalization is required for selecting and expressing only the main point, and the explanation in which only the main points are picked up is exactly abstract. If explanation becomes much too abstract rather than realistic, it will be difficult to understand like esoteric philosophy.

Realistic expression	Middle	Abstract expression
Express minute details of the whole; too many expressions, making it difficult to grasp the whole.	Good balance between main points and comments to support them.	Esoteric philosophy book having too few main points.
Circumlocutory	Clear	Difficult to understand

Conclusion

Episodic memory works based on the function of associative memory and semantic memory works based on the function of direct memory. In Asperger’s syndrome, when the patient is poorer at associative memory and more excellent in direct memory than usual, he/she exhibits prodigious memory, characteristic of Savant syndrome. Since associative memory is a function required for understanding of  abstract concepts and that direct memory is poor at generalization, a brain in which direct memory is dominant has difficulty in understanding the abstract. Asperger’s syndrome patients are poor at generalization, thereby characterized by difficulty in keeping to the point in explanation and by circumlocutory expressions.