Autism and memory

Autism is a spectrum disorder which presents many challenges to the study of autism and memory function. It is important for researchers to be able to collect data across the spectrum and develop experimental designs to study both individuals with high functioning autism (HFA) and those with moderate-low functioning autism (M-LFA).[5] Methods to classify individuals into one of these groups include intelligence testing, which enables researchers to make methodical comparisons and analyses between HFA and M-LFA individuals.[5] Alternatively, in recent years, “mixed” studies of both HFA and M-LFA participants are done as well.[5]

Some of the earliest references to the topic of autism and memory date back to the 1960s and 70s when several studies appeared proposing that autism should be classified as an amnesic disorder.[4] What is now diagnosed as autism, was formerly diagnosed as developmental amnesia.[5] Subsequent studies had mixed results; some found support for impaired memory, others found evidence of relatively intact memory function.[4] Even though the view of autism as an amnesic disorder of memory has now been rejected,[6] there are still many studies done on the deficits in memory function that are associated with autism.[6] Furthermore, in the memory studies there were observations of memory dysfunctions in autism that were consistent with a deficit in executive functions.[4] Theories have been developed stating that the memory deficits are a reflection of primary deficits in executive function, or of a primary deficit in the processing of complex information.[1]

It has been difficult to get consistent results in autism research. One of the reasons for this is that the autistic population is very diverse, with differences in development and cognitive levels.[1] However, there are a couple of findings that have been replicated in several studies:

• Children with autism do not use organizational strategies or context to support memory. For example, when remembering words, children with autism demonstrate the same level when they are in a random group and when they are semantically or syntactically organized.[1][7]
• Compared to other children, those with autism use fewer strategies spontaneously in order to retrieve information.[1]
• Children with autism have much more difficulties with memory for complex material - for instance, for young children, recall of digits was easiest, of sentences more difficult, and of stories the most difficult.[1]
• Visual memory for some types of material is an area of strength, but children with autism also show certain difficulties with complex material.[1]

Declarative memory is memory which can be consciously recalled, such as facts and knowledge,.[8] For instance, autobiographical memory is an example of declarative memory. Declarative memory includes semantic and episodic memory. Semantic memory involves the recollection of facts, and episodic memory involves the recollection of previous experiences in life.[9] Studies on individuals with ASD have shown impairments to their episodic memory but a relative preservation of their semantic memory.[9] The brain regions that play a major role in declarative learning and memory are the hippocampus and regions of the medial temporal lobe.[9] Little research has been conducted on M-LFA individuals and memory function. Memory profiles of M-LFA individuals and of HFA individuals seem to be similar, but there is some evidence that declarative memory impairment is consistently greater for M-LFA individuals than for HFA individuals.[5]

Implicit memory is non-declarative memory that relies on past experiences to help recall things without actively thinking of them. Procedural memory, classical conditioning and priming are all included in implicit memory. For example, procedural skills, such as riding a bike, become so natural over time that one does not have to explicitly think about them. The brain regions that process implicit memory are the basal ganglia and the cerebellum. Research suggests that both HFA and M-LFA individuals show strong implicit memory function.[5] HFA individuals display intact implicit memory for non-social stimuli, unimpaired classical conditioning and performance on other implicit learning tasks. HFA individuals displayed normal perceptual and conceptual priming. Studies concerning implicit memory in M-LFA individuals are sparse and further study is needed.

As mentioned above, there are very few reliable studies of non-declarative memory for M-LFA. However, there are some speculations. Some consider that the impaired motor skills evident in many cases of M-LFA may suggest impaired procedural learning. Other studies, including Walenski (2006) and Romero-Muguia (2008),[5] also think that ASD behavior is indicative of implicit memory function. For example, many ASD individuals have exceptional implicit perceptual processing abilities in mathematics, the arts and in musical improvisation.[5] Furthermore, there is speculation that because M-LFA individuals are often characterized by habit and routine, habit formation is likely unimpaired.[5] Gordon et al. (2007) studied how procedural learning is affected by autism and found that even M-LFA individuals are capable of learning an implicit sequence with the help of behavioral training.[17] Behavioral treatments and therapies used with M-LFA individuals are usually very helpful, suggesting that implicit knowledge can be acquired and conditioning is intact.[5]

Behavioral treatments and therapies used with M-LFA individuals are usually very helpful, suggesting that implicit knowledge can be acquired and conditioning is intact.[5]

Although many people who have been diagnosed with autism suffer some memory difficulties, there are some who excel with memory. There are some individuals with HFA who have been diagnosed with Savant syndrome, such as Kim Peek.[18] Those who are considered savants have abilities, usually related to memory, that are far above average, while also experiencing mental disabilities. Savants can also excel in a range of skills other than memory, including math, art and music. While those who are diagnosed with autism have a higher probability of having savant skills, men are also more likely that women to exhibit these skills.[19][20] Howlin et al. (2009) studied a group of 137 individuals with autism, ranging from HFA to M-LFA, and found that 28.5% of them had savant skills.[19]

Another well-known savant is Daniel Tammet, who gave a Ted talk on his experience with synesthesia.[21] Synesthesia is a condition that causes the senses to be perceived differently. Those who have it may experience colors, tastes, sounds and shapes while perceiving numbers, letters and people’s faces or names. It is more common for individuals with autism to have synesthesia or savant syndrome, compared to the rest of the population.[22]

Studies suggest that memory deficit observed in ASD has a biological explanation linked to abnormalities in the hippocampus and other neural regions responsible for strategic regulation, such as the amygdala and the frontal cortex.[11]

Across the board, it is agreed that there is an urgent need for more research concerning M-LFA memory function. Specifically, there are about half as many M-LFA studies on memory compared to HFA.[5] Very few studies of implicit/non-declarative memory exist and almost no brain studies. Almost all of the M-LFA studies are conducted with school-aged children, so there is a great need for a wider age range in memory studies.[5] Very little mapping of the developmental process of ASD has happened, so there is an overall need for longitudinal studies of individuals with ASD across their lifetime.[13] Replication and extension of prospective memory research is needed[13] as well as further cross-sectional and comparison studies for HFA and M-LFA. Recently a specific call has been issued for the investigation of total loss of declarative memory in significantly low-functioning, nonverbal individuals with ASD.[5]