I have had the unique privilege of working with patients aged 14 through the late 80's. As an adult neuropsychologist (specialist in brain-behavior relationships), I have served adults with brain illness/injury in hospital settings for decades (e.g., traumatic brain injury, dementia, stroke, infection, autoimmune disease, brain tumor, seizures, alcohol abuse).
My son was diagnosed with autism spectrum disorder through our local Easter Seals clinic when he was 5 years old (after receiving developmental therapies for several years prior). It was through this personal experience that my specialization in adult brain conditions collided with my personal knowledge of autism.
Because of my current position as a certified autism specialist and adult brain-behavior specialist, I have performed many evaluations to determine autism versus dementia.
Here's what I've learned about autism and memory:
FIRST UNDERSTAND: Before I list the lessons I've learned, it is important for you to understand that there are many different types of memory difficulty, each with unique patterns. The patterns will be rather specific based on what parts of the brain are involved in the specific condition (for example, Alzheimer's Disease is classically known as impacting the hippocampus, while Multiple Sclerosis is a white matter condition-- these diagnoses present with DIFFERENT pattern of memory loss. So, the pattern of the memory profile is important in distinguishing conditions.
1. MEANINGFUL MEMORIES (personal information about others, meaningful summaries of events or seasons - e.g., what did you guys do this weekend?)
I am of the opinion that a core problem in autism is difficulty assigning meaning to information. For example, one individual in the spectrum may feel that the color red is particularly important, whereas feedback from his boss seems uncompelling.
One thing I do when someone presents with memory concerns and there may be a (diagnosed or undiagnosed) autism spectrum condition is to analyze the type of examples of memory loss. Consider the case of Mr. X who presents with his wife. She complains that he forgets their conversations (e.g., about family birthday celebrations coming up, plans for vacation as a couple, a surgery his daughter in law had last month, and worries that his wife has about their son). Interestingly, however, he just finished a book about the planets, and recently monopolized a dinner conversation by spouting off facts and tidbits about space (e.g., the temperature on venus, etc). Many of my autistic clients have poor memory for facts important to those around them but have very strong rote memory for facts within their special interest.
Additionally, it is common for my ASD clients to remember information but struggle to summarize the facts to others. If I ask, "What did you do over your summer holiday?"-- it is as if the individual sees in her mind hundreds of data points but doesn't know how to group them based on meaning and importance. The neurotypical mind would sort by categories such as "these are things I had never done before" or "these were really unusual and interesting things that happened" and then be able to give "the highlights" of her summer based on this sorting.
The neurotypical would also be able to adjust her summary to the listener. If she were speaking to her sister, she would give a different summary than if she were speaking to an elderly neighbor. In contrast, for the ASD individual, there seems to be difficulty assigning and sorting information into meaningful categories and generalizations and matching the summary to the listener.
2. INEFFICIENT LEARNING
Executive function is always a problem in some way within the autism spectrum. For some, this manifests in an inefficient learning process. This type of memory problem occurs when the individual can't take in as much new information at a time as expected.
Imagine a conveyor belt with information coming at the individual with some speed. In this scenario, the ASD individual can't keep up with all the items coming down the belt so details get missed. Although the person takes in less information, he does hang on to the information after a delay. This person benefits from repetition.
In the case of executive function difficulty, the inefficiency can also be seen attending appropriately to the details of the new information and storing the information in an organized manner (in order to be retrieved later). This person may appear "scattered" or "disorganized" with memories.
3. RAPID FORGETTING
Rapid forgetting is a hallmark of a classic Alzheimer's profile. The brain is supposed to hold onto new information and store it for later use. With hippocampal atrophy in Alzheimers Disease, the patient's brain is more like a "sieve", the new information entering and leaving the brain nearly simultaneously.
I have NEVER seen this pattern in a pure autism spectrum condition. Therefore, if the individual is on the spectrum, but then presents in later life with a rapid forgetting profile, a neurodegenerative condition (a dementia that worsens over time such as Alzheimer's or Lewy Body Dementia) is suspected.
4. NORMAL AGING
One of our hypotheses is that the normal aging process itself can release more of the autism symptoms in later decades. That is, the neurology of the individual has always expressed multiple features of autism spectrum, but perhaps there is the emergence of a few new elements (e.g., never had stereotyped motor movements but now shows them) OR that the individual shows all the SAME behaviors as in the past, but they appear significantly more noticeable. These cases appear to reflect the impact of normal aging on the brain (these individuals do not show significant decline over one to three years, for example; there is not a degenerative component).
Emotional dysregulation is always present in some form within the autism spectrum (sometimes with overt meltdowns, sometimes with hiding, quitting, escaping, and at other times with freezing and shutting down behaviors under stress). Part of the freezing and escaping profile may include dissociative episodes where the individual may lose memory for whole parts of the day or for days at a time before recovering to more typical functioning. This stress-induced amnesia may also occur for certain conversations (e.g., forgetting the details of an argument or conflict). This situation is an expression of psychological distress where the brain "helps" the individual cope by shutting down awareness of the memory process for periods of time.
There are many types of memory inefficiencies the ASD individual may experience, although most are not indicative of a degenerative dementia process. More research is needed to see if the ASD individual is at any more at risk for degenerative dementias than neurotypicals. Always see your own personal physician for advice about your own symptoms.