SAVANT SYNDROME

Introduction

In savant syndrome, the contrast between extraordinary abilities and marked disabilities is stunning. The word “savant” comes from the French savoir, which means “to know.” A savant is a person with encyclopedic knowledge in diverse areas of knowledge.

The savant syndrome, with its “islands of genius”, has a long history. The first account was in a scientific paper featured in the German psychology journal, Gnothi Sauton, in 1783, describing the case of Jedediah Buxton, a lightning calculator with extraordinary memory (Mortiz 1783).

Rush (1789), the father of American psychiatry, also provided one of the earliest reports when he described the lightning calculating ability of Thomas Fuller, who could comprehend scarcely anything, either theoretical or practical, more complex than counting. However, when Fuller was asked how many seconds a man had lived who was 70 years, 17 days and 12 hours old, he gave the correct the answer of 2 210 500 800 in 90s, even correcting for the 17 leap years included (Scripture 1891).

Of interest was the cases of the so-called “calculating twins”—identical twin brothers with autism—which brought the autistic savant to new attention. At the 1964 American Psychiatric Association Annual meeting Horwitz and his co-workers presented a paper describing the phenomenal calendar calculating memory abilities of these twin brothers. They are examples of savant syndrome occurring in autistic disorder.

The brothers can identify on what day a particular date fell or will fall over a time-span of 80 000 years, or can tell, for example what date the second Tuesday of April will fall in the next 40 years, or what years, in the next 100, Easter will fall on March 18th. They also can remember the weather for each day of their adult life.

Sacks describes these two brothers swapping 20 digit prime number for amusement when they were hospitalized together, yet were unable to multiply the simplest of numbers. They also were able to count matches as they fell to the floor instantly, almost before they hit the floor.

If those scenes sound familiar, they are, because those were some of the savant abilities incorporated into the composite autistic savant Raymond Babbitt Opens in new window, portrayed so accurately by Dustin Hoffman Opens in new window in the award winning movie Rain Man which made “autistic savant” a household term.

Savant Syndrome Today — What We Do Know

There are a number of things we do know about savant syndrome even though there is still much we need to explore further. But after several centuries of reports and observations, certain things can be said of what we know:

1. Incidence

Savant syndrome is rare. In Rimland’s survey of 5400 autistic children, 531 (9.8%) were reported by parents to have special abilities. Hermelin puts that figure much lower, however, stating,

Although she goes on to point out, importantly, “though a reliable frequency estimate does not exist as yet.” Hill found that the incidence of savant skills was 1: 2000 (0.06%) in an institutionalized population with a diagnosis of mental retardation Opens in new window.

A recent study in Finland, based on a survey of 583 facilities serving persons with developmental disabilities, found 45 cases of savant syndrome creating an incidence of 1.4 per thousand, or approximately double the Hill incidence estimate, but still very uncommon. It is not unusual to encounter a clinician who has not seen a person with savant syndrome throughout years of a busy practice in private or public settings even if seeing a substantial number of persons with developmental disabilities.

Whatever the exact figures, savant syndrome, although rare overall, is seen much more frequently, conspicuously so, in autistic disorder Opens in new window than in other developmental disabilities or in mental retardation.

However since mental retardation particularly is much more common than autistic disorder, about 50% of persons with savant syndrome have autistic disorder, and the other 50% have other forms of developmental disability or mental retardation. Thus not all autistic persons are savants, and not all savants have autistic disorder.

2. Sex Ratio

Consistent in all the reports in the literature, males outnumber females in an approximate 6: 1 ratio. Of 103 persons classified as savants in 63 publications, Hill reported 89 were male and 14 were female providing that 6: 1 male: female ratio.

Part of the reason for the higher male incidence of savant syndrome is the relatively high incidence of savant syndrome in autistic disorder which itself has an already high 4: 1 male: female ratio. Contributing to the male: female discrepancy in both disorders are newer findings on the role of testosterone on cerebral lateralization, which will be discussed below.

3. Congenital vs. Acquired Etiology

The vast majority of savant syndrome cases occur in those conditions, including developmental disabilities, present from birth. But cases do occur where the special skill arises after injury or disease to the central nervous system in infancy, childhood or even adult life, including recent cases of striking savant abilities emerging as a fronto-temporal dementia proceeds.

Other etiologies for acquired savant abilities have been head injury, encephalitis, epilepsy or stroke. These cases of acquired savant abilities raise special questions about buried potential, perhaps, within us all and point out as well the plasticity, and compensatory potential, of the central nervous system in some persons.

4. Mental Handicap, Blindness and Musical Genius

Conspicuously prominent in all the cases of savant syndrome in the past, and present cases as well, is the recurrent, curious triad of developmental disability, blindness and musical genius.

While this musical genius and blindness can sometimes be linked with mental retardation or other forms of developmental disability, the link with autism has particularly striking, and seemingly disproportionate.

The link of music with mental handicap and blindness has a long history. Tredgold (1914) described of a case of a blind, musical savant at the Salpetriere in 1861 and he observed that “most aments are fond of music.” Later that century Thomas Greene Wiggins, known more popularly as “Blind Tom” Buthunel became internationally well known, and may have been the highest paid black performer of that era. He was described by some as “the eighth wonder of the world.”

A number of recent cases, with autism Opens in new window as the basic disability, have become particularly prominent and well known. In a closer look at these cases two additional factors almost always surface—premature birth and blindness is usually from retinopathy of prematurity (retrolental fibroplasias).

Keeler point out the frequent occurrence of infantile autism in patients blinded from retrolental fibroplasias, compared to blindness from other causes, and raised the question of whether some vascular capillary process similar to that which occurs in the retina (which is brain tissue) might occur elsewhere in the brain and lead to the characteristic autistic symptoms seen in these patients.

Rimland also raised that same possibility commenting on the high frequency of premature births in autistic children, some of whom developed retrolental fibroplasias suggesting the same process on the retina may be duplicated in the reticular activating system particularly.

The Nature of the Special Skills

Considering all the skills in the human repertoire, it is striking savant skills, through all the reports this past several centuries, occur within a consistent and intriguingly narrow range. Those are generally in five areas:

1. music;
2. art;
3. calendar calculating;
4. lightning calculating and
5. mechanical or spatial skills.

Calendar calculating is often the most frequently reported skill. Why this obscure ability appears with such regularity among almost all savants is a particularly intriguing question.

The musical skill is most often performance, and usually piano playing although complex composing has been reported as well as facility with as many as 20 instruments.

Art skills are usually drawing or painting although sculpting is reported as well. Lightning calculating includes rapid calculation of complex equations or fascination and facility with prime numbers, for example.

Mechanical or spatial skills include the ability to measure distances precisely without benefit of instruments, for example, or the ability to construct complex models or structures with painstakingly fine accuracy.

Other skills have been reported less often. They include:

• prodigious language facility—polyglot savants;
• unusual sensory discrimination in smell, touch or vision;
• perfect appreciation of passing time without knowledge of clock face;
• superior coordination and balance skills and athletic ability; and
• outstanding knowledge in specific fields such as neurophysiology, statistics or navigation, for example.

In Rimland’s sample of 543 autistic children in whom special skills were reported musical ability was the most frequently reported skill followed by memory (which he listed as a special skill), then art, pseudo verbal abilities, mathematics, maps and directions, coordination, calendar calculating and extrasensory perception in that order.

Generally a single, special skill exists but in some savants several skills exist simultaneously. Rimland and Fine noted that the incidence of multiple skills appeared to be higher in autistic savants than in savants with other developmental disabilities. Sometimes the multiple skill surfaces with the same enormity, and surprise, as the original skill.

While right brain/left brain terminology is an oversimplification, because of cross connections and cross representations, the two brain hemispheres do tend to specialize in certain functions.

Savant skills tend to be those associated with the right hemisphere—non-symbolic, artistic, concrete, directly perceived—in contrast to those associated with the left hemisphere which are more sequential, logical, symbolic and including language specialization.

Whatever the skills they are always associated with prodigious memory within the skill area itself. It is a memory of special type—vastly deep but exceedingly narrow. Some observers list prodigious memory as a special skill, adding it as a skill in addition to the five general areas listed above. However prodigious memory ability is a skill all savants possess cutting across all of the skill areas a shared, integral part of the syndrome. That is, the special skill + prodigious memory is is the savant syndrome.

Finally, these skills exist over a spectrum of abilities. The most common savant abilities are called “splinter skills. These include behaviors such as obsessive preoccupation with, and memorization of, music and sports trivia, license plates numbers, maps, historical facts, or obscure items such as vacuum cleaner motor sounds, for example.

Talented savants are those persons in whom musical, artistic, mathematical or other special skills are more prominent and highly honed, usually within an area of single expertise, and are very conspicuous when viewed against their overall handicap.

The term prodigious savant is reserved for those very rare persons in an already uncommon condition where the special skill or ability is so outstanding that it would be spectacular even if it were to occur in a non-handicapped person.

There are probably fewer than 50 prodigious savants living worldwide at the present time who would meet this very high threshold of special skill. The placement on this spectrum is admittedly subjective but there does seem to be a natural division between these three levels of ability and expertise.

The Extraordinary Memory of the Savant

Whatever the special skills the savant demonstrates, a remarkable memory of a unique and uniform type welds the condition together. Terms such as automatic, mechanical, concrete and habit-like have been applied to this extraordinary memory of the savant by clinicians and researchers alike this past century.

Down used the term verbal adhesion to describe a memory adept at remembering facts without comprehension of their meaning. Critchley described savant memory as exultation of memory or memory without reckoning. Tredgold used the term automatic and Barr characterized his patient with prodigious memory as an exaggerated form of habit.

Such unconscious memory—memory without reckoning—suggests what Mishkin and Petri referred to a non-cognitive habit formation system rather than a cognitive memory system.

They proposed two different neural circuits for these two different types of memory, a higher level cortico-limbic circuit for so called semantic or cognitive memory, and a lower level, cortico-striatal circuit for the more primitive habit memory which is sometimes referred to as procedural memory Opens in new window.

It may be that the same factors that produced left hemisphere damage, including prenatal hormonal influences in some cases, are instrumental in producing damage to the higher level cognitive memory circuits leaving the savant to rely on the more primitive, but spared, habit memory circuits and thus producing the characteristic right brain skills coupled with habit memory capabilities.

Others have suggested defects and dysfunction in the hippocampus and amygdala may produce the uniform type of memory that savants display. Rimland and Fine suggested that defects in amygdala function produced over-reliance on the hippocampus in memory function and retrieval, producing the extraordinary memory in the savant.

In support of that hypothesis Bauman and Kemper found histopathologic changes in the hippocampus, amygdala, cerebellum and other areas of the forebrain in a post-mortem examination of a 25 year old autistic patient. They concluded such pathology occurred in the prenatal period and included neuron destruction in the affected areas. They further suggested “although defects in memory have been little studied in autism, they may well underlie the pronounced difficulties in social interaction, language function, and learning that characterize these patients.”