Savantism

Savantism: Islands of Genius
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Source: Wisconsin Medical Society

Savantism is a neurological phenomenon that has manifested itself within savants as islands of genius, which refer to the talent in music, visual arts [11], exceptional memory, and enhanced calculation abilities [23]. Savant skills tend to be associated with the right hemisphere because the lack of top-down contribution allows the right hemisphere to become the dominant hemisphere [2]. An investigation using MRI into the neuroanatomy and neurochemistry of the savant brain revealed a larger right cerebral hemisphere in comparison to the left, increased hippocampal volume, and larger fiber tract bundle volumes in these sections [5]. Another study by Bor et al in 2007 observed hyperactivity in the lateral prefrontal cortex in their savant participant. Many of the above structures and connections are implicated in memory and learning [5], so the increases in these structures may have a correlation with the enhancement in cognitive abilities such as how an increase in hippocampi volume improves memory [8]. Many of these changes observed in the savant brain are also observed in the autistic brain; therefore further research into understanding how these changes in neural structures affect cognitive abilities can aid both understanding savantism and autism spectrum disorder (ASD) [5] and possibly explain why 50% of savants are coupled with ASD but only 10% of autistics are also savants [23].

1.0 Savant Abilities

Multiplication of 2 Numbers
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A rare insight into how a synaesthetic
savant performs mathematical calculations.
Source: Born On A Blue Day

Savantism is a neurological phenomenon that manifests itself in islands of genius, usually in the areas of calendar calculations, visual arts, and music, accompanied by exceptional memory [11][23]. These are the skills most associated with savantism, but are not the most common. The most common skills in savantism are splinter skills, which encompass only obsessiveness and memorization of trivia, maps, area and zip codes, and historical facts [23]. Talent in calculations, visual arts, or music are found only in talented savants and prodigious savants, who respectively possess one highly honed skill or several highly honed skills [23]. However, this semantic difference is rarely observed as most papers use “savant” to refer to talented or prodigious savants, hence this wiki article will do the same.

Savant skills generally manifest in five categories and grant a relatively narrow but deep expertise in certain aspects of the skill, though there are prodigious savants who attain a more complete mastery of the skill [18][23]. Savants with talent in music are generally limited to performance on the piano, perfect pitch, but there are reports of savants that can play multiple instruments. Those talented in art are usually restricted to drawing, painting, and sculpting. The most common mathematical ability displayed is extremely quick calendar calculation, with some talented in quick calculations of extremely big numbers and prime numbers. The last two skills are mechanical and spatial skills, which grant the savant the ability to accurately construct models and to measure distances without using tools [23].

In addition to these five general skills, there have been reports of savants who have talent in language, allowing them mastery over multiple languages. Synaesthesia and the ability to know the amount of time passed without the aid of a clock have also been reported over the years [23].

In contrast to the aforementioned savant skills, the one savant skill that does not vary from savant to savant is exceptional memory. All savants possess exceptional memory for information typically to their area of expertise or interest [23], but they seem to be unable to make use of the information as some report their memory as memory without reckoning [6] or memory without understanding [14]. This memory appears to be automatic [22][23], therefore, it may be more implicit or procedural memory than explicit or semantic memory, using the lower level cortico-striatal circuit rather than the higher level corticolimbic circuit [12][23].

2.0 Case Studies

2.1 Kim Peek

Kim Peek - The Real Rain Man Part 1
Source: Youtube.com

Kim Peek is a savant who is an extraordinary example of the abilities and disabilities savantism can bestow upon those described as a savant. He is able to recall the pages describing a character in Tom Clancy’s The Hunt for Red October and recite passages of description verbatim [24]. He can do quick calendar calculations on the scale of milliseconds and identify a classical composition just by listening to it. If asked about his 15 or more interests, he is able to provide information as well as an expert in that field due to his exceptional memory and reading speed of 1 page per 8-10 seconds [24]. However, these impressive abilities come with a cost. He lacks fine motor control, requires someone to take care of him daily as he cannot perform general daily chores, walks with a side-long gait, and cannot mentally handle abstraction as well as the average person [24].

A look at his brain reveals a malformed cerebellum, which may attribute to his motor difficulties. He also lacks a corpus callosum, the brain structure that serves as a bridge between the left and right hemispheres and allows the two to communicate with each other [24]. Intrigue surrounds this defect because may help explain how savant abilities surface. Many epileptics have their corpus callosum ablated to prevent seizures from travelling from one hemisphere to the other, resulting in “split brain” syndrome, but not savant abilities. Therefore, some surmise that a congenital lack of a corpus callosum may play a role in the development of savantism because the brain hemispheres would develop back channels of communication which may differ in strength and/or connectivity from those developed from ablation of the corpus callosum after birth [24].

Abnormalities in Kim Peek’s left hemisphere may also contribute to his savantism. Left hemisphere abnormalities are a common feature in savantism and may play a role in the development of savantism; a notion that is strongly supported by the development of savantism in patients who have suffered damage to the left hemisphere [18][24]. Abnormalities in the left hemisphere impair its function, causing it to lose its dominance over the right hemisphere. The right hemisphere may compensate for that decreased functioning through recruitment of brain areas and tissue otherwise used for other purposes, resulting in the development of savantism [23][24]. Another possible explanation is that decreased functioning of the left hemisphere allows the right to be released from the “tyranny of the left hemisphere”, unlocking savant abilities that are otherwise dormant in the right hemisphere [23][24].

2.2 Daniel Tammet

Different Ways of Knowing
Danial Tammet's Tedtalk. Source: Ted.com

Daniel Tammet is a savant with high-functioning autism and Asperger syndrome. He has synaesthesia, causing him to see words and numbers in distinct shapes, colours, and emotions [20]. Synaesthesia may play a role in Daniel Tammet’s exceptional memory [16] and complement his savant skills, allowing him to rapidly perform mental calculations, break the 2004 European record for most Pi digits recited [13], and learn Icelandic in one week [20]. Due to being a high-functioning autistic, he is able to communicate and verbally describe his perception of words and numbers, granting researchers a deeper insight into savantism.

3.0 Neural Structures and Patterns of Activation in Savantism

3.1 Cerebral Hemispheres

rTMS Inducing Virtual Lesion
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In Left Anterior Temporal Lobe
Source: Eide Neurolearning Blog

The existence of savantism may be due to the savant have “privileged” access to incoming sensory information that a typical human does not [17][18]. A fully functioning left hemisphere would automatically organize incoming sensory information into concepts and categories, but the savant brain will perceive the sensory information as individual percepts due to the impaired function of the left hemisphere [17]. The impaired function of the left hemisphere is usually compensated for by the right hemisphere [2][17], therefore the right hemisphere is larger than the left [5] because increased function correlates with increased volume [8].

Previous studies show that repetitive Transcranial Magnetic Stimulation or rTMS used to produce virtual lesions in the left anterior temporal lobe were able to induce savant-like skills in drawing, proofreading, and numerosity, which is the savant-like ability to accurately estimate numbers of items [17]. Inhibition of the more semantic left hemisphere resulted in a more literal perception of sensory information [17] and an increased awareness to sensations [18]. Some hypothesize that the right hemispherical network concerned with details is inhibited by the left hemispherical network for concepts, so when the left hemisphere is impaired, the network for details dominates, producing the heightened perception of details typical of savant skills [18].

3.2 Increased Hippocampal Volume

Exceptional memory observed in savantism may be, in part, due to the increased hippocampal volume in savants [5]. The increased volume could be a result of a heightened rate of neurogenesis [21] that correlates to an increased rate of learning in mice [9]; therefore it could be one of the underlying mechanisms of the heightened learning savants possess. An increased hippocampal volume has also been shown to be directly correlated with improved memory function, though the study in question tested only for spatial memory [8]. However, the activation of a left fronto-temporal network including the hippocampus was observed during the performance of calendar calculations in a savant [1], therefore an increased hippocampal volume may correlate with improvements in other types of memory in addition to spatial memory. Also, the left fronto-temporal network is typically used in delayed memory retrieval in controls [7], indicating the savant brain overdevelops normal brain circuits in a disorganized fashion, producing atypical circuits that may manifest as savantism [1].

3.3 Hyperactivity in Lateral Prefrontal Cortex

Prefrontal Cortex Highlighted
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Source: Wikipedia.org

A study in 2007 by Bor et al revealed hyperactivity in the lateral prefrontal cortex in savant DT who also has Asperger syndrome and synaesthesia when encoding digits in a digit span task. Increased activity in the later prefrontal cortex may indicate the use of chunking, a process in which information is organized into groups to facilitate memorization of the information [4], or the recruitment of additional processes in working memory [25], though the latter is less likely to be the case [3]. Hyperactivity in DT’s lateral prefrontal cortex may also be recruitment during DT’s perception of digits as he lacks the additional activation of other sensory areas such as the visual brain regions typically observed in synaesthetes. This supports the idea that DT is more on the recently observed conceptual end of the synaesthesia spectrum rather than the more commonly studied perceptual end [3], though more research is required to support this idea.

DT also showed no difference between encoding digits of structured and unstructured digit span tasks whereas the controls showed a statistically significant increase in chunking for the structured digit span task. The control showed an increased activation of the lateral prefrontal cortex during the structured digit span task, indicating increased use of the chunking process due to the ease of chunking organized information [3]. However, DT showed no difference in activation of his lateral prefrontal cortex between the two types of digit span tasks, therefore DT chunks digits regardless of whether they are structured or unstructured. These results and DT’s description of his perception of digits as a complex 3D “mental landscape” [20] suggest that DT’s chunking of digits is an automatic process [3].

Automatic hyper activation of DT’s lateral prefrontal cortex during the encoding of digits coupled with his more abstract, conceptual type of synaesthesia may be what grants DT his savant skill of exceptional memory, being able to memorize Pi to 22 514 decimal places [13], and his ability to rapidly perform mental calculations such as multiple two six-digit numbers together [3].

4.0 Savantism and Autism Spectrum Disorder

4.1 Commonalities

Daniel Tammet
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An autistic savant.
Source: Wikipedia.org

Talent in music, specifically the absolute pitch ability, is observed in both savants and non-savant autistics [11]. Much like savants, non-savant autistics do not require previous training to acquire absolute pitch [10], therefore absolute pitch in autism is acquired in an atypical route that may be shared by savantism.

In terms of neurobiochemistry, both the savant and non-savant autistic brain exhibit decreased function of the GABAergic system and increased right caudate volumes [5]. Atypical neural connections and brain morphometry are also observed in the two, with abnormalities appearing during early development [1][5]. This suggests that savantism may arise from autism if the abnormalities in the neural connections and brain structures are such that they can manifest as prodigious skills [5], which could explain why 50% of savants are autistic [23]. The other 50% of savants may encompass only those who acquired savantism after birth through left brain damage or a neurodegenerative disease such as fronto-temporal dementia [19]. The low probability of achieving savantism through the correct abnormalities in autism may explain why only 10% of autistics have savantism [23].

4.2 Future Implications

Currently, there is a lack on research in the areas of savantism, specifically what patterns of activation, neural circuits, and cortical structures are involved in savant skills. Further research into these areas will further our understanding of savant skills and possible how to induce them in normal people. Also, further investigation into commonalities between ASD and savantism may reveal why 50% of savants are coupled with ASD but only 10% of autistics are also savants [23].

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