<p>The extra finger seen in polydactyly is often connected only with a bit of skin, but it may contain bone and even joints (Fig. 1). According to the <a href="https://www.childrenshospital.org/conditions-and-treatments/conditions/p/polydactyly" rel="nofollow noreferrer">Boston's children's hospital</a>, the extra finger (or thumb) is normally surgically removed at a young age. Surgery is deemed necessary to prevent disruption of normal motor behavior early in life.</p>
<p>However, in some instances the additional finger is fully functional (Fig. 2). In a small study including two persons with polydactyly (each had 6 fingers on their hands) the authors <a href="https://www.nature.com/articles/s41467-019-10306-w#MOESM8" rel="nofollow noreferrer">(Mehring <em>et al</em>., 2019)</a> concluded that</p>
<ul>
<li>The supernumerary finger (between thumb and index) is actuated by nerves and muscles not existent in 5-fingered hands;</li>
<li>That the extra finger has a distinct cortical representation.</li>
<li>Both subjects could manipulate the extra finger independently from the others and were in fact able to perform tasks single-handedly with the aid of the extra finger that the control subjects were unable to do barred with two hands.</li>
</ul>
<p>The study describes a radial type of polydactyly. You are interested in the ulnar type (Fig. 3). Because I think the functionality of the finger is determined mainly by its mechanical functionality, innervation and cortical representation, I don't think then location on the hand is the determining factor. Hence I think that the <a href="https://www.nature.com/articles/s41467-019-10306-w#MOESM8" rel="nofollow noreferrer">Mehring <em>et al</em>. (2019)</a> paper would apply to a ulnar case as well, barred the finger is fully developed.</p>
<p><a href="https://i.sstatic.net/7D5hl.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/7D5hl.png" alt="Polydactyly" /></a><br />
<sup>Fig. 1. Types of polydactyly. source: <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225879/" rel="nofollow noreferrer">Chopin <em>et al</em>. (2018)</a></sup></p>
<p><a href="https://i.sstatic.net/qHC36.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/qHC36.png" alt="polydactyly" /></a><br />
<sup>Fig 2. Mechanically fully functional extra index finger. source: <a href="https://www.nature.com/articles/s41467-019-10306-w#MOESM8" rel="nofollow noreferrer">(Mehring <em>et al</em>. (2019)</a></sup></p>
<p><a href="https://i.sstatic.net/0ClVE.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/0ClVE.png" alt="Types polydactyly" /></a><br />
<sup>Fig. 3. Types of polydactyly. source: <a href="https://www.news-medical.net/health/Incidence-of-Polydactyly.aspx" rel="nofollow noreferrer">Medical News Life Sciences</a></sup></p>
<p><sub><strong>References</strong><br />
<strong>-</strong> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225879/" rel="nofollow noreferrer">Chopin <em>et al</em>., <em>Hand (NY)</em> (2020); <strong>15</strong>(3): 303–10</a><br />
<strong>-</strong> <a href="https://www.nature.com/articles/s41467-019-10306-w#MOESM8" rel="nofollow noreferrer">Mehring <em>et al</em>., <em>Nature Comm</em> (2019); <strong>10</strong>: 2410</a></sub></p>

CC BY-SA 4.0
2021-12-01T08:45:43.897Z
2021-12-01T08:45:43.897Z
AliceD
<p>I have been reading about <a href="https://en.wikipedia.org/wiki/Polydactyly" rel="nofollow noreferrer">polydactyly</a> and found that surgery is only necessary in certain cases.  It depends on way the extra digit on the hand or foot is attached.</p>

<p>For example, central polydactyly (a very rare situation, in which the extra digit is on the ring, middle or index finger) requires early osteotomy and ligament reconstructions to prevent deformities, such as angular growth deformities.</p>

<p>What I am wondering about is the most common type which is ulnar polydactyly also called postaxial polydactyly (the extra digit is on the ulnar side of the hand, thus the side of the little finger).</p>

<p>Neuroscience and psychology have studied the consequences for humans of losing a limb or other body parts, including documenting the pain caused by the <a href="https://en.wikipedia.org/wiki/Phantom_limb" rel="nofollow noreferrer">phantom limb effect</a> (usually explained as due to reorganisation of the brain’s representation of missing part). </p>

<p>What has neuroscience been able to establish regarding the extra sensorimotor information the brain would be dealing with?  Can those with extra fingers use their extra digits with no problems with coordination etc?</p>

CC BY-SA 4.0
2019-06-24T15:30:06.067Z
Often in polydactyly there are tendon anomalies that supercede any CNS relevance for motor function.
Bryan Krause
<neuroscience><cognitive-neuroscience><brain><sensory-perception><coordination>
Has there been any neuroscientific study of polydactyly?
Chris Rogers
# Has there been any neuroscientific study of polydactyly?

(Asked by: username_0 on 2019-06-24)

I have been reading about [polydactyly](https://en.wikipedia.org/wiki/Polydactyly) and found that surgery is only necessary in certain cases. It depends on way the extra digit on the hand or foot is attached.

For example, central polydactyly (a very rare situation, in which the extra digit is on the ring, middle or index finger) requires early osteotomy and ligament reconstructions to prevent deformities, such as angular growth deformities.

What I am wondering about is the most common type which is ulnar polydactyly also called postaxial polydactyly (the extra digit is on the ulnar side of the hand, thus the side of the little finger).

Neuroscience and psychology have studied the consequences for humans of losing a limb or other body parts, including documenting the pain caused by the [phantom limb effect](https://en.wikipedia.org/wiki/Phantom_limb) (usually explained as due to reorganisation of the brain’s representation of missing part).

What has neuroscience been able to establish regarding the extra sensorimotor information the brain would be dealing with? Can those with extra fingers use their extra digits with no problems with coordination etc?

**Tags:** neuroscience, cognitive-neuroscience, brain, sensory-perception, coordination

> **Comments:**
> **username_1**: Often in polydactyly there are tendon anomalies that supercede any CNS relevance for motor function.  

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## 1 answers

### Answer by username_2 on 2021-12-01. Score: 1 | Accepted answer

The extra finger seen in polydactyly is often connected only with a bit of skin, but it may contain bone and even joints (Fig. 1). According to the [Boston's children's hospital](https://www.childrenshospital.org/conditions-and-treatments/conditions/p/polydactyly), the extra finger (or thumb) is normally surgically removed at a young age. Surgery is deemed necessary to prevent disruption of normal motor behavior early in life.

However, in some instances the additional finger is fully functional (Fig. 2). In a small study including two persons with polydactyly (each had 6 fingers on their hands) the authors [(Mehring *et al*., 2019)](https://www.nature.com/articles/s41467-019-10306-w#MOESM8) concluded that

* The supernumerary finger (between thumb and index) is actuated by nerves and muscles not existent in 5-fingered hands;
* That the extra finger has a distinct cortical representation.
* Both subjects could manipulate the extra finger independently from the others and were in fact able to perform tasks single-handedly with the aid of the extra finger that the control subjects were unable to do barred with two hands.

The study describes a radial type of polydactyly. You are interested in the ulnar type (Fig. 3). Because I think the functionality of the finger is determined mainly by its mechanical functionality, innervation and cortical representation, I don't think then location on the hand is the determining factor. Hence I think that the [Mehring *et al*. (2019)](https://www.nature.com/articles/s41467-019-10306-w#MOESM8) paper would apply to a ulnar case as well, barred the finger is fully developed.

[![Polydactyly](https://i.sstatic.net/7D5hl.png)](https://i.sstatic.net/7D5hl.png)  
Fig. 1. Types of polydactyly. source: [Chopin *et al*. (2018)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225879/)

[![polydactyly](https://i.sstatic.net/qHC36.png)](https://i.sstatic.net/qHC36.png)  
Fig 2. Mechanically fully functional extra index finger. source: [(Mehring *et al*. (2019)](https://www.nature.com/articles/s41467-019-10306-w#MOESM8)

[![Types polydactyly](https://i.sstatic.net/0ClVE.png)](https://i.sstatic.net/0ClVE.png)  
Fig. 3. Types of polydactyly. source: [Medical News Life Sciences](https://www.news-medical.net/health/Incidence-of-Polydactyly.aspx)

**References**  
**-** [Chopin *et al*., *Hand (NY)* (2020); **15**(3): 303–10](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225879/)  
**-** [Mehring *et al*., *Nature Comm* (2019); **10**: 2410](https://www.nature.com/articles/s41467-019-10306-w#MOESM8)


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