1

Usage of the middle finger shapes reorganization of the

primary somatosensory cortex in patients with index finger amputation

Oelschläger M1*, Pfannmöller J1*, Langner I2, Lotze M1

1Functional Imaging Unit, Center for Diagnostic Radiology, University of Greifswald,

Germany

2Department of Trauma and Orthopaedic Surgery, University of Greifswald, Germany

*both authors contributed comparably

Corresponding author: Martin Lotze Functional Imaging Unit; Center for Diagnostic Radiology and Neuroradiology; University of Greifswald; Walther-Rathenau-Str. 46, D-17475 Greifswald, Germany; mail: martin.lotze@uni-greifswald.de Phone: +49-3834 866899 FAX: +49-3834 866898

Running title: Plasticity in S1 after finger amputation

Key words: amputation, cortical plasticity, usage factor, somatotopy, primary somatosensory

cortex, S1, reorganization, fMRI.

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Abstract

Purpose: The primary somatosensory cortex (S1) is somatotopically reorganized after limb

amputation. The duration of the amputation, the intensity of phantom limb pain but also a

multifactoral model of altered cerebral input have been discussed to be associated with

cortical changes. Patients with finger amputation rarely show phantom limb pain, the

deafferented cortical area is small but other fingers might well overtake function.

Method: We selected a group of index finger amputated patients and performed a high

resolution (in plane: 1.5 mm2) S1-mapping during tactile stimulation of finger tips.

Result: We found an interhemispheric imbalance of the distance between the thumb and

middle finger only for the patient-group. When patients used their middle finger more they

showed less interhemispheric imbalance, increased spatial tactile discrimination and increased

fMRI-activation in response to stimulation. Phantom limb pain was not associated with

somatotopic representation parameters in S1.

Conclusions: Overall, our fMRI-data point to a usage dependent plasticity of Brodmann’s

area 3b in man.

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1. Introduction

Investigations in monkeys (Merzenich, 1998; Pons et al., 1991) as well as

magnetoencephalographic (MEG) studys (Birbaumer et al., 1997; Elbert et al., 1994; Flor et

al., 1995), functional magnetic resonance imaging (fMRI) studies (Bjorkman et al., 2012;

Lotze et al., 2001; Lotze et al., 1999) or transcranial magnetic stimulation (TMS) studies

(Cohen et al., 1991; Karl et al., 2001; Roricht et al., 1999) in humans suggested that the

remapping after limb amputation occurs at the level of the primary motor (M1) or

somatosensory (S1) cortices. On the cortical level a decrease of lateral inhibition as a result of

amputation might account for some of the cortical reorganization (see Calford and Tweedale 1991).

Recent studies in monkeys show that after sensory loss, notable reorganization takes weeks to emerge

(Darian-Smith & Brown, 2000). When investigating the somatosensory domain it is important to

consider that S1 is subdivided in 4 cytoarchitecturally different areas 1, 2, 3a and 3b

(Brodmann, 1909). Each of these shows separate body representations (Merzenich et al.,

1978). While BA3b represents the information from the skin, BA3a represents the

information for limb proprioception. The information from BA3b is further processed in BA1

for texture discrimination, and combined with information from BA3a in BA2 for size and

shape recognition (Kandel et al., 2000). BA3b is shown to process information before BA1

and might therefore be the primary region for processing of stimuli from the body surface

(Papadelis et al., 2011). For the owl and squirrel monkey micro-electrode mapping techniques

in BA3b showed robust enlargement of fingers with somatosensory innervation from the

radial and the ulnar nerve after median nerve transsection. The invasion of deafferented

cortical territories by neighboring representation areas was much more variable in BA1

(Merzenich et al., 1983). In humans only anecdotic data on reorganization after finger

amputation have been reported using MEG (Weiss et al., 1998; Weiss et al., 2000). This

method does not allow to differentiate between cytoarchitectural representation sites, a

technique which is available for high resolution fMRI-studies (Fischl et al., 2008). Up to now,

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group data of patients with amputated fingers are absent although methods demonstrating

precise somatotopic mapping of the digits in S1 using high resolution fMRI have been

published (Martuzzi et al., 2012; Schweizer et al., 2008; Weibull et al., 2008a).

Currently, there is a vivid discussion on how phantom limb pain (PLP) after

amputation might be provoked and maintained (Flor et al., 2013; Flor et al., 2006; Makin et

al., 2013). Overall, multiple associations of adaptive plastic changes have been reported to

factors such as the duration of the deafferentation (Lotze et al., 2006), changes in spontaneous

activity of the peripheral nerve (Nystrom and Hagbarth, 1981), the intensity of phantom limb

pain (PLP) (Flor, 2008) but also the increased usage of body parts represented in neighboring

areas (Lotze et al., 1999).

Patients after finger amputation do less frequently present phantom limb pain than

those after amputation of the hand or even larger parts of the upper limb. Karle and colleagues

(Karle et al., 2002) reported only about 19% of their sample of 58 finger amputated patients

with PLP. In comparison, about 50% - 80% of patients with amputation of at least the whole

hand show PLP (Nikolajsen et al., 2006). One reason for a lower occurrence rates of PLP in

these patients might be a lower degree of functional reorganization of M1 and S1. This

assumption is based on the smallness of the deafferented cortical area after amputation of one

finger and a good functional compensation of the amputation by other fingers.

We were interested in associations of these parameters and especially in the

contribution of a functional overtake of the middle finger (D3), e.g. for pinch grip

movements. Therefore, we investigated the somatosensory finger tip representation in a small

group of patients with a traumatically amputated index finger (D2). The distance between

these representations were compared to the other hemisphere and to the corresponding

representations in a group of 18 healthy participants. In addition, we carefully tested the

compensational functional usage of D3 in different hand motor tasks, tested somatosensory

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function (Freyhair and spatial tactile resolution) of thumb (D1) and D3 and selected clinical

data (PLP, phantom sensations, stump pain).

2. Material and Methods

2.1. Participants

We studied 7 patients with D2 amputation each aged between 18-54 years (average 39 ±

(standard deviation) 15). Demographics and an overview on the tests are shown in Table 1.

6 patients were strongly right handed (laterality quotient (LQ) = 95.83 ± 4,17; range 89-100)

and 1 patient was left handed (laterality quotient (LQ) = - 80) according to the Edinburgh

Handedness Inventory (Oldfield, 1971). Overall, amputation was 61.29±20.25 months before

investigation (range 26-84 months). From the medial carpal joint the stump had a lenght of

4.07±2.31 cm on average. Data of the patients were compared to those of a group of 18

healthy participants (aged 31.4 ± 12; 11 women; Edinburgh Handedness Inventory score:

range = 0.77 - 1, average = 0.92). None of the participants suffered from any neurological

disorder or vascular disease. measured a distance on the cortical surface between d1 and d3

in both were medicated (one with Ibuprofen and one with beta blockers). All participants gave

their written and informed consent according to the Declaration of Helsinki, and the study

was approved by the ethics committee of the Medical Faculty of the University of Greifswald.

2.2. Clinical and functional scores:

For spatial tactile resolution (STR) of the finger tips a Grating Orientation Task (GOT) was

used as described by Van Boven et al. (Van Boven et al., 2000). D1 and D3 on the left hand

and right hand were tested. Due to amputation D2 was only tested on the non-affected

hand. Nine different types of hemispherical domes were used for assessment, measuring

grating distances between 0.5 and 3.0 mm. For each size type 16 trials were performed, and

testing started with the greatest distance of gratings (3.0 mm). Participants were required to

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make an instant statement about the perceived orientation of the gratings. Testing was aborted

when the error-rate of 25% was reached. A better STR is equal to a lower test score within the

GOT. In order to ease understanding of performance we inversely plotted GOT-values in

Figure 4C. High values in STR in Figure 4C therefore mean high performance.

For assessment of minimal force-detection threshold, Frey-Hair testing was performed at the

fingertips of D1-D3 of both hands. On the affected hand only D1 and D3 were tested. The

order of digits being tested was randomized. Participants were asked to close their eyes and

report whenever they felt a sensation on their skin. The filaments were pressed against the

skin up to three times at a 90° angle until they bowed and were held in place for 1.5 seconds.

A questionnaire provided by the Department of Trauma and Orthopaedic Surgery from the

University of Greifswald was used to asses a possible functional overtake of the amputated

D2 by D3. We calculated a usage factor from 5 different questions (ordinal scaled from 0 to

100 in 11 steps; 0 = no functional overtake of D3; 100 = full functional overtake of D3). The

questions asked in detail about an overtake of function of the impaired finger by the

neighboring finger for pinching small objects, for turning keys, for holding objects during

manipulation with the other hand, for pointing towards objects, and for gestical manipula-

tions. The same questionnaire was used to assess if the stump of D2 was still in usage (0 =

stump of D2 was not used; 100 = stump was used as much as the former intact D2).

In addition we applied the DASH-questionnaire, a self-report about disabilities of the arm,

shoulder and hand consisting of 30 items (Hudak et al., 1996).

2.3. MRI measurements

Examinations were carried out on a 3T MRI-scanner (Verio, Siemens, Erlangen, Germany)

using a 32 channel head coil. Functional imaging was performed with a standard gradient-

echo EPI sequence modified after a protocol suggested by Schweisfurth et al. (Schweisfurth et

al., 2011). We measured 17 slices with an in plane resolution of 1.5 x 1.5 mm2 and a slice

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thickness of 2 mm. The field of view was 191 x 179 mm2 corresponding to an acquisition

matrix of 128 x 120 with a flip angle of 76°. Slices were oriented parallel to the post central

gyrus, corresponding to the phase encoding direction using the auto align scout head and a

transversal t2-weighted sequence. Prior to each functional run seven dummy scans were

performed in order to achieve identical pulse to pulse magnetization properties. The absolute

scan time per run was 3 min 34 sec.

A 3DTOF MR-angiography with a spatial resolution of 0.26 x 0.26 mm2 in plane and a slice

thickness of 0.5 mm was recorded with transversal-coronal slices, oriented using the inferior

points of the frontal brain and the cerebellum. A total of 48 slices was recorded with a slice

partial Fourier factor of 7/8, PAT mode GRAPPA with acceleration factor PE 2, reference

lines PE 32 and a HF-pulse with a bandwidth of 186 Hz/Px. The repetition time TR = 21 ms,

echo time TE = 3.6 ms and absolute scan time 8 min and 12 sec. Structural imaging was

carried out using a standard Siemens sagittal T1-weighted 3D MPRAGE and the FreeSurfer

protocol recommended for segmentation of the cortex.

2.4. Functional Paradigm

Pneumatic stimulus finger clips (MEG International Services Ltd., Coquitlam, Canada) were

used to apply tactile stimuli to the subject’s finger tips. Finger tips of D1, D2 (if existing) and

D3) of the right and left hand were stimulated separately in each run and runs were

randomized to avoid time effects between fingers. The stimulators were composed of a

support structure and a membrane, where the membrane has a diameter of about 1 cm.

Stimulators were mounted via the support structure and adhesive tape was used to retain their

positioning. The membrane was actuated by a computer controlled pneumatic valve. During

stimulation pulses with a length of 50 ms and a randomly chosen inter-stimulus interval, with

an average duration of 300 ms, were applied for 10 s. Resulting in a stimulation frequency of

about 3 Hz, which elicited a feeling of pulsating pressure mainly transmitted by Merkel cells

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(McGlone and Reilly, 2010). Followed by a rest period of 10s, this blocked design was

repeated 10 times resulting in a total number of 300 stimulations per fingertip. In order to

focus the attention of the subjects to the stimulation, to avoid habituation to an unattended

stimulation and to monitor the participants’ attention we applied several stimulation pulses

with a length of 150 ms (about 1 to 5 per stimulation block). The particular number and time

at which these pulses were presented was randomly chosen for each block. Subjects were

instructed to count the total number of the 150 ms second pulses and to report those in the

pause between stimulation sessions. Their result was compared to the applied pulses and the

session was rated as valid if at least 50% of the 150 ms pulses were correctly perceived. Prior

to the examination a short training session, including a maximum number of three stimulation

blocks, was performed in order to ensure a proper perception of the 150 ms pulses. An

additional benefit of this procedure was an identical instruction for each of the subjects, which

avoided effects induced by different instructions (Braun et al., 2000). Stimuli application and

scanner synchronization were controlled by presentation (Neurobehavioral Systems Inc.,

Albany, USA).

2.5. Data processing

Figure 1 illustrates data processing. Data were analyzed with the FreeSurfer software suite 5.1

(Fischl, 2012). Structural scans of each subject were reconstructed using recon-all. The

functional scans were evaluated using fs-fast, from which the surface-based stream and native

space features were used. After motion correction the functional images were coregistered to

the subjects anatomical scans using boundary based register (BBR). The same was performed

with the angiography. The resulting transformation matrices were combined with

mri_matrix_multiply to register the functional activation to the angiography. This result was

used to quantify the effect of individual draining vessels on the activation pattern. The

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contrast of the activation was computed against baseline using a general linear model (GLM)

without further smoothing. Functional maps were thresholded at p = 0.001, uncorrected.

The analysis was restricted to the FreeSurfer BA3b region (Fischl et al., 2008). In superior-

inferior direction the BA3b region was limited using the position of the thumb and middle

finger defined in previous investigations (Weibull et al., 2008b). Therefore, the average

position of the thumb served as the inferior limit the average position of the middle finger as

the superior limit. The limits were enlarged by two standard deviations for the position of the

thumb and the middle finger in order to account for the full confidence interval of each finger.

Since the average values were known only for the right hand (Weibull et al., 2008b), the

region for the left hand was generated by mirroring the region to the right hemisphere. In

order to account for the uncertainty due to the mirroring, four standard deviations were used

to enlarge the region on the right hemisphere. This was necessary to include the somatotopic

thumb region for all of the subjects. BA3b overlaps with the other BAs in SI (Fischl et al.,

2008). A large inter-individual variability in the fingertip somatotopy in BA3b was reported

before (Schweisfurth et al., 2011). Therefore, data evaluation in group space was avoided in

this publication and data analysis was performed on the individual brains (see Figure 2).

Activation from neighboring BAs was removed from the surface based analysis, by weighting

the activation using the probabilities given in the BA3b ROI. Clusters remaining after the

weighting were analyzed in native volume space. In order to remove partial volume effects

only voxels with an overlap to the gray matter of more than 50% were included in the

analysis. The MR-angiography was used to minimize contributions from vessel activation

(Schweisfurth et al., 2011) by exclusion of voxels with an overlap to vessels. Overall we

applied the following 3 criteria for activation maxima selected:

I) Localization within the BA 3b and reference area of the fingers,

II) Overlap with the cortex of more than 50%, and

III) No overlap with detected vessels of the angiography.

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In addition, we calculated a lateralization index (LI) for the highest amplitude of the blood

oxygenation level dependent effect (BOLD) within the BA 3b ROI of each hemisphere

(Mohamed, 2008).

3. Results

Behavioral data and testing

Somatosensory testing with Freyhair revealed comparable values for both hands with an

average value of 3.46±0.67 for D1 and 3.34±0.52 for D3 on the affected hand and 3.47±0.48

for D1 and 3.38±0.58 for D3 on the non-affected hand. The spatial tactile resolution (STR)

showed thresholds of 2.48±0.52 for D1 and 2.66±0.99 for D3 of the affected and 2.20±0.57

for D1 and 2.81±0.74 for D3 of the unaffected hand. These data were again comparable

between sides. The usage factor for D2 of the affected side was 35.71±35.11 and for D3

60.57±35.45 on average. This indicates that D3 is overtaking the D2 stump function in most

of the patients.

fMRI- evaluation of distances between finger representation maxima

Whereas in HC the distances D1 to D3 did not differ between hemispheres (t(17) = 1.18; n.s)

and the lateralization index (LI) was quite symmetric (average -0.04; SD ±0.14) patients

showed an imbalance of the LI (-0.22 ± 0.23; see Figure 3). Overall, the LI did significantly

differ between patients compared to HC (t(23) = 2.43; p = 0.024). The imbalance was caused

by a significant difference between the D1-D3 distances in the patients between the affected

(average: 9.70 ±5.23mm) and non-affected (average: 14.05 ±3.83mm) hemispheres (t(6) =

2.64; p = 0.038). BOLD-magnitude during D3-stimulation in BA 3b of the affected

hemisphere was increased in comparison to healthy controls (t(23) = 1.92; p = 0.034; one

sided). This was not observed for the non-affected hemisphere (t(23) = 0.91; n.s.).

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Correlation between imaging data and behavioral and clinical measures

Correlation analysis revealed positive associations between the DASH score and the usage of

D3 (r = 0.75; p < 0.05). Higher usage of D3 was associated with increased BOLD-magnitude

during D3-stimulation in BA 3b (r = 0.75; p < 0.05; Figure 4A). When correlating the brain

imaging data of distance and BOLD-magnitude we used the lateralization indexes. The more

the middle finger (D3) was used (usage factor) the more symmetric was the LI (r = -0.69; p <

0.05; Figure 4B). We found an association between LI of D1-D3 distance and LI of BOLD-

magnitude during D3 stimulation (r = -0.67; p ≤ 0.05). The BOLD-response to D3-stimulation

in BA 3b in patients showed a tendency for an increase on the affected side (average affected:

4.52±1.77; unaffected: 2.97 ±0.99; t(6) = 1.85; n.s.) and D1-D3 distance was significantly

different between hemispheres. Thus, a large BOLD-response to D3-stimulation was

positively associated with a large distance between D1-D3 (trend: r = 0.64; p=0.06). There

was also an association between the spatial tactile resolution (STR) of D3 and the BOLD-

magnitude in response to D3-stimulation in BA 3b (r = 0.69; p < 0.05). In addition, LI of the

surface distance between D1 and D3 representation was positively associated with STR (r =

0.76; p < 0.05; Figure 4C). There was no association between the distance between D1 and

D3 and PLP (r = 0.27; n.s).

4. Discussion

When comparing the activation maxima in BA 3b of fingers adjacent to the amputated

index finger we found a decrease in the distance between D1 and D3 (D1 – D3) on the

affected side, both in comparison to healthy controls and to the non-affected side. In addition,

we found that BOLD-magnitude during D3 stimulation, on the affected hemisphere, was

positively associated with use of the finger and somatosensory discrimination performance

(both von Frey hair and spatial tactile resolution; STR). In contrast to numerous investigations

on patients with upper limb amputation, we found no associations of fMRI-parameters (D1 –

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D3 distance, BOLD-magnitude) with the intensity of painful or non-painful phantom

sensations.

Our result of a decreased D1-D3 distance in BA 3b is in line with findings from

monkey studies (Merzenich et al., 1983; Merzenich et al., 1984) and anecdotal reports of

single-case finger amputee studies (Weiss et al., 1998; Weiss et al., 2000). However, there

was no association between the distance between somatosensory finger representations and

phantom limb pain, as has been reported for S1 and M1 after amputation of large parts of the

upper limb, i.e. the hand (Birbaumer et al., 1997; Diers et al., 2010; Elbert et al., 1994; Flor et

al., 1995; Karl et al., 2001).

This apparent discrepancy might be best explained by two substantial differences

between the loss of a finger and the loss of a hand. The first is that finger amputation leads to

a relatively small deafferented S1 area (we measured a cortical surface D1 – D3 distance in

healthy participants of approximately 12 mm). This is in sharp contrast to the situation after

amputation of the whole hand; the somatotopic representation of the elbow and the lip are

more than 30 mm apart on average (for M1 see Lotze et al., 2000). The second possible

explanation is that the remaining fingers might take over the function of the former index

finger. Thus, the amount of functional impairment resulting from loss of the index finger is

somehow neglectable. However, an increase in the use of a limb – in this case the middle

finger - does have an impact on its representation size in healthy people (Elbert et al., 1995).

It has been suggested before that associations between phantom limb pain and cortical

representation changes in S1 in patients with traumatic loss of large parts of the upper limb

are rather due to re-routing than to actual anatomical changes (Ramachandran and Hirstein,

1998). It is well conceivable that only after considerable deafferentation this re-routing is

triggered and that this might rather be associated with phantom limb pain.

The positive correlation between the D1 – D3 representation distance and the STR is

in agreement with findings in musicians (Ragert et al., 2004). In the primary motor cortex, a

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positive association has been found to exist between repetitive use of a finger and increased

primary motor cortex representation in extent and amplitude, in monkeys (Nudo et al., 1996)

and humans (Classen et al., 1998; Karni et al., 1995). That we found that increased use of the

middle finger was associated with increased BOLD-magnitude during D3-stimulation, and a

larger D1 – D3 distance on the affected side, might indicate that the more the middle finger

was used, the more symmetry there was in D1 – D3 distance between hemispheres. A

symmetric representation in BA 3b was indeed shown, using the same mapping techniques, in

the healthy participants. This supports the argument that enhanced use of the affected hand is

reflected in near-to-normal representation maps. It has been discussed that alterations in the

internal representation of the body might drive maladaptive behaviors and painful, as well as

non-painful, phantom limb phenomena (Maihofner and Peltz, 2011).

We found a slight increase in activation magnitude for D3, but not for D1. Both are

neighboring the deafferentation site. Reports of an increase in activation (BOLD-magnitude,

TMS-excitability) of neighboring representation sites to the deafferented area are inconsistent

(motor system: TMS: Karl et al., 2001; fMRI: Lotze et al., 2001). This might not simply be

explained by the different investigation techniques, because the TMS–MEP amplitude during

TMS-elicitation of a movement pattern and the fMRI-magnitude during performance of a

comparable movement have been found to be highly associated (Lotze et al., 2006). The

increase in BOLD-magnitude might not be caused by a general effect of decreased lateral

inhibition, but more probably by increased usage of the middle finger after amputation, a

proposition which is indeed strengthened by the association of use with BOLD-magnitude in

the current results.

We selected a homogeneous patient group with respect to the finger amputated (D2) and the

cause of amputation (traumatic). However, patients were quite different with respect to the

length of the stump and the time duration since the amputation. Variation in both of these

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parameters increased the power of correlation analyses. An important limitation of this study

is the small number of patients recruited. Larger groups of patients with finger amputations

should, however, confirm the high association between functional use and reorganization.

Especially with respect to more definite conclusions on the interaction of small

deafferentation areas in S1 and PLP larger samples are needed.

Even the amputation of a finger such as the index finger, which is frequently used, can

functionally be compensated by increased usage of the middle finger. This functional

compensation is associated with a more normal representation of the fingers – at least with

respect to the distances between somatosensory representation maxima in BA 3b. A small

functional impact of an amputation might therefore well be associated with less maladaptive

processes and a lower risk for phantom limb pain.

Acknowledgements

ML was supported by a grand of the BMBF (01DR12044) and the DFG (LO 795/12-2).

We would like to thank Flavia Di Petro for help with language correction.

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Tables

Table 1: Clinical, behavioral and demographic data of each participant

Subject/

gender1  

age

[years]  

time since

amputation

[months]  

Side/domi

-nance  

Amputa

-tion

level  

Stump

length

[cm]   PLP/VAS  

Stump

Pain/V

AS  

Teles-

coping  

Non-painful-

phantom

sensation  

01/f   54   26   R/R   2   5.5   Y/2.0   Y/7,2   N   N  

02/m   39   57   R/R   0   1.5   Y/ 4.5   Y/2   Y   Y  

03/m   24   48   R/L   2   6.5   N   N   N   N  

04/f   18   70   L/R   2   3.5   N   N   N   N  

05/m   53   84   R/R   2   6.0   N   Y/3,4   N   N  

06/m   52   62   R/L   1   5.0   N   N   N   N  

07/m   36   82   R/R   0   0.5   N   N   N   Y  

1 F: female; m: male

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Figure legends

Figure 1: Procedure of the evaluation method for somatotopic representation in BA 3b demonstrated for the right hemisphere. (a) The cytoarchitectural probability map for S1 is overlaid in white. The omega indicates the primary motor cortex (M1) hand knob. (b) BA 3b is overlaid and indicated as part of S1 after inflation of the brain. (c) The overlay of S1 and BA 3b is shown in black after applying cuts for a 2 dimensional flatmap. (d) The BA 3b is restricted to the confidence interval of finger tip representation after the results presented by Weibull et al. (2008). (e) Zoom on the 2D-region of interest (ROI) with BA 3b and the confidence interval of the D1 and D3 representation maxima.

Figure 2: Method of measurement of distances on the cortical surface flat map between representation sites of D1 and D3 (black spots) in the BA 3b region of interest (indicated by a white line). (a) finger digit of D 1, 2, 3 representation in BA 3b of the left hemisphere of a healthy participant; (b) representation of D1 and D3 of a patient after index finger amputation. Distances between the activation maxima between D1 and D3 are indicated with a white line. The omega indicates the M1 hand knob.

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Figure 3: Schematic drawing of group results. The left side shows the hemisphere contralateral to the affected hand (as symbolized with a hand without an index finger), the right side shows the hemisphere contralateral to the intact hand. Average distances between the D1-D3 representation maxima are plotted.

Figure 4: Correlation graphs between behavioral and mapping parameters in the patients investigated. R2-indicates the goodness of fit. A) Positive correlation between the usage of D3 with BOLD-magnitude (beta estimates) during D3-stimulation in BA 3b (r = 0.75; p = 0.026). B) Positive correlation between the usage of D3 and the distance between D1 and D3 as calculated for the lateralization index (LI; affected versus non-affected hemisphere). The more the middle finger was used of the the more symmetric the representation distances between hemispheres were (r = 0.69; p = 0.043). C) Positive correlation between the lateralization index for the distance between D1 and D3 and the spatial tactile resolution (STR, inverse domes grid; r = 0.76; p = 0.025).