This study compared two techniques, Voxel-Based Lesion Symptom Mapping (VLSM) and Voxel-Based Morphometry (VBM), to identify lesion sites associated with language impairments in 20 patients with chronic post-stroke aphasia. Both techniques found overlapping associations between auditory sentence comprehension deficits and lesions in the superior and middle temporal gyri. However, VBM identified additional regions while VLSM found more posterior and subcortical associations. The techniques also showed differences in mapping word repetition and object naming deficits. While using both techniques can increase mapping reliability, each has advantages and answering somewhat different questions.

1. A comparison of VLSM and VBM in a
cohort of patients with post-stroke aphasia

2. Introduction
• Studies attempting to map post-stroke cognitive or motor symptoms to lesion location have been
available in the literature for over 150 years. In the last two decades, two computational techniques
have been developed to identify the lesion sites associated with behavioural impairments. Voxel
Based Morphometry (VBM) has now been used extensively for this purpose in many different patient
populations. More recently, Voxel-based Lesion Symptom Mapping (VLSM) was developed specifically
for the purpose of identifying lesion–symptom relationships in stroke patients, and has been used
extensively to study, among others functions, language, motor abilities and attention. However, no
studies have compared the results of these two techniques so far. In this study we compared VLSM
and VBM in a cohort of 20 patients with chronic post-stroke aphasia.

3. Materials and methods
• Participants
• Patients were tested cognitive-behavioral tests
• Imaging data acquisitionusing a 3 T Siemens Magentom Trio Tim MRI scanne and 1.5 T MRI Siemens
scanner
• Data pre-processing for VLSM and VBM
• Data analysis

4. Material and methods
1. Participants

5. Material and methods
2. Behavioral test
• Comprehensive Aphasia Test were analysed:
• 1) Auditory sentence comprehension: participants
were read a sentence and were asked to point to
one of four pictures which best fitted the sentence.
The task had 16 trials.
• 2) Word repetition: participants were asked to
repeat words read out by the examiner. This task
included 16 short words.
• 3) Object naming: participants were asked to name
24 pictures of objects. In all tasks, a correct answer
was given 2 points. A delayed answer or a correct
answer following self-correction was given 1 point.
In the auditory sentence comprehension and the
word repetition tasks, if the participant asked the
examiner to repeat the question, and this was
followed by a correct answer, 1 point was given as
well. Maximum possible scores and the cut-off
score for defining impaired function are presented
in Fig 1
Fig. 1. Behavioural scores for all patients in
the various language tasks. Red lines
represent the cut-off score for defining
impaired function in each task.

6. 3. Imaging data acquisition
• Imaging was performed using a 3 T Siemens Magentom Trio Tim MRI
scanner. Four patients could not undergo a 3 T MRI scan due to
cardiac stents (n = 2) or PFO devices (n = 2) which were not 3 T
compatible. These four patients were scanned using a 1.5 T MRI
Siemens scanner (Erlangen, Germany) and the effect of using a
different scanner on the results was considered

7. Data pre-processing for VLSM
1.Lesion Identification
2.Validation:
3.Mask Creation:
4.Spatial Normalization:
VBM
• 1. Creation of masks.
• 2. Data pre-processing for VBM.

8. • Fig. 2. An overlay of all
patients' lesions. Colours
represent number of patients
with a lesion to a specific
voxel. Warmer areas indicate
areas of greater lesion
overlap. Colour range runs
from 1 (the lowest value in the
image) to 14 (the highest
value in the image).

9. Auditory sentence comprehension
1.Common Findings:
1.Both VBM and VLSM found associations with auditory sentence
comprehension in the superior and middle temporal gyri (STG/MTG).
2.Poor performance correlated with lower gray matter (GM) voxel
intensity in the STG/MTG border and lower white matter (WM) voxel
intensity.
3.Adding age as a covariate did not alter the pattern of results.
2.Differences Between VBM and VLSM:
1.VBM extended more laterally and medially, involving the post-central
gyrus and the supramarginal gyrus (SMG).
2.VLSM extended more posteriorly, including the post-central gyrus,
superior parietal lobule, pre-central gyrus, inferior frontal gyrus (IFG),
and insula.

10. • Fig. 3. Colour maps of significant regions in the VBM (top); VLSM (middle);
and both methods (bottom) in the auditory sentence comprehension task
(p b 0.05, FDR correction). All voxels lesioned in at least 5% of patients are
included. Colours represent Z-scores.

11. Word Repetition:
• Overlap and Differences:Limited overlap between VBM and
VLSM in the supramarginal gyrus (SMG) and superior temporal
gyrus (STG).
• VBM highlighted larger clusters, including the insula, inferior
frontal gyrus (IFG), and pre-central gyrus.
• VLSM identified small unconnected clusters in frontal and
parietal lobes.

12. Object Naming:
1.Common Findings:
1.Both methods associated poorer performance in object naming with
the IFG, insula, STG, and SMG.
2.Differences:
1.VBM found additional associations in IFG pars triangularis/BA 45 and
subcortical regions.
2.VLSM found associations with white matter regions.

13. Analysis of Variations and Covariates:
1.VBM Analysis:
1.No significant correlations at corrected thresholds for auditory
sentence comprehension.
2.Effects of scanner type and number of voxels analyzed did not
significantly affect results.
2.VLSM Analysis:
1.No differences between analyzing 5% or 20% of damaged voxels.
2.Changes in VBM cluster sizes with different percentages of damaged
voxels.

14. Conclusions
• We compared the use of VBM and VLSM in the study of language
impairments in a cohort of chronic stroke patients. Areas where the
two techniques gave overlapping results are those areas previously
shown to be relevant for the cognitive functions tested. This suggests
that using both techniques and looking for overlaps can potentially
increase results reliability when seeking to map cognitive functions in
the brain. However, the two techniques do not produce precisely the
same results and potentially answer somewhat different questions.
Since each method has some clear advantages over the other, we
suggest that in future studies of chronic stroke patients, researchers
consider the differences between the techniques when evaluating
results and their implications.

15. Differences
• VBM extended more laterally and medially, involving the post-
central gyrus and the supramarginal gyrus (SMG).
• VLSM extended more posteriorly, including the post-central
gyrus, superior parietal lobule, pre-central gyrus, inferior frontal
gyrus (IFG), and insula.

16. Specific Voxels:
• Voxel [− 60, − 6, − 6] in the anterior MTG was significant in both
analyses.
• A posterior voxel [− 66, − 24, 4] was significant only in VBM.
• A frontal lobe voxel [− 30, 48, − 8] was significant only in VLSM.