Assessing somato- and mototopic organisation in Focal Hand Dystonia using high-resolution 7T fMRI

Poster No:

W356 

Submission Type:

Abstract Submission 

Authors:

Daisie Pakenham1, Michael Asghar1, Paul Glover1, George O'Neill1, Ayan Sengupta1, Denis Schluppeck1, Rosa Sanchez Panchuelo1, Miles Humberstone1, Susan Francis1

Institutions:

1University of Nottingham, Nottingham, United Kingdom

E-Poster

Introduction:

Somatotopic mapping of the digits in primary somatosensory cortex is highly reproducible in healthy controls (HC) using high-resolution (7T) BOLD-fMRI and a travelling wave (TW) paradigm[1,2], while event-related (ER) fMRI has demonstrated cortical digit overlap[3]. Previous studies suggest Focal Hand Dystonia (FHD) patients have reduced inter-digit distances[4] and increased overlapping activity[5] compared to HCs[6]. Further, somatosensory temporal discrimination thresholds (TDT)[7] and spatial acuity thresholds[8] are often raised in both affected and unaffected hands of FHD patients compared to HCs, correlating with disease severity.

Here, we study FHD patients using a behavioural (TDT, amplitude thresholding, and spatial acuity using a grating orientation task (GOT)) and fMRI (somatotopy TW and ER paradigm, and mototopy TW paradigm) battery. This protocol will be performed on patients 4-weeks post-Botulinum-Toxin A (Botox) treatment and pre-Botox to determine whether treatment induces cortical reorganisation compared to HCs.

Methods:

The protocol has been collected on six FHD patients (5 right-handed (RH) affected hand, all post-Botox) and three age-matched HCs (all RH) to date.

Behavioural: TDT: Short stimuli were presented consecutively to index (D2) and middle (D3) fingers via piezo-electric stimulators using a descending staircase procedure. TDT was also conducted using a Brain Gauge[9]. Amplitude thresholding: Performed on D2 at 31 and 200Hz in both hands. GOT: Plastic domes with square-wave gratings of several widths were presented to D2 of the affected hand in proximal and lateral directions.

fMRI: Data were acquired on a 7T Philips Achieva scanner, using GE-EPI with multiband3, TE=25ms, SENSE1.5 and 1.5mm isotropic voxels. Somatosensory & Mototopy TW: TR=2000ms, FA=80°, 48 slices, 80 dynamics. TW was performed in forward (D1-D5) and reverse directions (D5-D1) (20s/cycle, 8 repeats, both hands). Fourier analysis produced maps of coherence and phase (digit correspondence). Mototopy was visually cued for 1Hz digit movement and quality controlled using an MR-compatible custom-built accelerometer. For somatotopy and mototopy, digit distance on the cortical surface was measured from the centre of mass of each digit-phase ROI (coherence=0.3, uncorrected p=0.0034) and the Dijkstra's and 3D-Euclidean distance of D1-D5. Event-related/ON-OFF: TR=1000ms, FA=57°, 36 slices, 285 dynamics. The ON-OFF paradigm (5s-ON, 24s-OFF) was performed on the affected hand with stimuli randomly presented to D2/D3/D4. GLM analysis derived digit-specific HRFs and Z-score maps of digit location from which digit overlap was assessed.

Results:

Behavioural: FHD patients had higher amplitude discrimination (31Hz:HC:2.8±1.9, FHD:6.8±7.5; 200Hz:HC:3.1±1.7, FHD:8.4±9.2) and TDT (piezos HC:37±22, FHD:94±43ms) thresholds and GOT acuity (HC:2.0±0.5, FHD:3.3±1.4mm) than HCs.

fMRI: Somatotopy coherence and phase maps are shown for HCs (Fig. 1A) and FHD patients (Fig. 1B) along with Dijkstra's and 3D-Euclidean D1-D5 distance (Fig. 1C). All HCs showed clear somatotopic maps in the postcentral gyrus, S1, while only FHD patients PA1, PA3, and PA5 show clear maps. For the event-related paradigm, each digit produced significant activation but with little difference between HCs and FHD patients. Mototopy shows clear digit mapping in S1 for HCs (Fig. 2A) with less apparent maps in FHD patients (Fig. 2B). Fig. 2D shows the phase difference histograms in S1 between somatotopy and mototopy.
Supporting Image: figure1.png
Supporting Image: figure2new.png
 

Conclusions:

A behavioural and fMRI battery has been developed to assess somatomotor function in FHD patients. Behavioural measures (amplitude, temporal discrimination and spatial acuity) increased in FHD patients compared to HCs. Somato- and mototopic maps are presented. Digit separation was difficult to detect with the event-related paradigm, but digit-specific HRFs were obtained. In future, FHD patient data will be compared to follow-up assessment 3 months post-Botox treatment.

Disorders of the Nervous System:

Disorders of the Nervous System Other 2

Imaging Methods:

BOLD fMRI 1

Keywords:

FUNCTIONAL MRI
HIGH FIELD MR
Motor
Neurological
Touch

1|2Indicates the priority used for review

My abstract is being submitted as a Software Demonstration.

No

Please indicate below if your study was a "resting state" or "task-activation” study.

Task-activation

Healthy subjects only or patients (note that patient studies may also involve healthy subjects):

Patients

Was any human subjects research approved by the relevant Institutional Review Board or ethics panel? NOTE: Any human subjects studies without IRB approval will be automatically rejected.

Yes

Was any animal research approved by the relevant IACUC or other animal research panel? NOTE: Any animal studies without IACUC approval will be automatically rejected.

Not applicable

Please indicate which methods were used in your research:

Functional MRI

For human MRI, what field strength scanner do you use?

7T

Which processing packages did you use for your study?

Free Surfer
Other, Please list  -   mrTools

Provide references using author date format

[1] Sanchez-Panchuelo, R. et al. (2014), ‘Regional structural differences across functionally parcellated Brodmann areas of human primary somatosensory cortex.’ NeuroImage,vol. 93, pp. 221-230.
[2] Sengupta, A. et al. (2018) ‘A Probabilistic Atlas of Digit Somatotopy in the Human Primary Somatosensory Cortex’, Proceedings of the International Society for Magnetic Resonance in Medicine, 26, abstract 0876
[3] Besle, J. et al. (2014) ‘Event‐related fMRI at 7T reveals overlapping cortical representations for adjacent fingertips in S1 of individual subjects’, Human Brain Mapping, vol. 35 no. 5, pp. 2027-2043.
[4] Butterworth, S. et al. (2003) ‘Abnormal cortical sensory activation in dystonia: An fMRI study’, Movement Disorders, vol.18, no. 6, pp. 673-682.
[5] Nelson, A.J. et al. (2009) ‘Digit‐specific aberrations in the primary somatosensory cortex in Writer's cramp’, Annals of Neurology, vol. 66, no. 2, pp. 146-154.
[6] Dresel, C. et al. (2014), ‘Multiple changes of functional connectivity between sensorimotor areas in focal hand dystonia’, Journal of Neurology, Neurosurgery & Psychiatry, vol. 85, no. 11, pp. 1245-1252.
[7] Bara-Jimenez, W. et al. (2000), ‘Sensory discrimination capabilities in patients with focal hand dystonia’, Annals of Neurology, pp. 361-407.
[8] Molloy, F. et al. (2003), ‘Abnormalities of spatial discrimination in focal and generalized dystonia’, Brain, vol. 126, no.10, pp. 2175-2182.
[9] Brain Gauge. Cortical Metrics, Chapel Hill, NC, USA www.corticalmetrics.com