Kousik Sarathy Sridharan

Studying somatosensory function in Parkinson’s disease using Magnetoencephalography

Research output: Contribution to conferencePosterResearch



Deep  brain stimulation  (DBS)  of subthalamic  nucleus  (STN) significantly alleviates cardinal  motor  symptoms and improves quality of life in Parkinson’s disease (PD)(1).Specifically,  PD  patients have  problems  with sensory  processing,  sensorimotor integration  and  kinesthetic awareness. Somatosensory  evoked fields  (SEF) is  an effective tool to study  thesensory perception  and  cortical processing(2).


SixPD patients were recruited from the population of STN DBS treated patients atAarhus University Hospital . A clinical interview  including  mini -mental state  examination  (MMSE), major depression inventory (MDI) andunified Parkinson disease rating scale motor score (UPDRS-III) as well assigned informed consent.

Patients  are asked  not  to take  anti-PD  medication from  the  evening before interview. After the interview, the patient continues toMEG-preparation and assessment. MEG-assessments were performed “OFF medication,ON DBS”, “OFF medication, OFF DBS” for each half hour until two hours and then“ON medication, OFF DBS”.  For each hour,patient symptoms are evaluated with the UPDRS-III.  Repetitive median nerve stimulation wasperformed at 2.5 Hz with an inter-stimulus interval of 350 ms. Current was setat the level of an observable twitch of the thumb.

MEGdata were filtered using MaxFilter, a software that implements the tSSS(Temporal signal space separation) algorithm to remove DBS artefacts. The datais processed using the Fieldtrip toolbox. After preprocessing steps toeliminate artefacts the data is averaged and the signals orthogonal gradiometerpairs are combined. Grand averages are computed across subjects withinconditions. Gradiometer pairs showing maximum amplitude and it’s latency insensori-motor areas are searched. Repeated-measures ANOVA with a Tukey post-hoctests was performed to determine significant differences in both amplitude andlatency.


tSSSalgorithms suppressed the DBS artefacts enabling visualization of SEFresponses. The early SEF responses namely N20 and P35 were clearly localized incentral areas. The mid-latency P60 and later P80 were also clearly visible inthe same region. The SEF amplitudes and latencies did not significantly differwith DBS therapy or medication.


Theevoked fields preserve the phase-locked content in the response and these didnot show any significant variation with therapy. The lack of differences in N20is in congruence with previous studies (3,4). The mid-latency and lateresponses also do not seem affected. It is probable induced oscillatoryactivity that is non-phase locked to the stimulus might contain more usefulinformation. The study of induced activity might be useful to ascertainproblems in early sensory cortical processing in PD patients(5).


[1]Just H, Ostergaard K. Health-related quality of life in patientswith advanced Parkinson’s disease treated with deep brain stimulation of thesubthalamic nuclei. Mov. Disord. [Internet]. 2002 May [cited 2013 Nov8];17(3):539–45.

[2]Abbruzzese G, Berardelli A. Sensorimotor integration in movement disorders.Mov. Disord. [Internet]. 2003 Mar;18(3):231–40.

[3]Pierantozzi M, Mazzone P, Bassi A, Rossini PM, Peppe A, Altibrandi MG. Theeffect of deep brain stimulation on the frontal N30 component of somatosensoryevoked potentials in advanced Parkinson’s disease patients. 1999;110:1700–7

[4]Rossini PM, Filippi MM, Vernieri F. Neurophysiology of sensorimotor integration inParkinson’s disease. Clin. Neurosci. [Internet]. 1998 Jan [cited2013 Nov 5];5(2):121–30.

[5]Fukuda M, Nishida M, Juhász C, Muzik O, Sood S, Chugani HT, et al.Short-latency median-nerve somatosensory-evoked potentials and inducedgamma-oscillations in humans. Brain [Internet]. 2008 Jul [cited 2013 Nov4];131(Pt 7):1793–805

Original languageEnglish
Publication year23 Jan 2015
Publication statusPublished - 23 Jan 2015
EventPhD day 2015 - Aarhus University, Denmark
Duration: 23 Jan 201523 Jan 2015


ConferencePhD day 2015
CityAarhus University

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