Effects of DBS on auditory and somatosensory processing in Parkinson's disease

Abstract

Motor symptoms of Parkinson's disease (PD) can be relieved by deep brain stimulation (DBS). The mechanism of action of DBS is largely unclear. Magnetoencephalography (MEG) studies on DBS patients have been unfeasible because of strong magnetic artifacts. An artifact suppression method known as spatiotemporal signal space separation (tSSS) has mainly overcome these difficulties. We wanted to clarify whether tSSS enables noninvasive measurement of the modulation of cortical activity caused by DBS. We have studied auditory and somatosensory-evoked fields (AEFs and SEFs) of advanced PD patients with bilateral subthalamic nucleus (STN) DBS using MEG. AEFs were elicited by 1-kHz tones and SEFs by electrical pulses to the median nerve with DBS on and off. Data could be successfully acquired and analyzed from 12 out of 16 measured patients. The motor symptoms were significantly relieved by DBS, which clearly enhanced the ipsilateral auditory N100m responses in the right hemisphere. Contralateral N100m responses and somatosensory P60m responses also had a tendency to increase when bilateral DBS was on. MEG with tSSS offers a novel and powerful tool to investigate DBS modulation of the evoked cortical activity in PD with high temporal and spatial resolution. The results suggest that STN-DBS modulates auditory processing in advanced PD. Hum Brain Mapp, 2011. © 2010 Wiley-Liss, Inc.

Figure 1

Spontaneous MEG activity over the left hemisphere of one patient with DBS on before (A) and after (B) applying tSSS. The DBS device and connecting wires are on the left side. Artifacts were strongest over the wires on the left temporal region.

Figure 2

Auditory‐evoked fields (AEFs) to right‐ear stimuli in one patient before (A) and after (B) applying tSSS. The responses are viewed from above, with the nose pointing upwards. AEFs in the squares are shown in enlarged form in the inserts. DBS (on blue line, off red line) enhanced ipsilateral N100m. In magnetic field patterns, red lines indicate flux out and blue lines into the head. The contour step is 50 fT. The arrow indicates the equivalent current dipole, estimated from the corresponding field pattern. The corresponding dipole strength versus time curve and the goodness‐of‐fit of the model (g values) are shown under the magnetic field pattern.

Figure 3

Somatosensory‐evoked fields (SEFs) to electrical pulses to left median nerve in one patient before (A) and after (B) applying tSSS. Blue lines indicate DBS on and red lines DBS off. The contour step is 100 fT. The arrows indicate the equivalent current dipoles, estimated from the corresponding field patterns. Source location and orientation are superimposed on the brain MRI of the patient. The signal exceeds the scale on some magnetometer channels when DBS is on.

Figure 4

Dipole strengths versus time curves of SEFs from left and right hemispheres in all patients with DBS on and off. B indicates bipolar and M monopolar DBS stimulation. Bipolar stimulation seems to increase late responses in 11 hemispheres out of 17 and monopolar only in 2 cases out of 7.