Okay, our next presentation is from Ms. Arati Minnesundaram, electrophysiological mapping of cortical networks activated by dorsal versus ventral STN deep brain stimulation. Hi, everyone, thanks for inviting me to speak today. I'm a third year medical student as of yesterday at Tufts Medical. I'm going to be talking today about electrophysiological mapping of cortical networks activated by dorsal versus ventral subthalamic deep brain stimulation. All right, so deep brain stimulation of the subthalamic nucleus or the globus pallidus internus has been used to improve the motor symptoms of treatment-resistant Parkinson's disease. Anatomical adjacent areas serve very different functions, so we want to differentiate the networks being stimulated. Specifically, we're looking at the cortical networks activated by dorsal versus ventral STN DBS stimulation. Given the connectivity and the close proximity of these regions, shifting the electrode by just a couple of millimeters can drastically change the networks engaged. The subthalamic nucleus contains a dorsolateral sensory motor network as well as ventromedial limbic and associative networks as shown in this image. Here's an example of DBS lead placement in the STN with both the dorsolateral and ventromedial leads, which are expected to preferentially stimulate the sensory motor and associative limbic networks respectively. Stimulation of ventral and dorsal STN targets the gray matter ideally, but can spill over a little bit into the surrounding white matter, potentially stimulating unwanted networks. We use source localization of evoked potentials to compare networks activated by dorsolateral versus ventromedial STN stimulation. We hypothesize that the dorsolateral STN stimulation would target the motor cortex preferentially, while ventromedial stimulation has more generalized activity. For methods, we used pre- and post-operative imaging of subjects to reconstruct the lead localization of their DBS leads and identified the STN contacts that were more dorsal versus ventral. We stimulated subjects with single pulses at five hertz to focus on the evoked potentials and collected data for different conditions at 20 kilohertz using a high-density EEG cap. In the data presented, we had three subjects implanted in the STN, and we had six subjects implanted in GPI. After recording, we mapped the locations of the EEG electrodes to the patient's pre-operative scans using photogrammetry. We then used the FieldTrip and Chronix toolboxes in MATLAB to analyze the raw data and then fed that data into the PreSurfer and M&E Python to recreate and plot source localization. Here's an example of the evoked potential raw data from a subject after MATLAB processing. This shows the 200 milliseconds after stimulation. This was fed into the M&E Python pipeline for signal localization in source space, which we will see in the following slides. So for the result slides, we have the group analysis of source reconstruction separated by row based on hemisphere with the hemisphere that is ipsilateral to stimulation on the top and the contralateral hemisphere on the bottom. And we have the panels across representing different time points after stimulation. So we have 15, 20, and 25 milliseconds because we thought that showed the best signals. With left dorsal stimulation, we are seeing more ipsilateral, prefrontal, and primary motor cortex stimulation as shown here. And we're seeing more generalized activation on the contralateral hemisphere. We see similar patterns with right dorsal stimulation where we're seeing motor cortex and prefrontal cortex stimulation and more generalized activity on the contralateral hemisphere. With left ventral STN stimulation, we're seeing more sensory activation back in both hemispheres as well as some ipsilateral prefrontal cortex activation. And we see a similar broad activation in both hemispheres with right-sided ventral STN stimulation. Here is a comparison of dorsal versus ventral source localization for all four conditions that were just shown. And this is shown at 20 milliseconds post-stimulation. The networks that are activated by dorsal stimulation are shown in red, and the networks that are activated by ventral are shown in blue. These are primary results, but they do show that our hypothesis of dorsal stimulation preferentially activating the motor cortex, especially with left-sided stimulation as shown here. There is sufficient ventral motor stimulation as well, but we do also see an anterior to posterior gradient of other networks also being activated. Out of interest, we also looked at GPI patients compared to our STN patients to see if there was a difference in cortical networks that were activated between the two different implant areas. We found that GPI stimulation was showing a broader occipital lobe activation that we did not observe in our STN data. This is perhaps due to the proximity of the GPI lead over the optic tract as shown here. So we compare data for STN patients versus GPI patients. With GPI patients, we had two different currents that we were stimulating at. So we have 3 milliamp and 6 milliamp on the bottom. And we see that as the current density increases, the activated field expands ventrally to encompass the occipital lobe with the 6 milliamp GPI, especially shown here at 15 milliseconds. So in conclusion, preliminary findings are showing that dorsal stimulation elicits a stronger motor response in both hemispheres compared to ventral stimulation, which shows a more widespread distribution of activity, including sensory, associative, and limbic regions. Both dorsal and ventral STN stimulation show activation in the dorsolateral prefrontal cortex. And an interesting additional finding from our data shows occipital lobe activation from GPI stimulation, perhaps due to the proximity of the GPI lead to the optic tract. Our next steps, gather data from a lot more subjects and do a larger group analysis. I would like to thank the Harrington Lab at MGH, as well as the Eskindar Lab for their support. And this work was funded in part by the Parkinson's Disease Summer Student Fellowship. Thank you. Thank you very much. It's very nice work. Any questions from the audience? Yeah. Sorry, I couldn't hear. Yes. Yeah, we chose contacts that were specifically inside the STN and almost completely within the STN based on our lead localization. And we're trying to do dorsal versus ventral. And then when you had GPI and you had that localization, did it work? Not to my knowledge. One question. Is it okay? Yeah. Yeah. I'm wondering how specific are your images? We did a similar study on this where we did tractography seeding GPI or seeding STN. And when you do that, the tractography is very spread and goes all over the brain with GPI compared to the STN. That's way less and more specific in the motor area. Yeah. How specific is your imaging on this? It's pretty broad. We didn't want to limit our localization too much. So we did choose a broader way of looking at the images. So we did lower the threshold a little bit just to make sure that we were not cutting out any networks that were being stimulated or that our data was showing were being stimulated. Thank you. Yeah.

electrophysiological mapping

cortical networks

dorsal subthalamic deep brain stimulation

ventral subthalamic deep brain stimulation

Parkinson's disease