Effects of ON/OFF deep brain stimulation on cognitive control in treatment-resistant depression (EEG)

Please cite the following reference if you use the afMSIT data:

Widge, A. S., Zorowitz, S., Basu, I., Paulk, A. C., Cash, S. S., Eskandar, E. N., Deckersbach, T., Miller, E. K., Dougherty, D. D. Deep Brain Stimulation of the Internal Capsule Enhances Human Cognitive Control and Prefrontal Cortex Function. Nature Communications. https://doi.org/10.1038/s41467-019-09557-4

Please cite the following reference if you use the resting state data:

Widge, A. S., Zorowitz, S., Link, K., Miller, E. K., Deckersbach, T., Eskandar, E. N., & Dougherty, D. D. (2016). Ventral capsule/ventral striatum deep brain stimulation does not consistently diminish occipital cross-frequency coupling. Biological psychiatry, 80(7), e59-e60. http://doi.org/10.1016/j.biopsych.2015.10.029

afmsit
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To probe cognitive flexibility, we employed a modified version of the Multi-Source Interference Task (MSIT). The MSIT requires subjects to identify which of a set of three numbers is different than its neighbors. Subjects must keep three fingers of their right hand positioned over response keys corresponding to the digits 1-3. In Control (non-interference) trials, the target is in the same spatial position as its corresponding response key, and the flanking digits are not valid responses (i.e., they are 0s). In Interference trials, the target is out-of-position relative to its corresponding key-press and is flanked by other viable targets. MSIT has been shown to produce robust functional MRI and electrophysiologic changes, with a significant (Interference-Control) difference often detectable at the individual subject level. 

We further added an emotional interference dimension, based on a hypothesis that subjects with severe treatment-resistant illness would be attentionally biased towards negative pictures. Before each MSIT trial, an image selected from the International Affective Picture System, or IAPS, was presented. The image remained on-screen, partially obscured by the MSIT stimulus, for the trial duration. A fixed subset of 144 images were selected from the overall IAPS dataset to cover the range of available valence (positive, neutral, negative) and emotional arousal ratings.

Each block of trials contained 72 Control and 72 Interference trials. We assigned positive, neutral, and negative IAPS images assigned to each trial type in a counterbalanced fashion, such that each image was presented once in a Control and once in an Interference context. The 144 images were split between these two 144-trial blocks in a manner that minimized the mean squared pairwise differences between image ratings when rank-ordered by their valence. To prevent response sets or habituation, trial sequence in each block was pseudo-randomized so that subjects never had more than two trials in a row that shared the same valence, interference level, or desired response finger. This highly interleaved trial design was expected to place greater demands on cognitive control systems by reducing predictability of the stimuli. Subjects viewed the IAPS picture alone for 400 ms, were presented with the MSIT stimulus and given up to 1500 ms to respond, and then viewed a fixation cross for 3-5 seconds (randomized with a uniform distribution). They were instructed to minimize eye blinking during the trial and to blink freely during the fixation period. Before data collection, subjects performed a block of 20 trials where they received correct/incorrect feedback, followed by another block of 40 trials without feedback. They repeated this practice, if necessary, until they achieved over 90% correct responses (counting missed trials as incorrect). 

eeg
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Electroencephalographic data were acquired at 1450 Hz (Nexstim eXimia EEG) from 60 channels placed according to the international 10-20 system and the manufacturer's standard cap. The ground electrode was placed on the bridge of the nose. One diagonal bipolar electro-oculogram (EOG) channel was placed around the right eye. Channels were prepared to less than 5 kiloOhms impedance. The scalp location of each channel was digitized after cap preparation and prior to recordings. We also digitized the nasion and both pre-auricular points, plus 100 additional scalp points not corresponding to any EEG sensor, to improve the quality of MRI-to-digitization co-registration. 

All subjects first completed an MSIT block with their DBS on at its usual clinical settings (DBS ON).  A trained clinician then de-activated the bilateral implanted neurostimulators, and the subject rested for at least 1 hour without removing the EEG cap.  After re-preparing any high-impedance channels, subjects again performed MSIT (DBS OFF) before neurostimulator re-activation. Subjects were aware of their device status, as were the experimenters, although no subject experienced adverse psychological consequences from the study manipulation.

Three anatomical fiducials were digitized for aligning the EEG with the pre-operative MRI: the nasion (lowest depression between the eyes) and the left and right ears (lowest depression between the tragus and the helix, above the tragus). This procedure is illustrated here: http://neuroimage.usc.edu/brainstorm/CoordinateSystems#Subject_Coordinate_System_.28SCS_.2F_CTF.29

The following triggers are included in the trigger channels of the .fif files:

Channel    Event       Description
Trig1          Onset      Start of trial (onset of IAPS)
Trig2          Onset      Start of response window (onset of MSIT)
Trig1          Offset      Response time
Trig2          Offset      End of trial

rest
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In addition, we were able to collect several minutes of eyes-open resting state data with both DBS ON and OFF in several (but not all) patients. Please see participants.tsv to find which patients have resting state data.

code
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The code used for data analysis is publicly available at:
https://github.com/mghneurotherapeutics/EMOTE-afMSIT