Attention and Eye Movement in Parkinson's Disease

Facial Expression Rating

Participants will rate facial expression along a continuous scale using a computerized slider, following the affective bias task (ABT) of Bijanki et al. (2014). The scale is anchored with three descriptors, "Very Sad" at slider value 0 (left), "Neutral", at position 0.5 (middle), and "Very Happy" at 1.0 (right). Responses are compared between two time points: (1) at the initial pre-surgical testing session and post DBS implantation and (2) at the post-implantation session following clinical optimization of therapeutic parameters, 2-3 weeks after surgery. The comparison will examine both the direction of any bias of the rating, against normative ratings, and the magnitude of average deviation from normative ratings. Finally, the ratings will be incorporated into a generalized linear model of gaze position (Kovach 2014) to identify the association between perceived facial expression and characteristic fixation patterns.

Eye Tracking

The location and duration of gaze fixations will be recorded with a remote eye tracking camera. The location of gaze fixations will be treated as the dependent measure within a generalized linear modeling (GLM) framework for spatial point processes, described in Kovach and Adolphs (2014). Parameter estimates of the model give the log relative risk of fixation at different locations in the visual scene as a function of the independent measures of the model. Independent measures include the main effect of (1) Fourier basis functions encoding scene location and its interactions with (2) image rating in the affective bias task of Bijanki et. al (2014), (3) session and (4) DBS stimulation state. Measures derived from the GLM model will also include the statistical deviation (e.g. Kullback-Leibler divergence) from the average distribution of fixations observed in healthy comparison subjects for each image.

Intraoperative Microrecordings

During the Aim 2 portion of the study, patients undergoing awake DBS surgery as part of standard clinical care will engage in a subset of the face rating tasks during the surgery. Invasive recordings will be obtained from DBS target structures, including STN, VIM, and GPi using microelectrodes that are placed as part of standard clinical practice. Spike sorting will be used to identify firing of individual cells and firing rate will compared to eye movements to identify responses associated with shifts of attention in the targeted deep brain structures . These measures will be compared across movement-disorders populations using mixed-effects linear modeling and other standard statistical procedures.

EEG beta-band power during emotional face rating

Spectral power in the beta frequency band (12-30 Hz), expressed in microvolts squared (µV²) and normalized to a pre-stimulus baseline, computed from non-invasive scalp EEG over posterior electrodes during the emotional face rating component of the task. Measurement tool: 64-channel research-grade scalp EEG with time-frequency decomposition (demodulated band transform). Group comparisons across PD, ET, DT, and healthy controls and within-participant comparisons across DBS conditions will be made using mixed-effects linear models, comparing power at baseline and modulation of power within a -0.5 to 0.5 s peri-saccade window.

EEG event-related potential (ERP) amplitude at saccade onset

Mean amplitude (µV) of the stimulus-locked event-related potential at saccade onset, measured over occipito-temporal electrodes during the 100-300 ms post-stimulus interval (encompassing the N170 component). Measurement tool: 64-channel research-grade scalp EEG with stimulus-locked averaging.

EEG beta burst rate, frequency and amplitude during emotional face viewing

Modulation of beta band activity (12-30 Hz), will be studied in scalp EEG recordings using a published method (Kovach 2026) for identifying oscillatory bursts based on estimation and decomposition of the fourth order spectrum (trispectrum). Group comparisons across PD, ET, DT, and healthy controls and within-participant comparisons across DBS conditions will be made using mixed-effects linear models, comparing burst rate, amplitude and frequency comparing power at baseline and modulation of power within a -0.5 to 0.5 s peri-saccade window.

LFP beta-band (12-30 Hz) power during emotional face viewing

Spectral power in the beta band (12-30 Hz), expressed in microvolts squared (µV²), recorded from chronically implanted DBS electrodes targeting the subthalamic nucleus during eye-tracked task performance. Measurement tool: voltage telemetry through clinical leads using the BrainSense capability of the Medtronic Percept implantable pulse generator. Power will be computed via time-frequency decomposition (demodulated band transform) and compared across DBS conditions (normal therapeutic, reduced current, reduced frequency) and across movement-disorder populations using mixed-effects linear models.