DOI: 10.5061/dryad.9cnp5hqk7
title: Picture ordering task EEG

description: Daily activities like preparing a meal rely on the ability to arrange
 thoughts and actions in the right order. Patients with Parkinson’s disease
 (PD) have difficulties in sequencing tasks. Their deficits in sequential
 working memory have been associated with basal ganglia dysfunction. Here
 we demonstrate that altered parietal alpha-theta oscillations correlate
 with sequential working memory in PD. We included 15 PD patients (6 women,
 mean age 66.0 years), 24 healthy young (HY, 14 women, mean age 24.1
 years), and 16 older participants (HO, 7 women, mean age 68.6 years).
 Participants completed a picture ordering task with scalp EEG recording,
 where they arranged five pictures in a specific order and memorized them
 over a delay. During encoding and the delay, the baseline alpha peak
 frequency for ordered trials was 10.0 Hz in HY, 10.1 Hz in HO, and 8.9 Hz
 in PD. PD showed a lower baseline alpha peak frequency with higher alpha
 power than HY and HO. PD with a higher baseline alpha power tended to
 respond more slowly. In response to sequence manipulation, the frequency
 of maximal power change between random and ordered trials (Fmax) was 10.0
 Hz in HY, 11.3 Hz in HO, and 7.7 Hz in PD. PD showed a lower
 Fmax than HY and HO, whereas HO showed a higher
 Fmax than HY. Compared to PD with Fmax in the alpha band
 (8-15 Hz, n=11), PD with Fmax in the theta band (4-7
 Hz, n=4) tended to show a higher ordering-related accuracy cost
 in the picture ordering task and lower accuracy and slower responses in an
 independent working memory task. In conclusion, altered baseline alpha
 oscillations and task-dependent modulation of alpha-theta oscillations may
 be a neural marker of poor sequential working memory in PD. 
description: Sample: 24 healthy young participants, 16 healthy older participants, 15 patients suffering from idiopathic Parkinson's Disease. Recording: EEG data were recorded from 29 tin electrodes mounted on an elastic cap using an BrainAmp amplifier (Brain Products GmbH, Gilching, Germany). The electrodes were placed according to the international 10-20 system. Two additional electrodes were placed on the bilateral mastoids. The vertical electrooculogram (EOG) was recorded from electrodes above and below the left eye. The horizontal EOG was recorded from electrodes on the outer canthi of each eye. The data were sampled at 250 Hz, referenced online against the right mastoid, and filtered with a bandpass filter of 0.016 Hz to 1kHz. Electrode impedances were kept below 5 kΩ.  Preprocessing: EEG data were preprocessed with the EEGLAB toolbox. The data were filtered with a low-pass filter of 48 Hz, re-referenced to the mean signal of the bilateral mastoids, and segmented into EEG epochs encompassing the entire trial ([-2.5 20] s around the trial onset). The epoched data were subjected to an independent component analysis algorithm to remove eye movement and other artifacts. The ICA corrected epochs were then visually inspected, and artifact afflicted epochs excluded from further analysis. EEG epochs were baseline-corrected by subtracting the mean voltage before the trial onset. Approximate 24% of ordered trials and 31% of random trials were rejected as artifacts. There was no group difference in the number of artifact-free trials. For the subsequent time frequency analyses data were exported to the Fieldtrip format. 
description: For group assignment see file subject_group.txt
 For task description and meaning of trigger codes see
 file subject_group.txt