BOLD variability during cognitive control for an adult lifespan sample

Project: Trajectories of the neural correlates of cognitive control across adulthood

Scan Years: 2016-2019

Task Overview: The main purpose of this study was to investigate how age differences in brain function influence age differences in cognitive control. This was achieved through assessment of three fundamental aspects of cognitive control: inhibition (go/no-go task), task switching (letter categorization task) and working memory (n-back task). Brain activation was measured throughout these tasks, as well as during a rest period (fixation), using fMRI. BOLD variability was then computed using the Variability Toolbox in SPM (https://github.com/LNDG/vartbx).

Independent Variables: Age, Task
Dependent Variable: BOLD Variability

Subjects: A total of 158 adults (aged 20–86) were recruited from the greater Toronto area, either through online advertising or from an existing participant database. Participants were screened to be healthy (i.e., free from any major psychiatric, or neurological conditions; no history of head trauma), cognitively normal (MMSE > 26), right-handed, fluent English speakers, with normal or corrected-to-normal vision (at least 20/30) and if necessary, vision was corrected using MRI-compatible lenses during scanning.

Apparatus: Lying down in an MRI scanner, participants viewed and followed task prompts on a screen through a head coil mirror. A Siemens Trio 3T magnet in a shielded room at Baycrest Health Sciences was used to scan all subjects.

Initial Setup: Upon arrival, subjects underwent a 30-min mock-scanning session, practicing each of the three fMRI tasks in a demagnetized MRI simulator.

Task Organization: Participants underwent a 1.5-hr MRI scan that included T2-weighted fluid-attenuated inversion recovery, 10-min BOLD resting state, T1-weighted anatomical imaging, three BOLD fMRI tasks (detailed below), diffusion-weighted imaging, and, if time permitted, arterial spin labeling. The BOLD fMRI tasks each measured a different domain of cognitive control (inhibition, shifting, and working memory), and the order of the three fMRI tasks was counter balanced across participants.

Task Details (https://doi.org/10.1162/jocn_a_01685)

Go/No-Go: Participants were presented with a series of letters and told to respond (i.e., go) when they saw the letter “X” and not respond (i.e., no-go) for all other letters. Letters were presented for 400 msec with a mean ISI of 1200 msec (jittered between 900 and 1500 msec), during which a fixation cross was presented. The task had two blocks (with the order randomized across participants): an “inhibition” block in which there were more go trials than no-go trials (120 go, 40 no-go) and a shorter “initiation” block in which there were more no-go trials than go trials (20 go, 60 no-go). In total, the go/no-go task lasted 6 min 26 sec.

Task Switching: Participants were shown a letter in the center of the screen, as well as one of two cues above the letter, prompting them to categorize it as either uppercase/lowercase or a consonant/vowel. The cues and letters were also presented in two different colors (e.g., blue and green) to differentiate between the two kinds of judgments and facilitate performance. There were 60 total trials (50% uppercase/lower case judgments; 50% vowel/consonant judgments) organized such that half of the trials involved switching between judgments (i.e., vowel/consonant and then uppercase/lowercase) and half of the trials repeated the same judgment (i.e., vowel/consonant and then vowel/consonant). Letters were presented for 2000 msec with a mean ISI of 4500 msec (jittered between 1500 and 7500 msec), during which a fixation cross was presented. In total, task switch lasted 7 min 26 sec.

N-back: a paradigm with 0-, 1-, and 2-back loads was utilized, where participants saw a series of letters and had to respond if the letter was a “target” or “nontarget”. For 0-back, the targets were “X.” For 1-back, the targets were letters that matched the previously presented letter. For 2-back, the targets were letters that matched the letter presented two positions back. The task was organized into three blocks (one for each load level), the order of which was randomized across participants, and each block (0-back, 1-back, and 2-back) had 90 total trials (30 target and 60 nontarget). Letters were presented for 500 msec with a mean ISI of 1200 msec (jittered between 900 and 1500 msec), during which a fixation cross was presented. The total time for the n-back task was 8 min 52 sec.

Additional Data Acquired: In a separate session, subjects also completed a series of written questionnaires (Montreal Cognitive Assessment (MoCA), Mini-Mental State Examination (MMSE), Morningness–Eveningness Questionnaire (MEQ), Positive and Negative Affect Schedule (PANAS), Shipley-2 Vocabulary Test and Global Physical Activity Questionnaire (GPAQ)), as well as a battery of tests from the National Institutes of Health (NIH) Cognitive Toolbox. Results from most of these tests are available at https://osf.io/wgs7k/.

Missing Data:

Artifact in sub-020 dwi; missing _dwi.nii file.
Time constraints prevented sub-068, sub-081 and sub-098 from completing dwi.
sub-143 had to end session early; missing task switch and dwi data.