Attention Networks in ADHD Adults after Working Memory Training with a Dual n-Back Task

Abstract

Patients affected by Attention-Deficit/Hyperactivity Disorder (ADHD) are characterized by impaired executive functioning and/or attention deficits. Our study aim is to determine whether the outcomes measured by the Attention Network Task (ANT), i.e., the reaction times (RTs) to specific target and cue conditions and alerting, orienting, and conflict (or executive control) effects are affected by cognitive training with a Dual n-back task. We considered three groups of young adult participants: ADHD patients without medication (ADHD), ADHD with medication (MADHD), and age/education-matched controls. Working memory training consisted of a daily practice of 20 blocks of Dual n-back task (approximately 30 min per day) for 20 days within one month. Participants of each group were randomly assigned into two subgroups, the first one with an adaptive mode of difficulty (adaptive training), while the second was blocked at the level 1 during the whole training phase (1-back task, baseline training). Alerting and orienting effects were not modified by working memory training. The dimensional analysis showed that after baseline training, the lesser the severity of the hyperactive-impulsive symptoms, the larger the improvement of reaction times on trials with high executive control/conflict demand (i.e., what is called Conflict Effect), irrespective of the participants' group. In the categorical analysis, we observed the improvement in such Conflict Effect after the adaptive training in adult ADHD patients irrespective of their medication, but not in controls. The ex-Gaussian analysis of RT and RT variability showed that the improvement in the Conflict Effect correlated with a decrease in the proportion of extreme slow responses. The Dual n-back task in the adaptive mode offers as a promising candidate for a cognitive remediation of adult ADHD patients without pharmaceutical medication.

Keywords: ADHD subtype; attentional network task; conflict effect; dimensional analysis; ex-Gaussian parameters; executive control; methylphenidate.

Figure 1

Experimental procedure of the Attention Network Task (ANT). The steps in a trial are summarized as follows: (T1) The participant is requested to fix a cross at the center of the screen for a random interval in the range 400–1600 ms. (T2) A cue appears for 100 ms, in the upper window, the four cue conditions. (T3) The cue disappears. (T4) A target stimulus with flankers appears, marked in the red circle in this figure; the related panel shows the six stimuli used in the present experiment. The participant is requested to select as quickly as possible the button corresponding to the direction of the target stimulus. In this example, the correct choice is to press the right button of the computer mouse. (T5) A final interval with participant’s gaze focused on the central cross is set until the next trial is started.

Figure 2

Example of level $n=2$ of the Dual n-back task. The task consisted of 20 blocks of at least 20 trials. Each trial was composed of an auditory and visual stimulus presented simultaneously. Participants were asked to detect and to press a key if any of the current stimuli corresponded to the one presented in the previous trial. They had to press the ‘A’ keyboard letter to report the correspondence with a visual target while the auditory target required the pressing of the ‘L’ key. Modified from [21].

Figure 3

Dimensional analysis of reaction times as a function of the severity of ADHD symptoms measured by Conners’ Adult ADHD Rating Scales-Self Report (Screening Version, CAARS-S:SV). (a) Scatterplot as a function of $\mathrm{CAARS}:\mathrm{A}$ (DSM-IV Inattentive Symptoms Subscale). (b) Scatterplot as a function of $\mathrm{CAARS}:\mathrm{B}$ (DSM-IV Hyperactive-Impulsive Symptoms Subscale). (c) Scatterplot as a function of $\mathrm{CAARS}:\mathrm{C}$ (DSM-IV Total ADHD Symptoms Subscale). (d) Scatterplot as a function of $\mathrm{CAARS}:\mathrm{D}$ (‘ADHD Index’, the normalized T-score of CAARS). Each point shows the median and the median absolute deviation for one participant. Participants’ groups are identified by distinct shapes, i.e., triangles for controls, circles and squares for non-medicated and medicated ADHD patients, respectively. Data points before training (all subgroups merged together) are plotted in black. Data points after training are plotted in red for the baseline level (fixed at 1-back) and in blue for the adaptive level of the Dual n-back. Color lines refer to the robust regression of the corresponding data points. Notice that the slope for participants before training and after baseline training tended to be very similar. Notice also that the slopes tended to flatten after adaptive training, irrespective of the $\mathrm{CAARS}$ subscale.

Figure 4

Reaction Times (means ± SEM) for all conditions: Cue × Target × Group × Training level. Participants’ groups: CTL: control subjects; MADHD: ADHD patients with medication; ADHD: ADHD patients without medication.

Figure 5

Attention network effects within groups before and after training. The yellow circles in the violin plots correspond to the average values of the corresponding network effects. The p-values and Cohen’s d effect sizes are reported for paired Student’s t tests. Notice that WMT affected only the conflict network. In particular, for ADHD only the adaptive training provoked a large and significant effect. Groups: CTL: control subjects; MADHD: patients with medication; ADHD: patients without medication.