Enhancement of object detection with transcranial direct current stimulation is associated with increased attention

Abstract

Background: We previously found that Transcranial Direct Current Stimulation (tDCS) improves learning and performance in a task where subjects learn to detect potential threats indicated by small target objects hidden in a complex virtual environment. In the present study, we examined the hypothesis that these effects on learning and performance are related to changes in attention. The effects of tDCS were tested for three forms of attention (alerting, orienting, and executive attention) using the Attention Network Task (ANT), which were compared with performance on the object-learning task.

Results: Participants received either 0.1 mA (N = 10) or 2.0 mA (N = 9) tDCS during training and were tested for performance in object-identification before training (baseline-test) and again immediately after training (immediate test). Participants next performed the Attention Networks Task (ANT), and were later tested for object-identification performance a final time (delayed test). Alerting, but not orienting or executive attention, was significantly higher for participants receiving 2.0 mA compared with 0.1 mA tDCS (p < 0.02). Furthermore, alerting scores were significantly correlated with the proportion of hits (p < 0.01) for participants receiving 2.0 mA.

Conclusions: These results indicate that tDCS enhancement of performance in this task may be related in part to the enhancement of alerting attention, which may benefit the initial identification, learning and/or subsequent recognition of target objects indicating potential threats.

Figures

Figure 1

Effects of tDCS on Alerting, Orienting, and Executive Attention. Participants receiving 30 minutes of 2.0 mA anodal tDCS over right inferior frontal cortex (dark bars) had significantly greater alerting scores from the ANT than those receiving 0.1 mA (light bars). Differences between tDCS groups for scores of orienting attention and executive attention were nonsignificant. Error bars represent standard error of the measurement.

Figure 2

Correlation between Alerting Scores and Percent Hits at Baseline, Immediate, and Delay Tests. Alerting scores were significantly correlated with the percent of hits in the immediate and delayedtests for participant receiving 2.0 mA tDCS (solid lines). There was no correlation for participants receiving 0.1 mA tDCS (dotted lines), nor was there a significant correlation for either group between alerting and percent hits during baseline testing. Four data points below 40% are not visible in the baseline figure (top).

Figure 3

Object Detection Task Training and Test Stimuli. Examples of training (left) and test (right) stimuli are depicted. Images in the top row contain a target object, while those in the lower row do not. In this example, the target object is a small bomb hidden behind the boxes, as indicated by a dark patch.

Figure 4

Timeline of Events. Each test period (blue) lasted about 15 min. Training (green) lasted approximately 1 h. Immediate and delayed tests were separated by 1 h. The Attention Networks Test (ANT; orange) was administered immediately before the delay test and lasted approximately 20 min. TDCS (red) was administered starting 5 min before training and lasted for a total of 30 min. Participants were asked to indicate the amount of tDCS-induced sensation that was present at three time points (1, 5 and 20 min after start of tDCS administration).