Transcranial direct current stimulation over right dorsolateral prefrontal cortex enhances error awareness in older age

Abstract

The ability to detect errors during cognitive performance is compromised in older age and in a range of clinical populations. This study was designed to assess the effects of transcranial direct current stimulation (tDCS) on error awareness in healthy older human adults. tDCS was applied over DLPFC while subjects performed a computerized test of error awareness. The influence of current polarity (anodal vs cathodal) and electrode location (left vs right hemisphere) was tested in a series of separate single-blind, Sham-controlled crossover trials, each including 24 healthy older adults (age 65-86 years). Anodal tDCS over right DLPFC was associated with a significant increase in the proportion of performance errors that were consciously detected, and this result was recapitulated in a separate replication experiment. No such improvements were observed when the homologous contralateral area was stimulated. The present study provides novel evidence for a causal role of right DLPFC regions in subserving error awareness and marks an important step toward developing tDCS as a tool for remediating the performance-monitoring deficits that afflict a broad range of populations.

Keywords: cognitive aging; error awareness; performance monitoring; prefrontal cortex; tDCS.

Figure 1.

The EAT (Hester et al., 2005). Subjects were required to make a button press (“A”) to all congruent stimuli (word and color matching) and to withhold from responding to incongruent stimuli (Stroop No-go) or when a word was repeated on consecutive trials (Repeat No-go). Subjects were also required to press a separate button (“B”) as soon as possible after commission errors to signal error awareness.

Figure 2.

Effects of transcranial direct current stimulation (tDCS) on error awareness in Experiments 1–4. A, Experiment 1: anodal tDCS over right dorsolateral prefrontal cortex (DLPFC) was associated with a significant improvement in error awareness for Repeat No-go trials. B, Experiment 2: anodal tDCS over left DLPFC was not associated with any changes in error awareness. C, Experiment 3: cathodal tDCS over right DLPFC was not associated with any changes in error awareness. D, Experiment 4: the results of Experiment 1 were recapitulated in Experiment 4. Anodal tDCS over right DLPFC was again associated with a significant improvement in error awareness for Repeat No-go trials. Error bars represent SEM.

Figure 3.

Histogram displaying individual variability in response to the intervention. Response to the intervention was defined as each subject's mean difference score between percentage error awareness for Repeat No-go trials at Real versus Sham stimulation conditions. Positive values indicate better error awareness for Repeat No-go trials at Real compared with Sham stimulation.