A functional near-infrared spectroscopy investigation of item-method directed forgetting

Whether directed forgetting is passive or active remains debated. Using functional near-infrared spectroscopy (fNIRS), blood-oxygen level-dependent responses of intentional forgetting were investigated in the item-method directed forgetting (DF) paradigm. During the study phase, each word was followed by a random remembering or forgetting cue indicating whether the word is to be remembered (TBR) or to be forgotten (TBF). A recognition test was used in the test phase and four cue-response conditions were obtained: remembering/forgetting cues associated with the subsequently remembered (TBR-r/TBF-r) or forgotten (TBR-f/TBF-f) words. Data from 16 healthy adult participants showed a DF effect. The fNIRS data revealed that, during the 5–9 s time window, the oxygenate hemoglobin (oxy-Hb) levels were higher during intentional forgetting compared to intentional remembering in the left inferior frontal (TBF-f vs. TBR-f) and right superior frontal gyrus (TBF-r vs. TBR-r), indicating more frontal inhibition involved during intentional forgetting. During the 9–11 s time window, the oxy-Hb level in the frontal and parietal gyrus was higher for forgetting than remembering cues, indicating that the TBF words might be automatically encoded. In sum, the TBF words might receive inhibition control triggered by forgetting cues and then be automatically encoded with the increase of the post-cue interval.