Brain stimulation improves memory for detail

Lay summary by Stephen Rhodes

Recalling a past event often evokes the specific contextual details surrounding the experience itself, such as where you were and who was with you. This recollection of specific detail is what gives our episodic memory such richness, allowing us to mentally time travel back to the original experience. Neuroimaging studies have repeatedly found that recollection of detail engages part of the frontal lobes of the brain, the dorsolateral prefrontal cortex (dlPFC), especially when retrieval is more demanding. However, activity during a task does not necessarily mean that the area is causally involved in the underlying cognitive processes.

In the present study, Gray and colleagues from The University of Chicago used non-invasive brain stimulation (transcranial direct current stimulation or tDCS) to assess whether they could improve participants recollection of detail. They applied a small amount of electrical current through the front of 48 individuals’ scalps over the dlPFC (24 on the left side, 24 on the right side). In doing so, they aimed to temporarily increase the brain activity in the area under the stimulation site. They also gave 24 individuals “fake” placebo stimulation, which mimics the procedure of real stimulation without any change in current. Real or fake stimulation was administered after participants had already studied lists of words, but before a memory test. Crucially their memory test required participants to recall specific details from the initial study period, such as whether the word was presented in a coloured font or with a picture. The pictures used were distinctive so recalling this aspect was assumed to be less demanding than recalling whether or not a word was presented in a coloured font.

Individuals who received real stimulation were more accurate at remembering words presented in a coloured font than individuals who received fake stimulation. However, there was no clear difference between the groups in remembering whether or not pictures had accompanied the words. This supports a role for the dlPFC in cognitively demanding retrieval of contextual detail.

Gray and colleagues’ findings clearly demonstrate a role for the dlPFC in searching through memory for information that is difficult to recollect and underlines the critical importance of this area for remembering details of our past. This study is an important step forward in the understanding of the neuroanatomical basis of our episodic memories.

For further information

Read the Cortex original research article which this summary is based on Electrically stimulating prefrontal cortex at retrieval improves recollection accuracy (September 2015).

Visit the profile of the research ambassador, Stephen Rhodes, who wrote this summary.

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