Short theta burst stimulation to left frontal cortex prior to encoding enhances subsequent recognition memory

Abstract

Deep semantic encoding of verbal stimuli can aid in later successful retrieval of those stimuli from long-term episodic memory. Evidence from numerous neuropsychological and neuroimaging experiments demonstrate regions in left prefrontal cortex, including left dorsolateral prefrontal cortex (DLPFC), are important for processes related to encoding. Here, we investigated the relationship between left DLPFC activity during encoding and successful subsequent memory with transcranial magnetic stimulation (TMS). In a pair of experiments using a 2-session within-subjects design, we stimulated either left DLPFC or a control region (Vertex) with a single 2-s train of short theta burst stimulation (sTBS) during a semantic encoding task and then gave participants a recognition memory test. We found that subsequent memory was enhanced on the day left DLPFC was stimulated, relative to the day Vertex was stimulated, and that DLPFC stimulation also increased participants’ confidence in their decisions during the recognition task. We also explored the time course of how long the effects of sTBS persisted. Our data suggest 2 s of sTBS to left DLPFC is capable of enhancing subsequent memory for items encoded up to 15 s following stimulation. Collectively, these data demonstrate sTBS is capable of enhancing long-term memory and provide evidence that TBS protocols are a potentially powerful tool for modulating cognitive function.

Impact of different intensities of intermittent theta burst stimulation on the cortical properties during TMS‐EEG and working memory performance

“…We were unable to replicate the previous study of iTBS demonstrating a significant increase in the accuracy of 2‐back task following iTBS compared to sham stimulation (Hoy et al, ). The reason for this discrepancy remains unclear, and further research is required as currently only a few studies have been performed in this area to date (Cheng et al, ; Debarnot et al, ; Demeter, Mirdamadi, Meehan, & Taylor, ; Hoy et al, ; Ryals, Rogers, Gross, Polnaszek, & Voss, ). A recent study investigated the effect of prefrontal TBS on a series of cognitive tasks, such as Digits Backward, 3‐back task, Stroop Colour and Word Test, and the Tower of Hanoi (Viejo‐Sobera et al, ).…”

Continuous theta-burst stimulation over the dorsolateral prefrontal cortex inhibits improvement on a working memory task

“…This might be supported by the lack of practice effect reported in neurocognitive disorders 47 , 48 , which are characterized by deficits in memory consolidation and acquiring new information 49 . Considering that memory processes may be modified by TBS 50 , 51 , and theta frequency oscillations are associated with memory consolidation processes 12 , it might be possible that prefrontal stimulation affected the consolidation of task-related skills. Future studies assessing whether consolidation may also play a role in TBS-related WM performance changes, seem warranted.…”

Impact of different intensities of intermittent theta burst stimulation on the cortical properties during TMS-EEG and working memory performance

“…This is contrary to a previous finding which demonstrated a significant increase in the accuracy of 2-back task following iTBS compared to sham stimulation (Hoy et al, 2015). The reason for this discrepancy remains unclear, and further research is required as currently only a few studies have been performed in this area to date (Cheng et al, 2016; Debarnot et al, 2015; Demeter et al, 2016; Hoy et al, 2015; Ryals et al, 2016). However, a similar lack of behavioural changes in the presence of robust neurophysiological effects after tDCS has also been described with a larger sample size (n = 20) (Hill et al, 2016), suggesting neurophysiological measures may provide a more sensitive index for assessing changes following neuromodulatory paradigms.…”