Rationale:
Our pilot study has shown that electrical stimulation of specific brain regions through responsive neurostimulation (RNS) can improve memory consolidation [1]. With improvements to the study design and increased sample size, the current study aims to reinforce and investigate whether responsive neurostimulation (RNS) devices can improve memory function through the administration of verbal and non-verbal learning tasks. We hypothesize that direct cortical stimulation with RNS could improve memory.
Methods:
In an outpatient setting, a verbal learning task (Hopkins Verbal Learning Test-Revised) was administered to patients with RNS implants in various brain regions (hippocampal, temporal, and insular) [2]. For the verbal task, patients read a list of 12 semantically related words and tried to recall the list in the three different trials, along with a delayed recall and recognition trial performed 20 minutes later. True or sham stimulations were administered to patients through Neuropace. The memory task was synced with a computer program to coordinate the delivery of stimulation with the exposure of the word.
Results:
In regard to the demographics of the study population, there were 34 participants with an even distribution of male-to-female ratio with a mean age of 32.18±12.99 years and mean years of education of 12.76±2.62 years. These study participants were composed of 22 White/Caucasian Americans, 10 Hispanic Americans, and 2 Asian Americans (88.2% right-handed, 11.8% left-handed). Regarding electrode placements, 44.1% had their first electrode in the hippocampus, while 38.3% had their second electrode in the hippocampal cortex.
Although not statistically significant, the results indicated a trend such that the stim group (M = 7.31, SD = 3.03) performed better than the sham group (M = 6.65 SD = 2.74) on delayed recall (
t(28) = 1.660,
p = .108). The trend also applied to the recognition trial such that stim (M = 87%; SD = 7.79) performed better than the sham group (75.24%, SD = 25.9%) (
t(28) = 1.660,
p = .108).
Conclusions:
Previous research has found that RNS stimulation can improve memory; however, with the limits of the smaller sample size due to the design of the previous study, this prompted continuing investigation and analysis of RNS impact on memory. Although the current results show no statistically significant differences between stim and sham stimulations of the verbal tasks, there is still a trend consistent with previous research such that those undergoing stimulation at the time of learning perform better on recall than those with sham stimulation. We aim to continue acquiring additional data to perform a stronger analysis and interpretation of the effects of RNS on memory.
Funding: Mike Hogg Foundation Grant