Soyeon Jun1, Sang Ah Lee2, June Sic Kim3, Woorim Jeong4, Chun Kee Chung5. 1. Department of Brain & Cognitive Sciences, Seoul National University, Seoul, 03080, Republic of Korea; Department of Neurosurgery, Seoul National University Hospital, Seoul, 03080, Republic of Korea. Electronic address: soy0326@hbf.re.kr. 2. Department of Bio & Brain Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea. 3. Department of Brain & Cognitive Sciences, Seoul National University, Seoul, 03080, Republic of Korea; Research Institute of Basic Sciences, Seoul National University, Seoul, Republic of Korea. Electronic address: junesic.kim@gmail.com. 4. Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, 03080, Republic of Korea; Department of Neurosurgery, Seoul National University Hospital, Seoul, 03080, Republic of Korea. 5. Department of Brain & Cognitive Sciences, Seoul National University, Seoul, 03080, Republic of Korea; Department of Neurosurgery, Seoul National University Hospital, Seoul, 03080, Republic of Korea. Electronic address: chungc@snu.ac.kr.
Abstract
BACKGROUND: Despite its potential to revolutionize the treatment of memory dysfunction, the efficacy of direct electrical hippocampal stimulation for memory performance has not yet been well characterized. One of the main challenges to cross-study comparison in this area of research is the diversity of the cognitive tasks used to measure memory performance. OBJECTIVE: We hypothesized that the tasks that differentially engage the hippocampus may be differentially influenced by hippocampal stimulation and the behavioral effects would be related to the underlying hippocampal activity. METHODS: To investigate this issue, we recorded intracranial EEG from and directly applied stimulation to the hippocampus of 10 epilepsy patients while they performed two different verbal memory tasks - a word pair associative memory task and a single item memory task. RESULTS: Hippocampal stimulation modulated memory performance in a task-dependent manner, improving associative memory performance, while impairing item memory performance. In addition, subjects with poorer baseline cognitive function improved much more with stimulation. iEEG recordings from the hippocampus during non-stimulation encoding blocks revealed that the associative memory task elicited stronger theta oscillations than did item memory and that stronger theta power was related to memory performance. CONCLUSIONS: We show here for the first time that stimulation-induced associative memory enhancement was linked to increased theta power during retrieval. These results suggest that hippocampal stimulation enhances associative memory but not item memory because it engages more hippocampal theta activity and that, in general, increasing hippocampal theta may provide a neural mechanism for successful memory enhancement.
BACKGROUND: Despite its potential to revolutionize the treatment of memory dysfunction, the efficacy of direct electrical hippocampal stimulation for memory performance has not yet been well characterized. One of the main challenges to cross-study comparison in this area of research is the diversity of the cognitive tasks used to measure memory performance. OBJECTIVE: We hypothesized that the tasks that differentially engage the hippocampus may be differentially influenced by hippocampal stimulation and the behavioral effects would be related to the underlying hippocampal activity. METHODS: To investigate this issue, we recorded intracranial EEG from and directly applied stimulation to the hippocampus of 10 epilepsypatients while they performed two different verbal memory tasks - a word pair associative memory task and a single item memory task. RESULTS: Hippocampal stimulation modulated memory performance in a task-dependent manner, improving associative memory performance, while impairing item memory performance. In addition, subjects with poorer baseline cognitive function improved much more with stimulation. iEEG recordings from the hippocampus during non-stimulation encoding blocks revealed that the associative memory task elicited stronger theta oscillations than did item memory and that stronger theta power was related to memory performance. CONCLUSIONS: We show here for the first time that stimulation-induced associative memory enhancement was linked to increased theta power during retrieval. These results suggest that hippocampal stimulation enhances associative memory but not item memory because it engages more hippocampal theta activity and that, in general, increasing hippocampal theta may provide a neural mechanism for successful memory enhancement.
Authors: Uma R Mohan; Andrew J Watrous; Jonathan F Miller; Bradley C Lega; Michael R Sperling; Gregory A Worrell; Robert E Gross; Kareem A Zaghloul; Barbara C Jobst; Kathryn A Davis; Sameer A Sheth; Joel M Stein; Sandhitsu R Das; Richard Gorniak; Paul A Wanda; Daniel S Rizzuto; Michael J Kahana; Joshua Jacobs Journal: Brain Stimul Date: 2020-05-21 Impact factor: 8.955
Authors: Ethan A Solomon; Michael R Sperling; Ashwini D Sharan; Paul A Wanda; Deborah F Levy; Anastasia Lyalenko; Isaac Pedisich; Daniel S Rizzuto; Michael J Kahana Journal: Brain Stimul Date: 2021-08-21 Impact factor: 9.184
Authors: Brent M Roeder; Mitchell R Riley; Xiwei She; Alexander S Dakos; Brian S Robinson; Bryan J Moore; Daniel E Couture; Adrian W Laxton; Gautam Popli; Heidi M Clary; Maria Sam; Christi Heck; George Nune; Brian Lee; Charles Liu; Susan Shaw; Hui Gong; Vasilis Z Marmarelis; Theodore W Berger; Sam A Deadwyler; Dong Song; Robert E Hampson Journal: Front Hum Neurosci Date: 2022-07-25 Impact factor: 3.473