Memory enhancement and deep-brain stimulation of the entorhinal area.
BACKGROUND
The medial temporal structures, including the hippocampus and the entorhinal cortex, are critical for the ability to transform daily experience into lasting memories. We tested the hypothesis that deep-brain stimulation of the hippocampus or entorhinal cortex alters memory performance.


METHODS
We implanted intracranial depth electrodes in seven subjects to identify seizure-onset zones for subsequent epilepsy surgery. The subjects completed a spatial learning task during which they learned destinations within virtual environments. During half the learning trials, focal electrical stimulation was given below the threshold that elicits an afterdischarge (i.e., a neuronal discharge that occurs after termination of the stimulus).


RESULTS
Entorhinal stimulation applied while the subjects learned locations of landmarks enhanced their subsequent memory of these locations: the subjects reached these landmarks more quickly and by shorter routes, as compared with locations learned without stimulation. Entorhinal stimulation also resulted in a resetting of the phase of the theta rhythm, as shown on the hippocampal electroencephalogram. Direct hippocampal stimulation was not effective. In this small series, no adverse events associated with the procedure were observed.


CONCLUSIONS
Stimulation of the entorhinal region enhanced memory of spatial information when applied during learning. (Funded by the National Institutes of Health and the Dana Foundation.).
Department of Neurosurgery, David Geffen School of Medicine and Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, CA 90095-7039, USA.
Nanthia
N
Suthana
Zulfi
Z
Haneef
John
J
Stern
Roy
R
Mukamel
Eric
E
Behnke
Barbara
B
Knowlton
Itzhak
I
Fried
D046690:Deep Brain Stimulation; D004567:Electrodes, Implanted; D004569:Electroencephalography; D018728:Entorhinal Cortex; D004827:Epilepsy / Q000601:surgery; D006624:Hippocampus; D006801:Humans; D007360:Intelligence; D007858:Learning; D008279:Magnetic Resonance Imaging; D008568:Memory; D013037:Spatial Behavior