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Published on: August 24, 2012
Artificial theta stimulation impairs encoding of contextual fear memory
Arto Lipponen1, Bisrat T Woldemichael, Kestutis Gurevicius
1A. I. Virtanen Institute, University of Eastern Finland, Kuopio, Finland. Arto.Lipponen@uef.fi
Plos One
|November 8, 2012
Summary
Restoring hippocampal theta rhythm via electrical stimulation did not improve memory deficits in rats after fimbria-fornix lesions. This suggests theta rhythm alone is insufficient for memory encoding and may even impair it.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Memory Research
Background:
- Hippocampal theta rhythm (4-12 Hz) is closely linked to memory function.
- Lesions to the medial septum or fimbria-fornix abolish theta rhythm and impair declarative memory.
Purpose of the Study:
- To determine if restoring hippocampal theta rhythm by electrical stimulation can reverse memory deficits caused by fimbria-fornix lesions.
- To investigate the causal role of theta rhythm in memory formation using a fear conditioning paradigm in rats.
Main Methods:
- Male Wistar rats underwent sham or fimbria-fornix lesions.
- Artificial 8 Hz theta stimulation was applied to the ventral hippocampal commissure during memory encoding.
- Memory was assessed via fear conditioning and freezing behavior 24 and 28 hours post-conditioning.
Main Results:
- Fimbria-fornix lesions impaired fear memory and reduced hippocampal theta power.
- Artificial theta stimulation generated continuous theta oscillations.
- Contrary to hypotheses, artificial theta stimulation impaired conditioned fear responses in both sham and lesioned rats.
Conclusions:
- Restoration of theta oscillation alone is insufficient to support memory encoding after fimbria-fornix lesions.
- A fixed-frequency, universal theta oscillation in the hippocampus may negatively impact memory formation.
