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The Journal of Neuroscience, July 1, 2002, 22(13):5694-5704
Sleep States Differentiate Single Neuron Activity Recorded from
Human Epileptic Hippocampus, Entorhinal Cortex, and Subiculum
Richard J.
Staba1,
Charles L.
Wilson2, 4,
Anatol
Bragin2, 4,
Itzhak
Fried3, 4, and
Jerome
Engel Jr1, 2, 4
Departments of 1 Neurobiology, 2 Neurology,
and 3 Neurosurgery, and 4 The Brain Research
Institute, David Greffen School of Medicine at University of California
Los Angeles, Los Angeles, California 90095
Animal models of epilepsy have shown that synchronous burst firing
is associated with epileptogenesis, yet the evidence from human studies
linking neuronal synchrony and burst firing to epileptogenesis remains
equivocal. Sleep-wake states have been shown to differentially modulate the generation of epileptiform EEG spikes between brain regions of greater and lesser seizure-generating potential, providing information that helps to identify the primary epileptogenic region. Using these state-dependent mechanisms to assist us in identifying neuronal correlates of human epilepsy, we recorded interictal neuronal
activity from mesial temporal lobe (MTL) areas in epileptic patients
implanted with depth electrodes required for medical diagnosis during
polysomnographically defined sleep-wake states. Results show that
single neurons recorded ipsilateral to seizure-initiating MTL
("epileptic") areas had significantly higher firing rates (p = 0.01) and burst propensity
(p = 0.01) and greater synchrony of
discharges (p = 0.003) compared with neurons
recorded from contralateral non-seizure-generating MTL
("non-epileptic") areas. In particular, during episodes of slow
wave sleep (SWS) and rapid eye movement (REM) sleep, epileptic
hippocampal neurons had significantly higher burst rates compared with
non-epileptic hippocampal neurons (both p = 0.01).
In contrast, during episodes of wakefulness (Aw), no difference in
burst firing between epileptic and non-epileptic hippocampal neurons
was observed. Furthermore, synchronous firing was significantly higher
between epileptic MTL neurons compared with non-epileptic MTL neurons
during SWS (p = 0.04) and REM sleep (p = 0.02), but no difference in neuronal
synchrony was found between epileptic and non-epileptic neurons during
Aw. These results provide evidence that sleep states differentially
modulate abnormal epileptogenic neuronal discharge properties within
human MTL and confirm that neuronal burst firing and enhanced neuronal
synchrony observed in experimental animal models of epilepsy
characterizes human epilepsy as well.
Key words:
slow wave sleep; REM sleep; bursting; synchrony; epilepsy; limbic system
Copyright © 2002 Society for Neuroscience 0270-6474/02/22135694-11$05.00/0
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