Three-dimensional surface maps link local atrophy and fast ripples in human epileptic hippocampus.
OBJECTIVE
There is compelling evidence that pathological high-frequency oscillations (HFOs), called fast ripples (FR, 150-500Hz), reflect abnormal synchronous neuronal discharges in areas responsible for seizure genesis in patients with mesial temporal lobe epilepsy (MTLE). It is hypothesized that morphological changes associated with hippocampal atrophy (HA) contribute to the generation of FR, yet there is limited evidence that hippocampal FR-generating sites correspond with local areas of atrophy.


METHODS
Interictal HFOs were recorded from hippocampal microelectrodes in 10 patients with MTLE. Rates of FR and ripple discharge from each microelectrode were evaluated in relation to local measures of HA obtained using 3-dimensional magnetic resonance imaging (MRI) hippocampal modeling.


RESULTS
Rates of FR discharge were 3 times higher in areas of significant local HA compared with rates in nonatrophic areas. Furthermore, FR occurrence correlated directly with the severity of damage in these local atrophic regions. In contrast, we found no difference in rates of ripple discharge between local atrophic and nonatrophic areas.


CONCLUSIONS
The proximity between local HA and microelectrode-recorded FR suggests that morphological changes such as neuron loss and synaptic reorganization may contribute to the generation of FR. Pathological HFOs, such as FR, may provide a reliable surrogate marker of abnormal neuronal excitability in hippocampal areas responsible for the generation of spontaneous seizures in patients with MTLE. Based on these data, it is possible that MRI-based measures of local HA could identify FR-generating regions, and thus provide a noninvasive means to localize epileptogenic regions in hippocampus.
Ogren
Jennifer A
JA
Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-7169, USA.
Wilson
Charles L
CL
Bragin
Anatol
A
Lin
Jack J
JJ
Salamon
Noriko
N
Dutton
Rebecca A
RA
Luders
Eileen
E
Fields
Tony A
TA
Fried
Itzhak
I
Toga
Arthur W
AW
Thompson
Paul M
PM
Engel
Jerome
J
Staba
Richard J
RJ
D000328:Adult; D001284:Atrophy / Q000473:pathology; D001931:Brain Mapping; D004569:Electroencephalography / Q000379:methods; D004833:Epilepsy, Temporal Lobe / Q000473:pathology* / Q000503:physiopathology; D005260:Female; D006624:Hippocampus / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D055815:Young Adult