Detection of abnormal cerebral excitability by coincident stimulation and recording.
OBJECTIVE
A method for mapping brain excitability and detecting abnormalities, by concurrently stimulating and recording 'focal' compound responses through one microelectrode, was evaluated in three rat epilepsy models in comparison with distal stimulation of perforant path afferents.


METHODS
A fixed trajectory from neocortex to dentate gyrus was mapped under halothane anesthesia. Several weeks earlier, tetanus toxin or vehicle was microinjected into the dentate polymorphic layer, or else rats were genetically epilepsy-prone (GEPR-9) or epilepsy-resistant (GERR-0). Other (unmapped) rats received acute penicillin microinjections within the dentate granular layer.


RESULTS
Focal responses, although widespread, proved largest in the dentate (>+/-0.5 mV). Tetanus toxin diminished focal responses near the microinjection site versus vehicle-microinjected (66%) or contralateral controls (55%), but enhanced them elsewhere in the dentate. It enhanced distal responses at all hippocampal locations. Focal but not distal responses were higher in GEPR-9 than in GERR-0 rats at widespread forebrain locations (mean 233%). Penicillin facilitated both focal and distal dentate responses, but the focal facilitation peaked sooner (about 75 versus 180 min).


CONCLUSIONS
Focal responses better uncover pervasive or discrete excitability differences.


CONCLUSIONS
Focal mapping may aid in diagnostic imaging and intraoperative targeting, offering high resolution, rapid performance, low stimulus currents and minimal invasion.
Hentall
Ian D
ID
University of Illinois College of Medicine at Rockford 1601 Parkview Avenue Rockford, IL 61107-1897, USA. ianh@uic.edu
D000818:Animals; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D018891:Dentate Gyrus / Q000503:physiopathology; D004558:Electric Stimulation; D004827:Epilepsy / Q000139:chemically induced / Q000235:genetics / Q000503:physiopathology*; D020022:Genetic Predisposition to Disease; D006624:Hippocampus / Q000503:physiopathology; D007113:Immunity, Innate / Q000235:genetics; D008297:Male; D008845:Microinjections; D010406:Penicillins / Q000008:administration & dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D013744:Tetanus Toxin / Q000008:administration & dosage
D010406:Penicillins; D013744:Tetanus Toxin