Direct demonstration of long latency cortico-cortical inhibition in normal subjects and in a patient with vascular parkinsonism.
OBJECTIVE
The motor evoked potential to a single suprathreshold transcranial magnetic stimulus (TMS) is suppressed by a preceding stimulus given 100-200 ms before (long latency intracortical inhibition, LICI). The effect is enhanced in patients with Parkinson's disease. Although previous studies have agreed that the effect is cortical, there is disagreement over exactly which cortical mechanisms are involved. The aim of this study was to provide further evidence for cortical involvement in LICI.


METHODS
Recordings of corticospinal volleys evoked by the TMS stimulation were made from electrodes inserted into the cervical epidural space of 4 conscious subjects. Three of the patients had received the electrodes for treatment of lumbo-sacral pain; the other patient had vascular parkinsonism, and had the electrode implanted to evaluate its effect on cerebral blood flow. The number and amplitude of the volleys were compared with and without a conditioning stimulus.


RESULTS
In 3 pain patients, a conditioning stimulus suppressed the later components of the corticospinal volley (I2 and later waves) when the interval between stimuli was 100-150 ms; at 50 ms the responses were enhanced. Early components of the volley were not affected. Inhibition was much more pronounced and involved all descending volleys except the D wave in the patient with vascular parkinsonism.


CONCLUSIONS
LICI, which is conventionally described in EMG recordings, is also evident in recordings of descending corticospinal volleys and appears enhanced in a patient with vascular parkinsonism.
Di Lazzaro
V
V
Institute of Neurology, Università Cattolica, Largo A. Gemelli 8, 00168 Rome, Italy. vdilazzaro@rm.unicatt.it
Oliviero
A
A
Mazzone
P
P
Pilato
F
F
Saturno
E
E
Insola
A
A
Visocchi
M
M
Colosimo
C
C
Tonali
P A
PA
Rothwell
J C
JC
D001416:Back Pain / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology; D002561:Cerebrovascular Disorders / Q000473:pathology / Q000503:physiopathology*; D004567:Electrodes, Implanted; D004574:Electromagnetic Fields; D004824:Epidural Space; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000473:pathology / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology; D010300:Parkinson Disease / Q000473:pathology / Q000503:physiopathology*; D013116:Spinal Cord / Q000503:physiopathology; D004561:Transcutaneous Electric Nerve Stimulation