Effect of transcranial magnetic stimulation on single-unit activity in the cat primary visual cortex.
Transcranial magnetic stimulation (TMS) has become a well established procedure for testing and modulating the neuronal excitability of human brain areas, but relatively little is known about the cellular processes induced by this rather coarse stimulus. In a first attempt, we performed extracellular single-unit recordings in the primary visual cortex (area 17) of the anaesthetised and paralysed cat, with the stimulating magnetic field centred at the recording site (2 x 70 mm figure-of-eight coil). The effect of single biphasic TMS pulses, which induce a lateral-to-medial electric current within the occipital pole of the right hemisphere, was tested for spontaneous as well as visually evoked activity. For cat visual cortex we found that a single TMS pulse elicited distinct episodes of enhanced and suppressed activity: in general, a facilitation of activity was found during the first 500 ms, followed thereafter by a suppression of activity lasting up to a few seconds. Strong stimuli exceeding 50 % of maximal stimulator output could also lead to an early suppression of activity during the first 100-200 ms, followed by stronger (rebound) facilitation. Early suppression and facilitation of activity may be related to a more or less direct stimulation of inhibitory and excitatory interneurons, probably with different thresholds. The late, long-lasting suppression is more likely to be related to metabotropic or metabolic processes, or even vascular responses. The time course of facilitation/inhibition may provide clues regarding the action of repetitive TMS application.
Moliadze
Vera
V
Department of Neurophysiology, Ruhr-University Bochum, 44780 Bochum, Germany.
Zhao
Yongqiang
Y
Eysel
Ulf
U
Funke
Klaus
K
D000200:Action Potentials / Q000502:physiology*; D000758:Anesthesia; D000818:Animals; D002415:Cats; D003627:Data Interpretation, Statistical; D005074:Evoked Potentials, Visual / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology