Vahe E. Amassian

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Magnetic coil (MC) stimulation percutaneously of human occipital cortex was tested on perception of 3 briefly presented, randomly generated alphabetical characters. When the visual stimulus-MC pulse interval was less than 40-60 msec, or more than 120-140 msec, letters were correctly reported; at test intervals of 80-100 msec, a blur or nothing was seen.(More)
Pairs of threshold magnetic stimuli were applied over the motor cortex at interstimulus intervals of 1-6 ms, and EMG responses recorded from the relaxed or active first dorsal interosseous muscle of 7 normal subjects. In relaxed subjects, when the interval between the stimuli was around 1.0-1.5 ms, 2.5-3.0 ms or 4.5 ms or later, the size of the response to(More)
This contribution includes a selective review of previously published material, findings from some new experiments, and discussion of some relationships between animal and recent human data. The major questions are: What descends from the cerebral cortex after a brief surface stimulus? What explains the various components of the corticofugal discharge? What(More)
Human transcallosal responses (TCRs) were elicited by focal magnetic coil (MC) stimulation of homologous sites in contralateral frontal cortex and compared with those to focal anodic stimulation. With MC stimulation, the TCR consisted of an initially positive wave with an onset latency of 8.8-12.2 msec, a duration of 7-15 msec, and an amplitude which(More)
THE EFFECT of exciting motor cortical areas is usually studied by recording muscle contractions or observing limb movements. Such studies yield little information about the central excitatory events which ultimately funnel into the final common motor pathway. Adrian and Moruzzi (1) were the first to recognize the importance of recording activity in the(More)
Percutaneous stimulation of human motor cortex electrically (focal anode) and with magnetic coils (MCs) of various designs is compared. The theoretical prediction was confirmed that positioning the standard round MC laterally and orientating it more towards the vertical induces an electric field appropriate for directly exciting corticospinal neurons (cf.,(More)
Focal stimulation over human cerebellum with a figure 8 magnetic coil (MC) results in an evoked wave recorded from bipolar scalp electrodes on the interaural line and more anteriorly. In 3 subjects, the wave responses along the interaural line had latencies of 8.8-13.8 msec, lasted 17.4-29.0 msec and had a maximum amplitude of 14.4-26.8 microV. The(More)
The amplitudes of motor evoked potentials to transcranial magnetic stimulation from muscles immediately proximal to a temporarily anaesthetized (Bier's block) human forearm increase in minutes after the onset of anaesthesia and return to control values after the anaesthesia subsides. In order to determine the level at which the early modulation of human(More)
The effects of different orientations of a Cadwell round magnetic coil (MC) were compared with each other and with surface electrical stimulation of motor cortex in monkeys anesthetized with pentobarbital or urethane. Recordings were made from within the lateral corticospinal tract, either from axonal populations or with a microelectrode from individual(More)
The authors critically reviewed experiments in which transcranial magnetic stimulation (TMS) and repetitive TMS (rTMS) of the higher visual pathway were used. Topics include basic mechanisms of neural excitation by TMS and their relevance to the visual pathway (excitatory and inhibitory effects), TMS and rTMS of calcarine cortex (suppression, unmasking, and(More)