Facilitation of muscle evoked responses after repetitive cortical stimulation in man

Abstract

The technique of repetitive transcranial magnetic stimulation (rTMS) allows cortical motor areas to be activated by trains of magnetic stimuli at different frequencies and intensities. In this paper, we studied long-term neurophysiological effects of rTMS delivered to the motor cortex at 5 Hz with an intensity of 120% of motor threshold. Each stimulus of the train produced muscle-evoked potentials (MEPs) in hand and forearm muscles, which gradually increased in size from the first to the last shock. After the end of the train, the response to a single-test stimulus remained enhanced for 600-900 ms. In contrast, the train had no effect on the size of the MEPs evoked by transcranial electrical stimulation, while it suppressed H-reflexes in forearm muscles for 900 ms. We conclude that rTMS of these parameters increases the excitability of the motor cortex and that this effect outlasts the train for almost 1 s. At the spinal level, rTMS may increase presynaptic inhibition of Ia afferent fibers responsible for the H-reflex.

Transcranial magnetic stimulation: studying the brain--behaviour relationship by induction of ‘virtual lesions’

“…Indeed, in the blind subjects rTMS to the occipital cortex resulted in a greater disruption of tactile Braille reading than rTMS to the somatosensory cortex contralateral to the reading hand (¢gure 5). rTMS appears to be able to modulate the level of excitability of a given cortical area beyond the duration of the rTMS train itself (Chen et al 1997;Berardelli et al 1998;Pascual-Leone et al 1998). Remarkably, depending on the stimulation frequency and intensity, it seems possible to potentiate or depress cortical excitability (Pascual-Leone et al 1998).…”

Probing changes in corticospinal excitability following theta burst stimulation of the human primary motor cortex

“…Conventional rTMS approaches involve a constant rate of stimulation, with low frequencies (≤1 Hz) reducing cortical excitability (Chen et al, 1997) and high frequencies (≥5 Hz) increasing cortical excitability (Berardelli et al, 1998). More recently, however, patterned protocols such as theta burst stimulation (TBS) have been developed which require less stimulation time and lower stimulation intensities than conventional rTMS protocols.…”

The modulating effects of brain stimulation on emotion regulation and decision-making

“…rTMS increases or decreases excitability of the corticospinal tract according to the intensity of stimuli, the direction of the coil, and the frequency used [65,73]. High frequency (HF) (5-20 Hz) rTMS increases cortical response, which is identified by a reduced motor-evoked potential threshold [2,55]. Low frequency (LF) (≤1 Hz) rTMS inhibits the cortical response [11] (Fig.…”