Direct comparison of corticospinal volleys in human subjects to transcranial magnetic and electrical stimulation.

Abstract

SUMMARY1. The effects of graded transcranial magnetic and anodal electrical stimulation of the human motor cortex were compared in human subjects undergoing orthopaedic operations on the spine, before and after withdrawal of volatile anaesthesia.Corticospinal volleys were recorded from the spinal cord in the low-cervical and lowthoracic regions (six subjects) or the mid-thoracic region (two subjects) using bipolar electrodes inserted into the epidural space.2. Electrical stimuli were delivered using anode at the vertex and cathode 7 cm laterally. The corticospinal volley at threshold consisted of a single deflection with a mean latency to peak of 4*17 ms at the rostral recording site. With further increases in stimulus strength the latency of this D wave shortened in two steps, first by 0-89 ms (seven subjects) and then by a further 0-8 ms (two subjects), indicating that the site of activation of some corticospinal neurones had shifted to deep subcortical sites.3. When volatile anaesthetics were given, a corticospinal volley could not be defined in three subjects with magnetic stimuli of 70, 80 and 100% maximal stimulator output with the coil at the vertex (Novametrix Magstim 200, round coil, external diameter 14 cm). In the remaining five subjects, the component of lowest threshold was a D wave recorded at the rostral site at 4 0 ms when stimulus intensity was, on average, 70 %. With stimuli of 90-100 % a total of five small I waves could be defined in the five subjects (i.e. on average one I wave per subject).4. After cessation of volatile anaesthetics in seven subjects, the thresholds for D and I waves were lower and their amplitudes were greater. The D wave remained the component of lowest threshold in all subjects, appearing at the low-cervical level with magnetic stimuli of 50 %. However, in three subjects I waves also appeared at D wave threshold, and the D wave was smaller than with electrical stimulation at I wave threshold. There was no consistent change in latency of the magnetic D wave as stimulus intensity was increased to 100 %.5. These findings suggest that the previously reported difference in latency of the

Assessment of corticospinal excitability after traumatic spinal cord injury using MEP recruitment curves: a preliminary TMS study

“…3,31 As TMS activates cells with monosynaptic and polysynaptic connections with spinal motoneurons, MEP amplitude is sensitive to the excitability state of segmental neural circuits. [32][33][34][35] By contrast, RMT provides information about a central core of neurons in the muscle representation in the motor cortex and is likely to reflect both neuronal membrane excitability, as well as non-N-methyl-D-aspartate receptor-mediated glutamatergic neurotransmission. 29 Therefore, the electrophysiological pattern (altered MEP recruitment curve and normal RMT) that we found in SCI patients seems to be due to an enhanced spinal excitability rather than to an increased cortical excitability.…”

Chronic resistance training enhances the spinal excitability of the biceps brachii in the non-dominant arm at moderate contraction intensities

“…TMS uses magnetic impulses that are applied at the motor cortex, to produce multiple descending volleys. These volleys can be recorded over the spinal cord with epidural electrodes (Burke et al, 1993). The direction of the current from the coil is selected to preferentially activate the left or right side of the body .…”

Direct Corticospinal Control of Force Derivative

“…These may fire repeatedly in response to a single TMS pulse. The indirect excitation of cortical output neurons is favored at low stimulation intensities (Day et al, 1989b;Burke et al, 1993;Berardelli et al, 1994;Fujiki et al, 1996;Rothwell, 1997), which may hypothetically enhance the ability of this technique to reproduce physiological processing (Cros et al, 2007). Increased cortical excitability during voluntary static contractions is evidenced as an increased size of descending corticospinal volleys compared to rest (Di Lazzaro et al, 1998).…”