Fig 1.
Assessment of the effects of changing the recording site on ITV of CMAP area and latency.
Single maximal CMAPs recorded from Tibialis Anterior (TA), Peroneus Longus (PL) and Extensor Digitorum Brevis (EDB). Recording was repeated twice the following day a) using the same recording site (O) or b) randomly moving the cathode 1 cm medial (M), lateral (L), rostral (R) or caudal (C) to O, as shown in the figure for TA. Note the significant ITV reduction of CMAP area using the same recording site and the precise replication of the morphological features of individual CMAPs.
Fig 2.
Neurophysiological mapping of central and peripheral motor function in lower limbs.
CMAPs to root stimulation (r-CMAPs) using the dorsoventral montage (Fig 2A) were simultaneously recorded from proximal and distal muscles of both lower limbs (VM, Vastus Medialis; VL, Vastus Lateralis; TA, Tibialis Anterior; PL, Peroneus Longus; FHB, Flexor Hallucis Brevis) (Fig 2B). The optimal vertebral stimulation site was located by testing several sites over the dorso-lumbar junction of the spinal cord by means of a multielectrode (Fig 2A). MEPs to TMS using the double cone coil were recorded from the same sites. The correct position of the coil was reproduced by measuring the distance between nasion and the anterior edge of the coil (Fig 2C). Simultaneous and controlled voluntary activation of all muscle districts was obtained by asking the subject to perform a sequence of 3 movements of fixed amplitude and to maintain the reached position with the aid of a simple purpose-made device (Fig 2D: further explanation in the text).
Fig 3.
Marking of recording and stimulating sites.
In selected patients for whom a long-term neurophysiological follow-up was planned, all recording sites and the stimulation site on the vertebral column were tagged with a small, indelible skin mark.
Table 1.
Intertrial variability of CMAP latency and area as a function of the recording site.
Fig 4.
Subject n.25 (M.L., f, 32 ys). Rectified, single r-CMAPs bilaterally recorded from all sites during the first (upper trace) and second (lower trace) recording session. Latencies, Latency ITVs, Areas, raw and normalized Area ITVs are listed for each couple of responses. All normalization procedures were performed using custom made Excel® sheets. Note the stability of latencies and the faithful replication of individual morphological features of all responses. VM, vastus medialis; VL, vastus lateralis; TA, tibialis anterior; PL, peroneus longus; FHB, flexor hallucis brevis.
Fig 5.
Subject n.25 (M.L., f, 32 ys). Averaged and rectified activated MEPs bilaterally recorded from all sites during the first (upper trace) and second (lower trace) recording session. Latencies, Latency ITVs, Areas, raw and normalized Area ITVs are listed for each couple of responses. As for CMAPs, note the stability of latencies and the precise replication of the individual shape of all responses. Further details in legend of Fig 4. VM, vastus medialis; VL, vastus lateralis; TA, tibialis anterior; PL, peroneus longus; FHB, flexor hallucis brevis.
Fig 6.
Reproducibility of voluntary MEP activation in subsequent trials.
The degree of voluntary activation, expressed as the ratio between activated and basal MEP area, was similar in the two recording sessions in all tested muscles; in the different recording sites, the degree of facilitation showed a proximal-distal gradient, ranging from a maximum value of 7.3 (1st trial) and 8.6 (2nd trial) for VM to a minimum value of 2.2 (1st trial) and 1.9 (2nd trial) for FHB. VM, vastus medialis; VL, vastus lateralis; TA, tibialis anterior; PL, peroneus longus; FHB, flexor hallucis brevis.
Table 2.
Root-CMAP latencies, MEP latencies and CMCTs.
Fig 7.
Regression lines correlating area and ITV.
Regression lines correlating ITV and Area for r-CMAP (A), MEP (C) and a-Ratio (E). Note that responses of smaller area tend to have a greater ITV as expressed by the Coefficient of Variability. Normalization of raw ITV values (see S1 Appendix) resulted in a complete removal of the variability component inversely correlated to area, as shown in B, D and F for r-CMAP, MEP and a-Ratio respectively. Note that ITV correction, minimum for responses of large area, increases as a function of the decrease of area.
Table 3.
Root-CMAP areas, MEP areas and a-Ratios.