Functional Variability of the Human Cortical Motor Map: Electrical Stimulation Findings in Perirolandic Epilepsy Surgery

Abstract

The purpose of this study was to assess the cortical representation of sensorimotor functions in patients undergoing perirolandic epilepsy surgery, focusing on somatotopy, mosaicism, and variability of function in relation to the classic motor homunculus. The authors studied 36 patients in whom intraoperative or extraoperative electrical cortical stimulation to map motor functions was performed. A computer program was devised to register electrode number, stimulation parameters, and response to each stimulus. Electrode position was represented graphically whenever a stimulus was delivered. A total of 43 maps from 36 patients were analyzed. The authors found variations in the organization of M1 (primary motor cortex) in seven patients (19.4%). Four patients (11.1%) presented mosaicism (overlapping of functional areas), two (5.6%) presented variability (inverted disposition of M1 functional areas), and one (2.8%) had both. The results of this study challenge the notion of orderly topographic relationships between the human sensorimotor functions and their representation in the primary motor cortex. These results confirm those of other studies with animals and humans using novel imaging techniques, suggesting that the motor homunculus may not always be considered a definite and absolute representation of M1.

Neural representations of ethologically relevant hand/mouth synergies in the human precentral gyrus

“…Second, previous data in monkeys could be biased toward intraindividual variability (multiple replications in two animals), whereas our data in humans could be rather slanted toward interindividual variability (few replications in nine subjects). In agreement with this second hypothesis, it appears that interindividual variability of motor representations is large in the human PrG (9) and that the degree of clustering in monkey PrG A nonresponsive muscle is shown to illustrate the specificity of the evoked response (extensor digitorum communis, EDC). nc, latency could not be computed reliably; ns, not significant.…”

“…In agreement with this view, additional analyses presented in SI Text, Individual Factors show that none of the following factors could account for the presence/absence of integrated responses in our subjects: nature (neoplastic versus malformation), location (center of mass), absolute and relative volume of the brain injury, age of the patient, and spatial distribution of the stimulation sites. As shown in a now large number of peroperative studies, motor responses that are clearly present at the population level cannot be easily evidenced, in most cases, at the individual level (5,9,35,36). This was clearly emphasized by Penfield and Boldrey in their pioneering study (5).…”

“…With respect to this point, Penfield and other researchers have clearly reported complex multijoint motor responses following cortical stimulation (5)(6)(7)(8), including concurrent movements of the hand and mouth (9). Nevertheless, these movements were not investigated systematically in several subjects, described in detail, or related to the existence of integrated neural representations for ethologically relevant behaviors.…”

Spectral Changes in Cortical Surface Potentials during Motor Movement

“…Pfurtscheller et al (2003), using self-paced movement, reaffirmed the finding of spatially broad and ␤ ERD in ECoG, with more focused high gamma ERS. Loose somatotopy, unbound by rigid homuncular representation, was also reported in ECoG by Marsden et al (2000), Hoshida and Sakaki (2003), and Branco et al (2003).…”

“…S2, available at www.jneurosci.org as supplemental material). Electrical stimulation of the cortex to create transient lesions or to induce overt movements, extraoperatively or intraoperatively, is the established gold-standard method to functionally localize motor cortex in the human brain (Ojemann et al, 1989;Chitoku et al, 2001;Branco et al, 2003). The present method contrasts with the classical stimulation method for functional localization because the method detailed here measures natural cortical change in response to functional behavioral change.…”