title: A probabilistic map of the human ventral sensorimotor cortex using electrical stimulation.
abstract: OBJECTIVE
  The human ventral sensorimotor cortex (vSMC) is involved in facial expression, mastication, and swallowing, as well as the dynamic and highly coordinated movements of human speech production. However, vSMC organization remains poorly understood, and previously published population-driven maps of its somatotopy do not accurately reflect the variability across individuals in a quantitative, probabilistic fashion. The goal of this study was to describe the responses to electrical stimulation of the vSMC, generate probabilistic maps of function in the vSMC, and quantify the variability across individuals.
  
  
  METHODS
  Photographic, video, and stereotactic MRI data of intraoperative electrical stimulation of the vSMC were collected for 33 patients undergoing awake craniotomy. Stimulation sites were converted to a 2D coordinate system based on anatomical landmarks. Motor, sensory, and speech stimulation responses were reviewed and classified. Probabilistic maps of stimulation responses were generated, and spatial variance was quantified.
  
  
  RESULTS
  In 33 patients, the authors identified 194 motor, 212 sensory, 61 speech-arrest, and 27 mixed responses. Responses were complex, stereotyped, and mostly nonphysiological movements, involving hand, orofacial, and laryngeal musculature. Within individuals, the presence of oral movement representations varied; however, the dorsal-ventral order was always preserved. The most robust motor responses were jaw (probability 0.85), tongue (0.64), lips (0.58), and throat (0.52). Vocalizations were seen in 6 patients (0.18), more dorsally near lip and dorsal throat areas. Sensory responses were spatially dispersed; however, patients' subjective reports were highly precise in localization within the mouth. The most robust responses included tongue (0.82) and lips (0.42). The probability of speech arrest was 0.85, highest 15-20 mm anterior to the central sulcus and just dorsal to the sylvian fissure, in the anterior precentral gyrus or pars opercularis.
  
  
  CONCLUSIONS
  The authors report probabilistic maps of function in the human vSMC based on intraoperative cortical electrical stimulation. These results define the expected range of mapping outcomes in the vSMC of a single individual and shed light on the functional organization of the vSMC supporting speech motor control and nonspeech functions.
authors.affiliation: Departments of 1 Neurological Surgery.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Breshears
authors.affiliation: Departments of 1 Neurological Surgery.|Epidemiology and Biostatistics, and.
authors.forename: Annette M
authors.initials: AM
authors.lastname: Molinaro
authors.affiliation: Departments of 1 Neurological Surgery.|Physiology, and.|Center for Integrative Neuroscience, University of California, San Francisco; and.|Center for Neural Engineering and Prostheses, University of California, Berkeley and San Francisco, California.
authors.forename: Edward F
authors.initials: EF
authors.lastname: Chang
mesh_terms: D000328:Adult; D000368:Aged; D001927:Brain Diseases / Q000503:physiopathology / Q000601:surgery*; D001931:Brain Mapping / Q000379:methods*; D003399:Craniotomy; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D066191:Sensorimotor Cortex / Q000502:physiology*; D055815:Young Adult
keywords: AIC = Akaike information criterion; AP = anterior-posterior; CN = cranial nerve; CS = central sulcus; DV = dorsal-ventral; ECS = electrocortical stimulation; ECoG = electrocorticography; MNI = Montreal Neurological Institute; SF = sylvian fissure; SMC = sensorimotor cortex; brain mapping; corticobulbar; dSMC = dorsal SMC; diagnostic and operative techniques; fMRI = functional MRI; probabilistic maps; sensorimotor cortex; vSMC = ventral SMC