title: Congenital foot deformation alters the topographic organization in the primate somatosensory system.
abstract: Limbs may fail to grow properly during fetal development, but the extent to which such growth alters the nervous system has not been extensively explored. Here we describe the organization of the somatosensory system in a 6-year-old monkey (Macaca radiata) born with a deformed left foot in comparison to the results from a normal monkey (Macaca fascicularis). Toes 1, 3, and 5 were missing, but the proximal parts of toes 2 and 4 were present. We used anatomical tracers to characterize the patterns of peripheral input to the spinal cord and brainstem, as well as between thalamus and cortex. We also determined the somatotopic organization of primary somatosensory area 3b of both hemispheres using multiunit electrophysiological recording. Tracers were subcutaneously injected into matching locations of each foot to reveal their representations within the lumbar spinal cord, and the gracile nucleus (GrN) of the brainstem. Tracers injected into the representations of the toes and plantar pads of cortical area 3b labeled neurons in the ventroposterior lateral nucleus (VPL) of the thalamus. Contrary to the orderly arrangement of the foot representation throughout the lemniscal pathway in the normal monkey, the plantar representation of the deformed foot was significantly expanded and intruded into the expected representations of toes in the spinal cord, GrN, VPL, and area 3b. We also observed abnormal representation of the intact foot in the ipsilateral spinal cord and contralateral area 3b. Thus, congenital malformation influences the somatotopic representation of the deformed as well as the intact foot.
authors.affiliation: 301 Wilson Hall, Department of Psychology, Vanderbilt University, 111 21st Avenue South, Nashville, TN, 37212, USA. chia-chi.liao@vanderbilt.edu.
authors.forename: Chia-Chi
authors.initials: CC
authors.lastname: Liao
authors.affiliation: 301 Wilson Hall, Department of Psychology, Vanderbilt University, 111 21st Avenue South, Nashville, TN, 37212, USA.
authors.forename: Hui-Xin
authors.initials: HX
authors.lastname: Qi
authors.affiliation: 301 Wilson Hall, Department of Psychology, Vanderbilt University, 111 21st Avenue South, Nashville, TN, 37212, USA.
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Reed
authors.affiliation: 301 Wilson Hall, Department of Psychology, Vanderbilt University, 111 21st Avenue South, Nashville, TN, 37212, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Miller
authors.affiliation: 301 Wilson Hall, Department of Psychology, Vanderbilt University, 111 21st Avenue South, Nashville, TN, 37212, USA.
authors.forename: Jon H
authors.initials: JH
authors.lastname: Kaas
mesh_terms: D000200:Action Potentials; D000818:Animals; D001931:Brain Mapping / Q000662:veterinary; D001933:Brain Stem / Q000503:physiopathology; D054022:Cerebrum / Q000503:physiopathology*; D004569:Electroencephalography / Q000662:veterinary; D005528:Foot / Q000294:innervation*; D005532:Foot Deformities, Congenital / Q000503:physiopathology / Q000662:veterinary*; D008252:Macaca fascicularis; D008255:Macaca radiata; D008992:Monkey Diseases / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology; D056347:Neuroanatomical Tract-Tracing Techniques / Q000662:veterinary; D009473:Neuronal Plasticity; D013003:Somatosensory Cortex / Q000503:physiopathology*; D013116:Spinal Cord / Q000503:physiopathology; D013788:Thalamus / Q000503:physiopathology
keywords: Congenital limb deficiency; Macaque; Plasticity; Reorganization; Somatotopy