TY - JOUR
T1 - Diversity of Cortico-descending Projections
T2 - Histological and Diffusion MRI Characterization in the Monkey
AU - Innocenti, Giorgio M.
AU - Caminiti, Roberto
AU - Rouiller, Eric M.
AU - Knott, Graham
AU - Dyrby, Tim B.
AU - Descoteaux, Maxime
AU - Thiran, Jean Philippe
PY - 2019/2/1
Y1 - 2019/2/1
N2 - The axonal composition of cortical projections originating in premotor, supplementary motor (SMA), primary motor (a4), somatosensory and parietal areas and descending towards the brain stem and spinal cord was characterized in the monkey with histological tract tracing, electron microscopy (EM) and diffusion MRI (dMRI). These 3 approaches provided complementary information. Histology provided accurate assessment of axonal diameters and size of synaptic boutons. dMRI revealed the topography of the projections (tractography), notably in the internal capsule. From measurements of axon diameters axonal conduction velocities were computed. Each area communicates with different diameter axons and this generates a hierarchy of conduction delays in this order: a4 (the shortest), SMA, premotor (F7), parietal, somatosensory, premotor F4 (the longest). We provide new interpretations for i) the well-known different anatomical and electrophysiological estimates of conduction velocity; ii) why conduction delays are probably an essential component of the cortical motor command; and iii) how histological and dMRI tractography can be integrated.
AB - The axonal composition of cortical projections originating in premotor, supplementary motor (SMA), primary motor (a4), somatosensory and parietal areas and descending towards the brain stem and spinal cord was characterized in the monkey with histological tract tracing, electron microscopy (EM) and diffusion MRI (dMRI). These 3 approaches provided complementary information. Histology provided accurate assessment of axonal diameters and size of synaptic boutons. dMRI revealed the topography of the projections (tractography), notably in the internal capsule. From measurements of axon diameters axonal conduction velocities were computed. Each area communicates with different diameter axons and this generates a hierarchy of conduction delays in this order: a4 (the shortest), SMA, premotor (F7), parietal, somatosensory, premotor F4 (the longest). We provide new interpretations for i) the well-known different anatomical and electrophysiological estimates of conduction velocity; ii) why conduction delays are probably an essential component of the cortical motor command; and iii) how histological and dMRI tractography can be integrated.
KW - Axon diameters
KW - Conduction velocity
KW - Corticofugal projections
KW - Diffusion tractography
KW - Histology
U2 - 10.1093/cercor/bhx363
DO - 10.1093/cercor/bhx363
M3 - Journal article
C2 - 29490005
AN - SCOPUS:85054013852
SN - 1047-3211
VL - 29
SP - 788
EP - 801
JO - Cerebral Cortex
JF - Cerebral Cortex
IS - 2
ER -