RT Journal Article SR Electronic T1 Diameter, Length, Speed, and Conduction Delay of Callosal Axons in Macaque Monkeys and Humans: Comparing Data from Histology and Magnetic Resonance Imaging Diffusion Tractography JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 14501 OP 14511 DO 10.1523/JNEUROSCI.0761-13.2013 VO 33 IS 36 A1 Caminiti, Roberto A1 Carducci, Filippo A1 Piervincenzi, Claudia A1 Battaglia-Mayer, Alexandra A1 Confalone, Giuseppina A1 Visco-Comandini, Federica A1 Pantano, Patrizia A1 Innocenti, Giorgio M. YR 2013 UL http://www.jneurosci.org/content/33/36/14501.abstract AB Three macaque monkeys and 13 healthy human volunteers underwent diffusion tensor MRI with a 3 Tesla scanner for diffusion tract tracing (DTT) reconstruction of callosal bundles from different areas. In six macaque monkeys and three human subjects, the length of fiber tracts was obtained from histological data and combined with information on the distribution of axon diameter, so as to estimate callosal conduction delays from different areas. The results showed that in monkeys, the spectrum of tract lengths obtained with DTT closely matches that estimated from histological reconstruction of axons labeled with an anterogradely transported tracer. For each sector of the callosum, we obtained very similar conduction delays regardless of whether conduction distance was obtained from tractography or from histological analysis of labeled axons. This direct validation of DTT measurements by histological methods in monkeys was a prerequisite for the computation of the callosal conduction distances and delays in humans, which we had previously obtained by extrapolating the length of callosal axons from that of the monkey, proportionally to the brain volumes in the two species. For this analysis, we used the distribution of axon diameters from four different sectors of the corpus callosum. As in monkeys, in humans the shortest callosal conduction delays were those of motor, somatosensory, and premotor areas; the longer ones were those of temporal, parietal, and visual areas. These results provide the first histological validation of anatomical data about connection length in the primate brain based on DTT imaging.