Editing Neuroscience and intelligence (section)

===White matter===

Similar to grey matter, [[white matter]] has been shown to correlate positively with intelligence in humans.<ref name=Luders2009 /><ref name=Gur1999 /> White matter consists mainly of myelinated neuronal axons, responsible for delivering signals between neurons. The pinkish-white color of white matter is actually a result of these myelin sheaths that electrically insulate neurons that are transmitting signals to other neurons. White matter connects different regions of grey matter in the cerebrum together. These interconnections make transport more seamless and allow us to perform tasks easier. Significant correlations between intelligence and the [[corpus callosum]] have been found, as larger callosal areas have been positively correlated with cognitive performance.<ref name=Luders2009 /> However, there appear to be differences in importance for white matter between verbal and nonverbal intelligence, as although both verbal and nonverbal measures of intelligence correlate positively with the size of the corpus callosum, the correlation for intelligence and corpus callosum size was larger (.47) for nonverbal measures than that for verbal measures (.18).<ref name="Fletcher1992">{{cite journal | last1 = Fletcher | first1 = J. M. | last2 = Bohan | first2 = T. P. | last3 = Brandt | first3 = M. E. | last4 = Brookshire | first4 = B. L. | last5 = Beaver | first5 = S. R. | last6 = Francis | first6 = D. J. | last7 = Miner | first7 = M. E. | year = 1992 | title = Cerebral white matter and cognition in hydrocephalic children | journal = Archives of Neurology | volume = 49 | issue = 8| pages = 818–824 | doi=10.1001/archneur.1992.00530320042010| pmid = 1524514 }}</ref> Anatomical mesh-based geometrical modelling<ref name="Thompson1996a">{{cite journal | last1 = Thompson | first1 = P. M. | last2 = Schwartz | first2 = C. | last3 = Lin | first3 = R. T. | last4 = Khan | first4 = A. A. | last5 = Toga | first5 = A. W. | year = 1996 | title = Three-dimensional statistical analysis of sulcal variability in the human brain | journal = The Journal of Neuroscience | volume = 16 | issue = 13| pages = 4261–4274 | doi = 10.1523/JNEUROSCI.16-13-04261.1996 | pmid = 8753887 | pmc = 6578992 | doi-access = free }}</ref><ref name="Thompson1996b">{{cite journal | last1 = Thompson | first1 = P. M. | last2 = Schwartz | first2 = C. | last3 = Toga | first3 = A. W. | year = 1996 | title = High-resolution random mesh algorithms for creating a probabilistic 3D surface atlas of the human brain | journal = NeuroImage | volume = 3 | issue = 1| pages = 19–34 | doi=10.1006/nimg.1996.0003 | pmid=9345472| s2cid = 15940105 }}</ref><ref name="Thompson1997">{{cite journal | last1 = Thompson | first1 = P. M. | last2 = MacDonald | first2 = D. | last3 = Mega | first3 = M. S. | last4 = Holmes | first4 = C. J. | last5 = Evans | first5 = A. C. | last6 = Toga | first6 = A. W. | year = 1997 | title = Detection and mapping of abnormal brain structure with a probabilistic atlas of cortical surfaces | journal = Journal of Computer Assisted Tomography | volume = 21 | issue = 4| pages = 567–581 | doi=10.1097/00004728-199707000-00008| pmid = 9216760 }}</ref> has also shown positive correlations between the thickness of the corpus callosum and Intelligence in healthy adults.<ref name="Luders2007">{{cite journal | last1 = Luders | first1 = E. | last2 = Narr | first2 = K. L. | last3 = Bilder | first3 = R. M. | last4 = Thompson | first4 = P. M. | last5 = Szeszko | first5 = P. R. | last6 = Hamilton | first6 = L. | last7 = Toga | first7 = A. W. | year = 2007 | title = Positive correlations between corpus callosum thickness and intelligence | journal = NeuroImage | volume = 37 | issue = 4| pages = 1457–1464 | doi=10.1016/j.neuroimage.2007.06.028| pmid = 17689267 | pmc = 2754582 }}</ref>

White matter integrity has also been found to be related to intelligence.<ref name=Penke2012 /> White matter tract integrity is important for information processing speed, and therefore reduced white matter integrity is related to lower intelligence.<ref name=Penke2012 /> The effect of white matter integrity is mediate entirely through information processing speed.<ref name=Penke2012 /> These findings indicate that the brain is structurally interconnected and that axonal fibres are integrally important for fast information process, and thus general intelligence.<ref name=Penke2012 />

Contradicting the findings described above, VBM failed to find a relationship between the corpus callosum and intelligence in healthy adults.<ref name=Haier2004 /> This contradiction can be viewed to signify that the relationship between white matter volume and intelligence is not as robust as that of grey matter and intelligence.<ref name=Luders2009 />