Editing Neuroscience and intelligence (section)

===Grey matter===

[[Grey matter]] has been examined as a potential biological foundation for differences in intelligence. Similarly to brain volume, global grey matter volume is positively associated with intelligence.<ref name=Luders2009 /> More specifically, higher intelligence has been associated with larger cortical grey matter in the prefrontal and posterior temporal cortex in adults.<ref name=Narr2007 /> Furthermore, both verbal and nonverbal intelligence have been shown to be positively correlated with grey matter volume across the parietal, temporal and occipital lobes in young healthy adults, implying that intelligence is associated with a wide variety of structures within the brain.<ref name="Colom2006">{{cite journal | last1 = Colom | first1 = R. | last2 = Jung | first2 = R. E. | last3 = Haier | first3 = R. J. | year = 2006 | title = Distributed brain sites for the g-factor of intelligence | journal = NeuroImage | volume = 31 | issue = 3| pages = 1359–1365 | doi=10.1016/j.neuroimage.2006.01.006 | pmid=16513370| s2cid = 33222604 }}</ref>

There appear to be [[Sex differences in psychology|sex differences]] between the relationship of grey matter to intelligence between men and women.<ref name="Haier2005">{{cite journal | last1 = Haier | first1 = R. J. | last2 = Jung | first2 = R. E. | last3 = Yeo | first3 = R. A. | last4 = Head | first4 = K. | last5 = Alkire | first5 = M. T. | year = 2005 | title = The neuroanatomy of general intelligence: sex matters | journal = NeuroImage | volume = 25 | issue = 1| pages = 320–327 | doi=10.1016/j.neuroimage.2004.11.019 | pmid=15734366| s2cid = 4127512 }}</ref> Men appear to show more intelligence to grey matter correlations in the frontal and parietal lobes, while the strongest correlations between intelligence and grey matter in women can be found in the frontal lobes and [[Broca's area]].<ref name=Haier2005 /> However, these differences do not seem to impact overall Intelligence, implying that the same cognitive ability levels can be attained in different ways.<ref name=Haier2005 />

One specific methodology used to study grey matter correlates of intelligence in areas of the brain is known as [[voxel-based morphometry]] (VBM). VBM allows researchers to specify areas of interest with great spatial resolution, allowing the examination of grey matter areas correlated with intelligence with greater special resolution. VBM has been used to correlate grey matter positively with intelligence in the frontal, temporal, parietal, and occipital lobes in healthy adults.<ref name="Haier2004">{{cite journal | last1 = Haier | first1 = R. J. | last2 = Jung | first2 = R. E. | last3 = Yeo | first3 = R. A. | last4 = Head | first4 = K. | last5 = Alkire | first5 = M. T. | year = 2004 | title = Structural brain variation and general intelligence | journal = NeuroImage | volume = 23 | issue = 1| pages = 425–433 | doi=10.1016/j.neuroimage.2004.04.025 | pmid=15325390| s2cid = 29426973 }}</ref> VBM has also been used to show that grey matter volume in the medial region of the prefrontal cortex and the dorsomedial prefrontal cortex correlate positively with intelligence in a group of 55 healthy adults.<ref name="Gong2005">{{cite journal | last1 = Gong | first1 = Q. Y. | last2 = Sluming | first2 = V. | last3 = Mayes | first3 = A. | last4 = Keller | first4 = S. | last5 = Barrick | first5 = T. | last6 = Cezayirli | first6 = E. | last7 = Roberts | first7 = N. | year = 2005 | title = Voxel-based morphometry and stereology provide convergent evidence of the importance of medial prefrontal cortex for fluid intelligence in healthy adults | journal = NeuroImage | volume = 25 | issue = 4| pages = 1175–1186 | doi=10.1016/j.neuroimage.2004.12.044 | pmid=15850735| s2cid = 6986485 }}</ref> VBM has also been successfully used to establish a positive correlation between grey matter volumes in the anterior cingulate and intelligence in children aged 5 to 18 years old.<ref name="Wilke2003">{{cite journal | last1 = Wilke | first1 = M. | last2 = Sohn | first2 = J. H. | last3 = Byars | first3 = A. W. | last4 = Holland | first4 = S. K. | year = 2003 | title = Bright spots: correlations of gray matter volume with IQ in a normal pediatric population | journal = NeuroImage | volume = 20 | issue = 1| pages = 202–215 | doi=10.1016/s1053-8119(03)00199-x| pmid = 14527581 | s2cid = 14583968 }}</ref>

Grey matter has also been shown to positively correlate with intelligence in children.<ref name=Wilke2003 /><ref name="Frangou2006">{{cite journal | last1 = Frangou | first1 = S. | last2 = Chitins | first2 = X. | last3 = Williams | first3 = S. C. | year = 2004 | title = Mapping IQ and gray matter density in healthy young people | journal = NeuroImage | volume = 23 | issue = 3| pages = 800–805 | doi=10.1016/j.neuroimage.2004.05.027| pmid = 15528081 | s2cid = 16808023 }}</ref><ref name="Reis2006">{{cite journal | last1 = Reiss | first1 = A. L. | last2 = Abrams | first2 = M. T. | last3 = Singer | first3 = H. S. | last4 = Ross | first4 = J. L. | last5 = Denckla | first5 = M. B. | year = 1996 | title = Brain development, gender and IQ in children A volumetric imaging study | journal = Brain | volume = 119 | issue = 5| pages = 1763–1774 | doi=10.1093/brain/119.5.1763| pmid = 8931596 | doi-access = free }}</ref> Reis and colleagues<ref name=Reis2006 /> have found that grey matter in the prefrontal cortex contributes most robustly to variance in Intelligence in children between 5 and 17, while subcortical grey matter is related to intelligence to a lesser extent. Frangou and colleagues<ref name=Frangou2006 /> examined the relationship between grey matter and intelligence in children and young adults aged between 12 and 21, and found that grey matter in the [[orbitofrontal cortex]], cingulate gyrus, cerebellum and thalamus was positively correlated to intelligence, while grey matter in the [[caudate nucleus]] is negatively correlated with intelligence. However, the relationship between grey matter volume and intelligence only develops over time, as no significant positive relationship can be found between grey matter volume and intelligence in children under 11.<ref name=Wilke2003 />

An underlying caveat to research into the relationship of grey matter volume and intelligence is demonstrated by the hypothesis of [[#Neural efficiency|neural efficiency]].<ref name="Haier1988"/><ref name="Haier1992">{{cite journal | last1 = Haier | first1 = R. J. | last2 = Siegel | first2 = B. | last3 = Tang | first3 = C. | last4 = Abel | first4 = L. | last5 = Buchsbaum | first5 = M. S. | year = 1992 | title = Intelligence and changes in regional cerebral glucose metabolic rate following learning | journal = Intelligence | volume = 16 | issue = 3| pages = 415–426 | doi=10.1016/0160-2896(92)90018-m}}</ref> The findings that more intelligent individuals are more efficient at using their neurons might indicate that the correlation of grey matter to intelligence reflects selective elimination of unused synapses, and thus a better brain circuitry.<ref name="Shaw2006">{{cite journal | last1 = Shaw | first1 = P. | last2 = Greenstein | first2 = D. | last3 = Lerch | first3 = J. | last4 = Clasen | first4 = L. | last5 = Lenroot | first5 = R. | last6 = Gogtay | first6 = N. | last7 = Giedd | first7 = J. | year = 2006 | title = Intellectual ability and cortical development in children and adolescents | url = https://zenodo.org/record/1233291| journal = Nature | volume = 440 | issue = 7084| pages = 676–679 | doi=10.1038/nature04513 | pmid=16572172| bibcode = 2006Natur.440..676S | s2cid = 3079565 }}</ref>