Brain size

Magnetic resonance imaging (MRI) or computed tomography (CT) is used to measure changes in brain size and volume and rule out stroke, brain tumor, or a cerebral edema. 

Increased ventricular size, decreased brain size, and brain asymmetry have been reported. Lower hippocampal volume may correspond to impairment in neuropsychological testing and poorer response to first-generation antipsychotics (PGAs). 

Bartley, A.J., Jones, D.W., and Weinberger, D.R. (1997) Genetic variability of human brain size and cortical gyral patterns. Brain... 

Hazlett HC, Poe M, Gerig G, Smith RG, Provenzale J, Ross A, Gilmore J, Piven J (2005) Magnetic resonance imaging and head circumference study of brain size in autism birth through age 2 years. Arch Gen Psychiatry 62 1366-1376. 

Many chemicals cause a decrease in brain size during fetal development. Changes in brain size can be caused in various ways. A decreased brain weight may be a consequence of general undernutrition caused by effects on placental functioning. Examples of other possible mechanisms are inhibition of cell multiplication or cell growth, increased cell death, disrupted trophic effects induced by changes in cell maturation and neurochemistry. 

I.S. Zagon and P.J. McLaughlin, Increased brain size and cellular content in infant rats treated with an opiate antagonist, Science, 221 (1983) 1179-1180. 

Wahlsten, D., Bachmanov, A., Finn, D. A. and Crabbe, J. C. (2006) Stability of inbred mouse strain differences in behavior and brain size between laboratories and across decades. Proc Natl Acad Sci USA 103, 16364-16369. 

The theory boldly suggests that the tripling of human brain size from Homo hablis was facilitated by mutagenic, psychoactive plants that functioned as a chemical missing link. While this proposal certainly does not represent a mainstream scientific view, it illustrates, nevertheless, the impact that plants, particularly psychoactive ones, continue to have in our attempts to define ourselves. 

Dorph-Petersen, K.-A., Pierri, J., Perel, J., Sun, Z., Sampson, A., Lewis, D. (2005). The influence of chronic exposure to antipsychotic medications on brain size before and after tissue fixation A comparison of haloperidol and olanzapine in macaque monkeys. Neuropsychopharmacology, 30, 1649-1661. 

Spittaels K, Van den Haute C, Van Dorpe J, Terwel D, Vandezande K, Lasrado R, Bruynseels K, Irizarry M, Verhoye M, Van Lint J, Vandenheede JR, Ashton D, Mercken M, Loos R, Hyman B, Van der Linden A, Geerts H, Van Leuven F (2002) Neonatal neuronal overexpression of glycogen synthase kinase-3 beta reduces brain size in transgenic mice. Neuroscience 113 797-808... 

Ponting CP (2006) A novel domain suggests a cihary function for ASPM, a brain size determining gene. Bioinformatics 22 1031-1035... 

General allometric correlations such as these can obscure some interesting and important interspecies differences. Brain size in humans and nonhuman pri-mateS/ for example is considerably larger than would be expected from other mammals. Some implications of this have been discussed with reference to regional drug delivery to the brain (2). 

The second assumption is that intelligence has been subject to strong selection. On the face of it, it would seem obvious that this must have been the case. In support, Pinker (1997) pointed to the tripling in brain size during the time period between some 4 million years ago and some 100 000 years ago, and to the... 

Head size as a correlated proxy for brain size (0.65). 

Humphrey I want to come back to the question of correlation and causation. It s tempting of course to assume that a relation between two variables is causal when we can see how it would work, but to assume it s a mere correlation when we can t see it. So, when we find that IQ correlates with brain size or head size, we think that s probably because large brains do indeed cause high IQ. But when we find IQ... 

Humphrey This has evolutionary implications. It suggests that our Homo erectus ancestors, who had brains of about 750-800 cm3, may well have had the capacity for an IQ or g equivalent to that of modern humans. We should perhaps therefore be thinking of explanations of the doubling of brain size since then, other than that it was just needed to increase general cognitive abilities. 

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