Intelligence and the weight of evidence

The “weight of evidence” is a phrase included in the book The Neuroscience of Intelligence by Richard J. Haier (Cambridge University Press, 2017, New York).  In many areas of study including neuroscience research results may vary somewhat or even give opposite results. The concept of evidence-based medicine suggests we should trust the evidence but – which evidence if there is differing results? The National Clearinghouse Guidelines listed in a recent post were screened for quality of evidence – was there a preponderance of studies that had fairly similar results?

In the last post I mentioned that it was good news that the medical use of magnesium or Epsom salts was mentioned as early as the 17th century and written about in a medical journal in the early 1900’s – it suggests a preponderance of evidence – a “weight of evidence” regarding the medical benefit of magnesium.

In the introduction of the book The Neuroscience of Intelligence the author states that the information in the book is screened and included based on three laws that could be applied to most areas of scientific evidence – paraphrased:

  1. no story about medical evidence is simple;
  2. no one research study is adequate to prove a theory on its own;
  3. it generally takes many years to rule out conflicting and inconsistent research results and establish a weight of evidence. (p xiv, The Neuroscience of Intelligence,  Richard J. Haier)

The book is written for the non-neuroscientist who is interested in gaining an in depth overview of the advances made in the study of the intelligence and the brain for the purpose of general knowledge or for creating policies that are based on realistic expectations of human ability. There have been theories that have not been upheld when larger groups were involved. Intelligence can be affected positively or negatively by early childhood experiences and by better nutrition however  by later adolescence and adulthood years the differences are more affected by genetic potential whether parents were rich or poor, whether schools were average or above average. Many genes are involved however, affecting many pathways throughout the brain. Intelligence and creativity isn’t just located in the frontal area of the brain or in just the right hemisphere.

From a magnesium perspective an interesting point that stood out for me was on page 61. Genes that have been found to be involved in intelligence include several that encode glutamate receptors. Background information: Alzheimer’s disease tends to cause more damage in areas of the brain that have a greater number of glutamate receptors – and adequate magnesium is necessary to help protect brain cells from being overexcited by too much glutamate (an amino acid used in flavoring agents, a commonly known type is MSG, Mono sodium glutamate). Glutamate can open the receptors in the cell membranes while the presence of magnesium inside of the cell can keep them closed. NMDA receptors are discussed on pages 101-102 of the book Magnesium and the Central Nervous System and is mentioned 249 times in the book, (the ebook has a useful search feature). (2) 

Excess calcium being allowed to enter the cell can also overexcite cells to the point of cell death. Too much or too little activity of the NMDA receptors can cause problems with health or damage cells. Overexcitatory activity of the NMDA receptors has been associated with damage from ischemic stroke, traumatic brain injury, neonatal brain injury, and neurodegenerative conditions (which include Alzheimer’s Disease, p 104, (2)). Too much magnesium has been known to cause neonatal brain injury when given intravenously or intramuscularly for the expectant mother during preeclampsia/eclampsia to reduce seizures (3), or for other causes of preterm labor – some magnesium is protective for the fetal brain but too much can negatively affect fetal brain cells. (p103, Mg & the CNS, (2)) 

On page 61 of the book The Neuroscience of Intelligence (1)  genes involved with pathways that influence  glutamate binding with NMDA receptors are mentioned including KNCMA1, NRXN1, POU2F3, and SCRT. (1Both books mention that the NMDA receptors and glutamate as a neurotransmitter are involved with learning and memory. (p101, 2) 

A brief look at what might be known about those genes suggests differences in them may be associated with spasticity, (4), “epilepsy, ataxia, mental retardation, and chronic pain,” (7), alcohol abuse, (5), cervical cancer, (6), – a wide variety of conditions not just learning and memory. Take home point – magnesium is important for learning and memory and general health in an adequate amount, but not excessive amount if given intravenously or intramuscularly.

/Disclosure: This information is provided for educational purposes within the guidelines of fair use. While I am a Registered Dietitian this information is not intended to provide individual health guidance. Please see a health professional for individual health care purposes./ 

  1. Richard J. Haier, The Neuroscience of Intelligence, (Cambridge University Press, 2017, New York), (1)
  2. Robert Vink, Mihai Nechifor, editors, Magnesium in the Central Nervous System, University of Adelaide Press, 2011,, free ebook pdf,  (2) 
  3. Magnesium Sulfate for Seizure Prevention During Pregnancy, American College of Cardiology,, (3)
  4. Baker D., Big conductance calcium-activated potassium channel openers control spasticity without sedation., Queen Mary University of London, (4)
  5. Jill C. Bettinger, Andrew G. Davies, The role of the BK channel in ethanol response behaviors: evidence from model organism and human studies. Front. Physiol., 09 September 2014, (5)
  6. Z Zhang, PC Huettner, L Nguyen, M Bidder, MC Funk, J Li, JS Rader, Aberrant promoter methylation and silencing of the POU2F3 gene in cervical cancer, Oncogene vol 25, pp 5436–5445 (31 August 2006), (6)
  7. C. Contet, S. P. Goulding, D. A. Kuljis, and A. L. Barth, BK Channels in the Central Nervous System, Europe PMC Article,  Int Rev Neurobiol. 2016; 128: 281–342. (7)