The TEDx Users Guide to Dr Caroline Leaf

On the 4th of February 2015, Dr Caroline Leaf gave her debut TED presentation, at TEDx Oakes Christian School, California.

Most TED watchers wouldn’t have heard of her before, but Caroline Leaf is a well-known name in western Christendom. She has spoken from pulpits on every continent. She’s authored one of the best selling books in the Christian market and has her own TV show on cable in the US. She’s followed by more than one hundred thousand people on Facebook, and she’s even run her own conference, with another in the pipeline. She’s a mega-star in the Christian world.

So who is this woman with the stiletto-heels and slick presentation? What was her training and background? How did she make it to the TEDx stage?

This aim of this post is to provide some context and background for those in the TED universe who have seen Dr Leaf’s TEDx presentation, and want some more information in assessing her TEDx debut, and indeed, the global Caroline Leaf phenomenon.

This review will be in four main parts: first I will give some basic information on Dr Leaf, I will compare Dr Leaf’s claims in her TEDx presentation to her published research results and some basic neuroscience, and lastly I’ll outline Dr Leaf’s general work and it’s accuracy compared to current science.


Dr Caroline Leaf was born and raised in South Africa, where she completed her school education and went on to attain the following degrees:

  1. Bachelors of Science (Logopaedics) – University of Cape Town 1985
  2. Masters in Audiology and Speech Pathology – University of Pretoria 1990
  3. Doctor Philosophiae (Communication Pathology) – University of Pretoria 1997 (

Officially, Dr Leaf is qualified as a communication pathologist (which is a specialized combination of Speech Pathology and Audiology – see also:

Dr Leaf worked for a number of clinics and school boards as a communication pathologist in the few years following the completion of her PhD (

Dr Leaf has written a number of articles for publication in minor journals (see Three of her papers were published in a small Medline indexed journal, “The South African Journal of Communication Disorders”. These are:

  1. “Mind-Mapping approach (MMA): a culture and language “free” technique”, 1993 (
  2. “The development of a model for geodesic learning: the geodesic information processing model”, 1997 (
  3. “An alternative non-traditional approach to learning: the metacognitive-mapping approach”, 1998 (

The journal happened to be edited by her supervisor and co-author, Dr Brenda Louw (see, though I’m sure the selection of her articles for this journal was purely on merit.

Dr Leaf states on a number of occasions that she is a “cognitive neuroscientist”, and “a scientific and Biblical expert in the power of the human mind”.Leaf Cognitive NeuroscientistAbout Dr Leaf

This is despite the fact that Dr Leaf:

  1. does not have formal qualifications in neuroscience,
  2. has not worked at a university as a neuroscientist,
  3. has not worked in any neuroscience research labs,
  4. has not published any papers in neuroscience journals, and
  5. has not had any formal theological training.

Given the weight of evidence, Dr Leaf would be better described as an academic speech pathologist and lay preacher rather than a cognitive neuroscientist.


Throughout her TEDx presentation, Dr Leaf repeatedly made reference to the results of her own research, suggesting that her pioneering work resulted in radically improved outcomes for the students involved in her research, and that her work with students one-on-one and through teacher education profoundly changed the learning of every student in her various programs.

For example, she said, “Well her IQ was 100 before the accident, it was 120 after the accident. So here with holes in her brain, and brain damage, she changed … she actually increased her intelligence. Now I’m pretty convinced at this stage, cause I’ve been working … besides her I’ve been working with lots and lots of other patients, seeing the same thing, when these students applied their mind, their brain was changing, their academic results were changing.”

Later she stated, “I wasn’t sure if this was going to have the same impact cause until this point I’d been working one on one. Well I’m happy to tell you that we had the same kind of results … The minute that the teachers actually started applying the techniques, we altered the trend significantly.”

And also, “I stand up here saying this with conviction because I have seen this over and over and over in so many different circumstances … in this country I worked in Dallas for three years in charter schools, and we found the same thing happening.”

However, her published results differ significantly from her claims.

The first research that Dr Leaf spoke of was of the sixteen-year-old girl who was the victim of a motor vehicle accident. This particular girl was Dr Leaf’s prime patient. The case study of this patient was presented in Dr Leaf’s unpublished Masters thesis, and was discussed in more detail in Dr Leaf’s paper, “Mind-Mapping approach (MMA): a culture and language “free” technique” [1], though it should be noted that no statistics were published in this paper, and on the third page of the article, Dr Leaf admitted that the result could actually have been spontaneous recovery rather than her own intervention.

Dr Leaf did further work within a number of schools for her PhD research. Dr Leaf compared the academic results for three schools for the years 1991 and 1992 to the results for 1993, during which she introduced her mind mapping approach (MMA). Generally, the results for 1993 were better than the results for 1992, which seems to indicate that Dr Leaf’s MMA training was effective. However, the results from 1991 to 1992 were already improving without her input [2: p182]. The difference in average marks between 1991 and 1992 was 1.76%, while the difference between 1992 and 1993 (the introduction of Dr Leaf’s MMA) was only 2.19%. If Dr Leaf’s program really was the cause of that improvement, then her program only resulted in a 0.43% improvement on average.

I have reproduced Dr Leaf’s original graph of the average overall results obtained in her PhD study. While Dr Leaf’s original graph makes her data look spectacular, when appropriately rescaled, the data looks quite ordinary.

Leaf1997 Thesis overall academic trends


At best, Dr Leaf’s program gave the already positive momentum of the students a gentle nudge.

However, it should be noted that her program may have also hindered some students. Dr Leaf notes in her analysis: “The results obtained indicate that in general the academic trend in the three primary remedial schools was altered with the introduction of the MMA methods in 1993. Furthermore, it appears that the most positive response occurred in phase one (grades 1 and 2, standard 1). A positive response also occurred in phase two (standards 2-4) but this change was just outside the significance level. Phase three (standard 5), by contrast, experienced negative effects with the introduction of the MMA methods.” [2: p181]

So to summarise, according to Dr Leaf’s own data, there was no clear benefit derived from her MMA program.

Dr Leaf then discussed her work in a number of charter schools that she performed in Dallas. This was part of testing of a program called the Switch On Your Brain 5-step learning process.

Dr Leaf claims that, “The Switch On Your Brain with the 5-Step Learning Process® was assessed in a group of charter schools in the Dallas. The results showed that the students’ thinking, understanding and knowledge improved across the board. It was concluded that The Switch On Your Brain with the 5-Step Learning Process® positively changed the way the students and teachers thought and approached learning.”

However, there has been no independent research into Dr Leaf’s Switch On Your Brain learning program or even the Geodesic Information Processing Theory, the theory Dr Leaf devised and on which the Switch On Your Brain program is based.

Dr Leaf published her own internal research into the program on her website. The project was a two year program involving teachers and students at a group of four schools in the Advantage Academy group in Dallas, Texas. This involved working with more than 150 teachers and 2000 students.

Despite her glowing self-assessment, Dr Leaf’s own published numbers suggest that the program is ineffective, or quite possibly a hindrance. For example, the graph below demonstrates the qualitative analysis of “content mastery” (which the paper describes as a combination of knowledge and understanding) for reading across all grades from 3rd to 12th, compared with the results from the previous year before the Switch On Your Brain was implemented. Dr Leaf omits a basic statistical analysis, but just by looking at the similarity of the scores, these results are more likely to be a chance effect, except for the 12th grade, where the previous cohort of students increased dramatically, where as the Switch On Your Brain cohort got slightly worse.

Screen Shot 2015-02-02 at 11.27.37 pm

Rather than blame her program, Dr Leaf simply shifts the blame to the teachers: “The few cases where we see drops can be linked to teacher knowledge, attitude and skills and is diagnostic.”

The full research paper that Dr Leaf published is available at if you wish to review the results for yourself.

The ineffectiveness of Dr Leaf’s program may be for many reasons, but I believe one is that it is built on a theory that relies on mind-mapping. Dr Leaf renamed her version of mind-mapping “The Metacog”, though it’s clear from her early academic work [1] that the Metacog and the Geodesic Information Processing Model [3] were based on the work of Tony Buzan. Buzan’s concept of mind-mapping has been used across multiple professional fields [4] and remains a valuable resource for brainstorming or gathering thoughts in a visual way. However, modern research (including a controlled trial within a primary school classroom environment) shows that mind mapping is a poor tool for learning [5-8].


Dr Leaf openly contradicts herself throughout her presentation, failing to realise that the stories she shared of her own patients disproved her vacuous inspirational memes.

Our biology affects each and every one of us. Our mind is a function of our brain. Our mind is to our brain as our breath is to our lungs. Put simply, without our brain, we would have no thoughts. If the structure and function of specific networks in our brains are altered, this changes our thinking. This is confirmed in everyday life – when someone suffers a brain injury or a stroke and they sustain damage to their brain, they suddenly lose the function of some, or all of their mind or body. Trans-cranial Magnetic Stimulation, Trans-cranial Direct Current Stimulation, metabolic states, prescription medications, illicit drugs, or everyday drugs like caffeine or alcohol have all been proven to change the subjects mental state through changes to the function of their brain. Any suggestion that our brain does not control our mind is simply ludicrous.

Clearly then our biology does control our psychology. Real cognitive neuroscientists have shown that our stream of thought is simply a tiny fraction of our overall neural activity, a conscious glimpse of the brains overall function [9-11], like the tachometer is for the engine in your car. Thus, our mind does not change our brain at all. Rather, it is our brain’s directed activity causing the growth of new synaptic branches to support it, something which the brain does without the function of conscious thought from the time when we were embryos.

Dr Leaf actually confirms this fact through her stories of her brain injured patients. After all, if “the mind is separate from the brain but influencing the brain”, then how could those victims of acquired brain injury lose cognitive function after their injury? If it were true that “each and every one of us is not a victim of our biology. We are a victor over and above our biology. We control our brain, our brain does not control us”, then how could those people with damage to their brains from strokes suddenly lose function?

The fact that Dr Leaf’s patients lost their mental or cognitive function because of damage to their brains directly contradicts her insistence that our brain and our mind are separate, and that our brain does not control our mind.


Considered altogether, Dr Leaf’s teaching boils down to a few fundamentals;
* Thought is the main driving force that controls every other aspect of our lives (and our physical world).
* We have full control over our thoughts.
* Thought causes stress.
* Stress is directly responsible for nearly all serious physical and mental illness.
* Therefore thought causes the vast majority of human disease, making thoughts toxic, and
* If toxic thoughts cause disease, “detoxing” thoughts will cure or prevent disease.

On first inspection, each individual postulate doesn’t seem so bad. However, when fully considered and taken to their natural conclusions, they veer into conjecture and pseudoscience, as evidenced by Dr Leaf’s published works and public appearances.

For example, Dr Leaf states in her books:

“Thoughts influence every decision, word, action and physical reaction we make.” [12: p13]
“Our mind is designed to control the body, of which the brain is a part, not the other way around. Matter does not control us; we control matter through our thinking and choosing.” [13: p33]
“DNA actually changes shape according to our thoughts.” [13: p35]

On Facebook and in interviews, this translates to:

“Our genetic makeup fluctuates by the minute based on what we are thinking and choosing.” 27/9/2014
“The toxic thoughts in our minds become physical baggage in our brain, which literally cause brain damage.” 5/12/2014, 27/10/2014 and 7/10/2014
“Your mind will adjust your body’s biology and behaviour to fit with your beliefs.” 21/6/2014

“SID ROTH: But when you told me that we could change our genes I wish every doctor in the world would understand this cutting edge research because, you know, you go to a doctor and say your cholesterol was high, and they say, well, exercise, change your diet, but it could be your genes and there’s nothing you can do, so take this medicine that will have a zillion side effects. But you say, according to the latest brain research, if you follow what Jesus said you can change your genes. That’s just so amazing.
DR. LEAF: I know. It is phenomenal. If you think of it, it’s logical too, Sid …” Full transcript:

Dr Leaf draws her erroneous conclusions from the poor interpretation of poor evidence. For example, one of Dr Leaf’s favourite factoids is her statement that “Research shows that 75 to 98 percent of mental, physical and behavioral illness comes from one’s thought life.” [13: p33] Dr Leaf’s sources for this statement include, among others, an article that not only doesn’t mention the figure she attributes to it, but also directly contradicts her fundamental premise [14], and the misleading paraphrasing of an already dubious quote from a pseudoscientific author [15].

Dr Leaf also has a number of pet theories which betray her preference for pseudoscience, the main one being her assertion that the heart is actually a mini-brain that has dedicated cognitive functions. For example, in her books, she says,

“Your heart is in constant communication with your brain and the rest of your body, checking the accuracy and integrity of your thought life.   As you are about to make a decision, your heart pops in a quiet word of advice, well worth listening to, because when you listen to your heart, it secretes the ANF hormone that gives you a feeling of peace.” [12: p62, 13: p127]

Dr Leaf directly quotes the work of an organisation called HeartMath for her evidence that the heart acts as a mini-brain. Dr Leaf, via Heartmath, states that:
> The heart has a network of 40,000 neurons within it, called sensory neurites, which detect circulating hormones, neurochemicals, and sense heart rate and blood pressure,
> The heart secretes “neurotransmitters” and other hormones, which have an effect on the brain, such as atrial natriuretic factor, and oxytocin,
> The heart communicates with the brain and the rest of the body through neurological, biophysical, biochemical and “energetic” (ie: electromagnetic) means [16, 17].

HeartMath clarifies, “The heart’s brain is an intricate network of several types of neurons, neurotransmitters, proteins and support cells like those found in the brain proper. Its elaborate circuitry enables it to act independently of the cranial brain – to learn, remember, and even feel and sense.” [16]

So the “evidence” looks plausible on the surface, but absurd when considered in a broader biological context. For example, my heart may have 40,000 neurons, many of which are sensitive to circulating hormones, neurochemicals and which sense and feel, but then again, so does my rectum. Does my rectum have a mini-brain as well? Clearly not. The only brain you have is the one in your cranium. We do not think with our heart, our rectum, or any other body part.

A more in-depth rebuttal of Dr Leaf’s scientific claims can be found in my book: “Hold That Thought – Reappraising the work of Dr Caroline Leaf”, via Smashwords ( or iTunes (


The opening question from Dr Leaf’s presentation at the 2015 TEDx Oaks Christian School was, “Can the mind change the brain?”

Clearly the answer is: “No, it can not.”

Others are welcome to disagree, but in my humble opinion, I suggest that Dr Leaf is a pseudoscientist, and that her appearance on the TEDx stage is not based on scientific acumen, but on popularity and reputation, which in turn, is based on slick self-promotion and an availability cascade (a self-reinforcing process by which an idea gains plausibility through repetition).

Dr Leaf’s ideas may have popular approval, but TEDx is a vehicle for ideas worth spreading, not ideas that are popular. According to its guidelines, TEDx requests that pseudoscience be avoided, specifically stating, “TED and TEDx are platforms for showcasing and explaining genuine advances in science … Speakers should avoid the misuse of scientific language to make unsubstantiated claims.” (

Dr Leaf’s claims, that her research has significantly changed the lives of the students who were blessed to receive it, is simply not born out by any of her own published data – from her original case study through to her MMA project and her Switch On Your Brain program. Whatever the underlying reason … whether its hubris, naivety, or denial that’s driving her continued promotion of her own programs … her claims are baseless, and therefore an argument can be made that she breached the TEDx guidelines in presenting them, and indeed, she should never have been invited to deliver them from a TEDx stage in the first place.

The theme for the 2015 TEDx Oaks Christian School event was “Ridiculous”. I would argue that it was ridiculous that Dr Leaf promoted her research as life changing when in reality, it’s not much better than a placebo. It was ridiculous that Dr Leaf would share stories of the changes to the cognitive functioning of her patients from their brain damage and then claim that the brain does not influence the mind. It seems that Dr Leaf’s presentation certainly fitted their theme, although probably not in the way they intended. Lets hope for their sake that their “ridiculous” decision doesn’t effect their ability to host future TEDx presentations.

Of course, that’s just my opinion. What do you think, TEDx universe?


  1. Leaf, C.M., et al., Mind-Mapping approach (MMA): a culture and language” free” technique. The South African journal of communication disorders. Die Suid-Afrikaanse tydskrif vir Kommunikasieafwykings, 1993. 40: 35
  2. Leaf, C.M., The Mind Mapping Approach: a model and framework for geodesic learning, in Department of Communication Pathology, Faculty of Arts1997, University of Pretoria: Pretoria. p. 266.
  3. Leaf, C.M., et al., The development of a model for geodesic learning: the geodesic information processing model. The South African journal of communication disorders. Die Suid-Afrikaanse tydskrif vir Kommunikasieafwykings, 1997. 44: 53
  4. Eppler, M.J., A comparison between concept maps, mind maps, conceptual diagrams, and visual metaphors as complementary tools for knowledge construction and sharing. Information Visualization, 2006. 5(3): 202-10
  5. Farrand, P., et al., The efficacy of the `mind map’ study technique. Medical Education, 2002. 36(5): 426-31 doi: 10.1046/j.1365-2923.2002.01205.x
  6. Wickramasinghe, A., et al., Effectiveness of mind maps as a learning tool for medical students. South East Asian Journal of Medical Education, 2007. 1(1): 30-2
  7. D’Antoni, A.V., et al., Does the mind map learning strategy facilitate information retrieval and critical thinking in medical students? BMC Med Educ, 2010. 10: 61 doi: 10.1186/1472-6920-10-61
  8. Merchie, E. and Van Keer, H., Spontaneous Mind Map use and learning from texts: The role of instruction and student characteristics. Procedia – Social and Behavioral Sciences, 2012. 69: 1387-94
  9. Baars, B.J., Global workspace theory of consciousness: toward a cognitive neuroscience of human experience. Progress in brain research, 2005. 150: 45-53
  10. Baars, B.J. and Franklin, S., An architectural model of conscious and unconscious brain functions: Global Workspace Theory and IDA. Neural Netw, 2007. 20(9): 955-61 doi: 10.1016/j.neunet.2007.09.013
  11. Franklin, S., et al., Conceptual Commitments of the LIDA Model of Cognition. Journal of Artificial General Intelligence, 2013. 4(2): 1-22
  12. Leaf, C., Who Switched Off My Brain? Controlling toxic thoughts and emotions. 2nd ed. 2009, Inprov, Ltd, Southlake, TX, USA:
  13. Leaf, C.M., Switch On Your Brain : The Key to Peak Happiness, Thinking, and Health. 2013, Baker Books, Grand Rapids, Michigan:
  14. Cohen, S., et al., Psychological stress and disease. JAMA: the journal of the American Medical Association, 2007. 298(14): 1685-7
  15. Lipton, B.H., The biology of belief: Unleashing the power of consciousness, matter and miracles. 2008, Hay House, Inc:
  16. Rosch, P. Emotional balance and health. Science of The Heart: Exploring the Role of the Heart in Human Performance – An Overview of Research Conducted by the Institute of HeartMath 2013 [cited 2013, 16/7/2013]; Available from:
  17. Rosch, P. Head-Heart Interactions. Science of The Heart: Exploring the Role of the Heart in Human Performance – An Overview of Research Conducted by the Institute of HeartMath 2013 [cited 2013, October 20]; Available from:

Bad choices cause brain damage?

“To err is human; to forgive, divine.”  Alexander Pope.

I’m not perfect.  At least, not the last time I checked.  And we’re all the same, aren’t we.  We all know through experience that we all stuff things up on a fairly regular basis.  We make bad choices.  We’re human!

Dr Caroline Leaf, Communication Pathologist and self-titled Cognitive Neuroscientist, believes that these bad choices literally cause brain damage.  Her fundamental assumption is that our thoughts control our brain [1: p33].  These thoughts can be healthy or they can be toxic.  Toxic thoughts “are thoughts that trigger negative and anxious emotions, which produce biochemicals that cause the body stress.” [2: p19]

Dr Leaf’s assumption is that thoughts and bad choices cause our brain cells to shrivel or die. “Once your body is truly in stress mode and the cortisol is flowing, dendrites start shrinking and even ‘falling off’” [2: p32].  She also says that, “We have two choices, we can let our thoughts become toxic and poisonous or we can detox our negative thoughts which will improve our emotional wholeness and even recover our physical health.” [2: p21]

It sounds a little extreme.  We all make bad choices, and we all experience stress.  When we’re stressed, do our memories really go missing, or the dendrites of nerve cells shake and fall like tree branches in a storm?  If we make a bad choice, do we really get brain damage?  Lets see what the scientific literature has to say.

Imagine walking along a path in a forest and you see a snake, only inches in front of you on the path.  What do you do? When faced with a high level of acute stress, the brain switches into a binary mode – fight/flight or freeze. Self-preservation has to kick in.  The only decision you have to make then and there is whether to run, to try and kill the snake before it kills you, or stop dead still and hope that the snake ignores you and slithers away.

At that point, most memory is redundant, as is a high-level analysis of snake species, or any other cognitive pursuit.  The brain doesn’t need them at that precise moment.  If they did engage, they would just get in the way.  Switching the thinking parts of your brain off focuses your attention on the immediate danger.  It’s an adaptive survival response.  Meantime, your memories and your theoretical knowledge about snakes don’t disappear.  They are still there, unchanged.  It is false to suggest that the memories “shrink”.

We’ve all experienced “mental block”.  Sometimes when we get into a situation, like an exam or a business meeting, our stress levels are high, and binary mode kicks in again, although this time it can be a hindrance.  This phenomenon of mental block under high stress was first proposed in 1908 and is currently known as the Yerkes-Dodson Law, a fundamental principle of the behavioural sciences [3].  Similar to the stress-productivity curve, Yerkes and Dodson proposed a U-shaped curve to represent the relationship between arousal (which could be either level of consciousness or stress) and behavioural performance.  At low arousal, there is poor performance.  At the mid-point of arousal, there is peak performance, and at high arousal, performance diminishes.

But again, our memories don’t shrink, and our nerve cell branches don’t fall off.  Once we reduce our level of arousal, we move away from the fight/flight/freeze mode, and everything is still there (and we perform better, according to Yerkes-Dodson).

Dr Leaf has a favourite analogy of “neurons as trees”.  And if neurons are trees, then the branches can “fall off”.  But neurons are not trees and dendrites are not tree branches.  The dendrites do not ‘fall off’ the neuron.  The neurons in the brain have mechanisms for ongoing brain plasticity – the ability of the brain to adapt to the challenges and changes in its internal and external environment that are constantly occurring.  If the brain needs to build a new circuit to encode a new piece of information, then it grows new dendrites and creates new synapses.  But the brain is limited by the amount of energy it can consume, and therefore the number of synapses it can maintain.  So the brain trims unnecessary dendrites, a process called “synaptic pruning”.

Synaptic pruning is a normal process. Chechik and Meilijson confirm that, “Human and animal studies show that mammalian brains undergoes massive synaptic pruning during childhood, removing about half of the synapses until puberty.” [4]

Synaptic pruning is not deleterious, but beneficial.  Chechik and Meilijson also note that, “synaptic overgrowth followed by judicial pruning along development improves the performance of an associative memory network with limited synaptic resources.” [4] So synaptic pruning is a normal physiological process, and occurs in all of us for many reasons, predominantly to improve the efficiency of our neural networks.  Perhaps synaptic pruning associated with the stress response is also an adaptive process?

Synaptic pruning also occurs in other physiological states that have nothing to do with stress or thought, such as the effects of oestrogen during the menstrual cycle and at menopause [5, 6].

A link between stress and dendrite loss has been discovered, but it is not consistent.  Some authors like Kopp and Rethelyi suggest that “severe stress for a prolonged period causes damage in hippocampal pyramidal neurons, especially in the CA3 and CA4 region and reductions in the length and arborization of their dendrites.” [7] However, Chen et al writes, “Whereas hippocampus-mediated memory deficits commonly were associated with—and perhaps result from—loss of synapse-bearing dendrites and dendritic spines, this association has not been universal so that the structure–function relationship underlying the effects of stress on hippocampal neurons has not been resolved.” [8]

It’s more accurate to think that chronic stress causes dendritic remodeling in animals [9], in which some nerve cells prune their synapses, which others grow them, and energy is diverted away from new nerve cell formation to the new synapses that are needed to cope with the stress.

A number of scientists have pointed out that patients with depression or anxiety, who normally have high levels of stress, have a smaller hippocampus and larger amygdala, so stress and depression must cause the smaller brain regions [9].  There may be some reduction in the number of synapses within the hippocampus and the frontal lobes of the brain, which may account for the change in size observed by a number of researchers.  But the modern thinking on these changes is that they are associated with depression, not caused by depression [10] (Correlation does not equal causation).

So, stress is associated with depression, but this is because genetic defects in one or multiple genes reduce the ability for the brain cells to produce synaptic branches.  It’s this decrease in the number of synapses that contributes to the typical changes in the brain seen at autopsy of patients who suffered from depression or anxiety [11].  The reduced ability of the nerve cells to grow synapses means that new branches can’t grow fast enough to process the stress signals properly [11, 12].  The poor signal transmission leads to a predisposition towards mood disorders like anxiety and depression [10, 11, 13-15], and less synaptic branches means both a smaller volume of the hippocampus, and an inability to process stress signals leads to a larger, overactive amygdala.

In summary, synaptic pruning is not due to toxic thinking or bad choices, unless every one of us engages in nothing but toxic thinking from early childhood to puberty, and menopause causes bad choices and toxic thoughts.  Stress doesn’t cause dendrites to fall off, but causes a reorganization of the dendrites to adapt to the new signals. The reduced capacity to form new dendrites makes those prone to mood disorders more vulnerable to stress, and depression or anxiety is the end result.

We are all bound to make bad choices and to have stress.  They don’t cause brain damage.  Which if you’re not perfect like me, is good news.


1.         Leaf, C.M., Switch On Your Brain : The Key to Peak Happiness, Thinking, and Health. 2013, Baker Books, Grand Rapids, Michigan

2.         Leaf, C., Who Switched Off My Brain? Controlling toxic thoughts and emotions. 2nd ed. 2009, Inprov, Ltd, Southlake, TX, USA:

3.         Cohen, R.A., Yerkes–Dodson Law, in Encyclopedia of Clinical Neuropsychology, Kreutzer, J.S., et al., Editors. 2011, Springer Science+Business Media LLC: New York ; London. p. 2737-8.

4.         Chechik, G., et al., Neuronal regulation: A mechanism for synaptic pruning during brain maturation. Neural Comput, 1999. 11(8): 2061-80

5.         Chen, J.R., et al., Gonadal hormones modulate the dendritic spine densities of primary cortical pyramidal neurons in adult female rat. Cereb Cortex, 2009. 19(11): 2719-27 doi: 10.1093/cercor/bhp048

6.         Dumitriu, D., et al., Estrogen and the aging brain: an elixir for the weary cortical network. Ann N Y Acad Sci, 2010. 1204: 104-12 doi: 10.1111/j.1749-6632.2010.05529.x

7.         Kopp, M.S. and Rethelyi, J., Where psychology meets physiology: chronic stress and premature mortality–the Central-Eastern European health paradox. Brain Res Bull, 2004. 62(5): 351-67 doi: 10.1016/j.brainresbull.2003.12.001

8.         Chen, Y., et al., Correlated memory defects and hippocampal dendritic spine loss after acute stress involve corticotropin-releasing hormone signaling. Proc Natl Acad Sci U S A, 2010. 107(29): 13123-8 doi: 10.1073/pnas.1003825107

9.         Karatsoreos, I.N. and McEwen, B.S., Psychobiological allostasis: resistance, resilience and vulnerability. Trends Cogn Sci, 2011. 15(12): 576-84 doi: 10.1016/j.tics.2011.10.005

10.       Palazidou, E., The neurobiology of depression. Br Med Bull, 2012. 101: 127-45 doi: 10.1093/bmb/lds004

11.       Karatsoreos, I.N. and McEwen, B.S., Resilience and vulnerability: a neurobiological perspective. F1000Prime Rep, 2013. 5: 13 doi: 10.12703/P5-13

12.       Russo, S.J., et al., Neurobiology of resilience. Nature neuroscience, 2012. 15(11): 1475-84

13.       Felten, A., et al., Genetically determined dopamine availability predicts disposition for depression. Brain Behav, 2011. 1(2): 109-18 doi: 10.1002/brb3.20

14.       Bradley, R.G., et al., Influence of child abuse on adult depression: moderation by the corticotropin-releasing hormone receptor gene. Arch Gen Psychiatry, 2008. 65(2): 190-200 doi: 10.1001/archgenpsychiatry.2007.26

15.       Hauger, R.L., et al., Role of CRF receptor signaling in stress vulnerability, anxiety, and depression. Ann N Y Acad Sci, 2009. 1179: 120-43 doi: 10.1111/j.1749-6632.2009.05011.x

Dr Caroline Leaf and the myth of optimism bias

“What are little girls are made of?  Sugar and spice, and all things nice.”

It sounds sweet doesn’t it?  We like to connect with these rosy little memes that warm our cockles and make us feel good about the world and ourselves.  We think of all of the examples in our own experience, which seems to confirm the saying.  We may think of a few examples that don’t quite fit, but they’re just the exception that proves the rule.

It doesn’t seem to matter what the saying or proverb is, we usually just assume it’s true.  Think of some other examples:
“Blondes have more fun.”
“Women can’t read maps.”
“White guys can’t dance.”

In all of these things, we tend to experience what psychologists call confirmation bias (Princeton University, 2014), our own mini-delusion in which we fool ourselves into believing a half-truth.  It looks right on first glance, and we can easily think of a few confirming examples, so without deeper inspection, we assume it must be true.

When Dr Leaf proclaims that,

“Science shows we are wired for love with a natural optimism bias”

the same process kicks in.  But in truth, science doesn’t show anything of the sort.  What science shows is that we learn love and fear, and our genetics influences the way we see the world, our personality.

We are prewired to LEARN to love and fear.  It doesn’t come naturally.  We require exposure to both love and to fear for these emotions to develop.  The Bucharest Early Intervention Project is a study looking at the long-term psychological and physical health of children in Bucharest, one group who remained in an orphanage, and the other, a group of children that were eventually adopted.  Analysis of the cohort of the two groups of children showed that negative affect was the same for both groups.  However positive affect and emotional reactivity was significantly reduced in the institutionalised children (Bos et al., 2011).  This shows that children who lived in an institution all of their lives and given limited emotional stimulation had lower levels of positive affect (ie: love, happiness) compared to a child that was adopted.

The children in the institution did not have high positive affect because they were not shown love.  Those children who were adopted were higher on positive affect because they were shown love by their adopted parents.  Both groups were exposed to distress and fear during their time in the orphanage, so their negative affect was the same across both groups.  Thus, love and fear don’t come naturally.  They need to be learned.

Personality is “the combination of characteristics or qualities that form an individuals distinctive character.” (“Oxford Dictionary of English – 3rd Edition,” 2010) As Professor Greg Henriques wrote in psychology today, “Personality traits are longstanding patterns of thoughts, feelings, and actions which tend to stabilize in adulthood and remain relatively fixed. There are five broad trait domains, one of which is labeled Neuroticism, and it generally corresponds to the sensitivity of the negative affect system, where a person high in Neuroticism is someone who is a worrier, easily upset, often down or irritable, and demonstrates high emotional reactivity to stress.” (Henriques, 2012) Personality is heavily influenced by genetics, with up to 60% of our personality pre-determined by our genes (Vinkhuyzen et al., 2012), expressed through the function of the serotonin and dopamine transporter systems in our brain (Caspi, Hariri, Holmes, Uher, & Moffitt, 2010; Chen et al., 2011; Felten, Montag, Markett, Walter, & Reuter, 2011).

So some people *ARE* natural optimists – their genetic heritage blessed them with a rosy outlook and their early life experiences cemented it in.  These naturally optimistic people, and the people who know them, are the ones who take Dr Leaf’s word as truth because they see it in themselves or their friends.  But the fact that some people are naturally wired for pessimism or a neurotic personality disproves Dr Leaf’s assertion.

Its important that Dr Leaf’s misleading meme is seen for what it is.  If we assume that we’re all pre-wired for love and optimism, then those who are pessimistic must be deficient or deviant, and the fact they can’t change must mean they are incompetent or lazy.  If we know the truth, those who are less optimistic won’t be unnecessarily judged or marginalised.

I should point out that what I’ve said isn’t a free licence to be cranky or sullen all the time.  The natural pessimist still needs to be able to negotiate their way through life, and being a misery-guts makes it hard to get what you need from other people in any business, social or interpersonal relationship.  We have the ability to learn, and the person with a neurotic personality can still learn ways of dealing with people in a positive way.

But if you naturally see the glass half-empty, don’t tell yourself that you’re abnormal, or that you aren’t good enough.  You are who you are.  Accept who you are, because while there are weaknesses inherent to having neurotic personality traits, there are also strengths, such as the enhanced awareness of deception, or protection from gullibility (Forgas & East, 2008).

A good thing to have when searching for the truth.


Bos, K., Zeanah, C. H., Fox, N. A., Drury, S. S., McLaughlin, K. A., & Nelson, C. A. (2011). Psychiatric outcomes in young children with a history of institutionalization. Harv Rev Psychiatry, 19(1), 15-24. doi: 10.3109/10673229.2011.549773

Caspi, A., Hariri, A. R., Holmes, A., Uher, R., & Moffitt, T. E. (2010). Genetic sensitivity to the environment: the case of the serotonin transporter gene and its implications for studying complex diseases and traits. Am J Psychiatry, 167(5), 509-527. doi: 10.1176/appi.ajp.2010.09101452

Chen, C., Chen, C., Moyzis, R., Stern, H., He, Q., Li, H., . . . Dong, Q. (2011). Contributions of dopamine-related genes and environmental factors to highly sensitive personality: a multi-step neuronal system-level approach. PLoS One, 6(7), e21636. doi: 10.1371/journal.pone.0021636

Felten, A., Montag, C., Markett, S., Walter, N. T., & Reuter, M. (2011). Genetically determined dopamine availability predicts disposition for depression. Brain Behav, 1(2), 109-118. doi: 10.1002/brb3.20

Forgas, J. P., & East, R. (2008). On being happy and gullible: Mood effects on skepticism and the detection of deception. Journal of Experimental Social Psychology, 44, 1362-1367.

Henriques, G. (2012). (When) Are You Neurotic?  Retrieved from

Oxford Dictionary of English – 3rd Edition. (2010)   (3rd edition ed.). Oxford, UK: Oxford University Press.

Princeton University. (2014). Confirmation bias.   Retrieved January 10, 2014, from

Vinkhuyzen, A. A., Pedersen, N. L., Yang, J., Lee, S. H., Magnusson, P. K., Iacono, W. G., . . . Wray, N. R. (2012). Common SNPs explain some of the variation in the personality dimensions of neuroticism and extraversion. Transl Psychiatry, 2, e102. doi: 10.1038/tp.2012.27