CHAPTER 7 - What else does Dr Leaf say about thought?

In the first half of the book, I discussed the current scientific understanding of thoughts and stress, and I compared that to Dr Leaf’s fundamental teaching.  In this second half of the book, I will be taking a more specific approach, reviewing some of Dr Leaf’s specific statements and contrasting them to current scientific opinion.  I do not have space to review all of Dr Leaf’s statements that contradict scientific principles, but I have chosen the most relevant and significant.

The next two chapters deal with Dr Leaf’s descriptions and assertions on thought.  In this chapter, I am going to critique some of Dr Leaf’s general statements on thought.  In chapter 8, I will review Dr Leaf’s statements specific to “toxic” thoughts.

Dr Leaf describes thoughts as toxic, poisonous, and dangerous.  She says, “thoughts are measurable and occupy mental real estate.”  She also says “Thoughts influence every decision, word, action and physical reaction we make.” [1: p13] She claims that “A massive body of research collectively shows that up to 80% of physical, emotional and mental health issues today could be a direct result of our thought lives.” [1: p14]

In chapter 2 of her 2009 book, she goes further, “Toxic thoughts are thoughts that trigger negative and anxious emotions, which produce biochemicals that cause the body stress”, and “They are stored in your mind, as well as in the cells in your body.” [1: p19]

And then, “Thoughts are basically electrical impulses, chemicals and neurons.  They look like a tree with branches.  As the thoughts grow and become permanent, more branches grow and the connections become stronger.” [1: p19] Then in the very next paragraph at the top of page 20 she writes, “As we change our thinking, some branches go away, new ones form, the strength of the connections change, and the memories network with other thoughts.”

Thoughts can’t become permanent, and still be changeable.  Which is it?  Despite contradicting herself, she doesn’t go on to clarify her statement.

Dr Leaf then goes on, “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.” [1: p21]

She also uses diagrams to further illustrate her explanation of what thoughts are.  In her 2009 book [1], on page 14 she illustrates “An Active Thought” showing a schematic diagram of a neuron and a synapse.  On page 61, she uses the same picture with the title, “An Active Thought.”  On page 20 she has a photograph of a histological section of the cerebral cortex, titled, “Thoughts Grouping Together Like Trees In A Forest - A schematic representation of the Neurons.”  On page 30, there is the “Schematic representation of branches (Dendrites) that hold toxic or non toxic thoughts.  And on page 33, again she labels a single neuron “A thought”.  She points to the dendrites and comments thus: “tree-like branches where memories are stored.”  On the bottom of the diagram she shows two ‘thoughts’ beside each other, one cell flourishing and the other withering, to which she explains: “Dendrites grow extensively on the nerve cell as we think.  Dendrites can shrink and fall off with continued high levels of stress.”  She also states that, “These toxic thoughts can even look distorted compared to healthy thoughts - chemicals released can even change the shape and even destroy parts of the neurons, causing change right down to the cellular level.” [1: p36]

On page 35, she attempts to demonstrate this in the top photo which, compared to the photo below it, shows the big black hole of “toxic thought” [1: p35].  Except it’s the same photo, but the toxic thought has been made “toxic” by artificially adding a black spot.

So in her 2009 book, Dr Leaf defines thoughts as neurons.  She says that the thoughts are stored in the branches of the neurons called dendrites, and if those thoughts are toxic, like stress, the branches will wither away and die.


“A million to one”

As I outlined early in chapter one, each thought is probably made up of the dynamic interaction of several million neurons and their dendrites.  In her first book, Dr Leaf says several times that thoughts just are single neurons and their dendrites, which is incorrect by a factor of several million.  In fairness, she did tighten her definition and description in her latest book.

“All your ills”

Dr Leaf makes two different claims about the impact of our thought lives.

On page 15 of “Who Switched Off My Brain”, Dr Leaf made a fairly astounding statement, “A massive body of research collectively shows that up to 80% of physical, emotional and mental health issues today could be a direct result of our thought lives.” [1: p15] That’s a pretty big number!  I’m an experienced GP, and compared to what I’ve seen in my office every day for the last ten years, Dr Leaf’s claim seemed extraordinary.

Unfortunately, none of her references listed any quotes or information citing thought as causing 80% of all illness.  Indeed, her endnote pointed to a collection of a few peer reviewed articles and official websites.  The rest were university links without any data at all, a few books, and a documentary talking about epigenetics.  Therefore, her statement that “a massive body of research” documented the relationship of thought and disease is an exaggeration.

She updated the statement in her 2013 book, “Switch On Your Brain”, but exaggerated the number even more [2: p36-8]. In chapter 10, I will show that the “evidence” she cites for this bizarre exaggeration do not support it, and are contrary to current scientific evidence.

From an independent perspective, it’s hard to see where she originally acquired such a large number.  Perhaps she arrived at the statement by incorrectly extrapolating a quote from one of her main source websites.  Dr Paul Rosch, M.D., President of the American Institute of Stress, said, "75 to 90% of all visits to primary care physicians result from stress-related disorders." [132]

Even then, research disagrees.  The BEACH study is an on-going survey, which provides information into the demographics and clinical statistics of patient presentations to Australian General Practice.  The BEACH data shows a total of about eight percent of presentations relate to stress and other mental health disorders [133], so unless the US population is radically different to Australia, Dr Rosch’s assertion is still overblown by nearly a factor of ten.

So then, it appears that one of Dr Leaf’s key tenets is nothing more than a misattribution of an exaggeration.   There is so much more to disease than stress or thought, and I’ll discuss this fully in chapter 10.

“The line up”

Dr Leaf believes that the neuron of a toxic thought appears different to the neuron of a healthy thought.  At best, this is extremely liberal poetic license.

As we discussed earlier, no single nerve cell is responsible for holding a thought.  Thoughts depend on the interaction of multiple neural networks, which in turn are made up of multiple nerve pathways involving millions of different nerve cells.

The nerve cells don’t know what they’re actually encoding; they just form the code utilised the nervous system, the neural equivalent to binary code used by a computer.  You may have a music file of Mozart and a music file of One Direction.  The computer doesn’t know that one file is a thing of beauty, while the other is a travesty of music.  It just reads the code.  In the same way, the pattern of synapses between the nerve cells simply encodes information.  Thought itself can’t cause the cells to wither or die.

“The mystery of the missing memories and deciduous dendrites”

She also states that under stress, memories shrink, like the mental block that one may experience going into an exam.  She goes on to state that, “Once your body is truly in stress mode and the cortisol is flowing, dendrites start shrinking and even ‘falling off’” [1: p32].    Do your memories go missing?  Do the dendrites of nerve cells shake and fall like tree branches in a storm?  No, on both counts.

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 [134].  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.

When faced with a high level of acute stress, the brain switches into a binary mode - fight/flight or freeze.  Imagine walking along a path in a forest and you see a snake, only inches in front of you on the path.  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, and 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 is 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”.

Dr Leaf also attempts to use her “neurons as trees” analogy to describe a process where the dendrites of a neuron shrink back under certain conditions.  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.” [135]

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.” [135] 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 [136, 137].

It should also be noted that the link between stress and dendrite loss 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.” [138] 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.” [139]

It’s more accurate to think that chronic stress causes dendritic remodeling in animals [140], in which some nerve cells prune their synapses, while 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.

In keeping with this explanation, there is decreased hippocampal cell proliferation during or immediately after stress but no change in survival of the cells that were dividing prior to stress [141]. That is, stress reduced the new cell formation, but the other cells did not die.  In addition, decreased new nerve cell growth is thought to result in decreased hippocampal volume, although several studies showed there was no change in the thickness of the main (granule) cell layer volume reported in many stress studies [142-144].

To add to the mixing pot of new discovery, there are a few recent studies that suggest stress does not decrease neurogenesis but actually can increase neurogenesis, and that this increase is functionally relevant [145-147].  Finally, many studies show that stress-induced decreases in one measurement of neurogenesis did not correlate with depressed or anxious traits [148].

In human depression, reduction in the size of the hippocampus is related to the loss of the surrounding glial cells, and not necessarily to changes in the nerve cells [140].   There may also 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 [149] (remember, correlation does not equal causation).

We know that 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 is this decrease in the number of synapses that contributes to the typical changes in the brain seen at autopsy [150].  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 [130, 150].  The poor signal transmission leads to both a predisposition towards mood disorders like anxiety and depression [11, 149-152].  Less synaptic branches mean 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.  It’s a normal process that takes place to make the synaptic network more efficient, and occurs in stress, but also in the maturation into adolescence, menopause and the menstrual cycle.  Stress doesn’t cause dendrites to fall off, but causes a reorganization of the dendrites to adapt to the new signals. In those people prone to depression, the underlying genetic changes in the proteins that enable nerve cells to grow branches increases vulnerability to stress.  This is why stress is associated with depression, but does not cause depression.

“Thoughts are real, take up mental real estate, and have a photocopy stored in the cells of the body”.

Dr Leaf states that, “Thoughts are real, physical things that occupy mental real estate.” [2: p32]

No one’s denying that thoughts are real.  The key issue is not whether thoughts are real, but what thoughts really are.  In the same way that a projection on a movie screen is a real series of images of a historical or fictional event, so thoughts are a real projection of the information from the deeper information stream within the brain.  Just because thoughts are real doesn’t mean they’re pre-eminent.

In her first book, Dr Leaf suggested that thoughts were measurable [1: p13].  Technically speaking, brain activity can be measured, of which thought is just one form.  There are parts of the brain that are involved in the processing of signals of the working memory slave systems that provide the stream of thought.  So, sure, thoughts occupy some ‘real estate’ in the brain.

However, the claim that these thoughts or memories are also stored as photocopies in the other cells in your body is incorrect.  That theory is the concepts of epigenetics taken to an extreme.  More will be discussed in the chapter on Epigenetics.

“The Geodesic Information Processing Model” and Dr Leaf’s other published research

Dr Leaf proposed the Geodesic Information Processing model in a PhD thesis in 1997.  PhD’s don’t just grow on trees.  They take years of hard work and dedication, and Dr Leaf deserves credit for earning hers.  According to her CV, Dr Leaf developed the Mind-Mapping Approach and the Metacognitive Map based on her PhD research [153].

Dr Leaf writes very highly of her own work, describing in her 2013 book how she abandoned traditional therapy and “trained (my patients) in a new technique I had developed” (the MMA, or the Mind Mapping Approach, which she didn’t develop herself, but borrowed from a British psychologist, Tony Buzan [154, 155]).

She goes on, “The changes were almost immediate: Improved focus, concentration, understanding, shifting efficiency, and overall effectiveness in producing positive work.  There were even positive emotional changes, specifically in self-motivation and self-esteem … In the ensuing past twenty years, I have seen these improvements in thousands of patients and clients.” [2: p98]

Later in the book, Dr Leaf states that, “My patients with closed-head injuries showed between 110 to 140 percent increase in their academic results … not only did it improve academic function, but intellectual, emotional and social skills showed dramatic change as well.” [2: p142]

A few general observations first, before I discuss the specifics of her research findings.  It should be noted that Dr Leaf’s model focused on the application of mind-mapping in a learning context, specifically, primary school education, not to thought in general.  Secondly, her Masters thesis and her PhD thesis were never published in peer-reviewed journals (which means that they missed out on broader critical review from the scientific community).

It should also be noted that in the twenty years since she published her first article, no one else has cited her[1].

That finding surprised me, since Dr Leaf often boasts over the application of her research to dramatically lift the pass rate of underprivileged students in the South African education system [Dr Leaf's CV: 153], and of the thousands of patients that have benefited from her methods [2: p142].

Does Dr Leaf’s published research support her claims?  For example, does she have documented results that show her patients had a 110 to 140 percent increase in their academic results? I haven’t found any evidence that verifies her statement.

According to her 1993 paper published in The South African Journal of Communication Disorders, her Masters thesis was based on the application of the Mind-Mapping Approach to a single patient [156].  There is no mention of other patients being involved in the research, or of any control groups to provide robust statistical analysis, in any of her three papers listed on PubMed[2] [156-158].  There was certainly no mention of the percentage improvement of this patient within the journal articles.  Perhaps Dr Leaf can provide independently verified evidence for her statement, but there is none readily available to confirm it.

Even if the figures of 110 to 140 percent were accurate, such results aren’t that spectacular.  The language is misleading, but a “110 percent improvement” means “the old score, plus 10 percent”, and “140 percent improvement” means “the old score, plus 40 percent.”  The average placebo effect is around 30 percent (“a 130 percent improvement”), so it’s entirely possible that the increase in scores were simply due to chance or a general treatment effect, and not the mind-mapping approach that she used.  Dr Leaf admitted this herself in her original article [156].

Dr Leaf officially published her Geodesic Information Processing Model in a journal article in 1997 [157].  Overall, I admit that I liked Dr Leaf’s 1997 paper.  There were a number of points that I think were, and probably still are applicable to learning within the school environment.  However, the Geodesic Information Processing Model itself has a number of fundamental flaws.  It assumes that non-conscious brain activity is equivalent to thought, which weakens its theoretical basis, since as we know from section one, not all brain activity is thought, or even accessible to thought.  The model was developed as a model of learning in an educational context, and since learning and thought are different processes, Dr Leaf’s model cannot be directly applied to thought [157].

It also puts reading and “reception” into the output side of the model [2: p126-7, 157], which is confusing since they are sensory, or input, processes.  Dr Leaf also says that, “The symbolic action level incorporates the five senses through which you express yourself and experience the world, serving as the contact between the external world and the internal world of your mind.” [2: p125&128] That’s also confusing, since we do not express ourselves through our senses, but through behaviour/action.

She explains that, “this model works in reverse as well, forming a perfect circle.  So information comes through the five senses, is received consciously by the conscious cognitive level, and then passes into the nonconscious metacognitive level where - if you have paid attention and started thinking and choosing - it becomes a physical thought as a result of genetic expression.” [2: p128] Later in the book she clarifies that the part of the brain that allegedly passes the information from the five senses to the rest of the brain is the thalamus [2: p165].

It may seem trivial, but the sense of smell bypasses the thalamus almost entirely [159], something that a cognitive neuroscientist would have known or discovered in their research.  The data streams from the other four senses are processed by the thalamus, which is non-conscious.  The information is sorted and passed to specific areas within the cerebral cortex, either to be discarded if it’s not salient, or processed by the executive areas of the brain in a non-conscious information stream, and only processed in our conscious working memory if required [20].  Most of the sensory information that we perceive will never reach our consciousness, because it’s unnecessary, and our brain has limited processing power available [160].  Thus, the information is not “sensory -> conscious -> unconscious”, but “sensory -> unconscious +/- conscious”.  Dr Leaf has the process backwards.

Does cognitive therapy really help?

If Dr Leaf was correct in her proposal that thought is responsible for the state of our mental health, then therapies specifically aimed at fixing thought would improve psychological problems.

But when examined scientifically, the opposite is true.  That is, cognitive therapy specifically targeting problem thoughts offers no extra improvement over behavioural therapy alone.  Herbert and Forman confirm this when they point out that, “proponents of behavioral activation point to the results of component control studies of CT, in which behavioral activation or exposure alone is compared to behavioral activation (or exposure) plus cognitive restructuring. The majority of these studies have failed to demonstrate incremental effects of cognitive restructuring strategies.” [161]

This fact has been further confirmed by a number of meta-analyses [101] and by a large randomised controlled trial comparing behavioural therapy and cognitive therapy side by side with medication for depression [102].

So therapies aimed at fixing thinking works equally as well as therapies aimed only at promoting therapeutic action.  However, when thinking therapies are added to behaviour therapies, they add no extra benefit over and above the behaviour therapies alone [101].  This suggests that action is the driver of the therapeutic effects of psychological therapy.  If thinking were the driving force of psychological change, the addition of cognitive therapy to behaviour therapy should have an incremental effect.

That cognitive therapy works equally well as behavioural therapy may be related to their fundamental similarities. Dobson et al explains, “Behavioural Activation is implemented in a manner that is intended to both teach coping skills and to reduce future risk. The same is true for Cognitive Therapy, which adds an emphasis on cognitive change, but otherwise takes a similar skills-training approach.” [102] In other words, cognitive therapy is just behavioural therapy with bling.

Herbert and Forman summarise it nicely, “The ideas that thoughts and beliefs lead directly to feelings and behavior, and that to change one’s maladaptive behavior and subjective sense of well-being one must first change one’s cognitions, are central themes of Western folk psychology.  We encourage friends to “look on the bright side” of difficult situations in order to improve their distress. We seek to cultivate “positive attitudes” in our children in the belief that this will lead to better academic or athletic performance. Traditional cognitively-oriented models of CBT (e.g., CT, stress inoculation training, and rational emotive behavior therapy) build on these culturally sanctioned ideas by describing causal effects of cognitions on affect and behavior, and by interventions targeting distorted, dysfunctional, or otherwise maladaptive cognitions.” [161]

I understand that many people will find this hard to accept.  We’re encouraged to think positive so often that it becomes a self-perpetuating cliché.  There can also be confusion around some of the semantics.  Many psychologists think of cognition as more than just thought, and newer psychological therapies like ACT seem to emphasise the cognitive as well as the behavioural.

It’s true that the first step in ACT is to defuse from our thoughts, although this isn’t changing our thoughts as per classical CBT (and repeated by Dr Leaf), but rather ignoring them so that meaningful action can then take place.  Depending on the therapy, and the definitions used, some may argue that successful therapy has a “cognitive” component, but semantic squabbling aside, the fundamental pillar of CBT/Dr Leaf - that psychological therapy begins with fixing problem thoughts - is outdated.

As noted by Harris, “If you look through the wide variety of writings on ACT, you will find over a hundred different cognitive defusion techniques. For example, to deal with an unpleasant thought, we might simply observe it with detachment; or repeat it over and over, out aloud, until it just becomes a meaningless sound; or imagine it in the voice of a cartoon character; or sing it to the tune of ‘Happy Birthday’; or silently say ‘Thanks, mind’ in gratitude for such an interesting thought. There is endless room for creativity. In contrast to CBT, not one of these cognitive defusion techniques involves evaluating or disputing unwanted thoughts.” [33]

Thus we improve our psychological health through action rather than fixing thought, although sometimes we need to stop fighting with our thoughts and give them some space first.  This has been proven in multiple research studies, and by the success of therapies such as ACT, which do not rely on evaluating, disputing or trying to fix unwanted thoughts to achieve their results.  Experts in psychological science confirm that Dr Leaf’s central teaching, that we have to change our thoughts to fix our behaviour, is nothing more than culturally sanctioned folklore.


Central to Dr Leaf’s teaching is her insistence that we need to change our thoughts in order to live a healthy and fulfilling life, but this is not what science tells us.  Dr Leaf’s teachings are the psychological equivalent of popular mythology.

Dr Leaf’s definition of thought is so broad as to be useless, and her explanation of the effects of stress and “toxic thought” on our brain cells is inconsistent with modern scientific understanding.  This is, in part, because Dr Leaf’s based her theories on her PhD research which was also fundamentally flawed, and contrary to her self-promotion, her work has not been cited by any independent researcher.  But there are a number of other ways in which Dr Leaf’s concept of toxic thoughts does not match scientific evidence or common sense, and that’s what we will discuss in the next chapter.

[1] Citation metric analysis performed using the “Publish or Perish” software application, which searches all available citations on Google Scholar and Microsoft Academic Search – see also

[2] The US National Library of Medicine’s database for the PUBlished MEDical literature.  “PubMed comprises more than 23 million citations for biomedical literature from MEDLINE, life science journals, and online books.” -