So Happy Together: Deconstructing The Right Brain/Left Brain Myth

Deep dive debunk of emotional lateralisation of human brain. Trigger warning: this piece might alter some of your cherished therapy assumptions.

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Nov 08, 2025

Emotions are therapy’s prime real estate. It’s no wonder, then, that they attract magic formulas promising to pinpoint exactly where emotions live in the brain, offering silver bullets as to how to tame them.

Consequently, neurobollocks around emotions abounds. Recently, in this substack, I have tried to add nuance to this story by playing with the ideas from the Theory of Constructed Emotions and its possible uses in therapy - this theory essentially wagers that emotions could be domain-general properties of the brain and, as an empirical theory, has lots of data to back it up. I like to think that, for some of you, this might have led to question ideas around the outdated triune brain theory, the amygdala as the seat of emotions or the infamous lizard brain.

However, when it comes to emotions, there is another influential myth that continues to be omnipresent in both psychotherapy literature and the therapy speak: the right brain/left brain myth. I am reposting this classic, where we delve into the nitty-gritty and scrutinise the various lateralisation claims against the most recent neuroscience findings (emotions, ‘right-brain psychotherapy’, attachment and more). If you have read it previously, my apologies. If not, you are in for a (longish) treat. Enjoy!

The story of the divide between the right and left brain has become one of the most cherished ideas in psychotherapy. It shows up virtually everywhere we look, branching into a myriad of techniques and approaches, creating an entire ecosystem. And to be fair, it’s not difficult to see why psychotherapists embrace it.

It offers a wonderfully simplified story about how the brain works, satisfying our strong intuition about the split between thinking and feeling. By drawing a physical line down the middle of the brain, it seems to give tangible, material proof of this cognitive-emotional divide. And beyond that, it echoes an even older narrative: the age-old split between soul and intellect.

It’s a compelling story - but if we want to use neuroscience meaningfully in psychotherapy, beyond loose metaphors and appealing but inaccurate narratives, how much truth is actually in it? To what extent, if any, is it supported by current neuroscience?

That’s exactly what I set out to find out with the help of Dr Pascal Vrticka, a social neuroscientist whose research focuses primarily on the neurobiology of attachment (you will find his full bio at the end of this article). His work touches on some of the areas of neuroscience most relevant to psychotherapy: affective neuroscience (i.e., the neuroscience of emotions), social neuroscience and the neuroscience of attachment.

Together, we try to separate the wheat from the chaff, facts from fiction - and don’t make me say it … rights from lefts.

Pieced together, the following claims put the ‘right brain’ at the very centre of emotion perception and regulation, child development, attachment, relational psychotherapy, and even at the core of how we relate to others:

The right brain is emotional, the left brain is rational.
There are two distinct modes of being, supposedly rooted in hemispheric use: right-mode functioning versus left-mode functioning.
Non-verbal communication is mediated by the right hemisphere.
Relational psychotherapy happens via “right-to-right brain” communication.
Bio-behavioural synchrony relies on right-to-right brain communication (including between caregivers and children).
Attachment is rooted in the right brain.
The right hemisphere is the first to develop in infants and therefore carries all the important (unconscious and emotional) learning.

Yet the whole “right brain/left brain” affair rests on rather shaky epistemic grounds. Making the case for it typically draws from three strands of argument: the lesion studies and split-brain experiments, certain bio-behavioural synchrony studies and research on brain lateralisation in infants. Much of said research is now considerably dated but could it still be proving the essential point?

We have laid it all out in a Q&A format, tackling the most common assertions found in psychotherapy around the “right brain/left brain” divide.

Here goes - enjoy!

First Things First: What Are We Really Talking About?

The statement “one hemisphere is emotional and the other hemisphere is rational” sounds simple enough, right? But on closer inspection, it is not actually that clear what it means or implies. Let’s take a moment to unpack this.

Left, Right but Where?

When we speak about the right brain and the left brain, what do we understand by that? We basically refer to the fact that the human brain is made of two hemispheres separated by a deep groove (the longitudinal fissure). The hemispheres are linked by several bundles of nerve fibres, most notably the corpus callosum, as well as a few smaller commissures. Naturally, this anatomical organisation creates a left and a right side of the brain that extends from cortical structures on the top all the way down to subcortical structures at the bottom.

Within this context, brain lateralisation simply means that for certain functions and processes, one hemisphere is more dominant than the other.

For example, language and speech are processed mainly by the left hemisphere. And sensory and motor functions are strongly lateralized to the contralateral hemisphere – e.g., sensory input from the right side of our environment is processed in the left hemisphere, and vice versa.

What Means ‘Emotional’?

The second question worth considering is what is meant by the statement that a part of the brain is ‘emotional’? Is it the part that processes incoming emotional information (i.e., emotion perception and recognition)? Is it the part that attributes relevance and meaning to emotions, creating (often complex) subjective experiences and feelings? Or is it the part that alters and thereby helps regulate emotions? So, when we say “the right brain is emotional,” which of these processes – or parts – are we actually referring to? Or are all of them just scrunched up in the right side of the brain?

To answer this, we’ll just have to dig in and find out.

Is the Right Brain Emotional?

One strand of argument in favour of the theory of emotional lateralisation comes from the body of work around split brain patients and brain lesions (see notable examples here and here). This seems to be especially the case in relation to the role of the right sensorimotor cortex for facial recognition of emotions. Is the right cortex in charge of facial recognition of emotions? If so, what are the implications for the idea that the right brain is in charge of emotions generally speaking?

Yes, there indeed is considerable evidence – from split-brain patient, lesion, visual half-field studies, etc. – for the right hemisphere having an advantage in, and thus being dominant for, facial emotion perception. However, as already explained above, facial emotion perception is just one element of the overall neural processing of emotions amongst many others. In addition, right-brain dominance does not mean that the entire left hemisphere is completely “offline”.

Emotion processing always occurs within several large, distributed and strongly interconnected neural networks spanning both hemispheres.

Accordingly, we should not deduce from the evidence showing a right-hemisphere lateralisation of facial emotion perception that the right hemisphere is dominant for all aspects of emotion processing at all times – as suggested by the Right-Hemisphere Hypothesis (RHH).

Are there other theories of hemispheric functional lateralisation of emotions?

Besides the Right-Hemisphere Hypothesis (RHH), there are two other prominent hemispheric functional brain lateralisation hypotheses. The first one, the Valence-Specific Hypothesis (VSH), proposes that there is lateralization in the preferential processing of negative (right hemisphere) versus positive (left hemisphere) emotions. However, current evidence does not support such a global hemispheric division based on emotional valence, but instead suggests that some valence-specific activations in areas like the prefrontal cortex are linked to specific emotional experiences. The second one, the Motivational Hypothesis (MH), postulates that there is lateralization related to withdrawal (right hemisphere) versus approach (left hemisphere) behavioural tendencies / motivations. Yet, there is controversy surrounding this hypothesis, particularly pertaining to the neural processing of anger, which is linked to both approach and withdrawal behavioural tendencies / motivations.

To accommodate the above-mentioned discrepancies associated with the RHH, VSH and MH, a new theory, the Hemispheric Functional-Equivalence (HFE) model, has recently been proposed. The HFE recognises that the brain may have an initial right-bias in the perception of emotions, and especially emotional faces.

At the same time, the Hemispheric Functional-Equivalence emphasises the flexibility and dynamic nature of brain lateralization in emotion perception, the functional capacity of both hemispheres to process emotions relatively successfully and that varying environmental demands, such as task difficulty or acute stress, can considerably modulate lateralization patterns.

In essence, the HFE model suggests that while the right hemisphere may have an initial advantage in perceiving emotions – including from faces –, the brain is highly flexible and adaptive, and dynamically engages both hemispheres to achieve optimal performance, especially under more demanding circumstances.

Synchrony studies

And how about the synchrony studies? Some researchers have found that during social interaction, increased synchrony emerges between the right centro-pariental areas of interacting individuals? Can you unpack this? What does it mean and what would it entail if it were true?

Interbrain synchrony means that the brain activities of two interacting individuals become aligned or “in sync” with one another, both in time and anatomical location. The interacting dyad then literally is “on the same wavelength”.

Yes, there are indeed several studies that report significantly increased interbrain synchrony between parts of the right cortices of interacting dyads. However, there are many other studies that found significantly increased interbrain synchrony either between parts of the left cortices of interacting dyads or between parts of the right cortex of one dyad member and parts of the left cortex of the other dyad member, and vice versa. Accordingly, lateralized interbrain synchrony is usually observed within specific cortical brain areas and not entire hemispheres, and relatively increased interbrain synchrony in (one area of) one hemisphere does not mean that there is no interbrain synchrony in the other hemisphere.

For informed conclusions regarding global interbrain synchrony lateralization, one needs to measure it across the entire cortex as well as subcortical areas – which is rarely done at the moment due to the predominant use of neuroimaging devices that lack whole-brain (i.e., cortical and subcortical) coverage.

Furthermore, lateralized interbrain synchrony often depends on the dyad composition, including factors such as participant age and/or biological sex. For example, in one of our own recent studies, we observed stronger interbrain synchrony in both the left temporo-parietal junction and right dorsolateral prefrontal cortex in father-child dyads as compared to mother-child dyads. Finally, interbrain synchrony – and its lateralization – strongly depends on the context within which it is measured, and more interbrain synchrony (within one hemisphere or the other) may not always be better.

Taken together, when looking at the overall interbrain synchrony literature over the last ten years, I cannot see any indication for a reliable and global right-brain lateralization that is associated with beneficial interpersonal outcomes.

Is the Right Brain First Developed In Infants?

There is a well publicised paper from 1997, based on PET scan study that makes a claim that the right hemisphere is dominant in infants. How does that align with what we know today?

Since the publication of the study by Chiron and colleagues almost 30 years ago, neuroimaging techniques have significantly evolved and improved. Furthermore, new longitudinal studies were conducted in which participants’ brains were scanned more than once over the course of some time. These developments have led to a more complex and nuanced understanding of brain lateralization emergence. The current perception is that it is a complex and dynamic process that begins early in life, possibly with structural asymmetries already present in newborns (or even before).

While the current evidence supports a general trend towards increasing left hemisphere specialization with age for certain functions like language, this development involves early bilateral contributions and a more subtle shift rather than an abrupt onset of a global hemispheric dominance.

Furthermore, structural and functional brain lateralization appears to follow different developmental trajectories, and lateralization patterns are tract-specific and time-varying, especially in early infancy. Overall, the field has moved beyond a simple concept of overall hemispheric dominance by recognizing the complementary and dynamic specialization - meaning changing over time - of both hemispheres throughout development.

Attachment and Lateralisation

In the psychotherapy world we hear a lot about attachment being rooted in the ‘right’ brain. Is this the case? If not, where is attachment found in the brain?

The notion that attachment is predominantly right-brain centred can be traced back to a combination of several assumptions about brain anatomy, function and development that were prominent during the 1990s and early 2000s. We have touched on many of them already. In a nutshell, the perception at the time was that attachment must be right-brain centered because it develops during infancy and early childhood, a time that allegedly coincides with a period of right-brain dominance. This notion was particularly related to the neural processing of non-verbal signals, perception and regulation of emotions as well as the formation of non-conscious memories –, which are all central for child-caregiver attachment formation and were believed to be predominantly localised within the right hemisphere.

Nowadays, we know that brain lateralization beyond highly specialized functions – like motor control, vision, language, etc. – that are maintained by localised neural circuits does not extend to complex behaviours and personality traits, including attachment.

From our own work on the social neuroscience of human attachment (SoNeAt) that includes the functional neuro-anatomical models of both organised and disrupted/disorganized attachment (NAMA and NAMDA) over the last twenty years, we furthermore know that attachment behaviour is orchestrated within several extended, strongly interconnected and bilateral neural networks spanning the entire brain. This includes networks involved in the encoding of both non-conscious and emotional processes as well as voluntary and cognitive emotion regulation and mental state representation. The key is an optimal dynamic, time- and context-specific balance of activity and connectivity within and between these different neural networks, not the involvement of one specific brain area or hemisphere alone at all times.

Right Brain Mode and Left Brain Mode Processing

There is a pervasive discourse in neuroscience-informed psychotherapy today about the “right mode processing” and “left mode processing”. Is there any neuroscience behind this? Do we, as therapists, need to help our clients work towards ‘integration’ of the two hemispheres in order to live a more fulfilling life? Can we communicate or do psychotherapy using one hemisphere of our brain?

As mentioned above, current neuroscientific evidence does not support the notion that brain lateralization beyond highly specialized functions – like motor control, vision, language, etc. – that are maintained by localised neural circuits extends to complex behaviours and personality traits.

Put simply, we are not “right-brained” or “left-brained” as individuals, nor can we communicate with others using only one of our hemispheres.

The latest neuroscience models of brain functioning related to wellbeing and health are heading into a different direction. As we understand it today, our brain’s main function is twofold. First, it aims to keep a steady state of bodily and psychological balance (i.e., homeostasis) within narrow limits. And second, it actively regulates important deviations from this balance to enable our body and mind to return back to balance as quickly as possible (i.e., allostasis).

Crucially, for our brain to most efficiently do so, a third process comes into play: the anticipation of what may happen in the future. This serves to re-adjust our current bodily and psychological balance according to the predicted future demands. Why does our brain do so? It does so because the more accurate its future predictions are, or the smaller its prediction error is, the smaller will the future deviance from balance be and the less active regulation to return back to it will be needed. I have written and talked about this in more detail with regards to attachment and social connection.

Taken together, for this complicated fine-tuning involving the keeping of homeostasis as well as engaging in allostasis and predicting future demands to function optimally, there must be a constant, extensive and flexible dialogue between many different and interconnected neural networks spanning both hemispheres.

The key is to maintain the brain’s optimal adaptive and predictive functioning, rather than having it develop rigid and poorly adjusted responses. In that sense, living a fulfilling life does indeed mean to have a brain that can make use of all of its resources. It’s just not the case – and a misleading oversimplification – that this can be achieved by tweaking “right versus left brain modes”.

Final Remarks

As a neuroscientist whose work overlaps with a number of neuroscience features that are essential for neuroscience-informed psychotherapy, do you have any concluding remarks for us to take on board?

The “right brain” versus “left brain” concept intuitively resonates with many people's self-perceived strengths and weaknesses. It offers a tangible explanation for understanding personality and cognitive styles and their underlying neurobiological mechanisms – including in a therapeutic setting. However, the concept’s underlying assumptions are not supported by current neuroscientific evidence.

Hence, we should not continue to promote a myth that has already been debunked many times just for the sake of its simplicity and user-friendly nature. What we should do instead is to refer to more appropriate and up-to-date neuroscience explanations, even if they are less intuitive and more complicated. It is really worth it and many people, including us two, are very happy to help and provide support along the way.

Wrapping Up

I always try to keep things light. I mean, we can talk about the good use of neuroscience in psychotherapy and have a laugh at the same time, can’t we?

But in this case, the stakes could not be higher. The “right brain/left brain” narrative is, for many, the pinnacle of what neuroscience has to offer to psychotherapy. So to realise that this very foundation - what some believe makes our work neuroscience-informed - is in fact a neuro-myth? I understand. It is a hard blow to take.

And yet, there is no need (or evidence) for this ontological divide between the two hemispheres of the brain. The right brain and the left brain seem to be so happy together.

As always, thank you for reading🙏.

Some Relevant Books

Seven and a Half Lessons About the Brain (especially the chapter Your Brain Is a Network), Lisa Feldman-Barrett
The Neuroscience of Emotions: The New Synthesis, Ralph Adolphs and David J. Anderson

A guest post by

Pascal Vrticka

Associate Professor and Principal Investigator of the Social Neuroscience of Human Attachment (SoNeAt) Lab at the Department of Psychology, University of Essex (Colchester, UK).

Behavior Scientists on Science

Nov 13Edited

Or simply stated: ONE brain, TWO hemispheres.

--Except for the very, very few who had a corpus callosotomy (mostly) for epileptic seizures, a few thousand at most since it was refined after Sperry's 1960s Nobel Prize-winning split-brain research. If you're not one of these, you have one brain and both hemispheres coordinate/share essentially all signals.

A few summary points:

1) Left 'brain', right 'brain' is pseudoscience, more of the biobunk left over from the 1990s.

2) Brains process; they never create something from nothing.

3) The only non-medicinal way to 'change a brain' is to change behaviour (thinking included).

Glad you wrote this, Ana. Hopefully, it gets broadly disseminated.

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5 replies by Ana Lund and others

I am Full of Shit

What I always find funny about left-brain/right-brain myths is that they try to impose a structure I’ve never actually experienced from the inside.

My inner life has never been divided into “the emotional side” and “the rational side.” It’s more like one integrated system running twelve processes at once and none of them asking permission.

Real neuroscience is inconvenient. So I appreciate posts like this because they break the illusion that we can hack the mind with a metaphor.

Some of us don’t have hemispheres fighting for dominance. We have one brain doing its chaotic best, and the only “mode” it operates in is: all of them, at once, all the time.

Thanks!

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