You spend about 10 per cent of your waking hours with your eyes shut, simply because of blinking. Every few seconds, each time you blink, your retinas are deprived of visual input for a period lasting anywhere between tens to hundreds of milliseconds (500 milliseconds is equivalent to half a second). You don’t usually notice this, because your brain suppresses the dark spells and stitches together the bursts of visual information seamlessly. But these dips in visual processing in the brain do have an impact: a new study in Psychological Science finds that, in an important way, they cause your sense of the passing of time to stop temporarily.
Now a new study sheds some light into what’s going in the brain when people smoke cannabis – and it turns out that the effects can be quite different depending on the specific strain of the drug. The research, published recently in the Journal of Psychopharmacology, suggests that cannabis disrupts particular brain networks – but some strains can buffer against this disruption.
In case you hadn’t noticed, there is an ongoing debate about the existence of differences between women’s and men’s brains, and the extent to which these might be linked to biological or to cultural factors. In this debate, a real game-changer of a study would involve the identification of clear-cut sex differences in foetal brains: that is, in brains that have not yet been exposed to all the different expectations and experiences that the world might offer. A recent open-access study published in Developmental Cognitive Neuroscience by Muriah Wheelock at the University of Washington and her colleagues, including senior researcher Moriah Thomason at New York University School of Medicine, claims to have done just that, hailed by the researchers themselves as “confirmation that sexual dimorphism in functional brain systems emerges during human gestation” and in various ways by the popular press as, for example, The Times of London’s headline: “Proof at last: women and men are born to be different”.
Does this study live up to the claims made by its authors and, more excitedly, those passing the message on? I think not.
Think about the concepts of “red” and “justice” and you’ll notice a key difference. If you’re sighted, you’ll associate “red” most strongly with the sensory experience, which relates to signals from cone cells in your eyes. “Justice”, in contrast, doesn’t have any associated sensory qualities – as an abstract concept, you’ll think about its meaning, which you learnt via language, understanding it to be related to other abstract concepts like “fairness” or “accountability”, perhaps. But what about blind people – how do they think about “red”?
A brain-imaging study of 12 people who had been blind from birth, and 14 sighted people, published recently in Nature Communications, shows that while for sighted people, sensory and abstract concepts like “red” and “justice” are represented in different brain regions, for blind people, they’re represented in the same “abstract concept” region.
It is not too long ago that mirror neurons were touted as one of the most exciting discoveries in neuroscience (or most hyped, depending on your perspective). First discovered in monkeys, these brain cells fire when an individual performs a movement or when they see someone else perform that movement. This automatic neural mirroring of other’s actions was interpreted by some scientists as the seat of human empathy. The cells’ most high-profile champion, US neuroscientist Vilayanur Ramachandran, described them as “the neurons that shaped civilisation” and, in 2000, he (in)famously said they would do for psychology what DNA did for biology. Nearly 20 years on, what evidence do we have that mirror neurons provide the basis for human empathy? According to a new meta-analysis and systematic review released as a preprint at PsyArXiv, the short answer is “not a lot”.
First-hand accounts of what it is like to come close to death often contain the same recurring themes, such as the sense of leaving the body, a review of one’s life, tunnelled vision and a magical sense of reality. Mystics, optimists and people of religious faith interpret this as evidence of an after life. Sceptically minded neuroscientists and psychologists think there may be a more terrestrial neurochemical explanation – that the profound and magical near death experience is caused by the natural release of brain chemicals at or near the end of life.
Supporting this, observers have noted the striking similarities between first-hand accounts of near-death experiences and the psychedelic experiences described by people who have taken mind-altering drugs.
“I had the feeling of floating, still tied to the remains of my heavy body, but floating nonetheless. I rocked and moved, at times as if on a liquid, undulating surface, at other times rising upwards, like a helium-filled flat container.” Excerpt from Amazing First-time Experience in the K-hole, published by Phaeton at the Erowid Experience vaults.
Perhaps, near death, the brain naturally releases the same psychoactive substances as used by drug takers, or substances that act on the same brain receptors as the drugs. It’s also notable that psychedelic drugs have been taken by the shamans of traditional far-flung cultures through history as a way to, as they see it, visit the after world or speak to the dead.
To date, however, much of the evidence comparing near death experiences and psychedelic trips has been anecdotal or it’s been based on questionnaire measures that arguably struggle to capture the complexity of these life-changing experiences. Pursuing this line of enquiry with a new approach, an international team of researchers led by Charlotte Martial at the University Hospital of Liège has conducted a deep lexical analysis, comparing 625 written narrative accounts of near death experiences with more than 15,000 written narrative accounts of experiences taking psychoactive drugs (sourced from the Erowid Experience vaults), including 165 different substances in 10 drug classes.
The famous studies of London’s taxi drivers – showing they have larger hippocampi (the comma-shaped brain structure in the temporal lobes) than controls – have become a staple of undergrad psychology courses and a classic example of how your brain changes according to what you do with it. Many other studies have also implied an association between hippocampal size and navigational ability – for instance, people with Alzheimer’s, who have lost neurons in this brain structure, tend to experience problems finding their way around. For some time, then, an obvious, though tentative, inference has been that better navigators have bigger hippcampi, with London taxi drivers (and their mastery of “the knowledge” of the city’s convoluted streets) and people with Alzheimer’s representing opposite extremes of the spectrum. However, a new study, released as a preprint at bioRxiv, raises questions about how far we can safely generalise from the taxi driver and Alzheimer’s-based research.
Steven Weisberg and his colleagues tested young adults’ navigation skills and assessed the size of their hippocampi and found the two were not significantly correlated. “The hippocampus plays a crucial role in spatial navigation in humans, but the volume of the hippocampus may not be a biological marker for navigation ability among typical populations,” the researchers concluded.
Of 135 surveyed fMRI papers that contained claims of replicating previous findings, over 40 per cent did not consider peak activity levels within brain regions – a flawed approach that allows almost any result to be claimed as a successful replication (from YongWooK Hong et al, 2019)
As the list of failed replications continues to build, psychology’s reproducibility crisis is becoming harder to ignore. Now, in a new paper that seems likely to ruffle a few feathers, researchers suggest that even many apparent successful replications in neuroimaging research could be standing on shaky ground.As the paper’s title bluntly puts it, the way imaging results are currently analysed “allows presenting anything as a replicated finding.”
The provocative argument is put forward by YongWook Hong from Sungkyunkwan University in South Korea and colleagues, in a preprint posted recently to bioRxiv. The fundamental problem, say the researchers, is that scientists conducting neuroimaging research tend to make and test hypotheses with reference to large brain structures. Yet neuroimaging techniques, particularly functional magnetic resonance imaging (fMRI), gather data at a much more fine-grained resolution.
This means that strikingly different patterns of brain activity could produce what appears to be the same result. For example, one lab might find that a face recognition task activates the amygdala (a structure found on each side of the brain that’s involved in emotional processing). Later, another lab apparently replicates this finding, showing activation in the same structure during the same task. But the amygdala contains hundreds of individual “voxels”, the three-dimensional pixels that form the basic unit of fMRI data. So the second lab could have found activity in a completely different part of the amygdala, yet it would appear that they had replicated the original result.
Anyone who has stood in the supermarket aisle trying to remember their shopping list might have wished for a larger brain. But when it comes to memory, bigger isn’t always better. A study published in Neuropsychologia has found that young children whose cerebral cortex is thinner in certain areas also tend to have better working memory.
The blue bars show reduced amygdala activity in the group that received real-time neural feedback while looking at negative images; from Herwig et al, 2019
By guest blogger Eleanor Morgan
Interventions like cognitive behavioural therapy help people better control their emotions by teaching them new ways of thinking. A recent study published in NeuroImage suggests this approach could be augmented by using “neurofeedback” to help regulate activity in a key brain structure – the amygdala.
By Emma Young
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