Psychology Blog

Cannabis smokers often report that when stoned, their thoughts have a free-wheeling quality and concepts seem connected in unusual and playful ways. A study just published online in Psychiatry Research suggests that this effect may be due to the drug causing ‘fast and loose’ patterns of spreading activity in memory, something known as ‘hyper-priming’.

Priming is a well studied effect in psychology where encountering one concept makes related concepts more easily accessible. For example, classic experiments show that if you see the word ‘bird’ you will react more quickly to words like ‘wing’ and ‘fly’ than words like ‘apple’ and ‘can’ because the former words are more closely related in meaning than the latter.

In fact, it has been shown that the more closely related the word, the quicker we react to it, demonstrating a kind of ‘mental distance’ between concepts. Think of it like dropping a stone into a pool of mental concepts. The ripples cause activity that reduces in strength as it moves away from the centre.

‘Hyper-priming’ is an effect where priming happens for concepts at a much greater distance than normal. For example, the word ‘bird’ might speed up reaction times to the the word ‘aeroplane’. To return to our analogy, the ripples are much stronger and spread further than normal.

The effect has been reported, albeit inconsistently, in people with schizophrenia and some have suggested it might explain why affected people can sometimes make false or unlikely connections or have disjointed thoughts.

As cannabis has been linked to a slight increased risk for psychosis, and certainly causes smokers to have freewheeling thoughts, the researchers decided to test whether stoned participants would show the ‘hyper-priming’ effect.

The experiment used a classic ‘lexical decision task‘ where the volunteers are shown an initial word (’time’) and then after a short gap are shown a nonsense word (’yipt’) and a true word (’date’) at the same time and have to indicate as quickly as possible which is the real world.

The experimenters altered how related the initial word and true word were to test for the semantic distance effect, and also varied the gap between the initial word and the test to see how long the priming effect might last.

Volunteers who were under the influence of cannabis showed a definite ‘hyper-priming’ tendency where distant concepts were reacted to more quickly. Interestingly, they also showed some of this tendency when straight and sober .

Cannabis also had the effect of causing temporary psychosis-like distortions as would be expected from a psychedelic drug, but the smokers did not make more errors and were not more likely to report psychosis-like symptoms when sober, suggesting the effect was not due to general mental impairment and couldn’t be explained by underlying tendency to mental distortion.

Although the debate is not completely settled, there is now good evidence that cannabis causes a small increased risk for developing schizophrenia particularly when smokers start young. In fact, additional evidence on this front was published only this week.

The researchers discuss the possibility that long-term smokers who spend a lot of time in a chronic ‘hyper-primed’ state might make psychosis more likely by loosening the boundaries of well-grounded thought, although exactly how cannabis raises the risk of psychosis, and indeed, how exactly it affects the brain, is still not understood well-enough to make a firm judgement.

Link to PubMed entry for cannabis ‘hyper-priming’ study.

Originally posted here:
How cannabis makes thoughts tumble

A brain scanning technology called MEG is being used to track the function of unborn babies’ brains as they grow inside the womb until after they’ve been born.

The full name for MEG is magnetoencephalography and it works by reading the magnetic fields created by the electrical signalling in the brain.

One of the advantages is that it can be used at various angles, doesn’t require the person to be in a cramped space, and is less sensitive to movement, so is ideally suited to scanning babies.

This includes unborn babies and with a bit of modification, as illustrated in the picture, researchers can pick up signals from the fetal brain in response to flashes or light or sounds.

We discussed the use of fMRI to scan the fetal brain previously, but this is a remarkable study that scanned the brains of babies inside the womb, every two weeks from week 27 until delivery, and then once after they were born.

Clearly, unborn babies are not the best at doing tasks set by experimenters, but there are various tests that just require the individual to experience changes in what’s presented to them.

One is called the auditory oddball task, where a series of tones are played that can either be similar (’beep beep beep’) or can have include an ‘oddball’ (’beep beep boop’). The brain is very good at picking out differences and the oddball is known to reliably trigger brain signals related to detecting changes.

This was the exact task used with the babies and the researchers looked to see if they could pick out a brain reaction to the ‘oddball’.

They found that they could detect this response 83% of the time in unborn babies, and that the reaction to the ‘oddball’ increased in speed throughout pregnancy. The newly born babies showed the response every time without fail.

This is an impressive finding as it shows how the brain development of the unborn child can be tracked over time with a brain scanner.

In a recent review article that discusses the development of this technology, the same group of researchers suggest that these and similar techniques could help track how different conditions in the mother affect the developing brain and even how the brain begins to develop its understanding of speech sounds before birth.

Link to PubMed entry for MEG study of developing fetus.
Link to PubMed entry for review article on fetal MEG.

Read the rest here:
Tracking the unborn brain into childhood

A new study has looked at the reliability of fMRI brain scanning results over time, finding that the same experiment will only only be moderately reproducible when conducted at two different times, suggesting that fMRI is much less reliable than most researchers assume.

The authors of the paper are the same ones who brought us the study showing that it’s possible to find ‘brain activity’ in a dead fish if the analysis is done in a way that is common but prone to false positives.

The paper will shortly appear in the Annals of the New York Academy of Sciences but they’ve put a copy online and, although it’s a scientific article, it’s remarkably easy to read.

They review all the studies to date on what is known as the ‘test-retest reliability‘ of fMRI. This refers to the ability of a measure to give reproducible results.

For example, if you’re measuring an adult’s height you want to make sure that your tape measure gives you similar results each time you use it on the same person. Of course, you may have readings that vary by a millimetre or two each time, but if you get wildly different results on Monday and Tuesday, you probably want to bin your tape measure.

In fMRI there are two types of results. One is ‘where in the brain’ and the other is ‘how strong’ is the activity.

We can examine the first by looking at how well the active brain areas overlap in scans taken at two different times, and we can examine the second by looking at the similarity of the strength of the results using a statistical test like a correlation.

The better the overlap and the statistical relationship between the results from the same test on the same people at different times, the more we can rely on our measurement technique.

This new analysis reviewed all the previous studies that have looked at the test-retest reliability of fMRI and found that overall, active brain areas overlap about 30% of the time and the correlation for the strength of the activity was about 0.5. To get some perspective a result of 1 would indicate perfectly reliable and reproducible results while a result of 0 would indicate no reliability at all.

An overlap of 30% and a correlation result of 0.5 shows fMRI has moderate reliability, but is much poorer than most people assume.

However, this overall result is perhaps a little too broad, and the authors make the point that the reliability varies depending on the type of scanner being used, what test is being carried out by the participants, what brain areas are being investigated and how the results are analysed.

Indeed, a recent study on the test-retest reliability of fMRI studies of the ‘reward system’ found the reproducibility of the results to be worse than this general figure while another study found an auditory detection task produced better results.

The authors conclude:

One thing is abundantly clear: fMRI is an effective research tool that has opened broad new horizons of investigation to scientists around the world. However, the results from fMRI research may be somewhat less reliable than many researchers implicitly believe. While it may be frustrating to know that fMRI results are not perfectly replicable, it is beneficial to take a longer-term view regarding the scientific impact of these studies. In neuroimaging, as in other scientific fields, errors will be made and some results will not replicate. Still, over time some measure of truth will accrue. This chapter is not intended to be an accusation against fMRI as a method. Quite the contrary, it is meant to increase the understanding of how much each fMRI result can contribute to scientific knowledge.

Link to full text of paper (via @hysell).

Excerpted from:
How reliable are fMRI results?

Discover Magazine has a great short article on misperceptions and counter-intuitive findings concerning alcohol and drinking.

The piece covers whether alcohol break-down product acetaldehyde plays as much a part in drunkenness as alcohol itself, misperceptions about the chances of women having their drink spiked to facilitate sexual assault, and mothers’ perceptions about their kids future drinking patterns.

Alcohol is so embedded in most cultures that perceptions and reality intermix in surprising ways. Last week psychologist Polly Palumbo discussed a 2008 study about mothers’ beliefs about their own kids’ drinking. You might think that if mothers were concerned about their young children becoming drinkers in high school, they might be more successful in preventing some of the kids from actually engaging in underage drinking. In fact, the study, led by Stephanie Madon and published in the Journal of Personality and Social Psychology, found the opposite. Mothers who worried their children might become drinkers had kids that were significantly more likely to drink.

The researchers are careful to point out that the study is just a correlation; we can’t say that the mothers’ belief about drinking is what caused their kids to drink. But because the study was administered over several years, it’s better than many correlational studies: We know the belief preceded the drinking, so it’s pretty much impossible that the kids’ drinking behavior itself led to the belief.

Link to Seed article ‘A Sober Assessment’.

Here is the original post:
Tipsy thinking

A new study just published in Psychological Bulletin has reviewed studies on the effects of violent video games and concludes that they cause a small but reliable increase in aggressive behaviour and anti-social thinking.

The study, led by psychologist Craig Anderson, is a type of meta-analysis which attempts to mathematically aggregate the results of past studies to see what the overall effect is.

There have been several similar studies in recent years which have come to different conclusions, based on whether the results have been thought to have been affected by publication bias or not. In other words, while the published studies suggest there is a small reliable effect of video games on aggression some reviews have suggested this is because fewer of the studies that don’t find a link actually get published.

This new study aimed to include unpublished studies and also looked at studies from both Western cultures, like the US and Europe, and Eastern cultures, such as Japan, to see if social environment influences any potential link.

The review included both observational studies, which look at what happens in the ‘real world’ but can’t tell us whether gaming causes aggression (it could be just that more aggressive people play more violent games), and experimental studies which can determine cause, because participants are randomly assigned to groups and given either violent or non-violent games, but are a little more removed from everyday life.

The researchers examined whether violent video games led to changes in aggressive behaviour, thoughts and emotions, and for changes in empathy and helpful behaviour to others.

Overall, the analysis concluded that violent video gaming causes a small but reliable increase in aggression and possibly a reduction in helpful behaviour and empathy.

The results on empathy were the weakest, however, as only study was an experiment and the researchers lumped together research that used questionnaires and which tested bodily desensitisation (whether people bodily react less to emotional events when they re-experience them) which is not a good measure of someone’s mental state.

One interesting aspect of the analysis is that the researchers looked at a number of game characteristics to see if they had an effect; for example, whether the people were playing in first- or third-person, whether the violence was towards human or non-human characters; and found that none of this made much difference.

What this suggests is that the effect is not due to non-specific priming, a psychological effect whereby experiencing one type of concept makes closely related concepts and actions more accessible and more likely. In this case, the fictional violence is assumed to make aggressive thoughts and actions more easily triggered.

It must be said that the overall effect was quite small. For the statistically inclined, the correlation was r = .19 for all studies and r = .24 when they looked only at the most rigorous research. This means that violent video games accounted for between about 3.6% and 5.8% of the total change in aggressiveness.

Interestingly, despite the fact that Japan, for example, is more culturally adverse to aggression than Western countries, the effects seems to be equally as apparent on either side of the world.

The journal published a discussion based on the study, including a criticism by psychologists Christopher Ferguson and John Kilburn, who have published previous analyses suggesting that the violence effect is down to publication bias.

The discussion focusses on various technical issues which are well answered by the original authors, although perhaps the most significant points of disagreement focus on two areas.

The first is that this new analyses only focused on simple relations, and didn’t take into account whether other factors could be having an influence. For example, a previous study suggested that when pre-existing emotional, family and social problems are accounted for, the aggression increasing effects of video games disappears.

The second concerns how important this small effect is. On an individual level a small change may be undetectable amid the to-and-fro of everyday life, but at the level of the population it could conceivably increase the number of aggressive incidents, although these are often the hardest effects to track.

Link to PubMed entry for study.
pdf of full text.

Here is the original post:
Violent video games: small causal link with aggression