Digest

Using brain imaging to re-evaluate psychology's three most famous cases
In Cerebral Cortex

It's 50 years since the American neurologist Norman Geschwind published his hugely influential Disconnexion Syndromes in Animals and Man, in which he argued that many brain disorders and injuries could best be understood in terms of the damage incurred to the white-matter pathways connecting different areas of the brain.

To mark this anniversary, an international team of researchers has used modern brain-imaging techniques to reveal, in an open-access article for Cerebral Cortex, the likely damage to brain connectivity suffered by three of psychology's most famous cases: the 19th-century rail worker Phineas Gage, who survived an iron rod passing through his brain; Louis Victor Leborgne, the 19th-century aphasic patient studied by Paul Broca who played a key role in our understanding of language function in the brain; and the most studied amnesiac in history, Henry Molaison (known as H.M. in the literature), who died in 2008.

Michel Thiebaut de Schotten and his colleagues first obtained existing information about the brains of these three cases. For Gage they used a CT scan taken of his skull by researchers in 2004 and mapped the signs of injury onto a simulation of his brain. Leborgne's brain is in preservation at the Dupuytren Museum in Paris, and they used an MRI scan of it taken in 2007. For Molaison's brain they used an MRI scan taken while he was still alive in 1993.

Next, the researchers created an intricately detailed map of the human brain's connective pathways. They used an advanced version of a technique known as diffusion tensor imaging to plot the connective tissues in the brains of 129 healthy volunteers (aged 18–79; 59 men). They combined the data from all these healthy people's brains to create an average roadmap of the human brain's connective tracts.

The final step involved applying the information on the brain damage incurred by the three famous cases onto this roadmap of the human brain's connective pathways, to see which important tracts had probably been affected.

In the case of Gage, the researchers estimate that he suffered widespread damage to several connective pathways in his frontal lobes, beyond the specific damage thought to have been inflicted by the passage of the iron bar. These pathways include the uncinate fasciculus, the frontal intralobar networks, and the fronto-striatal-thalamal-frontal network, with likely implications for his decision making and emotional functioning.

Mapping Leborgne's brain lesions onto the connectivity roadmap, the researchers estimate that he suffered extensive damage to many tracts, including almost all the dorsolateral tracts of the left hemisphere, which would have had profound implications for his language function (on top of the effects caused by localised damage to what is now known as Broca's area in the left frontal lobe). The researchers think Leborgne also likely suffered damage to pathways not involved in language, such as the left cortico-spinal tract (which could explain the documented paralysis of his right arm and leg).

Finally, turning to Molaison, the researchers again estimate widespread damage to connective tissues beyond the main brain regions, including the hippocampus, that were directly removed by surgery (Molaison became amnesic after radical neurosurgery to treat his epilepsy). This includes the fornix, the ventral cingulum, uncinate fasciculus and anterior commissure. Damage to that last tract, which is involved in processing smell, might explain lab reports that Molaison had problems with his odour discrimination.

What to make of these new insights? The researchers said they have 'demonstrated the validity of applying an atlas based approach to reappraise the effects of disconnection in 3 historic patients'. Their research is certainly a fitting tribute to the legacy of Geschwind, showing how 'social behaviour, language, and memory depend on the coordinated activity of different regions rather than single areas in the frontal or temporal lobes'. However, the researchers also admitted that much caution is needed: their research involved many ambitious leaps and generalisations. What is for sure is that these new insights will further fuel the mythical status of these three patients. Gage, Leborgne and Molaison are the psychological case studies that just keep giving. cj

The psychological toll of being off-duty but 'on call'  
In Journal of Occupational Health Psychology

That increasingly common end-of-day feeling: of physically leaving the office, only for it to tag along home. Thanks largely to technology, our availability – to clients, bosses and co-workers – extends into our evenings, weekends and even holidays. Getting a clear account of what this means for us isn't easy, as jobs that intrude more into leisure time are also distinguished by higher pace and further factors known and unknown, making it hard to pinpoint what harmful effects, if any, are specifically due to our constant availability.

A new study published in the Journal of Occupational Health Psychology, and led by Jan Dettmers at the University of Hamburg, takes a fresh tack on this, investigating workers who have two types of free time: on-call periods where they are free to please themselves but must remain available for potential work demands, and other periods where they are truly off-duty. For each individual participant, this set-up keeps job-role demands and responsibilities equal while varying the need to be available. The data suggest that extended work availability has a negative effect: dampening mood and also increasing markers of physiological stress.

The 132 participants – mostly men in 13 organisations ranging from IT to transport – spent periods of their calendar on-call, meaning they were available out of office hours to deal with special customer requests or troubleshoot technical emergencies. For the purposes of the study, the researchers focused on a four-day on-call period (including the weekend) and a similar period without on-call responsibilities.

During the study, participants completed morning mood diaries that showed them to be more tired, tense and unwell following an on-call day. The effect remained even after controlling for the number of work calls taken the previous day – suggesting it isn't explained purely by lengthy and draining interactions. It's likely that the mere anticipation of interruption, and the resulting loss of control over one's free time, eats away at the benefits of leisure, even if the interruptions turn out to be minor.

In addition to the diary information, 51 participants provided physiological data in the form of the hormone cortisol. Cortisol can be used as a physiological marker of stress: specifically, the degree of its post-waking climb in concentration, which appears to be a preparation for the anticipated stresses of the day. A larger increase suggests a more stress-oriented state, and Dettmers and his team were able to analyse this from cotton balls that participants chewed on immediately after waking, and 15 minutes and 30 minutes after waking, before popping them into the freezer to await collection. The cortisol awakening response was greater the morning after an on-call day, with this effect also persisting once the volume of the previous day's interruptions was controlled for.

We already know that use of work technology during free time makes it harder to relax and detach. Here we see further evidence that the mere prospect of work-related interruptions during free time can exacerbate stress. In the organisations researched in this study, on-call periods were formally identified as such and represented just a fraction of the work calendar; an unspoken truth in many organisations is that on-call is the unofficial default mode. In these cases, carving out truly off-call periods that allow people to reclaim control over their experiences is long overdue. af

Mental effort is contagious
In Psychonomic Bulletin and Review

If you're about to dive into a piece of work that requires intense mental focus, you might find it helps to sit next to someone else who is concentrating hard. According to an ingenious new study published in Psychonomic Bulletin and Review, mental exertion is contagious: if a person near you is straining their synapses in mental effort, their mindset will automatically intensify your own concentration levels.

Psychologists have known since at least the 1960s that the presence of other people affects our own performance in predictable ways. For example, the 1965 social facilitation theory describes how the presence of other people makes it easier to perform well-rehearsed, automatic behaviours. Yet company can also be distracting and make it more difficult to perform behaviours that require mental control.

Kobe Desender at Vrije Universiteit in Belgium and his colleagues wanted to build on these findings by testing whether it makes a difference to our performance what other people present are doing – and specifically, if someone else is using a lot of mental effort, does that affect how much mental effort we exert ourselves?

Thirty-eight participants (20 women; average age 22) performed a version of what's known as the 'Simon task' in pairs. Coloured squares appeared on either the left- or right-hand side of a computer screen. When two of the four possible colours of square appeared, the person sitting to the left of the screen was required to press the 'd' keyboard key as fast as possible with their left hand. When either of the two other possible coloured squares appeared, the person on the right was required to press the 'k' key as fast as possible with their right hand. Superior performance is revealed through faster responding and fewer errors. Although the task was performed in pairs in this way, there was no need or possibility for collaboration between partners, nor was there any competition.

An important thing to understand about this task is that it was easier for participants to respond to a target square (i.e. one that was a colour that they had been instructed to respond to) when it appeared on the same side that they were sitting, and that was therefore also the same side as the hand they were using to respond – that is, when the target and response were congruent. Also, the higher the proportion of congruent trials that a participant was subjected to, the easier the task would become, because they could switch to a more automatic mode of responding.

The researchers manipulated task difficultly individually for each person in a pair by varying their proportion of congruent versus incongruent trials. The issue of stimulus-response congruence also provided a ready indicator of a person's concentration levels. If a person was trying really hard, their performance would be less affected by whether their target squares were congruent or not.

Desender and his team were especially interested in those instances when they made the task super difficult for one participant (he or she had only 10 per cent congruent trials), but they kept the difficulty medium for the other participant (they had a 50/50 mix of congruent and incongruent trials). In this situation, the participant in the difficult version was required to use maximum mental effort to succeed. The intriguing finding is that this mental effort influenced their partner. A person playing alongside someone who was forced to concentrate really hard was themselves less influenced by their own targets' congruency – a sure sign they too were trying harder than normal. Somehow one person's hidden mental effort seemed to influence the other.

Further analysis confirmed that this effect was not caused simply by one player mimicking the other's response speed. Nor was it that the participants were influenced by looking at their partner's ratio of congruent and incongruent trials and seeing that their task was more difficult. The researchers ruled out this possibility in a follow-up study in which each player had their own display, and a piece of cardboard stopped them from being able to see their partner's squares.

The researchers don't know what led one player's levels of mental effort to contaminate their partner, but they speculate that perhaps it had to do with body posture. Maybe the person forced to concentrate extra hard adopted a more tense body posture and this sign of mental effort automatically influenced their partner to also concentrate extra hard. However, they added that a 'more radical hypothesis should also be considered, such as the possibility that effort exertion is influenced by a difference in scent of someone else exerting high or low effort'. cj

Looking for the brain basis of chimp personality  
In NeuroImage

Some chimps are more outgoing than others. Some like trying out new foods and games while their friends stick to the tried and tested. In short, chimps have personalities, just like we do. What's more, psychologists investigating chimp personality have found that their traits tend to coalescence into five main factors, again much like human personality. Three of these are named the same as their human equivalents: Extraversion, Openness and Agreeableness. The other two are Dominance (a bit like the opposite of the human trait of Neuroticism) and Reactivity/Undependability (opposite to the human trait Conscientiousness).

The neurobiological basis of human personality is a thriving area of research, but this study published in NeuroImage by a team of psychologists and primatologists is the first to look at the brains of chimpanzees to try to find the neural correlates of personality differences in our evolutionary cousin.

The chimps were residents at the University of Texas MD Anderson Cancer Center. There were 50 males with an average age of 22 and 57 females with an average age of 20. Robert Latzman and his colleagues relied on colony staff to rate the chimps' personalities using a 41-item personality questionnaire that tapped the chimp equivalent of the five main personality traits. The chimps then sedated while their brains were scanned by MRI.

Evidence has linked many aspects of human personality to features of the frontal cortex, so the researchers decided to focus their investigation in that part of the chimp brain. After controlling for age and sex (older chimps were less reactive and less extravert; males tended to be more extravert and dominant), they found that the more grey matter a chimp had in the frontal cortex, the more dominant, open and extravert the chimp tended to be. The researchers said this potentially reflects the broad role of the frontal cortex in 'the control of emotions in the service of goal-directed behaviour'.

Zooming in on a particular sub-structure in the frontal cortex, the anterior cingulate cortex (ACC; associated in humans with motivation and expectations, among other things), higher Extraversion and Openness were associated with more grey matter in this structure. The researchers also looked at asymmetries between the chimps' brain hemispheres, where they found that more grey matter volume in the right hemisphere was associated with higher Extraversion and Dominance, contradicting human research linking approach behaviours with the left hemisphere. However, when the they looked at asymmetries in specific structures, including the ACC and the medial prefrontal cortex, they found that more grey matter in the right hemisphere was associated with more reactivity, while a left-hemisphere bias was associated with more dominance, which is more consistent with human evidence.

The study makes a start at exploring the neurobiology of chimp personality, but it does have some problems, including the cross-sectional design (were the brain differences a cause or consequence of personality differences?), the exclusive focus on the frontal cortex, and the way the researchers translated each chimp's brain structure onto a common template, thus losing some of the individuality between chimps. Nonetheless, Latzman and his colleagues said their findings added further evidence to the idea that human personality has an evolutionary and biological basis, and confirmed 'the importance of neuroscientific approaches to the study of basic dispositions (i.e. personality)…suggest[ing] that many of these associations are comparable in chimpanzees'. cj

The material in this section is taken from the Society's Research Digest blog at www.bps.org.uk/digest, and is written by its editor Dr Christian Jarrett and contributor Dr Alex Fradera.

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