Joshua Skewes

Long-term meditation is associated with increased gray matter density in the brain stem

Extensive practice involving sustained attention can lead to changes in brain structure. Here, we report evidence of structural differences in the lower brainstem of participants engaged in the long-term practice of meditation. Using magnetic resonance imaging, we observed higher gray matter density in lower brain stem regions of experienced meditators compared with age-matched nonmeditators. Our findings show that long-term practitioners of meditation have structural differences in brainstem regions concerned with cardiorespiratory control. This could account for some of the cardiorespiratory parasympathetic effects and traits, as well as the cognitive, emotional, and immunoreactive impact reported in several studies of different meditation practices.

Extreme Rituals Promote Prosociality

Extreme rituals entail excessive costs without apparent benefits, which raises an evolutionary cost problem (Irons, 2001). It is argued that such intense rituals enhance social cohesion and promote cooperative behaviors (Atran & Henrich, 2010; Durkheim, 1912). However, direct evidence for the relation between ritual intensity and prosociality is lacking. Using economic measures of generosity and contextually relevant indicators of group identity in a real-world setting, we evaluated pro- social effects from naturally occurring rituals that varied in severity.

Dopaminergic stimulation enhances confidence and accuracy in seeing rapidly presented words

Liberal acceptance, overconfidence, and increased activity of the neurotransmitter dopamine have been proposed to account for abnormal sensory experiences, for instance, hallucinations in schizophrenia. In normal subjects, increased sensory experience in Yoga Nidra meditation is linked to striatal dopamine release. We therefore hypothesize that the neurotransmitter dopamine may function as a regulator of subjective confidence of visual perception in the normal brain. Although much is known about the effect of stimulation by neurotransmitters on cognitive functions, their effect on subjective confidence of perception has never been recorded experimentally before. In a controlled study of 24 normal, healthy female university students with the dopamine agonist pergolide given orally, we show that dopaminergic activation increases confidence in seeing rapidly presented words. It also improves performance in a forced-choice word recognition task. These results demonstrate neurotransmitter regulation of subjective conscious experience of perception and provide evidence for a crucial role of dopamine.

Continuous Theta-Burst Stimulation Demonstrates a Causal Role of Premotor Homunculus in Action Understanding

Although it is well established that regions of premotor cortex (PMC) are active during action observation, it remains controversial whether they play a causal role in action understanding. In the experiment reported here, we used off-line continuous theta-burst stimulation (cTBS) to investigate this question. Participants received cTBS over the hand and lip areas of left PMC, in separate sessions, before completing a pantomime-recognition task in which half of the trials contained pantomimed hand actions, and half contained pantomimed mouth actions. The results reveal a double dissociation: Participants were less accurate in recognizing pantomimed hand actions after receiving cTBS over the hand area than over the lip area and less accurate in recognizing pantomimed mouth actions after receiving cTBS over the lip area than over the hand area. This finding constrains theories of action understanding by showing that somatotopically organized regions of PMC contribute causally to action understanding and, thus, that the mechanisms underpinning action understanding and action performance overlap.

Perceptual Inference and Autistic Traits.

Autistic people are better at perceiving details. Major theories explain this in terms of bottom-up sensory mechanisms or in terms of top-down cognitive biases. Recently, it has become possible to link these theories within a common framework. This framework assumes that perception is implicit neural inference, combining sensory evidence with prior perceptual knowledge. Within this framework, perceptual differences may occur because of enhanced precision in how sensory evidence is represented or because sensory evidence is weighted much higher than prior perceptual knowledge. In this preliminary study, we compared these models using groups with high and low autistic trait scores (Autism-Spectrum Quotient). We found evidence supporting the cognitive bias model and no evidence for the enhanced sensory precision model.

What if I Get Busted? Deception, Choice, and Decision-Making in Social Interaction.

Deception is an essentially social act, yet little is known about how social consequences affect the decision to deceive. In this study, participants played a computerized game of deception without constraints on whether or when to attempt to deceive their opponent. Participants were questioned by an opponent outside the scanner about their knowledge of the content of a display. Importantly, questions were posed so that, in some conditions, it was possible to be deceptive, while in other conditions it was not. To simulate a realistic interaction, participants could be confronted about their claims by the opponent. This design, therefore, creates a context in which a deceptive participant runs the risk of being punished if their deception is detected. Our results show that participants were slower to give honest than to give deceptive responses when they knew more about the display and could use this knowledge for their own benefit. The condition in which confrontation was not possible was associated with increased activity in subgenual anterior cingulate cortex. The processing of a question which allows a deceptive response was associated with activation in right caudate and inferior frontal gyrus. Our findings suggest the decision to deceive is affected by the potential risk of social confrontation rather than the claim itself.

Synchronised and complementary coordination mechanisms in an asymmetric joint aiming task

Many forms of social interaction require that behaviour be coordinated in the here and now. Much research has been conducted on how people coordinate their actions in real time to achieve a joint goal, showing that people use both synchronised (i.e. symmetric) and complementary (i.e. asymmetric) strategies. These two mechanisms have been mostly studied independently, the former in the context of rhythmic tasks, and the latter in non-rhythmic tasks. However, people often balance these two strategies in real-life social interactions, in order to achieve a joint goal more effectively. Here, our aim was to investigate how people may implicitly balance synchronisation and complementarity in a continuous joint aiming task. We asked dyads to synchronise the timing of their clicks between targets, while changing task constraints for one member of the dyad (i.e. different task difficulties) to asymmetrically perturb the continuous interaction. This allowed us to investigate how individuals implicitly negotiate complementary leader–follower dynamics to achieve synchronisation. We found that dyads flexibly switch from mutual to asymmetric adaptation given variations in task constraints. Specifically, our results show that both members adapt equally up to a certain level of difficulty; after this point, the partner with the difficult task becomes less adaptive, and hence more of a leader, while the adaptability of the member with the easier task remains unchanged. This proves to be an effective strategy in this asymmetric task, as people synchronise better with an irregular, but adaptive partner, than with a completely predictable, but non-responsive metronome. These results show that given asymmetric task constraints, adaptability, rather than predictability, facilitates coordination.

Intact brain processing of musical emotions in autism spectrum disorder, but more cognitive load and arousal in happy vs. sad music

Music is a potent source for eliciting emotions, but not everybody experience emotions in the same way. Individuals with autism spectrum disorder (ASD) show difficulties with social and emotional cognition. Impairments in emotion recognition are widely studied in ASD, and have been associated with atypical brain activation in response to emotional expressions in faces and speech. Whether these impairments and atypical brain responses generalize to other domains, such as emotional processing of music, is less clear. Using functional magnetic resonance imaging, we investigated neural correlates of emotion recognition in music in high-functioning adults with ASD and neurotypical adults. Both groups engaged similar neural networks during processing of emotional music, and individuals with ASD rated emotional music comparable to the group of neurotypical individuals. However, in the ASD group, increased activity in response to happy compared to sad music was observed in dorsolateral prefrontal regions and in the rolandic operculum/insula, and we propose that this reflects increased cognitive processing and physiological arousal in response to emotional musical stimuli in this group.

Atypical perception of affective prosody in Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is characterized by impairments in language and social–emotional cognition. Yet, findings of emotion recognition from affective prosody in individuals with ASD are inconsistent. This study investigated emotion recognition and neural processing of affective prosody in high-functioning adults with ASD relative to neurotypical (NT) adults. Individuals with ASD showed mostly typical brain activation of the fronto-temporal and subcortical brain regions in response to affective prosody. Yet, the ASD group showed a trend towards increased activation of the right caudate during processing of affective prosody and rated the emotional intensity lower than NT individuals. This is likely associated with increased attentional task demands in this group, which might contribute to social–emotional impairments.

Enhancing effects of acetazolamide on neuronal activity correlate with enhanced visual processing ability in humans

Acetazolamide is a potent inhibitor of the reversible hydration of CO(2) catalyzed by the enzyme carbonic anhydrase and is commonly used to increase cerebral blood flow e.g. in order to estimate cerebrovascular reserve. However it is not known whether acetazolamide may positively affect the excitability of neurons in the brain in vivo or cortical processing abilities. To test these possibilities we intravenously administered a low dose (7 mg/kg) acetazolamide to volunteers who performed a demanding visual signal detection task while undergoing whole brain electroencephalographic examinations. Two groups were tested twice on the same task, while receiving acetazolamide or a saline treatment in between the two sessions. Our data indicate that, while the control group showed a decrease in global gamma (30-49 Hz) power across sessions, with no correlation to performance, the acetazolamide group showed increased global gamma power that strongly related to their performance in the signal detection task. This was accompanied by a decrease in the early part of the event related potential in the control group, a decrease not seen in the acetazolamide group. There were no significant differences in blood pressure, ventilation rate, or heart rate between the two groups. It is possible that the differences between the groups, observed in this study, are related to the enhancing effect of acetazolamide on the nitric oxide generation catalyzed by carbonic anhydrase, or to other actions of acetazolamide, e.g. opening of Ca(2+) activated K(+) channels and inhibition of Ca(2+) channels.