The Domain-General Multiple Demand network is More Active in Early Balanced Bilinguals than Monolinguals During Executive Processing

The bilingual experience may place special cognitive demands on speakers and has been argued to lead to improvements in domain-general executive abilities, like cognitive control and working memory. Such improvements have been argued for based on both behavioral and brain imaging evidence. However, the empirical landscape is complex and ridden by controversy. Here we attempt to shed light on this question through an fMRI investigation of relatively large, relatively homogeneous, and carefully matched samples of early balanced bilinguals (n=55) and monolinguals (n=54) using robust, previously validated individual-level markers of neural activity in the domain-general Multiple Demand (MD) network, which supports executive functions. We find that the bilinguals, compared to the monolinguals, show significantly stronger neural responses to an executive (spatial working memory) task, and a larger difference between a harder and an easier condition of the task, across the MD network. These stronger neural responses are accompanied by better behavioral performance on the working memory task. We further show that the bilingual-vs.-monolingual difference in neural responses is not ubiquitous across the brain as no group difference in magnitude is observed in primary visual areas, which also respond to the task. Although the neural group difference in the MD network appears robust, it remains difficult to causally link it to bilingual experience specifically. Dedication: We would like to dedicate this paper to the memory of Albert Costa, who we both knew well and loved as a mentor and a friend. Saima will always be grateful that Albert let her spend her senior year in his lab despite not even being from the same university; his support, mentorship and guidance helped her not stray away from academia when things got tough. And Ev will forever remember the weekly Friday night partying with Albert and the rest of the “crew” in The Cellar and The People’s Republik during her undergrad years in the Caramazza Lab in the late 1990s and early 2000s.

In Search of the Executive Cognitive Processes Proposed by Process-Overlap Theory

Process-Overlap Theory (POT) suggests that measures of cognitive abilities sample from sets of independent cognitive processes. These cognitive processes can be separated into domain-general executive processes, sampled by the majority of cognitive ability measures, and domain-specific processes, sampled only by measures within a certain domain. According to POT, fluid intelligence measures are related because different tests sample similar domain-general executive cognitive processes to some extent. Re-analyzing data from a study by De Simoni and von Bastian (2018), we assessed domain-general variance from executive processing tasks measuring inhibition, shifting, and efficiency of removal from working memory, as well as examined their relation to a domain-general factor extracted from fluid intelligence measures. The results showed that domain-general factors reflecting general processing speed were moderately and negatively correlated with the domain-general fluid intelligence factor (r = −.17–−.36). However, domain-general factors isolating variance specific to inhibition, shifting, and removal showed only small and inconsistent correlations with the domain-general fluid intelligence factor (r = .02–−.22). These findings suggest that (1) executive processing tasks sample only few domain-general executive processes also sampled by fluid intelligence measures, as well as (2) that domain-general speed of processing contributes more strongly to individual differences in fluid intelligence than do domain-general executive processes.

Sensory experience modulates the reorganisation of temporal auditory regions for executive processing

Crossmodal plasticity refers to the reorganisation of sensory cortices in the absence of their main sensory input. Understanding this phenomenon provides insights into brain function and its potential for change and enhancement. Using fMRI, we investigated how early deafness and consequent varied language experience influence crossmodal plasticity and the organisation of executive functions (EF) in the adult brain. Results from four visual EF tasks (working memory, switching, planning, inhibition) show that, as a function of the degree of deafness, deaf individuals specifically recruit “auditory” regions during switching. This recruitment correlates with performance, highlighting its functional relevance. We also observed recruitment of auditory temporal regions during planning, but only in deaf individuals with the highest language scores, suggesting differential use of linguistic skills to support EF. Our results show executive processing in typically sensory regions, suggesting that the development and ultimate role of brain regions are influenced by perceptual environmental experience.

Alpha and theta brain oscillations play a complementary role in inducing levels of altered consciousness during meditation practice

Background: Neurobiological changes accompanying meditation training are well-characterised. However, little is known about the neural and physiological basis of altered consciousness induced through meditation, despite such alteration being considered essential for the positive effects of meditation on mental health. The meditation depth questionnaire (MEDEQ) measures alteration of consciousness in five progressive levels of experiential “depth”: hindrances, relaxation, concentration, transpersonal qualities and nonduality. Methods: Using the MEDEQ, we investigated the brain (EEG) and bodily (pulse and respiration) correlates of meditation depth in two groups: long-term meditators (LTM) and meditation-naïve controls (CTL). Results: CTLs reported experiencing more hindrances than LTMs. Whereas, LTMs reported more transpersonal qualities and nonduality during practice compared to baseline. In both groups, theta (4–6 Hz) oscillations correlated positively with hindrances, and increasingly negatively with progressively deeper experiences. Alpha (7–13 Hz) amplitude followed the exact opposite pattern. Experiential deepening was accompanied by theta deactivation over different regions in the two groups—frontal-midline in LTMs and frontal-lateral in CTLs—which correspond to two different aspects of executive processing, monitoring and regulation respectively. Experiential deepening was also associated with reduced heart-rate in CTLs but not LTMs. Conclusions: Alpha and theta oscillations have long been reliably associated with meditation. Our study reveals how they relate to different subjective experiences accompanying such practices. We moreover find that—while critical for overcoming hindrances—executive neural processing is downregulated during deep meditation experiences, and that prolonged training enables downregulation of an earlier stage of executive processing. Finally, prolonged meditation training may help reduce interoceptive influences on conscious experience.