The brain dictionary

Natural speech reveals the semantic maps that tile human cerebral cortex
Alexander G. Huth, Wendy A. de Heer, Thomas L. Griffiths, Frédéric E. Theunissen & Jack L. Gallant.
Nature 532, 453–458 (28 April 2016)

The meaning of language is represented in regions of the cerebral cortex collectively known as the ‘semantic system’. However, little of the semantic system has been mapped comprehensively, and the semantic selectivity of most regions is unknown. Here we systematically map semantic selectivity across the cortex using voxel-wise modelling of functional MRI (fMRI) data collected while subjects listened to hours of narrative stories. We show that the semantic system is organized into intricate patterns that seem to be consistent across individuals. We then use a novel generative model to create a detailed semantic atlas. Our results suggest that most areas within the semantic system represent information about specific semantic domains, or groups of related concepts, and our atlas shows which domains are represented in each area. This study demonstrates that data-driven methods—commonplace in studies of human neuroanatomy and functional connectivity—provide a powerful and efficient means for mapping functional representations in the brain.

Explore the brain model for yourself here: http://gallantlab.org/huth2016

 

Sleep and emotion regulation

The interplay between sleep and emotion regulation: conceptual framework empirical evidence and future directions.
Gruber R, Cassoff J.
Curr Psychiatry Rep. 2014 Nov;16(11):500. 

Emotions are biologically-based responses that help an organism meet challenges and opportunities, and involve changes in subjective experience, behavior, and physiology. Emotions arise when something important to us is at stake. Although many factors have been associated with healthy emotional regulation, the role of sleep in this process has been largely ignored. Recent studies, however, have begun to delineate how sleep critically affects emotional functioning. Nighttime sleep affects daytime mood, emotional reactivity and the capacity to regulate positive and negative emotions; conversely, daytime experiences affect sleep. Hence, there is a complex interplay between sleep and emotional regulation. The objective of this article is to examine this interplay in adults. This objective is addressed by utilizing a framework that identifies key aspects of the relationship between sleep and emotion. We propose that the connectivity between the emotional centers of the brain - the prefontal cortex and the amygdala - is in part dependent on the homeostatic sleep system such that connectivity between these brain networks is higher when rested and lower when sleep deprived. High connectivity drives more efficient executive functioning, while a disconnect leads to poor executive functioning capacity including emotional reactivity and impulsivity. The cognitive effects of the homeostatic system are couple with the mood regulation effects of the circadian system together dictating the degree to which one experiences emotional regulation or dysregulation. Further, the affective brain systems of individuals with clinical symptomology and/or pathology are suggested to be more vulnerable to homeostatic pressure and circadian lows or misalignment resulting in increased affective clinical symptomology. We review empirical evidence that supports this framework and explore the implications of this framework. Finally, we describe future directions for this type of work.

Good sleep = good memory

Prefrontal atrophy, disrupted NREM slow waves and impaired hippocampal-dependent memory in aging
Bryce A Mander, Vikram Rao, Brandon Lu, Jared M Saletin, John R Lindquist, Sonia Ancoli-Israel, William Jagust & Matthew P Walker
Nature Neuroscience (2013) 

Aging has independently been associated with regional brain atrophy, reduced slow wave activity (SWA) during non–rapid eye movement (NREM) sleep and impaired long-term retention of episodic memories. However, whether the interaction of these factors represents a neuropatholgical pathway associated with cognitive decline in later life remains unknown. We found that age-related medial prefrontal cortex (mPFC) gray-matter atrophy was associated with reduced NREM SWA in older adults, the extent to which statistically mediated the impairment of overnight sleep–dependent memory retention. Moreover, this memory impairment was further associated with persistent hippocampal activation and reduced task-related hippocampal-prefrontal cortex functional connectivity, potentially representing impoverished hippocampal-neocortical memory transformation. Together, these data support a model in which age-related mPFC atrophy diminishes SWA, the functional consequence of which is impaired long-term memory. Such findings suggest that sleep disruption in the elderly, mediated by structural brain changes, represents a contributing factor to age-related cognitive decline in later life.

Small-world network organization during sleep

The functional connectivity of different EEG bands moves towards small-world network organization during sleep.
Ferri R, Rundo F, Bruni O, Terzano MG, Stam CJ.
Clin Neurophysiol. 2008 Sep;119(9):2026-36.

Background: To analyze the functional connectivity patterns of the different EEG
bands during wakefulness and sleep (different sleep stages and cyclic alternating
pattern (CAP) conditions), using concepts derived from Graph Theory.

Methods: They evaluated spatial patterns of EEG band synchronization between all possible pairs of electrodes (19) placed over the scalp of 10 sleeping healthy young normal subjects using two graph theoretical measures: the clustering coefficient (Cp) and the characteristic path length (Lp). The measures were obtained during wakefulness and the different sleep stages/CAP conditions from the real EEG connectivity networks and randomized control (surrogate) networks (Cp-s and Lp-s).

Results: They found the values of Cp and Lp compatible with a small-world network organization in all sleep stages and for all EEG bands. All bands below 15Hz showed an increase of these features during sleep (and during CAP-A phases in particular), compared to wakefulness.

Conclusion: The results of this study seem to confirm the initial hypothesis that during sleep there exists a clear trend for the functional connectivity of the EEG to move forward to an organization more similar to that of a small-world network, at least for the frequency bands lower than 15Hz. Sleep network "reconfiguration" might be one of the key mechanisms for the understanding of the "global" and "local" neural plasticity taking place during sleep.