Review: Kei Igarashi argues that learning-related changes in synchrony between oscillatory activity in the cortex and hippocampus enhances neural communication and thus supports memory storage and recall.
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Fries and colleagues report that coupling between theta and gamma rhythms support attention. The 4 Hz phase of gamma oscillations predicted the accuracy of the subject’s ability to detect stimulus dimming.
Landau, Ayelet Nina, et al. “Distributed Attention Is Implemented through Theta-Rhythmic Gamma Modulation.” Current Biology (2015).
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Voytek et al provide more evidence that oscillatory dynamics play a critical role in neural communication and cognitive control. As humans performed tasks that required greater abstraction, there was an increase in theta synchrony between anterior and posterior frontal cortex. This may allow more anterior frontal cortex is communicate the higher level goals to motor cortex.
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Kozma et al report brief periods of de-synchronization followed by intense synchronization. They speculate that this may correspond to an “aha!” moment when things “fall into place”. Interesting.
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Matt Wilson and colleagues describe how oscillatory cycles can be viewed as functional units, how different oscillation phases can represent distinct computations, and how all this can be organized across cycles. Phew!
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The title says it all (almost). Voloh et al found increased theta-gamma cross-frequency coupling between the anterior cingulate and prefrontal cortex during covert shifts of attention.
Theta–gamma coordination between anterior cingulate and prefrontal cortex indexes correct attention shifts
Benjamin Voloh, Taufik A. Valiante, Stefan Everling, and Thilo Womelsdorf
PNAS 2015 ; published ahead of print June 22, 2015, doi:10.1073/pnas.1500438112 -
Working memory has long been thought to depend on sustained firing of cortical neurons. However, single neurons showing unbroken sustained activity is rare and average population activity is often only strong near the end of a memory delay. Mark Stokes presents the intriguing hypothesis for activity-silent working memory. He suggests that working memory depends on patterns of functional connectivity between neurons, not sustained activity.
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Kundu et al recorded EEG from humans during a short-term memory task. They found fronto-parietal coherence in different frequencies were associated with different memory functions. Alpha coherence was associated with maintenance of the information in memory. By contrast, the top-down filtering of distractions was associated with beta coherence. This adds to mounting evidence that specific frequency bands are associated with specific types of cortical processing like, for example, beta and top-down control.
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Ardid et al use spike shape and firing variability to identify different classes in the primate prefrontal cortex. They ID four classes of broad spiking neurons and three classes of narrow spiking (inhibitory) neurons. These cell classes show different strength of synchrony to local field potential oscillations at specific frequencies. The authors suggest this reflects canonical cortical circuits with different functions.
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Georgia Gregoriou and colleagues review the role of oscillations in the focusing of attention. They suggest that different frequencies reflect the biophysical properties of different cell types and that synchrony allows selective routing of information through these cell populations.