Excellent review of how wide-spread brain areas use synchronized rhythms form networks for focusing attention. Very comprehensive and thorough on both a maco and micro-circuit level.
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It is widely thought that the volitional focusing of attention on a sensory input depends on top-down influences from the prefrontal cortex (PFC) acting on sensory cortex. However, much of the evidence for this is circumstantial. Halassa et al now provide direct evidence using optogenetic manipulation in mice. When they temporarily disrupted the PFC, mice had trouble focusing on a visual input in the face of an auditory distraction and vice-versa. Moreover, they went on to show that the PFC acts on sensory cortex, not directly but, through the thalamic reticular nucleus (TRN). Manipulation of thalamocortical circuits showed that behavior depended on PFC interactions with the thalamus, not on PFC interactions with sensory cortex. Further, thalamic activity was correlated with behavioral performance and its manipulation was causal to performance. This all suggests that attention is focused when the PFC acts on sensory cortex via the thalamus.
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Pascal Fries walks us through the latest in the communication through coherence theory.
Fries, Pascal. “Rhythms for Cognition: Communication through Coherence.”Neuron 88.1 (2015): 220-235.
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Tim Buschman and Sabine Kastner review work on visual attention and propose a new theory that ties together a wide range of observations. Here’s an outline of the theory in their own words:
- Attention can either be (a) automatically grabbed by salient stimuli or (b) guided by task representations in frontal and parietal regions to specific spatial locations or features.
- The pattern-completion nature of sensory cortex sharpens the broad top-down attentional bias, restricting it to perceptually relevant representations. Interactions with bottom-up sensory drive will emphasize specific objects.
- Interneuron-mediated lateral inhibition normalizes activity and, thus, suppresses competing stimuli. This results in increased sensitivity and decreased noise correlations.
- Lateral inhibition also leads to the generation of high-frequency synchronous oscillations within a cortical region. Inter-areal synchronization follows as these local oscillations synchronize along with the propagation of a bottom-up sensory drive. Both forms of synchrony act to further boost selected representations.
- Further buildup of inhibition acts to “reset” the network, thereby restarting the process. This reset allows the network to avoid being captured by a single stimulus and allows a positive-only selection mechanism to move over time.
Makes a lot of sense.
Buschman, Timothy J., and Sabine Kastner. “From Behavior to Neural Dynamics: An Integrated Theory of Attention.” Neuron 88.1 (2015): 127-144. -
Nice demo showing that cues that automatically draw attention can modulate activity in primary visual cortex.
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Erez and Duncan elegantly show that the prefrontal cortex only cares about behavioral (goal) relevance. Human subjects detected whether images from one of two visual categories were present in a scene. The prefrontal cortex did not distinguish between the two categories but did distinguish whether an image was one the two categories (i.e., a target) or not (a non-target).
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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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Micheli et al find that during sustained attention, successful near-threshold visual detection is predicted by increased phase synchrony between the frontal and temporal/parietal cortex. They suggest that beta coherent states in the prefrontal cortex regulate top-down expectancy and coupling with posterior cortex facilitates the gating of that information.
Evidence for the role of beta in top-down selection continues to mount.
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As the authors pun, the claustrum is worthy of attention given its extensive connections with the cortex. Goll, Atlan, and Citri propose a new hypothesis for the role of inputs from the prefrontal cortex to the claustrum in top-down attentional selection. The claustrum acts to control the output of selected cortical representations at the expense of others.
Goll, Yael, Gal Atlan, and Ami Citri. “Attention: the claustrum.” Trends in Neurosciences (2015).
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Bonnefond and Jenson used MEG in humans to find coupling between alpha and gamma rhythms during an attention-demanding task. High alpha power was associated with weak gamma power at the trough of the alpha cycle. This may provide a mechanism for top-down control of attention.