Wutz et al used a visual forward-masking paradigm (mask then target) to study the neural basis of visual perception. The mask sometimes interfered with perception of the target. Higher beta power before the mask was associated with incorrect perception of the target. Evoked alpha phase reset was associated with correct target perception. This shows how oscillatory dynamics may play a role in carving successive visual inputs into separate perceptions.
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This review examines evidence for a neurobiological explanation of executive functions of working memory. We suggest that executive control stems from information about task rules acquired by mixed selective, adaptive coding, multifunction neurons in the prefrontal cortex. Their output dynamically links the cortical-wide networks needed to complete the task. The linking may occur via synchronizing of neural rhythms, which may explain why we have a limited capacity for simultaneous thought.
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Is conscious perception continuous or discrete? Asplund et al use the attentional blink paradigm to demonstrate that conscious perception is discrete and quantal. Attention increases the probability that a representation will reach awareness.
We have argued that cognition is discrete and quantal because the backbone of neural communication used for cognition is oscillatory. For this discussion see:
- Buschman,T.J. and Miller, E.K. (2010) Shifting the Spotlight of Attention: Evidence for Discrete Computations in Cognition. Frontiers in Human Neuroscience. 4(194): 1-9. View PDF »
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VanRullen previews a recent paper by Kastner and colleagues and discusses evidence that covert attention involves rhythmic sampling of the environment.
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Cannon et al review the contributions of brain oscillations to neural computations and relate them to a variety of cognitive functions.
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Newman et al used the drug scopolamine to disrupt theta-gamma coupling in the medial entorhinal cortex of rats. Gamma power at the peak of theta was reduced and shifted to subsequent phases. Scopolamine also seemed to reduce the rats’ familiarity with the testing enclosure. The data support the hypothesis that memory encoding and retrieval occur at different theta phases.
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Sabine Kastner and crew show that when humans are cued to direct their attention to part of an object, uncued locations that are part of the same object are sampled periodically at about 8 Hz. Different, uncued, objects are also sampled at 4 Hz. This adds to a growing body of evidence that attention, and cognition in general, is rhythmic not continuous.
For reviews on this topic see:
- Buschman,T.J. and Miller, E.K. (2010) Shifting the Spotlight of Attention: Evidence for Discrete Computations in Cognition. Frontiers in Human Neuroscience. 4(194): 1-9. View PDF »
- Miller, E.K. and Buschman, T.J. “Brain Rhythms for Cognition and Consciousness”. Neurosciences and the Human Person: New Perspectives on Human Activities A. Battro, S. Dehaene and W. Singer (eds), Pontifical Academy of Sciences, Scripta Varia 121, Vatican City, 2013. View PDF
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Rouhinen et al provide evidence for the role of neural oscillations in the limitations of cognitive capacity. Subjects tracked multiple objects. Strength of oscillations were different preceding detected vs undetected objects. Suppression of low-frequency oscillations (<20 Hz) and strengthening of high-frequency oscillations (>20 Hz) in the frontoparietal cortex was correlated with attentional load. Load-dependent strengthening of 20-90 Hz oscillations was predictive of individual capacity. This supports hypotheses that oscillations play major role in attention and are responsible for the limited bandwidth of cognition.
Further reading on attention, capacity, and oscillations:
- Buschman,T.J. and Miller, E.K. (2010) Shifting the Spotlight of Attention: Evidence for Discrete Computations in Cognition. Frontiers in Human Neuroscience. 4(194): 1-9. View PDF »
- Miller, E.K. and Buschman, T.J. (2013) Cortical circuits for the control of attention. Current Opinion in Neurobiology. 23:216–222 View PDF »
- Buschman, T.J. and Miller, E.K. (2009) Serial, covert, shifts of attention during visual search are reflected by the frontal eye fields and correlated with population oscillations. Neuron, 63: 386-396. View PDF »
- Buschman, T.J. and Miller, E.K. (2007) Top-down versus bottom-up control of attention in the prefrontal and posterior parietal cortices. Science. 315: 1860-1862 The Scientist’s “Hot Paper” for October 2009. View PDF »
- Siegel, M., Warden, M.R., and Miller, E.K. (2009) Phase-dependent neuronal coding of objects in short-term memory. Proceedings of the National Academy of Sciences, 106: 21341-21346. View PDF »
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Roux and Uhlhaas propose an interesting and provocative theory: Different frequencies of neural oscillations carry different information in working memory. Gamma oscillations maintain information in working memory. Alpha suppresses irrelevant information. Theta orders information. Gamma is thought to be coupled to both alpha and theta.
This is consistent with our observations for phase-coding of different working memories in gamma (Siegel et al., 2009) and alpha suppressing a dominant, but current irrelevant, neural ensemble (Buschman et al., 2012).
Buschman, T.J., Denovellis, E.L., Diogo, C., Bullock, D. and Miller, E.K. (2012) Synchronous oscillatory neural ensembles for rules in the prefrontal cortex. Neuron. 76: 838-846. View PDF »
Siegel, M., Warden, M.R., and Miller, E.K. (2009) Phase-dependent neuronal coding of objects in short-term memory. Proceedings of the National Academy of Sciences, 106: 21341-21346. View PDF »
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Visual attention increases synchrony of neural activity in visual cortex. Fries and colleagues showed that synchronization differs for putative excitatory (broad-spiking) and inhibitory (narrow-spiking) neurons. The inhibitory neurons synchronize in the gamma band twice as strongly as excitatory neurons but the excitatory neurons synchronize to an earlier phase than inhibitory neurons. Further, attention increases gamma synchrony for the most active neurons but decreases synchrony for the least active neurons. These results show that attention-related neural synchrony is not uniform but instead an orchestration between different neuron types showing different types of synchrony. This lends further support for the role of neural synchrony in attention.