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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The modal model of working memory (WM) is that of sustained activity in the prefrontal cortex. Sreenivasan et al argue for a more complex model. High-fidelity WM representations are maintained in sensory cortex while the prefrontal cortex instead maintains representations of multiple goal-related variables. These PFC representations serve to bias stimulus-specific activity in sensory cortex.
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Roy et al show that the activity of neurons in the prefrontal cortex (pFC) are linked to categorical decisions. Monkeys were trained to categorize a set of computer-generated images as “cats” vs “dogs”. Then, they were shown ambiguous images were centered on a category boundary, that is, they were a mix of 50% of cats and dogs and therefore had no category information. The monkeys guessed at their category membership. Activity to the same ambiguous image differed significantly, depending on the monkey’s decision about the image’s category. Thus, pFC activity reflects categorical decisions.
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Earl Miller is quoted on NBCnews.com. In brief: Don’t multitask and if you do don’t drive.
NBCnews.com: The ‘smart life’: How connected cars, clothes and homes could fry your brain -
Eiselt and Nieder trained monkeys to make greater/less than judgments to line lengths and dot numerosities. They compared neural activity in the prefrontal cortex (PFC), anterior cingulate (AC), and premotor cortex (PMC). The greatest proportion of greater/less than rule neurons were found in the PFC. Further, only the PFC had neurons that were “generalists”; they signaled the greater/less than rules for both judgments. Neurons in other areas were specialized for one judgment or the other.
This is consistent with our work showing that a large proportion of PFC neurons are multifunction, mixed selectivity neurons. They may be key in providing the computational power for complex, flexible behavior. For further reading see:
Rigotti, M., Barak, O., Warden, M.R., Wang, X., Daw, N.D., Miller, E.K., & Fusi, S. (2013) “The importance of mixed selectivity in complex cognitive tasks”. Nature, 497, 585-590, doi:10.1038/nature12160. View PDF
Cromer, J.A., Roy, J.E., and Miller, E.K. (2010) Representation of multiple, independent categories in the primate prefrontal cortex. Neuron, 66: 796-807. 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.