Womeldorf et al observed bursts of firing in the anterior cingulate and prefrontal cortex during shifts of attention. These bursts (but not non-burst firing) synchronized over long distances (between the AC and PFC) to local field field potentials at beta and gamma frequencies. These bursts were proceeded by bursts of inhibitory neurons. The authors propose burst firing mechanisms help form functional networks to coordinate shifts of attention.
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Miller Lab Alumnus Tim Buschman is one of the winners of the NIH Director’s New Innovator Award.
According to the NIH website: The award “is designed specifically to support unusually creative new investigators with highly innovative research ideas at an early stage of their career when they may lack the preliminary data required for an R01 grant.”
We couldn’t be prouder of him if we were a Little Lebowski Urban Achiever.
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“Linked” is the operative term here. Earl Miller is quoted in a New York Magazine article about a study that finds less gray matter in people who multitask more. Earl points out that the study does not necessarily mean that multitasking decreases brain matter. It could be that people with less gray matter are more impulsive and thus more prone to multitasking.
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Kopell et al provide an excellent review of the role of neural rhythms in brain function and argue that we need to know more than anatomy, no matter how detailed. We also need to connect it to an understanding of brain dynamics. They review our current knowledge of brain rhythms and identify (many) open questions.
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Our lab and others (e.g., Buschman and Miller, 2007; Bastos et al 2012) has suggested that top-down (feedback) vs bottom-up (feedforward) cortical processing is mediated by synchrony between cortical areas at different frequencies: lower (e.g., beta band) for top-down vs higher (e.g., gamma band) for bottom-up. These two different frequency bands allow top-down vs bottom-signals to multiplex through the same circuits, much as different FM radio stations multiplex through the airwaves. They may also allow cortical microcircuits to engage in helpful things like predictive coding (Bastos et al., 2012).
Schmiedt et al (2014) provide new evidence for this. They recorded neural activity in visual area V4 after damage to primary visual area V1. V4 is higher in the cortical hierarchy, so V1 has a bottom-up influence on V4. They found that damage to V1 decreased the gamma in V4 that follows appearance of a visual stimulus. That is consistent with gamma carrying bottom-up or feedforward signals, lost after V1 damage. By contrast, V4 beta activity was minimally affected, reflecting the unaffected top-down influence on V4 Normally there is beta suppression during visual stimulation, presumably because the bottom-up inputs overwhelm or suppress beta-mediated top-down processing. After V1 damage, this suppression of top-down beta rhythms was diminished, presumably because it was no longer suppressed by bottom-up influences from V1.
For further reading:
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 »Bastos AM, Usrey WM, Adams RA, Mangun GR, Fries P, Friston KJ. Canonical microcircuits for predictive coding. Neuron. 2012 Nov 21;76(4):695-711. doi:
10.1016/j.neuron.2012.10.038. Review. -
At this risk of kvelling, in 2011 we published a paper (Buschman et al., 2011) showing independent visual working memory capacities in the right vs left visual hemifields. We were told “no way” and “that’s impossible”. Since then, a bunch of papers have supported this. Here’s another one.
Wang et al used FMRI and found that brain networks primarily interact with ipsilateral, not contralateral networks. Thus, the brain emphasizes processing within each hemisphere (visual hemifield) and minimizes across-hemisphere processing.
Also see:
Buschman,T.J., Siegel, M., Roy, J.E. and Miller, E.K. (2011) Neural substrates of cognitive capacity limitations. Proceedings of the National Academy of Sciences. 108(27):11252-5. View PDF » -
Ibos and Freedman show that area LIP is more than just space and spatial attention. They trained monkeys to make decisions based on conjunctions of motion and color. LIP neurons integrated color and motion when it was task-relevant.
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More evidence (this time in humans) that top-down vs bottom-up cortical processing depends on synchrony in different frequency bands, lower frequencies (beta) for top-down and higher frequencies (gamma) for bottom-up. There was cross-frequency coupling such that gamma power in auditory cortex was modulated by phase of beta in the anterior cingulate (but not the other way around). Top-down and bottom-up processing alternattively dominated. Thus, the brain uses both frequency- and time-multiplexing to optimize directional flow of information.
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There is increasing evidence and much discussion about the role of synchronized oscillations in fostering communication in neural networks. The flip side is that anti-synchronization (i.e., out of phase) should decrease or prevent neural communication. Stetson and Andersen find evidence for this between the parietal cortex and premotor cortex. During movement planning these areas oscillate at similar frequencies but out of phase of one another. This suggests decreased communication between them.
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Botvinick and Cohen provide a very nice overview of where computational modeling of executive control has been and where it is going.