Sacchet et al find that synchronization between the prefrontal and somatosensory cortex may underlie the disengagement of attention. When a cue signaled that a forthcoming tactile stimulus should be ignored, there was first an increase in alpha (7-14 Hz) synchrony between representations of the unattended stimulus, followed by an increase in beta (15-29 Hz) synchrony. This study shows how frequency specific interactions between frontal cortex and sensory cortex may underlie the focusing of attention.
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Bressler and Richter review evidence that top-down processing in the cortex depends on synchronization of oscillatory rhythms between brain areas. More specifically, they hypothesize that beta band (13-30 Hz) synchrony conveys information about behavioral context (task information) to neurons in sensory cortex.
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Braunlich et al compared stimulus identity vs categorization tasks using fMRI in humans. They applied a Constrained Principal Components Analysis. They found evidence for two distinct frontoparietal networks. One that rapidly analyzes the stimuli and a second one that more slowly categorizes them.
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Virtually all studies of the neural basis of attention to date average effects across independently recorded neurons and across multiple trials. This is obviously artificial because attention has to be allocated on-the-fly, from moment-to-moment, not averaged across time. Trembly et al show that the current locus of attention can be decoded from ensembles of simultaneously recorded prefrontal cortex neurons from single trials. Decoding of these ensembles was stable over weeks. Nice.
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Andre Bastos and colleagues review an update the communication-through-coherence (CTC) hypothesis. They propose that bi-directional cortical communication involves separate feedforward and feedback mechanisms that are separate both anatomically and spectrally.
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Task Dependence of Visual and Category Representations in Prefrontal and Inferior Temporal Cortices
Jillian L. McKee, Maximilian Riesenhuber, Earl K. Miller, and David J. FreedmanVisual categorization is an essential perceptual and cognitive process for assigning behavioral significance to incoming stimuli. Categorization depends on sensory processing of stimulus features as well as flexible cognitive processing for classifying stimuli according to the current behavioral context. Neurophysiological studies suggest that the prefrontal cortex (PFC) and the inferior temporal cortex (ITC) are involved in visual shape categorization. However, their precise roles in the perceptual and cognitive aspects of the categorization process are unclear, as the two areas have not been directly compared during changing task contexts. To address this, we examined the impact of task relevance on categorization-related activity in PFC and ITC by recording from both areas as monkeys alternated between a shape categorization and passive viewing tasks. As monkeys viewed the same stimuli in both tasks, the impact of task relevance on encoding in each area could be compared. While both areas showed task-dependent modulations of neuronal activity, the patterns of results differed markedly. PFC, but not ITC, neurons showed a modest increase in firing rates when stimuli were task relevant. PFC also showed significantly stronger category selectivity during the task compared with passive viewing, while task-dependent modulations of category selectivity in ITC were weak and occurred with a long latency. Finally, both areas showed an enhancement of stimulus selectivity during the task compared with passive viewing. Together, this suggests that the ITC and PFC show differing degrees of task-dependent flexibility and are preferentially involved in the perceptual and cognitive aspects of the categorization process, respectively.
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Several lines of evidence suggests that searching a visual scene depends on an intrinsic periodicity. We scan the scene by moving the spotlight of attention at regular intervals. For example, Buschman and Miller (2009) found neurophysiological evidence in the frontal eye fields for regular shifts of attention at 25 Hz (i.e., every 40 ms). Dugue et al (2014) have now found evidence in humans using EEG recording and TMS stimulation in humans. They found successful search was associated with oscillations and phase resetting at 6 Hz. TMS applied at different intervals found disruption of search at a periodicity corresponding to 6 Hz. This was slower than reported by Buschman and Miller (2009), but that could be because Dugue et al used a more difficult search task.
This paper:
Theta Oscillations Modulate Attentional Search Performance Periodically
Laura Dugué, Philippe Marque, and Rufin VanRullen Journal of Cognitive Neuroscience, 2014For further reading:
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 » -
Dotson et al recorded neural activity in the prefrontal and parietal cortex during a working memory task. As previous studies have reported (e.g., Buschman and Miller, 2007) they found long range synchronization of 8-25 Hz oscillations between the areas. Interestingly, there found both phase synchronization at 0 and 180 degrees suggesting that the 0 deg phase synchrony helped form networks between the areas whereas the 180 deg (anti-phase) synchrony helped segregate different networks.
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 View PDF » -
Womelsdorf et al found that bursts of neural activity in the prefrontal cortex and anterior cingulate synchronize at gamma and beta frequencies during focused attention. Non-burst activity did not show long-range synchronization. Burst synchronization may underlie the formation of long-range networks.
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Gamma-band oscillations have been associated with holding information in working memory. Is it just a general increase in gamma or do gamma oscillations actually maintain and convey specific information? A new study by Honkanen et al suggests that it does contain information. The strength and topography of gamma oscillations reflected memorized visual features as well as the amount of information in working memory.
We’ve also shown that information about two different objects can be carried in different phases of gamma band oscillations:
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 »
Read commentary by Vogel and Fukuda