The Miller Lab

  • Frontoparietal Correlation Dynamics Reveal Interplay between Integration and Segregation during Visual Working Memory

    Miller Lab

    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 »

  • Frontoparietal Correlation Dynamics Reveal Interplay between Integration and Segregation during Visual Working Memory

    Miller Lab

    Dotson et al report both 0 and 180 deg phase synchrony between the prefrontal and parietal cortices during a working memory task, suggestion both formation and segregation of different functional networks by neural synchrony.

  • Neuronal Correlates of Visual Working Memory in the Corvid Endbrain

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    A well-known correlate of working memory is sustained neural activity that bridges short gaps in time.  It is well-established in the primate brain, but what about birds?  They have working memory.  (In fact, there is a lot of classic work that detailed the behavioral characteristics of working memory in pigeons).

    Miller Lab alumnus Andreas Nieder and crew trained crows to perform a working memory task and found sustained activity in the nidopallium caudolaterale (NCL).  This is presumably a neural correlate of the crow’s visual working memory.

    Now if crows could only pass that causality test.

  • Induced Alpha Rhythms Track the Content and Quality of Visual Working Memory Representations with High Temporal Precision

    Miller Lab

    Anderson et al used scalp EEG recordings to decode the content of working memory and its quality.  Subjects performed a orientation working memory task.  Anderson et al found that the spatial distribution of alpha band power could be used to determine what orientation the subject was remembering and how precisely they were remembering it.  Cool.

  • Different Neuronal Computations of Working Memory Across Visual Hemifields

    Miller Lab

    Matsushima and Tanaka compared neural correlates of spatial working memory for locations within the same hemifield or across hemifields.  When the two remembered locations were in the same hemifield (right or left side of vision), the neural response in the prefrontal cortex was intermediate to the two cues presented alone.  When the cues were across hemifields, the neural response was the same as the preferred cue presented alone.  In other words, remembered locations within a hemifield seemed to be in competition with each other whereas locations across the hemifields seemed to be have no interaction at all.  In yet other words, it was as if the (intact) monkeys had their brains split down the middle. The authors concluded local inhibitory interactions between cues within, but not across, hemifields.

    This confirms Buschman et al (2011) who found that independent capacities for visual working memory in the right and left hemifields.

    Further reading:
    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 »

  • Executive control processes underlying multi-item working memory

    Miller Lab

    Does the prefrontal cortex (PFC) maintain the contents of working memory or does it direct the focus of attention?  Lara and Wallis asked this question by training monkeys to perform a multi-color change detection task.  Few PFC neurons encoded the color of the stimuli. Instead, the dominant signals were the spatial location of the item and the location of focal attention. This suggests that the PFC is more involved in directing attention than retaining information in working memory.  Supporting this was increased power in alpha and theta power in the PFC, frequency bands associated with long-range neural communication.

  • Different Neuronal Computations of Spatial Working Memory for Multiple Locations within versus across Visual Hemifields

    Miller Lab

    Matsushima and Tanaka examined the neural correlates of spatial working memory for one vs two locations.  When the two locations were in the same (right or left) hemifield, the level neural activity was intermediate between that elicited from either cue alone.  By contrast, when the cues were presented in opposite hemifields, neural activity to each cue was as if the cue was presented alone.  This lends support to other observations (e.g., Buschman et al 2011) that there are independent capacities for working memory in the right and left visual hemifields, as if the brain was split down the middle.

    Further reading:
    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 »

  • Noise in Neural Populations Accounts for Errors in Working Memory

    Miller Lab

    Working memory is limited in capacity.  As you load more “stuff” into working memory, errors increase. Bays shows how this may happen.  Errors with increasing working memory load may be due to decreased signal strength of spiking neurons.  Humans can increase the precision of high priority stimuli in working memory at the expense of low priority stimuli.  The reduction in drive to neurons representing high priority stimuli can explain this tradeoff.

  • The “working” of working memory

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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.

  • Revisiting the role of persistent neural activity during working memory

    Miller Lab

    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.