Causal evidence for a privileged working memory state in early visual cortex. Zokaei, N., Manohar, S., Husain, M., & Feredoes, E. J Neurosci, 34(1):158–162, 2014.
doi  abstract   bibtex   
Emerging evidence suggests that items held in working memory (WM) might not all be in the same representational state. One item might be privileged over others, making it more accessible and thereby recalled with greater precision. Here, using transcranial magnetic stimulation (TMS), we provide causal evidence in human participants that items in WM are differentially susceptible to disruptive TMS, depending on their state, determined either by task relevance or serial position. Across two experiments, we applied TMS to area MT+ during the WM retention of two motion directions. In Experiment 1, we used an "incidental cue" to bring one of the two targets into a privileged state. In Experiment 2, we presented the targets sequentially so that the last item was in a privileged state by virtue of recency. In both experiments, recall precision of motion direction was differentially affected by TMS, depending on the state of the memory target at the time of disruption. Privileged items were recalled with less precision, whereas nonprivileged items were recalled with higher precision. Thus, only the privileged item was susceptible to disruptive TMS over MT+. By contrast, precision of the nonprivileged item improved either directly because of facilitation by TMS or indirectly through reduced interference from the privileged item. Our results provide a unique line of evidence, as revealed by TMS over a posterior sensory brain region, for at least two different states of item representation in WM.
@Article{Zokaei2014,
  author      = {Zokaei, Nahid and Manohar, Sanjay and Husain, Masud and Feredoes, Eva},
  journal     = {J Neurosci},
  title       = {Causal evidence for a privileged working memory state in early visual cortex.},
  year        = {2014},
  number      = {1},
  pages       = {158--162},
  volume      = {34},
  abstract    = {Emerging evidence suggests that items held in working memory (WM)
	might not all be in the same representational state. One item might
	be privileged over others, making it more accessible and thereby
	recalled with greater precision. Here, using transcranial magnetic
	stimulation (TMS), we provide causal evidence in human participants
	that items in WM are differentially susceptible to disruptive TMS,
	depending on their state, determined either by task relevance or
	serial position. Across two experiments, we applied TMS to area MT+
	during the WM retention of two motion directions. In Experiment 1,
	we used an "incidental cue" to bring one of the two targets into
	a privileged state. In Experiment 2, we presented the targets sequentially
	so that the last item was in a privileged state by virtue of recency.
	In both experiments, recall precision of motion direction was differentially
	affected by TMS, depending on the state of the memory target at the
	time of disruption. Privileged items were recalled with less precision,
	whereas nonprivileged items were recalled with higher precision.
	Thus, only the privileged item was susceptible to disruptive TMS
	over MT+. By contrast, precision of the nonprivileged item improved
	either directly because of facilitation by TMS or indirectly through
	reduced interference from the privileged item. Our results provide
	a unique line of evidence, as revealed by TMS over a posterior sensory
	brain region, for at least two different states of item representation
	in WM.},
  doi         = {10.1523/JNEUROSCI.2899-13.2014},
  institution = {Department of Experimental Psychology, University of Oxford, Oxford, OX1 3UD, United Kingdom, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX3 9DU, United Kingdom, Institute of Cognitive Neuroscience, University College London, London, WC1N 3AR, United Kingdom, and School of Psychology and Clinical Language Sciences, University of Reading, RG6 7BE, United Kingdom.},
  keywords    = {Adult; Female; Humans; Male; Memory, Short-Term, physiology; Photic Stimulation, methods; Psychomotor Performance, physiology; Transcranial Magnetic Stimulation, methods; Visual Cortex, physiology; Young Adult},
  language    = {eng},
  medline-pst = {ppublish},
  pmid        = {24381277},
  timestamp   = {2015.08.31},
}

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