The Relationship between Working Memory Storage and Elevated Activity as Measured with Functional Magnetic Resonance Imaging

Departments of Psychology and Psychiatry, University of Wisconsin-Madison, Madison, Wisconsin 53706.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 09/2012; 32(38):12990-8. DOI: 10.1523/JNEUROSCI.1892-12.2012
Source: PubMed

ABSTRACT Does the sustained, elevated neural activity observed during working memory tasks reflect the short-term retention of information? Functional magnetic resonance imaging (fMRI) data of delayed recognition of visual motion in human participants were analyzed with two methods: a general linear model (GLM) and multivoxel pattern analysis. Although the GLM identified sustained, elevated delay-period activity in superior and lateral frontal cortex and in intraparietal sulcus, pattern classifiers were unable to recover trial-specific stimulus information from these delay-active regions. The converse-no sustained, elevated delay-period activity but successful classification of trial-specific stimulus information-was true of posterior visual regions, including area MT+ (which contains both middle temporal area and medial superior temporal area) and calcarine and pericalcarine cortex. In contrast to stimulus information, pattern classifiers were able to extract trial-specific task instruction-related information from frontal and parietal areas showing elevated delay-period activity. Thus, the elevated delay-period activity that is measured with fMRI may reflect processes other than the storage, per se, of trial-specific stimulus information. It may be that the short-term storage of stimulus information is represented in patterns of (statistically) "subthreshold" activity distributed across regions of low-level sensory cortex that univariate methods cannot detect.

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Available from: Bradley R Postle, Aug 05, 2014
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    • ", Zarahn et al . , 1997 ; Riggall and Postle , 2012 ) , we identified regions with elevated delay period activation with a random - effects general linear model ( GLM ) that included separate regressors marking the sample , delay , and probe epochs ( see Experimental Procedures ) . A statistical parametric map ( SPM ) showing cortical areas with elevated delay period activity is shown in Fig - ure 3 . "
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    ABSTRACT: Working memory (WM) enables the storage and manipulation of information in an active state. WM storage has long been associated with sustained increases in activation across a network of frontal and parietal cortical regions. However, recent evidence suggests that these regions primarily encode information related to general task goals rather than feature-selective representations of specific memoranda. These goal-related representations are thought to provide top-down feedback that coordinates the representation of fine-grained details in early sensory areas. Here, we test this model using fMRI-based reconstructions of remembered visual details from region-level activation patterns. We could reconstruct high-fidelity representations of a remembered orientation based on activation patterns in occipital visual cortex and in several sub-regions of frontal and parietal cortex, independent of sustained increases in mean activation. These results challenge models of WM that postulate disjoint frontoparietal "top-down control" and posterior sensory "feature storage" networks. Copyright © 2015 Elsevier Inc. All rights reserved.
    Neuron 08/2015; DOI:10.1016/j.neuron.2015.07.013 · 15.98 Impact Factor
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    • "As the contents of WM can be decoded from sensory cortices but not the PFC [31] [32] [33] , we propose here that, compared with the PFC, sensory cortices represent more precise information about the memorandum, and in this way serve as quality assurance in WM. "
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    ABSTRACT: The activity in sensory cortices and the prefrontal cortex (PFC) throughout the delay interval of working memory (WM) tasks reflect two aspects of WM-quality and quantity, respectively. The delay activity in sensory cortices is fine-tuned to sensory information and forms the neural basis of the precision of WM storage, while the delay activity in the PFC appears to represent behavioral goals and filters out irrelevant distractions, forming the neural basis of the quantity of task-relevant information in WM. The PFC and sensory cortices interact through different frequency bands of neuronal oscillation (theta, alpha, and gamma) to fulfill goal-directed behaviors.
    Neuroscience Bulletin 03/2015; 31(2). DOI:10.1007/s12264-014-1503-7 · 1.83 Impact Factor
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    • "This view is supported by studies showing overlapping activations for visual and verbal (Cowan et al., 2011; Majerus et al., 2010), verbal and spatial (Chein, Moore, & Conway, 2011), and verbal and tonal WM (Koelsch et al., 2009). For each sensory domain, there appears to be a domain-general frontoparietal network that directs attention to item-specific information stored in posterior sensory regions during WM maintenance (Harrison & Tong, 2009; Lewis-Peacock, Drysdale, Oberauer, & Postle, 2012; Riggall & Postle, 2012). This model too includes the central executive and it remains to be seen if Cowan's focus of attention and Baddeley's episodic buffer are different. "
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    ABSTRACT: Attention and memory are both established concepts in psy- chology and have been extensively studied since the late nine- teenth century (James, 1890). Attention refers to the process of preparing for and selecting specific subsets of external stimuli or internal representations stored in memory (Anderson, 2005). Memory refers to the encoding, storage, and retrieval of information (Atkinson & Shiffrin, 1968). Attention and memory are critical for everyday tasks. Ima- gine the following scenario. You are in the airport to pick up somebody that you met many years ago and only vaguely remember his appearance. You were told that he is wearing a blue jacket today. When the crowd of people comes out of the exiting gate, you keep the ‘blue jacket’ representation in mind and selectively attend only to those people wearing blue jackets. Suddenly, a man wearing a red shirt waves to you, capturing your attention. After checking other features of his appearance, you recognize that this is the person you are wait- ing to pick up. (It turns out that he forgot to put on his blue jacket.) In this common scenario, attention helps you focus on certain types of stimuli, such as voluntarily attending to people wearing blue jackets and involuntarily attending to someone waving at you. Memory helps you remember information that is relevant to the current task, such as short-term memory (STM) of the blue jacket and long-term memory (LTM) of the appearance of your guest. Both attention and memory have been conceptualized as each comprising multiple components (Atkinson & Shiffrin, 1968; Knudsen, 2007; Posner & Petersen, 1990), some of which are unique to attention or memory, with others inter- acting across the two. Such interactions have been a particular focus of research and have been investigated with behavioral, neuropsychological, electrophysiological, and, more recently, brain mapping methods (Awh, Vogel, & Oh, 2006; Chun & Turk-Browne, 2007). This article provides a brief introduction of these components of attention and memory as well as their interactions in the context of brain mapping studies in the last 2 decades.
    Brain Mapping: An Encyclopedic Reference, Edited by Aw Toga, R Poldrack, 01/2015: chapter Attention and memory: pages 275-279; Elsevier.
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