Article

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.

Download full-text

Full-text

Available from: Bradley R Postle, Aug 05, 2014
1 Follower
 · 
195 Views
  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Conscious processing is generally seen as required for flexible and willful actions, as well as for tasks that require durable information maintenance. Here we present research that questions the assumption that only consciously perceived information is durable (>500 ms). Using the attentional blink (AB) phenomenon, we rendered otherwise relatively clearly perceived letters non-conscious. In a first experiment we systematically manipulated the delay between stimulus presentation and response, for the purpose of estimating the durability of non-conscious perceptual representations. For items reported not seen, we found that behavioral performance was better than chance across intervals up to 15 s. In a second experiment we used fMRI to investigate the neural correlates underlying the maintenance of non-conscious perceptual representations. Critically, the relatively long delay period demonstrated in experiment 1 enabled isolation of the signal change specifically related to the maintenance period, separate from stimulus presentation and response. We found sustained BOLD signal change in the right mid-lateral prefrontal cortex, orbitofrontal cortex, and crus II of the cerebellum during maintenance of non-consciously perceived information. These findings are consistent with the controversial claim that working-memory mechanisms are involved in the short-term maintenance of non-conscious perceptual representations.
    Frontiers in Human Neuroscience 11/2014; 8:938: 1-10. DOI:10.3389/fnhum.2014.00938 · 2.90 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Visual working memory (VWM) capacity limitations are estimated to be ~4 items. Yet, it remains unclear why certain items from a given memory array may be successfully retrieved from VWM and others are lost. Existing measures of the neural correlates of VWM cannot address this question because they measure the aggregate processing of the entire stimulus array rather than neural signatures of individual items. Moreover, this cumulative processing is usually measured during the delay period, thereby reflecting the allocation of neural resources during VWM maintenance. Here, we use the steady-state visual evoked potential (SSVEP) to identify the neural correlates of individual stimuli at VWM encoding and test two distinct hypotheses: the focused-resource hypothesis and the diffuse-resource hypothesis, for how the allocation of neural resources during VWM encoding may contribute to VWM capacity limitations. First, we found that SSVEP amplitudes were larger for stimuli that were later remembered than for items that were subsequently forgotten. Second, this pattern generalized so that the SSVEP amplitudes were also larger for the unprobed stimuli in correct compared to incorrect trials. These data are consistent with the diffuse-resource view in which attentional resources are broadly allocated across the whole stimulus array. These results illustrate the important role encoding mechanisms play in limiting the capacity of VWM.
    Neuropsychologia 08/2014; 63. DOI:10.1016/j.neuropsychologia.2014.08.020 · 3.45 Impact Factor