scholarly journals Delay-period activity in frontal, parietal, and occipital cortex tracks different attractor dynamics in visual working memory

2020 ◽  
Author(s):  
Qing Yu ◽  
Matthew F. Panichello ◽  
Ying Cai ◽  
Bradley R. Postle ◽  
Timothy J. Buschman
Keyword(s):  
Working Memory ◽  
Parietal Cortex ◽  
Memory Load ◽  
Internal Noise ◽  
Occipital Cortex ◽  
Delay Period ◽  
Attractor Dynamics ◽  
Attractor Model ◽  
New Interpretation ◽  
Memory Precision

AbstractOne important neural hallmark of working memory is persistent elevated delay-period activity in frontal and parietal cortex. In human fMRI, delay-period BOLD activity in frontal and parietal cortex increases monotonically with memory load and asymptotes at an individual’s capacity. Previous work has demonstrated that frontal and parietal delay-period activity correlates with the decline in behavioral memory precision observed with increasing memory load. However, because memory precision can be influenced by a variety of factors, it remains unclear what cognitive processes underlie persistent activity in frontal and parietal cortex. Recent psychophysical work has shown that attractor dynamics bias memory representations toward a few stable representations and reduce the effects of internal noise. From this perspective, imprecision in memory results from both drift towards stable attractor states and random diffusion. Here we asked whether delay-period BOLD activity in frontal and parietal cortex might be explained, in part, by these attractor dynamics. We analyzed data from an existing experiment in which subjects performed delayed recall for line orientation, at different loads, during fMRI scanning. We modeled subjects’ behavior using a discrete attractor model, and calculated within-subject correlation between frontal and parietal delay-period activity and estimated sources of memory error (drift and diffusion). We found that although increases in frontal and parietal activity were associated with increases in both diffusion and drift, diffusion explained the most variance in frontal and parietal delay-period activity. In comparison, a subsequent whole-brain regression analysis showed that drift rather than diffusion explained the most variance in delay-period activity in lateral occipital cortex. These results provide a new interpretation for the function of frontal, parietal, and occipital delay-period activity in working memory.

scholarly journals The Role of Location-Context Binding in Nonspatial Visual Working Memory

2018 ◽  
Author(s):  
Ying Cai ◽  
Qing Yu ◽  
Andrew D. Sheldon ◽  
Bradley R. Postle
Keyword(s):  
Working Memory ◽  
Spatial Attention ◽  
Visual Working Memory ◽  
Parietal Cortex ◽  
Memory Load ◽  
Occipital Cortex ◽  
Delay Period ◽  
Fmri Signal ◽  
Associated Representation ◽  
Unique Context

AbstractSuccessful retrieval of an item from visual working memory (VWM) often requires an associated representation of the trial-unique context in which that item was presented. We dissociated the effects on fMRI signal of memory load versus context binding by comparing nonspatial VWM for one oriented bar vs. three bars individuated by their location on the screen vs. three items drawn from different categories (orientation, color, and luminance), for which location context was superfluous. Delay-period fMRI signal in frontal and parietal cortex was sensitive to stimulus homogeneity rather than to memory load per se. Behavioral performance revealed a broad range in swap errors, an index of the efficacy of context binding, and subjects were classified as high swap error or low swap error. During the delay period, the strength of the representation of stimulus location in parietal cortex predicted individual differences in swap errors. During recall, activity in occipital cortex revealed two dissociable neural correlates of context binding: high swap-error subjects allocated less spatial attention to the location of the probed item and more spatial attention the location of non-probed items; high swap-error subjects also represented the orientation of the probed item more weakly and the orientation of nonprobed items more strongly. Our results suggest context binding is a computation that influences all stages of VWM processing.Significance StatementAlthough we often think of the contents of visual working memory (VWM) as representations of the items that need to be remembered, each item’s trial-unique context is also critical for successful performance. For example, if one observes a red, then a black, then a blue car passing through an intersection, vivid memory for the colors, alone, wouldn’t allow one to execute the instruction “Follow the first of the three cars that just drove by.” Although manipulating load is commonly assumed to isolate storage functions, requiring memory for multiple items drawn from the same category also increases demands on the context binding needed to individuate these items. This experiment tracked the influence of context binding on VWM stimulus processing.

scholarly journals Occipital Cortex of Blind Individuals Is Functionally Coupled with Executive Control Areas of Frontal Cortex

2015 ◽  
Vol 27 (8) ◽  
pp. 1633-1647 ◽  
Author(s):  
Ben Deen ◽  
Rebecca Saxe ◽  
Marina Bedny
Keyword(s):  
Working Memory ◽  
Functional Connectivity ◽  
Sentence Comprehension ◽  
Memory Load ◽  
Memory Task ◽  
Occipital Cortex ◽  
Memory Systems ◽  
Functional Responses ◽  
Congenitally Blind ◽  
Blind Individuals

In congenital blindness, the occipital cortex responds to a range of nonvisual inputs, including tactile, auditory, and linguistic stimuli. Are these changes in functional responses to stimuli accompanied by altered interactions with nonvisual functional networks? To answer this question, we introduce a data-driven method that searches across cortex for functional connectivity differences across groups. Replicating prior work, we find increased fronto-occipital functional connectivity in congenitally blind relative to blindfolded sighted participants. We demonstrate that this heightened connectivity extends over most of occipital cortex but is specific to a subset of regions in the inferior, dorsal, and medial frontal lobe. To assess the functional profile of these frontal areas, we used an n-back working memory task and a sentence comprehension task. We find that, among prefrontal areas with overconnectivity to occipital cortex, one left inferior frontal region responds to language over music. By contrast, the majority of these regions responded to working memory load but not language. These results suggest that in blindness occipital cortex interacts more with working memory systems and raise new questions about the function and mechanism of occipital plasticity.

scholarly journals Delay-period activity in frontal, parietal, and occipital cortex tracks noise and biases in visual working memory

PLoS Biology ◽  
2020 ◽  
Vol 18 (9) ◽  
pp. e3000854 ◽  
Author(s):  
Qing Yu ◽  
Matthew F. Panichello ◽  
Ying Cai ◽  
Bradley R. Postle ◽  
Timothy J. Buschman
Keyword(s):  
Working Memory ◽  
Visual Working Memory ◽  
Occipital Cortex ◽  
Delay Period

scholarly journals Neural circuit basis of visuo-spatial working memory precision: a computational and behavioral study

2015 ◽  
Vol 114 (3) ◽  
pp. 1806-1818 ◽  
Author(s):  
Rita Almeida ◽  
João Barbosa ◽  
Albert Compte
Keyword(s):  
Working Memory ◽  
Neural Circuit ◽  
Spatial Working Memory ◽  
Memory Load ◽  
Memory Retention ◽  
Behavioral Experiments ◽  
Memory Traces ◽  
Topographic Organization ◽  
The Subject ◽  
Memory Precision

The amount of information that can be retained in working memory (WM) is limited. Limitations of WM capacity have been the subject of intense research, especially in trying to specify algorithmic models for WM. Comparatively, neural circuit perspectives have barely been used to test WM limitations in behavioral experiments. Here we used a neuronal microcircuit model for visuo-spatial WM (vsWM) to investigate memory of several items. The model assumes that there is a topographic organization of the circuit responsible for spatial memory retention. This assumption leads to specific predictions, which we tested in behavioral experiments. According to the model, nearby locations should be recalled with a bias, as if the two memory traces showed attraction or repulsion during the delay period depending on distance. Another prediction is that the previously reported loss of memory precision for an increasing number of memory items (memory load) should vanish when the distances between items are controlled for. Both predictions were confirmed experimentally. Taken together, our findings provide support for a topographic neural circuit organization of vsWM, they suggest that interference between similar memories underlies some WM limitations, and they put forward a circuit-based explanation that reconciles previous conflicting results on the dependence of WM precision with load.

scholarly journals Neural mechanisms underlying the precision of visual working memory

2018 ◽  
Author(s):  
Yijie Zhao ◽  
Shuguang Kuai ◽  
Theodore P. Zanto ◽  
Yixuan Ku
Keyword(s):  
Working Memory ◽  
Visual Working Memory ◽  
Memory Load ◽  
Neural Mechanisms ◽  
Behavioral Experiment ◽  
Working Memory Load ◽  
Lateral Occipital Complex ◽  
The Individual ◽  
Memory Precision ◽  
The Brain

AbstractThe neural mechanisms associated with the limited capacity of working memory has long been studied, but it is still unclear how the brain maintains the fidelity of representations in working memory. Here, an orientation recall task for estimating the precision of visual working memory was performed both inside and outside an fMRI scanner. Results showed that the trial-by-trial recall error (in radians) was correlated with delay period activity in the lateral occipital complex (LOC) during working memory maintenance, regardless of the memory load. Moreover, delay activity in LOC also correlated with the individual participant’s precision of working memory from a separate behavioral experiment held two weeks prior. Furthermore, a region within the prefrontal cortex, the inferior frontal junction (IFJ), exhibited greater functional connectivity with LOC when the working memory load increased. Together, our findings provide unique evidence that the LOC supports visual working memory precision, while communication between the IFJ and LOC varys with visual working memory load.

scholarly journals Behavioral prioritization enhances working memory precision and neural population gain

2021 ◽  
Author(s):  
Aspen H. Yoo ◽  
Alfredo Bolaños ◽  
Grace E. Hallenbeck ◽  
Masih Rahmati ◽  
Thomas C. Sprague ◽  
...  
Keyword(s):  
Working Memory ◽  
Brain Area ◽  
Brain Regions ◽  
Delay Period ◽  
Common Finding ◽  
Neural Population ◽  
Association Cortex ◽  
Absolute Amount ◽  
Neural Populations ◽  
Memory Precision

ABSTRACTHumans allocate visual working memory (WM) resource according to behavioral relevance, resulting in more precise memories for more important items. Theoretically, items may be maintained by feature-tuned neural populations, where the relative gain of the populations encoding each item determines precision. To test this hypothesis, we compared the amplitudes of delay-period activity in the different parts of retinotopic maps representing each of several WM items, predicting amplitude would track with behavioral priority. Using fMRI, we scanned participants while they remembered the location of multiple items over a WM delay, then reported the location of one probed item using a memory-guided saccade. Importantly, items were not equally probable to be probed (0.6, 0.3, 0.1, 0.0), which was indicated with a pre-cue. We analyzed fMRI activity in ten visual field maps in occipital, parietal, and frontal cortex known to be important for visual WM. In early visual cortex, but not association cortex, the amplitude of BOLD activation within voxels corresponding to the retinotopic location of visual WM items increased with the priority of the item. Interestingly, these results were contrasted with a common finding that higher-level brain regions had greater delay-period activity, demonstrating a dissociation between the absolute amount of activity in a brain area, and the activity of different spatially-selective populations within it. These results suggest that the distribution of WM resources according to priority sculpts the relative gains of neural populations that encode items, offering a neural mechanism for how prioritization impacts memory precision.

scholarly journals A Simultaneous EEG-fMRI Study of Thalamic Load-Dependent Working Memory Delay Period Activity

2020 ◽  
Author(s):  
Bernard A. Gomes ◽  
Chelsea Reichert Plaska ◽  
Jefferson Ortega ◽  
Timothy M. Ellmore
Keyword(s):  
Working Memory ◽  
Short Term Memory ◽  
Memory Load ◽  
Delay Period ◽  
Subcortical Structures ◽  
Related Information ◽  
Fmri Study ◽  
Posterior Parietal ◽  
Evoked Activity

AbstractWorking memory (WM) is an essential component of executive functions which depend on maintaining task-related information online for brief periods in both the presence and absence of interfering stimuli. Active maintenance occurs during the WM delay period, the time between stimulus encoding and subsequent retrieval. Previous studies have extensively documented prefrontal (PFC) and posterior parietal (PPC) cortex activity during the WM delay period, but the role of subcortical structures including the thalamus remains to be fully elucidated, especially in humans. Using simultaneous EEG-fMRI, we investigated the role of the thalamus during the WM delay period following low and high memory load encoding. During the delay, participants passively viewed scrambled images containing similar color and spatial frequency to serve as a perceptual baseline. Using individual fMRI-weighted source analyses centered around delay period onset, the effects of increased and decreased memory load on maintenance were observed bilaterally in thalamus with higher source activity evoked during low compared to high load maintenance. The main finding that thalamic activation was attenuated during high compared to low load maintenance suggesting a sensory filtering role for thalamus during consolidation of stimuli in WM where the highest evoked activity occurs when fewer stimuli need to be maintained in the presence of interfering perceptual stimuli during the delay. The results support the idea that the thalamus plays a role in short-term memory maintenance by regulating processing of interfering stimuli.

scholarly journals Behavioral Prioritization Enhances Working Memory Precision and Neural Population Gain

2021 ◽  
pp. 1-14
Author(s):  
Aspen H. Yoo ◽  
Alfredo Bolaños ◽  
Grace E. Hallenbeck ◽  
Masih Rahmati ◽  
Thomas C. Sprague ◽  
...  
Keyword(s):  
Working Memory ◽  
Brain Area ◽  
Brain Regions ◽  
Delay Period ◽  
Common Finding ◽  
Neural Population ◽  
Association Cortex ◽  
Absolute Amount ◽  
Neural Populations ◽  
Memory Precision

Abstract Humans allocate visual working memory (WM) resource according to behavioral relevance, resulting in more precise memories for more important items. Theoretically, items may be maintained by feature-tuned neural populations, where the relative gain of the populations encoding each item determines precision. To test this hypothesis, we compared the amplitudes of delay period activity in the different parts of retinotopic maps representing each of several WM items, predicting the amplitudes would track behavioral priority. Using fMRI, we scanned participants while they remembered the location of multiple items over a WM delay and then reported the location of one probed item using a memory-guided saccade. Importantly, items were not equally probable to be probed (0.6, 0.3, 0.1, 0.0), which was indicated with a precue. We analyzed fMRI activity in 10 visual field maps in occipital, parietal, and frontal cortex known to be important for visual WM. In early visual cortex, but not association cortex, the amplitude of BOLD activation within voxels corresponding to the retinotopic location of visual WM items increased with the priority of the item. Interestingly, these results were contrasted with a common finding that higher-level brain regions had greater delay period activity, demonstrating a dissociation between the absolute amount of activity in a brain area and the activity of different spatially selective populations within it. These results suggest that the distribution of WM resources according to priority sculpts the relative gains of neural populations that encode items, offering a neural mechanism for how prioritization impacts memory precision.

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